Response measurement of single-crystal chemical vapor deposition diamond radiation detector for intense X-rays aiming at neutron bang-time and neutron burnhistory measurement on an inertial confinement fusion with fast ignition T. Shimaoka, J. H. Kaneko, Y. Arikawa, M. Isobe, Y. Sato, M. Tsubota, T. Nagai, S. Kojima, Y. Abe, S. Sakata, S. Fujioka, M. Nakai, H. Shiraga, H. Azechi, A. Chayahara, H. Umezawa, and S. Shikata Citation: Review of Scientific Instruments 86, 053503 (2015); doi: 10.1063/1.4921482 View online: http://dx.doi.org/10.1063/1.4921482 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/86/5?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Ion kinetic effects on the ignition and burn of inertial confinement fusion targets: A multi-scale approach Phys. Plasmas 21, 122709 (2014); 10.1063/1.4904212 Energy deposition of MeV electrons in compressed targets of fast-ignition inertial confinement fusiona) Phys. Plasmas 13, 056314 (2006); 10.1063/1.2178780 High-density and high- ρ R fuel assembly for fast-ignition inertial confinement fusion Phys. Plasmas 12, 110702 (2005); 10.1063/1.2127932 Inertial confinement fusion ignition criteria, critical profiles, and burn wave propagation using self-similar solutions Phys. Plasmas 4, 1385 (1997); 10.1063/1.872314 Fiber scintillator/streak camera detector for burn history measurement in inertial confinement fusion experiment Rev. Sci. Instrum. 68, 621 (1997); 10.1063/1.1147667
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REVIEW OF SCIENTIFIC INSTRUMENTS 86, 053503 (2015)
Response measurement of single-crystal chemical vapor deposition diamond radiation detector for intense X-rays aiming at neutron bang-time and neutron burn-history measurement on an inertial confinement fusion with fast ignition T. Shimaoka,1,a) J. H. Kaneko,1 Y. Arikawa,2 M. Isobe,3 Y. Sato,4 M. Tsubota,1 T. Nagai,2 S. Kojima,2 Y. Abe,2 S. Sakata,2 S. Fujioka,2 M. Nakai,2 H. Shiraga,2 H. Azechi,2 A. Chayahara,5 H. Umezawa,5 and S. Shikata5 1
Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan Osaka University, 2-6 Yamada-Oka, Suita, Osaka 565-0871, Japan 3 National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan 4 The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan 5 Diamond Research Laboratory, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan 2
(Received 28 November 2014; accepted 11 May 2015; published online 26 May 2015) A neutron bang time and burn history monitor in inertial confinement fusion with fast ignition are necessary for plasma diagnostics. In the FIREX project, however, no detector attained those capabilities because high-intensity X-rays accompanied fast electrons used for plasma heating. To solve this problem, single-crystal CVD diamond was grown and fabricated into a radiation detector. The detector, which had excellent charge transportation property, was tested to obtain a response function for intense X-rays. The applicability for neutron bang time and burn history monitor was verified experimentally. Charge collection efficiency of 99.5% ± 0.8% and 97.1% ± 1.4% for holes and electrons were obtained using 5.486 MeV alpha particles. The drift velocity at electric field which saturates charge collection efficiency was 1.1 ± 0.4 × 107 cm/s and 1.0 ± 0.3 × 107 cm/s for holes and electrons. Fast response of several ns pulse width for intense X-ray was obtained at the GEKKO XII experiment, which is sufficiently fast for ToF measurements to obtain a neutron signal separately from X-rays. Based on these results, we confirmed that the single-crystal CVD diamond detector obtained neutron signal with good S/N under ion temperature 0.5–1 keV and neutron yield of more than 109 neutrons/shot. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4921482]
I. INTRODUCTION
Implosion methods in inertial confinement fusion are categorized as indirect implosion or direct implosion. The former is epitomized by the National Ignition Facility and Laser Mega Joule.1,2 A deuterium–tritium target is irradiated by X-rays generated from hohlraum, which consists of a high atomic number material, such as gold. This method is superior in terms of fuel implosion uniformity. Nevertheless, input energy of several megajoules is necessary for ignition because of the inefficiency of X-ray conversion. At Osaka University and Rochester University, however, the latter method was chosen. Controlling implosion uniformity is extremely difficult for Rayleigh–Taylor instability.3 A deuterium–tritium/deuterium–deuterium (DD) target is irradiated directly, with no X-ray conversion for implosion. Therefore, low input energy of several hundred joules is necessary for implosion and ignition. Osaka University and Rochester University have been developing a fast ignition method, which is expected to improve the ignition gain considerably.4 In this method, a a)Author to whom correspondence should be addressed. Electronic mail:
[email protected]. Tel.: +81 11 706 6705. Fax: +81 11 706 6705.
target composed of deuterium and a long gold cone is used. First, high-temperature and high-density plasma are formed by direct laser irradiation to the shell. Then a laser for heating, a so-called Laser for Fast ignition experiment (LFEX), with energy of 1 kJ and pulse width of less than 1 ps was irradiated to the gold cone. Results show that the plasma was heated efficiently by fast electrons generated by the gold cone. Using this heating method, only a tenth of the direct implosion input energy is expected to be necessary for ignition. To optimize fast ignition, obtaining information related to implosion instability, dynamics of imploded plasma, heating dynamics by high-energy electron, and neutron reaction dynamics are extremely important. Plasma diagnostics detectors using fusion products and X-ray spectroscopic images have been developed at the Institute of Laser Energy, Osaka University. Ion temperature and a fuel aerial density of imploded plasma, which is calculated using the ratio of the number of first and secondary neutrons, was obtained using ToF measurements using a multi-angle neutron detector at a large area (MANDALA) and a liquid scintillator with fast decay.5,6 In addition, time and space information for the imploded plasma was obtained using an X-ray streak camera.7,8 With fast ignition, however, the neutron bang time and burn history that correspond to a peak time of neutron reactions occurred. Their reaction history was not obtained.
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High-energy electrons are generated by interaction of the LFEX laser and gold cone. Consequently, high-intensity Xrays interrupt neutron detection. Therefore, a detector with a minimum of 100 ps time resolution is required for neutron bang time and neutron burn history measurements. Bang time and burn history detectors have been developed at the National Ignition Facility. Bang time and burn history measurement methods are of three types, using a plastic scintillation detector, gas Cherenkov detector, and polycrystalline CVD diamond detector. Under total neutron yield of less than 1015 neutrons/shot, a streak camera and a plastic scintillator coupled with a photomultiplier tube were used, respectively, for burn history measurement and bang time measurement. These detectors obtained neutron signal with time resolutions of 100 ps and 30 ps.9,10 Gas Cherenkov detectors were used as the gamma ray bang time and burn history detector under total neutron yield of more than 1015 neutron/shot. This detector measures 16.5 MeV gamma rays accompanied with 3He relaxation of DT reaction product. This measurement has the advantage of having no spread of arrival times. The detectors were coupled with a photomultiplier tube or a streak camera as well as a plastic scintillator.11–15 A polycrystalline CVD diamond detector was used in current mode as the neutron bang time detector under total neutron yield of less than 1015. Particularly, it was used also as a X-ray bang time detector and D3He reaction detector in indirect implosion experiments.16,17 The neutron bang time and burn history have not been obtained at the FIREX project. Two severe problems remain to be solved: low neutron yield and intense X-rays. The total neutron yield is 107 neutrons/shot caused by a DD shot, which has a small reaction cross section compared to the DT reaction. Low input energy also causes a low neutron yield. In addition, as described above, intense X-ray generated by laser heating of gold cone buries the neutron signal. In direct ignition experiments at GEKKO, Arikawa et al. obtained the neutron bang time using a plastic scintillator coupled with a photomultiplier tube having more than 106 neutrons/shot. In fast ignition, however, 1012–1015 photons/shot of intense Xray accompanied generation of fast electrons of several megaelectron volts. In this case, the plastic scintillator shows an extremely slow decay component with several microseconds. The neutron signal was buried in the intense X-ray signal. Therefore, the plastic scintillator coupled with the photomultiplier tube and streak camera were not capable of making the required measurements. A gas Cherenkov detector was also impossible to use because of the DD target.18,19 To obtain neutron bang time and burn history under severe conditions, we specifically examine the development of a single-crystal CVD diamond detector. Neutron bang time measurement has already been conducted using a polycrystalline CVD diamond detector at the National Ignition Facility as described above. Nonetheless, the neutron burn history measurement was not reported. We feel that this is true because the polycrystalline CVD diamond detector was not suitable for burn history measurement. Pulse height decrease in current signal occurs when induced charge is trapped/recombined due to grain boundary and impurities such as nitrogen.20,21 These results in imprecision of neutron yield transition. In this study, we evaluated the applicability of the neutron bang time
Rev. Sci. Instrum. 86, 053503 (2015)
and burn history monitor using single-crystal CVD diamond in a fast ignition experiment. Applicability was verified by comparing the arrival time of the neutron signal and intense X-ray signal. A single-crystal CVD diamond with nearly perfect charge collection, and fast response sufficient for ToF measurement was grown and fabricated into a detector. Then, the response function measurement for intense X-rays was conducted at GEKKO XII.
II. EXPERIMENTAL A. Fabrication of the diamond radiation detector
Single-crystal CVD diamond was grown homoepitaxially on (high pressure/high temperature) HP/HT type-IIa diamond substrate with an off-angle of three degrees for the ⟨110⟩ direction to suppress abnormal growth. CVD growth was done on the (001) direction using a microwave plasma reactor (5250; ASTeX). The gas pressure, substrate temperature, and microwave power were 110 Torr, 850 ◦C, and 1000 W, respectively.22 A self-standing layer was lifted off using the direct wafer method.23 The self-standing layer’s size was 5 × 5 × 0.1 mm. It was oxygen-terminated using dichromic acid. Subsequently, aluminum Schottky contact and titanium carbide/gold ohmic contact were fabricated on both sides of the crystal by evaporation. Titanium contact was annealed at 400 ◦C for 30 min to form carbide. The contacts were connected to a SMA coaxial cable and ground using silver paste. To compare charge transportation properties, the same design detectors were fabricated using conventional electronics-grade single-crystal CVD diamond (Element Six Ltd.). B. Alpha-particle-induced charge distribution measurements and drift velocity measurements using broadband current amplifier
Alpha-particle-induced charge distribution measurements were conducted for charge collection efficiency evaluation. We used 5.486 MeV alpha particles from an 241Am radioactive source, a charge-sensitive preamplifier (142A; Ortec), a spectroscopy amplifier (672; Ortec), and a multi-channel analyzer (WE7562; Yokogawa). A silicon surface barrier detector (BA2500-100S; Ortec) was used as the standard for charge collection efficiency. Average energies for electron and hole pair creation of silicon and CVD diamond, i.e., 3.67 eV and 13.1 eV,24 were used for charge collection efficiency calculations. In addition, the drift velocity was evaluated. Response functions for 5.5 MeV alpha particles of 241Am were obtained using a digital oscilloscope with 5 GHz analog bandwidth (Wavemaster8600AS; Lecroy Corp.) and a broadband current amplifier with 2 GHz analog bandwidth (broadband amplifier; cividec). The drift velocity was calculated using 30 shots of full-width half maximum of the current signal and crystal thickness. Gauss function was used to estimate FWHM of output pulse for Hokkaido University’s (HU) sample. On the other hand, FWHM of Element Six’s output pulse was estimated directly from raw numerical data because gauss fitting function was not suited.
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FIG. 1. Optical photograph of CVD diamond detector and measurement system of the X-ray response function measurement.
C. Response function measurements for intense X-ray at GEKKO XII
Response function measurements of single-crystal CVD diamond detector for intense X-ray were conducted at GEKKO XII, Institute of Laser Energy, Osaka University. Figure 1 shows an optical photograph of the diamond detector and measurement setup. A 16-GHz analog bandwidth Bias Tee (Picosecond Lab) detector power supply (428; Ortec) 600 MHz low analog bandwidth oscilloscope was used to prevent damage caused by a high output pulse. In practical use, a 20 GHz high analog bandwidth digital oscilloscope is expected to be used. In neutron ToF measurement, the energy distribution causes a spread of arrival time in their arrival times. The spread is given as 778 × d × Ti (2.45 MeV DD neutron) ∆t (ps) = 122 × d × Ti (14.1 MeV DT neutron) , where ∆t is the FWHM in picoseconds and d is the target to detector distance in meters. Ti is the plasma ion temperature in kilo-electron volts. The plasma ion temperature was 0.5–1.0 keV in the FIREX project.25 To keep ∆t below 100 ps,
d < 18 cm for DD neutrons is required. In this study, however, the target to detector distance was limited to 30 cm by the solid angle of other plasma diagnostics detectors. In this case, ∆t is 170–230 ps. Bias voltage of −100 V was applied to titanium/gold electrode of the CVD diamond detector. In fast ignition, electromagnetic noise makes it difficult to obtain a neutron signal. To avoid severe noise, the whole measurement system was set in the shield box and metal tube. The measurement system was floated between the target chamber and metal port using a battery and insulation. III. RESULTS A. Alpha-particle-induced charge distribution measurements and drift velocity measurements using broadband current amplifier
Charge collection efficiency, energy resolution, and drift velocity of Hokkaido University’s sample and Element Six’s sample are presented in Table I. Figure 2 presents an example of alpha-particle-induced charge measurement of the former one (HU_3). The charge collection efficiency of
TABLE I. Charge transportation property of the diamond detector. Charge collection efficiency (%)
Energy resolution (%)
Drift velocity (×107 cm/s)
Electric field (V/µm)
Sample I. D
Hole
Electron
Hole
Electron
Hole
Electron
Hole
Electron
Thickness (µm)
HU_1 HU_2 HU_3 HU_4 HU_5 HU_6
100 98.6 100 95.3 96.4 98.9
95.8 98.6 96.5 93.2 92.7 93.6
0.52 1.3 0.70 1.3 1.2 0.38
1.1 1.1 1.1 1.2 1.3 1.4
N/A N/A 1.5 0.81 1.0 N/A
N/A N/A 1.3 0.93 0.82 N/A
1.3 1.1 0.85 1.5 1.2 2.0
1.6 3.7 0.85 1.2 1.1 2.0
63 54 139 90 95 102
E6_1 E6_2 E6_3
99.4 98.0 95.7
99.7 95.7 95.7
1.5 1.4 1.0
2.3 1.6 1.0
N/A N/A 0.94
N/A N/A 0.68
0.68 0.68 0.80
0.68 0.68 0.80
500 500 500
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Induced charge in planar type radiation semiconductor detector was given as qN0 dx, w where Q stands for the induced charge, q signifies the elementary charge, w denotes the sample thickness, and N0 represents the number of the generated charge carrier. Current i(t) is given as dQ =
dQ qN0 dx qN0 = = v. dt w dt w If the induced charge is equal, the pulse height and pulse width are determined by the drift velocity and sample thickness. For neutron ToF measurement under intense Xrays, space charge limited current mode,28 i.e., induced charge exceeds capacitance-bias voltage product, sufficient electric field was not supplied between electrodes. This brings pulse tailing and neutron signal burial in X-ray signal. In this measurement, we chose Hokkaido University’s sample which was approximately 100 µm of low thickness to suppress induced charge accompanied with intense X-rays. i (t) =
FIG. 2. Alpha-particle-induced charge distribution measurement.
99.5% ± 0.8% and 97.1% ± 1.4% for holes and electrons and energy resolution of 0.84% ± 0.4% and 1.8% ± 0.4% for holes and electrons were obtained by the three-sample average (HU_1-3). The latter one achieved charge collection efficiency of 97.7% ± 1.5% and 97.0% ± 1.8% for holes and electrons, energy resolution of 1.3% ± 0.2%, and 1.6% ± 0.5% by threesample averages (E6_1-3). The former one showed equivalent charge collection efficiency and superior energy resolution to those of the latter one. Figure 3(a) presents an example of the output pulse of the sample HU_4 with 90 µm thickness. A drift velocity calculated using 30 shots of output pulses was 1.1 ± 0.4 × 107 cm/s and 1.0 ± 0.3 × 107 cm/s for holes and electrons by the three sample average (HU_3-5). An electric field was 0.8-1.5 V/µm, which is sufficient to saturate charge collection. A frequency band of the measurement system was limited by 2 GHz of analog bandwidth of the broadband current amplifier. Therefore, the drift velocity was expected to be even larger than the value obtained in this experiment. Figure 3(b) presents an example of the output pulse of the latter one with 500 µm thickness (E6_3). The drift velocity was 0.94 ± 0.2 × 107 cm/s and 0.68 ± 0.2 × 107 cm/s for holes and electrons by 30 shots at electric field of 0.80 V/µm. These results were in good agreement with the experimentally obtained values that Pernegger et al.26 and Jansen et al.27 reported. These papers report more than 1 × 107 cm/sec of saturation drift velocities for Element Six’s sample. In this study, bias voltage was limited by current amplifier thus electric filed is not sufficient to saturate drift velocity.
B. Response function measurements for intense X-rays
Figure 4 shows the response function of the CVD diamond detector (HU_6) for high-intensity X-rays generated by the LFEX laser. Sample thickness was 102 µm. The solid line shows the output pulse for intense X-rays. Fast pulse with full width at half maximum of less than 1 ns and full width of several ns with no slow decay component were obtained, although signal ringing due to inductive connections to cable was observed. The dotted line shows the output pulse of a dummy detector, i.e., a detector without diamond. Velocities of the photon and 2.45 MeV DD neutron were 30 cm/ns and 2.1 cm/ns, respectively. For this experiment, the target detector distance was 30 cm. Therefore, DD neutron arrives 14 ns later than the X-rays reached the detector. The induced charge generated by intense X-rays was 7.6 × 10−11 C. The capacitance-bias product was 3 × 10−10, which was larger than the induced charge. Therefore, no space charge limited current was observed. For detector–target distance of 18 cm, 2.8 times the induced charge would be generated in the diamond. Nonetheless, the space charge limited current would be suppressed to increase bias voltage up to 300 V. Consequently, the neutron signal would be obtained separately from
FIG. 3. (a) Output pulse of the Hokkaido University CVD diamond detector (HU_4). (b) Output pulse of the Element Six CVD diamond detector (E6_3). This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 128.6.218.72 On: Wed, 03 Jun 2015 08:35:46
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recombination of charge carriers when intense X-rays arrive. Moreover, for ToF measurements with neutron yield of less than 109 neutron/shot, improving the neutron sensitivity, i.e., fabrication of multichannel array and using a neutron–proton conversion layer such as polyethylene are also required. V. PERSPECTIVES
FIG. 4. Response function of single-crystal CVD diamond detector for intense X-rays.
high-intensity X-rays in cases where the plasma ion temperature was 0.5–1 keV and sufficient neutron yield was obtained. In this study, the estimated neutron sensitivity calculated using the energy deposit and drift velocity was 1 × 10−7mV/DD neutrons. The neutron signal was not observed because of the large rapid frequency noise, which was brought by a trigger box with a faulty electromagnetic shield. This RF noise would be eliminated to replace the trigger box with a signal-light converter; the trigger signal would be converted into a signal–light–signal in the shield box. Results revealed that single-crystal CVD diamond detects neutron signal with good S/N under high-intensity X-ray with sufficient neutron yield of more than 109 neutrons/shot. This promising detector is expected to be useful as a substitute of fast response plastic and liquid scintillator with slow components because of high-intensity X-rays.
To realize a neutron burn history monitor with fast ignition, we plan to take the following steps in the near future. First, we will install a time fiducial system with a light-signal converter such as a silicon PIN photodiode to eliminate rapid frequency noise completely. Second, we will optimize the diamond thickness. Third, we will install a gate bias system for suppressing the intense X-ray signal. These steps are necessary to obtain good S/N. Similarly, we will obtain a response function for unfolding method using electron LINAC, which is necessary to achieve 100 ps time resolution. ACKNOWLEDGMENTS
This work was done with the support and under the auspices of the National Institute for Fusion Science Collaboration Research program (No. NIFS13KUGK078) and partially supported by Research Fellowships of the Japan Society for the Promotion of the Science for Young Scientists Grant No. 13J02500. The author would like to thank the FIREX group for the GEKKO XII experiment. 1J.
Lindl, Phys. Plasmas 2, 3933 (1995). Besnard, Eur. Phys. J. D 44, 207 (2007). 3K. Shigemori, H. Azechi, M. Nakai, M. Honda, K. Meguro, N. Miyanaga, H. Takabe, and K. Mima, Phys. Rev. Lett. 78, 250 (1997). 4M. Koga, Y. Arikawa, H. Azechi, Y. Fujimoto, S. Fujioka, H. Habara, Y. Hironaka, H. Homma, H. Hosoda, T. Jitsuno, T. Johzaki, J. Kawanaka, R. Kodama, K. Mima, N. Miyanaga, M. Murakami, H. Nagatomo, M. Nakai, Y. Nakata, H. Nakamura, H. Nishimura, T. Norimatsu, Y. Sakawa, N. Sarukura, K. Shigemori, H. Shiraga, T. Shimizu, H. Takabe, M. Tanabe, K. A. Tanaka, T. Tanimoto, T. Tsubakimoto, T. Watari, A. Sunahara, M. Isobe, A. Iwamoto, IV. DISCUSSION T. Mito, O. Motojima, T. Ozaki, H. Sakagami, T. Taguchi, Y. Nakao, H. Cai, M. Key, P. Norreys, and J. Pasley, Nucl. Instrum. Methods Phys. Res., Sect. Neutron yield is expected to increase up to 1011 A 653, 84 (2011). neutron/shot at the end of the FIREX I project in 2016. The 5N. Izumi, K. Yamaguchi, T. Yamagajo, T. Nakano, T. Kasai, T. Urano, H. dashed line in Figure 4 shows the estimated output pulse of the Azechi, S. Nakai, and T. Iida, Rev. Sci. Instrum. 70, 1221 (1999). 6T. Nagai, Y. Ioka, A. Hasegawa, K. Wada, S. Takaoku, M. Takata, K. detector for 1011 neutrons/shot. The target–detector distance Noritake, Y. Minami, K. Watanabe, K. Yamanoi, Y. Arikawa, H. Hosoda, is less than 5.7 cm to suppress ∆t less than 100 ps in this case. H. Nakamura, T. Watari, M. Cadatal-Raduban, M. Koga, T. Shimizu, N. In addition, high-intensity X-ray signal return to baseline in Sarukura, H. Shiraga, M. Nakai, T. Norimatsu, and H. Azechi, Jpn. J. Appl. 2.5 ns to measure the neutron signal separately from the X-ray Phys., Part 1 50, 080208 (2011). 7M. Koga, T. Fujiwara, T. Sakaiya, M. Lee, K. Shigemori, H. Shiraga, and signal. H. Azechi, Rev. Sci. Instrum. 79, 10E909 (2008). The X-ray signal obtained in this study returned to the 8M. Heya, M. Nakasuji, H. Shiraga, N. Miyanaga, H. Azechi, H. Takabe, T. baseline in several ns although ringing was observed. Given Yamanaka, and K. Mima, Rev. Sci. Instrum. 68, 820 (1997). 9R. A. Lerche, D. W. Phillion, and G. L. Tietbohl, Rev. Sci. Instrum. 66, 933 the limitation of bandwidth of 600 MHz oscilloscope, the (1995). FWHM of current signal of the detector must be even shorter. 10V. Yu. Glebov, C. Stoeckl, T. C. Sangster, S. Roberts, R. A. Lerche, and G. In the case the induced charge below capacitance-bias voltage J. Schmid, IEEE Trans. Plasma Sci. 33(1), 70 (2005). 11C. J. Horsfield, S. E. Caldwell, C. R. Christensen, S. C. Evans, J. M. Mack, product, the neutron signal will be obtained separately from T. Sedillo, C. S. Young, and V. Yu. Glebov, Rev. Sci. Instrum. 77, 10E724 X-ray signal. The target–detector distance becomes shorter; (2006). however, the current signal intensity increases concomitantly 12A. M. McEvoy, H. W. Herrmann, C. J. Horsfield, C. S. Young, E. K. Miller, with the increase of the solid angle. In such a case, the neutron J. M. Mack, Y. Kim, W. Stoeffl, M. Rubery, S. Evans, T. Sedillo, and Z. A. signal is buried in the intense X-ray signal with increased Ali, Rev. Sci. Instrum. 81, 10D322 (2010). 13J. M. Mack, S. E. Caldwell, S. C. Evans, T. J. Sedillo, D. C. Wilson, C. S. pulse width, rise and fall times, and the slow decay component Young, C. J. Horsfield, R. L. Griffith, and R. A. Lerche, Rev. Sci. Instrum. accompanied with the space charge limited current mode. To 77, 10E728 (2006). prevent neutron signal burial in the X-ray signal, installing 14R. M. Malone, H. M. Herrmann, W. Stoeffl, J. M. Mack, and C. S. Young, high voltage with a gate bias function is required to enhance Rev. Sci. Instrum. 79, 10E532 (2008). This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 2D.
128.6.218.72 On: Wed, 03 Jun 2015 08:35:46
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Shimaoka et al.
J. Murphy, C. W. Barnes, R. R. Berggren, P. Bradley, S. E. Caldwell, R. E. Chrien, J. R. Faulkner, P. L. Gobby, N. Hoffman, J. L. Jimerson, K. A. Klare, C. L. Lee, J. M. Mack, G. L. Morgan, J. A. Oertel, F. J. Swenson, P. J. Walsh, R. B. Walton, R. G. Watt, M. D. Wilke, D. C. Wilson, C. S. Young, S. W. Haan, R. A. Lerche, M. J. Moran, T. W. Phillips, T. C. Sangster, R. J. Leeper, C. L. Ruiz, G. W. Cooper, L. Disdier, A. Rouyer, A. Fedotoff, V. Yu. Glebov, D. D. Meyerhofer, J. M. Soures, C. Stöckl, J. A. Frenje, D. G. Hicks, C. K. Li, R. D. Petrasso, F. H. Seguin, K. Fletcher, S. Padalino, and R. K. Fisher, Rev. Sci. Instrum. 72, 773 (2001). 16M. A. Barrios, Rev. Sci. Instrum. 83, 10E105 (2012). 17H. G. Rinderknecht, M. Gatu Johnson, A. B. Zylstra, N. Sinenian, M. J. Rosenberg, J. A. Frenje, C. J. Waugh, C. K. Li, F. H. Sèguin, R. D. Petrasso, J. R. Rygg, J. R. Kimbrough, A. MacPhee, G. W. Collins, D. Hicks, A. Mackinnon, P. Bell, R. Bionta, T. Clancy, R. Zacharias, T. Döppner, H. S. Park, S. LePape, O. Landen, N. Meezan, E. I. Moses, V. U. Glebov, C. Stoeckl, T. C. Sangster, R. Olson, J. Kline, and J. Kilkenny, Rev. Sci. Instrum. 83, 10D902 (2012). 18R. Lauck, M. Brandis, and B. Bromberger, IEEE Trans. Nucl. Sci. 56(3), 989 (2009). 19K. Watanabe, Y. Arikawa, K. Yamanoi, M. Cadatal-Raduban, T. Nagai, M. Kouno, K. Sakai, T. Nazakato, T. Shimizu, N. Sarukura, M. Nakai, T. Norimatsu, H. Azechi, A. Yoshikawa, T. Murata, S. Fujino, H. Yoshida, N. Izumi, N. Satoh, and H. Kan, J. Cryst. Growth 362, 288 (2013). 20J. H. Kaneko, T. Tanaka, T. Imai, Y. Tanimura, M. Katagiri, T. Nishitani, H. Takeuchi, T. Sawamur, and T. Iida, Nucl. Instrum. Methods Phys. Res., Sect. A 505, 187–190 (2003).
Rev. Sci. Instrum. 86, 053503 (2015) 21J.
Hammersberg, J. Isberg, E. Johansson, T. Lundstrom, O. Hjortstam, and H. Bernhoff, Diamond Relat. Mater. 10, 574–579 (2001). 22J. H. Kaneko, F. Fujita, Y. Konno, T. Gotoh, N. Nishi, H. Watanabe, A. Chayahara, H. Umezawa, N. Tsubouchi, S. Shikata, and M. Isobe, Diamond Relat. Mater. 26, 45 (2012). 23N. Tsubouchi, Y. Mokuno, A. Kakimoto, F. Fujita, J. H. Kaneko, H. Yamada, A. Chayahara, and S. Shikata, Nucl. Instrum. Methods Phys. Res., Sect. B 286, 313 (2012). 24S. F. Kozlov, IEEE Trans. Nucl. Sci. 22, 160 (1975). 25H. Shiraga, S. Fujioka, M. Nakai, T. Watari, H. Nakamura, Y. Arikawa, H. Hosoda, T. Nagai, M. Koga, H. Kikuchi, Y. Ishii, T. Sogo, K. Shigemori, H. Nishimura, Z. Zhang, M. Tanabe, S. Ohira, Y. Fujii, T. Namimoto, Y. Sakawa, O. Maegawa, T. Ozaki, K. A. Tanaka, H. Habara, T. Iwawaki, K. Shimada, H. Nagatomo, T. Johzaki, A. Sunahara, M. Murakami, H. Sakagami, T. Taguchi, T. Norimatsu, H. Homma, Y. Fujimoto, A. Iwamoto, N. Miyanaga, J. Kawanaka, T. Jitsuno, Y. Nakata, K. Tsubakimoto, K. Sueda, N. Morio, S. Matsuo, T. Kawasaki, K. Sawai, K. Tsuji, H. Murakami, T. Kanabe, K. Kondo, R. Kodama, N. Sarukura, T. Shimizu, K. Mima, H. Azechi et al., High Energy Density Phys. 8, 227 (2012). 26H. Pernegger, S. Ro, P. Weilhammer, H. Frais-Kölbl, E. Griesmayer, H. Kagan, S. Schnetzer, R. Stone, W. Trischuk, D. Twitchen, and A. Whitehead, J. Appl. Phys. 97, 073704 (2005). 27H. Jansen, D. Dobos, T. Eisel, H. Pernegger, V. Eremin, and N. Wermes, J. Appl. Phys. 113, 173706 (2013). 28J. Isberg, M. Gabrysch, S. Majdi, K. K. Kovi, and D. Twitchen, Solid State Sci. 13, 1065 (2011).
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REVIEW OF SCIENTIFIC INSTRUMENTS 86, 053503 (2015)
Response measurement of single-crystal chemical vapor deposition diamond radiation detector for intense X-rays aiming at neutron bang-time and neutron burn-history measurement on an inertial confinement fusion with fast ignition T. Shimaoka,1,a) J. H. Kaneko,1 Y. Arikawa,2 M. Isobe,3 Y. Sato,4 M. Tsubota,1 T. Nagai,2 S. Kojima,2 Y. Abe,2 S. Sakata,2 S. Fujioka,2 M. Nakai,2 H. Shiraga,2 H. Azechi,2 A. Chayahara,5 H. Umezawa,5 and S. Shikata5 1
Graduate School of Engineering, Hokkaido University, Sapporo 060-8628, Japan Osaka University, 2-6 Yamada-Oka, Suita, Osaka 565-0871, Japan 3 National Institute for Fusion Science, 322-6 Oroshi-cho, Toki 509-5292, Japan 4 The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan 5 Diamond Research Laboratory, National Institute of Advanced Industrial Science and Technology (AIST), 1-8-31 Midorigaoka, Ikeda, Osaka 563-8577, Japan 2
(Received 28 November 2014; accepted 11 May 2015; published online 26 May 2015) A neutron bang time and burn history monitor in inertial confinement fusion with fast ignition are necessary for plasma diagnostics. In the FIREX project, however, no detector attained those capabilities because high-intensity X-rays accompanied fast electrons used for plasma heating. To solve this problem, single-crystal CVD diamond was grown and fabricated into a radiation detector. The detector, which had excellent charge transportation property, was tested to obtain a response function for intense X-rays. The applicability for neutron bang time and burn history monitor was verified experimentally. Charge collection efficiency of 99.5% ± 0.8% and 97.1% ± 1.4% for holes and electrons were obtained using 5.486 MeV alpha particles. The drift velocity at electric field which saturates charge collection efficiency was 1.1 ± 0.4 × 107 cm/s and 1.0 ± 0.3 × 107 cm/s for holes and electrons. Fast response of several ns pulse width for intense X-ray was obtained at the GEKKO XII experiment, which is sufficiently fast for ToF measurements to obtain a neutron signal separately from X-rays. Based on these results, we confirmed that the single-crystal CVD diamond detector obtained neutron signal with good S/N under ion temperature 0.5–1 keV and neutron yield of more than 109 neutrons/shot. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4921482]
I. INTRODUCTION
Implosion methods in inertial confinement fusion are categorized as indirect implosion or direct implosion. The former is epitomized by the National Ignition Facility and Laser Mega Joule.1,2 A deuterium–tritium target is irradiated by X-rays generated from hohlraum, which consists of a high atomic number material, such as gold. This method is superior in terms of fuel implosion uniformity. Nevertheless, input energy of several megajoules is necessary for ignition because of the inefficiency of X-ray conversion. At Osaka University and Rochester University, however, the latter method was chosen. Controlling implosion uniformity is extremely difficult for Rayleigh–Taylor instability.3 A deuterium–tritium/deuterium–deuterium (DD) target is irradiated directly, with no X-ray conversion for implosion. Therefore, low input energy of several hundred joules is necessary for implosion and ignition. Osaka University and Rochester University have been developing a fast ignition method, which is expected to improve the ignition gain considerably.4 In this method, a a)Author to whom correspondence should be addressed. Electronic mail:
[email protected]. Tel.: +81 11 706 6705. Fax: +81 11 706 6705.
target composed of deuterium and a long gold cone is used. First, high-temperature and high-density plasma are formed by direct laser irradiation to the shell. Then a laser for heating, a so-called Laser for Fast ignition experiment (LFEX), with energy of 1 kJ and pulse width of less than 1 ps was irradiated to the gold cone. Results show that the plasma was heated efficiently by fast electrons generated by the gold cone. Using this heating method, only a tenth of the direct implosion input energy is expected to be necessary for ignition. To optimize fast ignition, obtaining information related to implosion instability, dynamics of imploded plasma, heating dynamics by high-energy electron, and neutron reaction dynamics are extremely important. Plasma diagnostics detectors using fusion products and X-ray spectroscopic images have been developed at the Institute of Laser Energy, Osaka University. Ion temperature and a fuel aerial density of imploded plasma, which is calculated using the ratio of the number of first and secondary neutrons, was obtained using ToF measurements using a multi-angle neutron detector at a large area (MANDALA) and a liquid scintillator with fast decay.5,6 In addition, time and space information for the imploded plasma was obtained using an X-ray streak camera.7,8 With fast ignition, however, the neutron bang time and burn history that correspond to a peak time of neutron reactions occurred. Their reaction history was not obtained.
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High-energy electrons are generated by interaction of the LFEX laser and gold cone. Consequently, high-intensity Xrays interrupt neutron detection. Therefore, a detector with a minimum of 100 ps time resolution is required for neutron bang time and neutron burn history measurements. Bang time and burn history detectors have been developed at the National Ignition Facility. Bang time and burn history measurement methods are of three types, using a plastic scintillation detector, gas Cherenkov detector, and polycrystalline CVD diamond detector. Under total neutron yield of less than 1015 neutrons/shot, a streak camera and a plastic scintillator coupled with a photomultiplier tube were used, respectively, for burn history measurement and bang time measurement. These detectors obtained neutron signal with time resolutions of 100 ps and 30 ps.9,10 Gas Cherenkov detectors were used as the gamma ray bang time and burn history detector under total neutron yield of more than 1015 neutron/shot. This detector measures 16.5 MeV gamma rays accompanied with 3He relaxation of DT reaction product. This measurement has the advantage of having no spread of arrival times. The detectors were coupled with a photomultiplier tube or a streak camera as well as a plastic scintillator.11–15 A polycrystalline CVD diamond detector was used in current mode as the neutron bang time detector under total neutron yield of less than 1015. Particularly, it was used also as a X-ray bang time detector and D3He reaction detector in indirect implosion experiments.16,17 The neutron bang time and burn history have not been obtained at the FIREX project. Two severe problems remain to be solved: low neutron yield and intense X-rays. The total neutron yield is 107 neutrons/shot caused by a DD shot, which has a small reaction cross section compared to the DT reaction. Low input energy also causes a low neutron yield. In addition, as described above, intense X-ray generated by laser heating of gold cone buries the neutron signal. In direct ignition experiments at GEKKO, Arikawa et al. obtained the neutron bang time using a plastic scintillator coupled with a photomultiplier tube having more than 106 neutrons/shot. In fast ignition, however, 1012–1015 photons/shot of intense Xray accompanied generation of fast electrons of several megaelectron volts. In this case, the plastic scintillator shows an extremely slow decay component with several microseconds. The neutron signal was buried in the intense X-ray signal. Therefore, the plastic scintillator coupled with the photomultiplier tube and streak camera were not capable of making the required measurements. A gas Cherenkov detector was also impossible to use because of the DD target.18,19 To obtain neutron bang time and burn history under severe conditions, we specifically examine the development of a single-crystal CVD diamond detector. Neutron bang time measurement has already been conducted using a polycrystalline CVD diamond detector at the National Ignition Facility as described above. Nonetheless, the neutron burn history measurement was not reported. We feel that this is true because the polycrystalline CVD diamond detector was not suitable for burn history measurement. Pulse height decrease in current signal occurs when induced charge is trapped/recombined due to grain boundary and impurities such as nitrogen.20,21 These results in imprecision of neutron yield transition. In this study, we evaluated the applicability of the neutron bang time
Rev. Sci. Instrum. 86, 053503 (2015)
and burn history monitor using single-crystal CVD diamond in a fast ignition experiment. Applicability was verified by comparing the arrival time of the neutron signal and intense X-ray signal. A single-crystal CVD diamond with nearly perfect charge collection, and fast response sufficient for ToF measurement was grown and fabricated into a detector. Then, the response function measurement for intense X-rays was conducted at GEKKO XII.
II. EXPERIMENTAL A. Fabrication of the diamond radiation detector
Single-crystal CVD diamond was grown homoepitaxially on (high pressure/high temperature) HP/HT type-IIa diamond substrate with an off-angle of three degrees for the ⟨110⟩ direction to suppress abnormal growth. CVD growth was done on the (001) direction using a microwave plasma reactor (5250; ASTeX). The gas pressure, substrate temperature, and microwave power were 110 Torr, 850 ◦C, and 1000 W, respectively.22 A self-standing layer was lifted off using the direct wafer method.23 The self-standing layer’s size was 5 × 5 × 0.1 mm. It was oxygen-terminated using dichromic acid. Subsequently, aluminum Schottky contact and titanium carbide/gold ohmic contact were fabricated on both sides of the crystal by evaporation. Titanium contact was annealed at 400 ◦C for 30 min to form carbide. The contacts were connected to a SMA coaxial cable and ground using silver paste. To compare charge transportation properties, the same design detectors were fabricated using conventional electronics-grade single-crystal CVD diamond (Element Six Ltd.). B. Alpha-particle-induced charge distribution measurements and drift velocity measurements using broadband current amplifier
Alpha-particle-induced charge distribution measurements were conducted for charge collection efficiency evaluation. We used 5.486 MeV alpha particles from an 241Am radioactive source, a charge-sensitive preamplifier (142A; Ortec), a spectroscopy amplifier (672; Ortec), and a multi-channel analyzer (WE7562; Yokogawa). A silicon surface barrier detector (BA2500-100S; Ortec) was used as the standard for charge collection efficiency. Average energies for electron and hole pair creation of silicon and CVD diamond, i.e., 3.67 eV and 13.1 eV,24 were used for charge collection efficiency calculations. In addition, the drift velocity was evaluated. Response functions for 5.5 MeV alpha particles of 241Am were obtained using a digital oscilloscope with 5 GHz analog bandwidth (Wavemaster8600AS; Lecroy Corp.) and a broadband current amplifier with 2 GHz analog bandwidth (broadband amplifier; cividec). The drift velocity was calculated using 30 shots of full-width half maximum of the current signal and crystal thickness. Gauss function was used to estimate FWHM of output pulse for Hokkaido University’s (HU) sample. On the other hand, FWHM of Element Six’s output pulse was estimated directly from raw numerical data because gauss fitting function was not suited.
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FIG. 1. Optical photograph of CVD diamond detector and measurement system of the X-ray response function measurement.
C. Response function measurements for intense X-ray at GEKKO XII
Response function measurements of single-crystal CVD diamond detector for intense X-ray were conducted at GEKKO XII, Institute of Laser Energy, Osaka University. Figure 1 shows an optical photograph of the diamond detector and measurement setup. A 16-GHz analog bandwidth Bias Tee (Picosecond Lab) detector power supply (428; Ortec) 600 MHz low analog bandwidth oscilloscope was used to prevent damage caused by a high output pulse. In practical use, a 20 GHz high analog bandwidth digital oscilloscope is expected to be used. In neutron ToF measurement, the energy distribution causes a spread of arrival time in their arrival times. The spread is given as 778 × d × Ti (2.45 MeV DD neutron) ∆t (ps) = 122 × d × Ti (14.1 MeV DT neutron) , where ∆t is the FWHM in picoseconds and d is the target to detector distance in meters. Ti is the plasma ion temperature in kilo-electron volts. The plasma ion temperature was 0.5–1.0 keV in the FIREX project.25 To keep ∆t below 100 ps,
d < 18 cm for DD neutrons is required. In this study, however, the target to detector distance was limited to 30 cm by the solid angle of other plasma diagnostics detectors. In this case, ∆t is 170–230 ps. Bias voltage of −100 V was applied to titanium/gold electrode of the CVD diamond detector. In fast ignition, electromagnetic noise makes it difficult to obtain a neutron signal. To avoid severe noise, the whole measurement system was set in the shield box and metal tube. The measurement system was floated between the target chamber and metal port using a battery and insulation. III. RESULTS A. Alpha-particle-induced charge distribution measurements and drift velocity measurements using broadband current amplifier
Charge collection efficiency, energy resolution, and drift velocity of Hokkaido University’s sample and Element Six’s sample are presented in Table I. Figure 2 presents an example of alpha-particle-induced charge measurement of the former one (HU_3). The charge collection efficiency of
TABLE I. Charge transportation property of the diamond detector. Charge collection efficiency (%)
Energy resolution (%)
Drift velocity (×107 cm/s)
Electric field (V/µm)
Sample I. D
Hole
Electron
Hole
Electron
Hole
Electron
Hole
Electron
Thickness (µm)
HU_1 HU_2 HU_3 HU_4 HU_5 HU_6
100 98.6 100 95.3 96.4 98.9
95.8 98.6 96.5 93.2 92.7 93.6
0.52 1.3 0.70 1.3 1.2 0.38
1.1 1.1 1.1 1.2 1.3 1.4
N/A N/A 1.5 0.81 1.0 N/A
N/A N/A 1.3 0.93 0.82 N/A
1.3 1.1 0.85 1.5 1.2 2.0
1.6 3.7 0.85 1.2 1.1 2.0
63 54 139 90 95 102
E6_1 E6_2 E6_3
99.4 98.0 95.7
99.7 95.7 95.7
1.5 1.4 1.0
2.3 1.6 1.0
N/A N/A 0.94
N/A N/A 0.68
0.68 0.68 0.80
0.68 0.68 0.80
500 500 500
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Induced charge in planar type radiation semiconductor detector was given as qN0 dx, w where Q stands for the induced charge, q signifies the elementary charge, w denotes the sample thickness, and N0 represents the number of the generated charge carrier. Current i(t) is given as dQ =
dQ qN0 dx qN0 = = v. dt w dt w If the induced charge is equal, the pulse height and pulse width are determined by the drift velocity and sample thickness. For neutron ToF measurement under intense Xrays, space charge limited current mode,28 i.e., induced charge exceeds capacitance-bias voltage product, sufficient electric field was not supplied between electrodes. This brings pulse tailing and neutron signal burial in X-ray signal. In this measurement, we chose Hokkaido University’s sample which was approximately 100 µm of low thickness to suppress induced charge accompanied with intense X-rays. i (t) =
FIG. 2. Alpha-particle-induced charge distribution measurement.
99.5% ± 0.8% and 97.1% ± 1.4% for holes and electrons and energy resolution of 0.84% ± 0.4% and 1.8% ± 0.4% for holes and electrons were obtained by the three-sample average (HU_1-3). The latter one achieved charge collection efficiency of 97.7% ± 1.5% and 97.0% ± 1.8% for holes and electrons, energy resolution of 1.3% ± 0.2%, and 1.6% ± 0.5% by threesample averages (E6_1-3). The former one showed equivalent charge collection efficiency and superior energy resolution to those of the latter one. Figure 3(a) presents an example of the output pulse of the sample HU_4 with 90 µm thickness. A drift velocity calculated using 30 shots of output pulses was 1.1 ± 0.4 × 107 cm/s and 1.0 ± 0.3 × 107 cm/s for holes and electrons by the three sample average (HU_3-5). An electric field was 0.8-1.5 V/µm, which is sufficient to saturate charge collection. A frequency band of the measurement system was limited by 2 GHz of analog bandwidth of the broadband current amplifier. Therefore, the drift velocity was expected to be even larger than the value obtained in this experiment. Figure 3(b) presents an example of the output pulse of the latter one with 500 µm thickness (E6_3). The drift velocity was 0.94 ± 0.2 × 107 cm/s and 0.68 ± 0.2 × 107 cm/s for holes and electrons by 30 shots at electric field of 0.80 V/µm. These results were in good agreement with the experimentally obtained values that Pernegger et al.26 and Jansen et al.27 reported. These papers report more than 1 × 107 cm/sec of saturation drift velocities for Element Six’s sample. In this study, bias voltage was limited by current amplifier thus electric filed is not sufficient to saturate drift velocity.
B. Response function measurements for intense X-rays
Figure 4 shows the response function of the CVD diamond detector (HU_6) for high-intensity X-rays generated by the LFEX laser. Sample thickness was 102 µm. The solid line shows the output pulse for intense X-rays. Fast pulse with full width at half maximum of less than 1 ns and full width of several ns with no slow decay component were obtained, although signal ringing due to inductive connections to cable was observed. The dotted line shows the output pulse of a dummy detector, i.e., a detector without diamond. Velocities of the photon and 2.45 MeV DD neutron were 30 cm/ns and 2.1 cm/ns, respectively. For this experiment, the target detector distance was 30 cm. Therefore, DD neutron arrives 14 ns later than the X-rays reached the detector. The induced charge generated by intense X-rays was 7.6 × 10−11 C. The capacitance-bias product was 3 × 10−10, which was larger than the induced charge. Therefore, no space charge limited current was observed. For detector–target distance of 18 cm, 2.8 times the induced charge would be generated in the diamond. Nonetheless, the space charge limited current would be suppressed to increase bias voltage up to 300 V. Consequently, the neutron signal would be obtained separately from
FIG. 3. (a) Output pulse of the Hokkaido University CVD diamond detector (HU_4). (b) Output pulse of the Element Six CVD diamond detector (E6_3). This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 128.6.218.72 On: Wed, 03 Jun 2015 08:35:46
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recombination of charge carriers when intense X-rays arrive. Moreover, for ToF measurements with neutron yield of less than 109 neutron/shot, improving the neutron sensitivity, i.e., fabrication of multichannel array and using a neutron–proton conversion layer such as polyethylene are also required. V. PERSPECTIVES
FIG. 4. Response function of single-crystal CVD diamond detector for intense X-rays.
high-intensity X-rays in cases where the plasma ion temperature was 0.5–1 keV and sufficient neutron yield was obtained. In this study, the estimated neutron sensitivity calculated using the energy deposit and drift velocity was 1 × 10−7mV/DD neutrons. The neutron signal was not observed because of the large rapid frequency noise, which was brought by a trigger box with a faulty electromagnetic shield. This RF noise would be eliminated to replace the trigger box with a signal-light converter; the trigger signal would be converted into a signal–light–signal in the shield box. Results revealed that single-crystal CVD diamond detects neutron signal with good S/N under high-intensity X-ray with sufficient neutron yield of more than 109 neutrons/shot. This promising detector is expected to be useful as a substitute of fast response plastic and liquid scintillator with slow components because of high-intensity X-rays.
To realize a neutron burn history monitor with fast ignition, we plan to take the following steps in the near future. First, we will install a time fiducial system with a light-signal converter such as a silicon PIN photodiode to eliminate rapid frequency noise completely. Second, we will optimize the diamond thickness. Third, we will install a gate bias system for suppressing the intense X-ray signal. These steps are necessary to obtain good S/N. Similarly, we will obtain a response function for unfolding method using electron LINAC, which is necessary to achieve 100 ps time resolution. ACKNOWLEDGMENTS
This work was done with the support and under the auspices of the National Institute for Fusion Science Collaboration Research program (No. NIFS13KUGK078) and partially supported by Research Fellowships of the Japan Society for the Promotion of the Science for Young Scientists Grant No. 13J02500. The author would like to thank the FIREX group for the GEKKO XII experiment. 1J.
Lindl, Phys. Plasmas 2, 3933 (1995). Besnard, Eur. Phys. J. D 44, 207 (2007). 3K. Shigemori, H. Azechi, M. Nakai, M. Honda, K. Meguro, N. Miyanaga, H. Takabe, and K. Mima, Phys. Rev. Lett. 78, 250 (1997). 4M. Koga, Y. Arikawa, H. Azechi, Y. Fujimoto, S. Fujioka, H. Habara, Y. Hironaka, H. Homma, H. Hosoda, T. Jitsuno, T. Johzaki, J. Kawanaka, R. Kodama, K. Mima, N. Miyanaga, M. Murakami, H. Nagatomo, M. Nakai, Y. Nakata, H. Nakamura, H. Nishimura, T. Norimatsu, Y. Sakawa, N. Sarukura, K. Shigemori, H. Shiraga, T. Shimizu, H. Takabe, M. Tanabe, K. A. Tanaka, T. Tanimoto, T. Tsubakimoto, T. Watari, A. Sunahara, M. Isobe, A. Iwamoto, IV. DISCUSSION T. Mito, O. Motojima, T. Ozaki, H. Sakagami, T. Taguchi, Y. Nakao, H. Cai, M. Key, P. Norreys, and J. Pasley, Nucl. Instrum. Methods Phys. Res., Sect. Neutron yield is expected to increase up to 1011 A 653, 84 (2011). neutron/shot at the end of the FIREX I project in 2016. The 5N. Izumi, K. Yamaguchi, T. Yamagajo, T. Nakano, T. Kasai, T. Urano, H. dashed line in Figure 4 shows the estimated output pulse of the Azechi, S. Nakai, and T. Iida, Rev. Sci. Instrum. 70, 1221 (1999). 6T. Nagai, Y. Ioka, A. Hasegawa, K. Wada, S. Takaoku, M. Takata, K. detector for 1011 neutrons/shot. The target–detector distance Noritake, Y. Minami, K. Watanabe, K. Yamanoi, Y. Arikawa, H. Hosoda, is less than 5.7 cm to suppress ∆t less than 100 ps in this case. H. Nakamura, T. Watari, M. Cadatal-Raduban, M. Koga, T. Shimizu, N. In addition, high-intensity X-ray signal return to baseline in Sarukura, H. Shiraga, M. Nakai, T. Norimatsu, and H. Azechi, Jpn. J. Appl. 2.5 ns to measure the neutron signal separately from the X-ray Phys., Part 1 50, 080208 (2011). 7M. Koga, T. Fujiwara, T. Sakaiya, M. Lee, K. Shigemori, H. Shiraga, and signal. H. Azechi, Rev. Sci. Instrum. 79, 10E909 (2008). The X-ray signal obtained in this study returned to the 8M. Heya, M. Nakasuji, H. Shiraga, N. Miyanaga, H. Azechi, H. Takabe, T. baseline in several ns although ringing was observed. Given Yamanaka, and K. Mima, Rev. Sci. Instrum. 68, 820 (1997). 9R. A. Lerche, D. W. Phillion, and G. L. Tietbohl, Rev. Sci. Instrum. 66, 933 the limitation of bandwidth of 600 MHz oscilloscope, the (1995). FWHM of current signal of the detector must be even shorter. 10V. Yu. Glebov, C. Stoeckl, T. C. Sangster, S. Roberts, R. A. Lerche, and G. In the case the induced charge below capacitance-bias voltage J. Schmid, IEEE Trans. Plasma Sci. 33(1), 70 (2005). 11C. J. Horsfield, S. E. Caldwell, C. R. Christensen, S. C. Evans, J. M. Mack, product, the neutron signal will be obtained separately from T. Sedillo, C. S. Young, and V. Yu. Glebov, Rev. Sci. Instrum. 77, 10E724 X-ray signal. The target–detector distance becomes shorter; (2006). however, the current signal intensity increases concomitantly 12A. M. McEvoy, H. W. Herrmann, C. J. Horsfield, C. S. Young, E. K. Miller, with the increase of the solid angle. In such a case, the neutron J. M. Mack, Y. Kim, W. Stoeffl, M. Rubery, S. Evans, T. Sedillo, and Z. A. signal is buried in the intense X-ray signal with increased Ali, Rev. Sci. Instrum. 81, 10D322 (2010). 13J. M. Mack, S. E. Caldwell, S. C. Evans, T. J. Sedillo, D. C. Wilson, C. S. pulse width, rise and fall times, and the slow decay component Young, C. J. Horsfield, R. L. Griffith, and R. A. Lerche, Rev. Sci. Instrum. accompanied with the space charge limited current mode. To 77, 10E728 (2006). prevent neutron signal burial in the X-ray signal, installing 14R. M. Malone, H. M. Herrmann, W. Stoeffl, J. M. Mack, and C. S. Young, high voltage with a gate bias function is required to enhance Rev. Sci. Instrum. 79, 10E532 (2008). This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 2D.
128.6.218.72 On: Wed, 03 Jun 2015 08:35:46
053503-6 15T.
Shimaoka et al.
J. Murphy, C. W. Barnes, R. R. Berggren, P. Bradley, S. E. Caldwell, R. E. Chrien, J. R. Faulkner, P. L. Gobby, N. Hoffman, J. L. Jimerson, K. A. Klare, C. L. Lee, J. M. Mack, G. L. Morgan, J. A. Oertel, F. J. Swenson, P. J. Walsh, R. B. Walton, R. G. Watt, M. D. Wilke, D. C. Wilson, C. S. Young, S. W. Haan, R. A. Lerche, M. J. Moran, T. W. Phillips, T. C. Sangster, R. J. Leeper, C. L. Ruiz, G. W. Cooper, L. Disdier, A. Rouyer, A. Fedotoff, V. Yu. Glebov, D. D. Meyerhofer, J. M. Soures, C. Stöckl, J. A. Frenje, D. G. Hicks, C. K. Li, R. D. Petrasso, F. H. Seguin, K. Fletcher, S. Padalino, and R. K. Fisher, Rev. Sci. Instrum. 72, 773 (2001). 16M. A. Barrios, Rev. Sci. Instrum. 83, 10E105 (2012). 17H. G. Rinderknecht, M. Gatu Johnson, A. B. Zylstra, N. Sinenian, M. J. Rosenberg, J. A. Frenje, C. J. Waugh, C. K. Li, F. H. Sèguin, R. D. Petrasso, J. R. Rygg, J. R. Kimbrough, A. MacPhee, G. W. Collins, D. Hicks, A. Mackinnon, P. Bell, R. Bionta, T. Clancy, R. Zacharias, T. Döppner, H. S. Park, S. LePape, O. Landen, N. Meezan, E. I. Moses, V. U. Glebov, C. Stoeckl, T. C. Sangster, R. Olson, J. Kline, and J. Kilkenny, Rev. Sci. Instrum. 83, 10D902 (2012). 18R. Lauck, M. Brandis, and B. Bromberger, IEEE Trans. Nucl. Sci. 56(3), 989 (2009). 19K. Watanabe, Y. Arikawa, K. Yamanoi, M. Cadatal-Raduban, T. Nagai, M. Kouno, K. Sakai, T. Nazakato, T. Shimizu, N. Sarukura, M. Nakai, T. Norimatsu, H. Azechi, A. Yoshikawa, T. Murata, S. Fujino, H. Yoshida, N. Izumi, N. Satoh, and H. Kan, J. Cryst. Growth 362, 288 (2013). 20J. H. Kaneko, T. Tanaka, T. Imai, Y. Tanimura, M. Katagiri, T. Nishitani, H. Takeuchi, T. Sawamur, and T. Iida, Nucl. Instrum. Methods Phys. Res., Sect. A 505, 187–190 (2003).
Rev. Sci. Instrum. 86, 053503 (2015) 21J.
Hammersberg, J. Isberg, E. Johansson, T. Lundstrom, O. Hjortstam, and H. Bernhoff, Diamond Relat. Mater. 10, 574–579 (2001). 22J. H. Kaneko, F. Fujita, Y. Konno, T. Gotoh, N. Nishi, H. Watanabe, A. Chayahara, H. Umezawa, N. Tsubouchi, S. Shikata, and M. Isobe, Diamond Relat. Mater. 26, 45 (2012). 23N. Tsubouchi, Y. Mokuno, A. Kakimoto, F. Fujita, J. H. Kaneko, H. Yamada, A. Chayahara, and S. Shikata, Nucl. Instrum. Methods Phys. Res., Sect. B 286, 313 (2012). 24S. F. Kozlov, IEEE Trans. Nucl. Sci. 22, 160 (1975). 25H. Shiraga, S. Fujioka, M. Nakai, T. Watari, H. Nakamura, Y. Arikawa, H. Hosoda, T. Nagai, M. Koga, H. Kikuchi, Y. Ishii, T. Sogo, K. Shigemori, H. Nishimura, Z. Zhang, M. Tanabe, S. Ohira, Y. Fujii, T. Namimoto, Y. Sakawa, O. Maegawa, T. Ozaki, K. A. Tanaka, H. Habara, T. Iwawaki, K. Shimada, H. Nagatomo, T. Johzaki, A. Sunahara, M. Murakami, H. Sakagami, T. Taguchi, T. Norimatsu, H. Homma, Y. Fujimoto, A. Iwamoto, N. Miyanaga, J. Kawanaka, T. Jitsuno, Y. Nakata, K. Tsubakimoto, K. Sueda, N. Morio, S. Matsuo, T. Kawasaki, K. Sawai, K. Tsuji, H. Murakami, T. Kanabe, K. Kondo, R. Kodama, N. Sarukura, T. Shimizu, K. Mima, H. Azechi et al., High Energy Density Phys. 8, 227 (2012). 26H. Pernegger, S. Ro, P. Weilhammer, H. Frais-Kölbl, E. Griesmayer, H. Kagan, S. Schnetzer, R. Stone, W. Trischuk, D. Twitchen, and A. Whitehead, J. Appl. Phys. 97, 073704 (2005). 27H. Jansen, D. Dobos, T. Eisel, H. Pernegger, V. Eremin, and N. Wermes, J. Appl. Phys. 113, 173706 (2013). 28J. Isberg, M. Gabrysch, S. Majdi, K. K. Kovi, and D. Twitchen, Solid State Sci. 13, 1065 (2011).
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 128.6.218.72 On: Wed, 03 Jun 2015 08:35:46
