Commissioning of helium injector for coupled radio frequency quadrupole and separated function radio frequency quadrupole acceleratora) Shixiang Peng, Jia Chen, Haitao Ren, Jie Zhao, Yuan Xu, Tao Zhang, Ailing Zhang, Wenlong Xia, Shuli Gao, Zhi Wang, Yuting Luo, Zhiyu Guo, and Jia'er Chen Citation: Review of Scientific Instruments 85, 02A712 (2014); doi: 10.1063/1.4828375 View online: http://dx.doi.org/10.1063/1.4828375 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/85/2?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Design, development, and acceleration trials of radio-frequency quadrupole Rev. Sci. Instrum. 85, 043304 (2014); 10.1063/1.4869337 Design and development of a radio frequency quadrupole linac postaccelerator for the Variable Energy Cyclotron Center rare ion beam project Rev. Sci. Instrum. 81, 023301 (2010); 10.1063/1.3280175 Direct plasma injection scheme with beam extraction in a radio frequency quadrupole linac cavitya) Rev. Sci. Instrum. 79, 02C716 (2008); 10.1063/1.2823898 High-order maps with acceleration for optimization of electrostatic and radio-frequency ion-optical elements Rev. Sci. Instrum. 73, 3174 (2002); 10.1063/1.1497499 Construction of a variable-frequency radio-frequency quadrupole linac for the RIKEN heavy-ion linac Rev. Sci. Instrum. 70, 4523 (1999); 10.1063/1.1150105
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REVIEW OF SCIENTIFIC INSTRUMENTS 85, 02A712 (2014)
Commissioning of helium injector for coupled radio frequency quadrupole and separated function radio frequency quadrupole acceleratora) Shixiang Peng,1,b) Jia Chen,1 Haitao Ren,1 Jie Zhao,1 Yuan Xu,1 Tao Zhang,1 Ailing Zhang,1,2 Wenlong Xia,1 Shuli Gao,1 Zhi Wang,1 Yuting Luo,1 Zhiyu Guo,1 and Jia’er Chen1,2 1 2
SKLNPT and IHIP, School of Physics, Peking University, Beijing 100871, People’s Republic of China University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
(Presented 12 September 2013; received 6 September 2013; accepted 10 October 2013; published online 15 November 2013) A project to study a new type of acceleration structure has been launched at Peking University, in which a traditional radio frequency quadrupole (RFQ) and a separated function radio frequency quadrupole are coupled in one cavity to accelerate the He+ beam. A helium injector for this project is developed. The injector consists of a 2.45 GHz permanent magnet electron cyclotron resonance ion source and a 1.16 m long low energy beam transport (LEBT). The commissioning of this injector was carried out and an onsite test was held in June 2013. A 14 mA He+ beam with the energy of 30 keV has been delivered to the end of the LEBT, where a diaphragm with the diameter of 7 mm is located. The position of the diaphragm corresponds to the entrance of the RFQ electrodes. The beam emittance and fraction were measured after the 7 mm diaphragm. Its rms emittance is about 0.14 π mm mrad and the fraction of He+ is about 99%. © 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4828375] I. INTRODUCTION
The traditional radio frequency quadrupole (RFQ) is widely used all over the world due to its capability of doing transversal beam focusing, longitudinal beam accelerating, and bunching synchronically. However, due to the constraint for the accelerating factor A and the focusing factor F of A + F = 1, the RF efficiency of RFQs is limited when beam is accelerated to relatively high energy, while the post RFQ structure like Draft Tube Linac (DTL) is restricted to accelerate these MeV beams with relatively low efficiency. To solve this dilemma, many post-RFQ and ante-DTL structures are proposed, such as Rf-Focused Interdigital (RFI) or hybrid RFQ.1, 2 With the same purpose, a structure called separated function radio frequency quadrupole (SFRFQ) was proposed in Peking University (PKU).3 This structure separates the focusing and accelerating functions of an RFQ by means of eliminating the RFQ surface modulation and adding accelerating diaphragms.4 Previous SFRFQ prototype experiments demonstrate higher RF efficiency and more compact accelerating length.5, 6 In order to combine both advantages of the RFQ and the SFRFQ, a coupled RFQ and SFRFQ (CRS) cavity is proposed in PKU to integrate these two structures into one cavity.6 This cavity is designed to accelerate He+ from 7.5 keV/u to 201.2 keV/u with a current of 5 mA, which would be used to do radiation research in PKU.7 The linac length is reduced from 3.25 m to 2.5 m. For the sake of producing and transporting qualified beam for this CRS cavity, a helium injector a) Contributed paper, published as part of the Proceedings of the 15th Interna-
tional Conference on Ion Sources, Chiba, Japan, September 2013. b) Author to whom correspondence should be addressed. Electronic mail:
with particular parameters, which are shown in Table I, was designed. In this paper, besides a brief introduction in Sec. I, the design and assembly of the injector and its measurement system will be presented in Sec. II, which is followed by the commissioning results in Sec. III and a discussion at the end. II. SYSTEM AND DIAGNOSTIC METHODS A. He+ injector
The helium injector for the CRS cavity was developed based on previous design experience accumulated at the Peking University neutron imaging facility (PKUNIFTY).8 Given the compact framework and the beam manipulating convenience, the helium injector was designed to consist of a permanent magnet electron cyclotron resonance ion source (PMECRIS) and a 1.16 m long low energy beam transport (LEBT) containing two solenoids. As Fig. 1 shows, the limited LEBT length of 1.16 m contains the following elements: a 20 mm gap for RFQ electrode safety, a 20 mm space occupied by the RFQ cavity front flange, a tri-electrode TABLE I. Injector design parameters. Parameters He+ beam current Energy Macro-pulse frequency Pulse length Emittance (norm rms) α β
Unit
Value
mA keV Hz ms π mm mrad cm/rad
10 30 166 or CW 1 0.15 1.447 7.7064
[email protected] 0034-6748/2014/85(2)/02A712/3/$30.00
85, 02A712-1
© 2013 AIP Publishing LLC
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02A712-2
Peng et al.
Rev. Sci. Instrum. 85, 02A712 (2014)
FIG. 3. The helium injector and the beam measurement system. FIG. 1. Mechanical view of the helium injector.
system, a faraday cup (FC), 2 solenoids, 2 steering magnets, a heavy ion collimator (HIC), a beam intensity tuning aperture (BITA), an alternating-current current transformer (ACCT), an electron trap, and 2 valves. For the ion source and first drift part, we kept our matryoshka structure that first developed for PKUNIFTY.9 Compared with PKUNIFTY, four improvements were adopted for the helium injector: a front compensation gas inlet, a kicker installation position, a BITA which was named as 4-quadrant diaphragm in the referred paper, and the LEBT length optimization.10
B. Beam measurement system
For the purpose of measuring the beam parameters of the beam coming from the injector, a beam measurement system was designed and manufactured. The schematic drawing of this measurement system is depicted in the box in Fig. 2. As it is shown, the measurement system consists of a 4-quadrant diaphragm (4-QD), a high intensity beam emittance measurement unit (HIBEMU) with its slit cup (FC2) and a dipole analysis magnet (DAM).11 The 4QD simulates the entrance of the RFQ poles, and has the same aperture diameter as the RFQ, i.e., 7 mm. The four sections of diaphragms are isolated to each other and each connected to ampere meters so that the trajectory deviation of the helium beam can be observed. The HIBEMU is used to measure the beam emittance and the Twiss parameters. The slit cup (FC2)
FIG. 2. The beam measurement system.
can also be used to measure the beam current. Figure 3 shows a complete view of the helium injector and its beam measurement system. III. COMMISSIONING RESULTS A. Optimized operational parameters
After the assembly of the helium injector and the beam measurement system had been completed, preliminary tests were performed yielding positive results.9 The ECR ion source is capable of ionizing helium gas and over 10 mA helium ion beam current was extracted at 30 keV. In order to inject a qualified ion beam into the CRS cavity, many operational parameters can be adjusted to manipulate the beam, among which the setting of the focus currents of the 2 solenoids are crucial. A two-dimensional scan of the currents of the 2 solenoids was performed, and the slit cup current was recorded as a function of the 2 solenoid currents. The scanning result is shown in Fig. 4. The red plateau in Fig. 4 indicates an area of effective solenoid current settings for which a relatively high beam current was delivered to the slit cup of HIBEMU. According to the scan results, the effective plateau is located in the range of 310 A–360 A for the first solenoid and 345 A–360 A for the second solenoid. For the subsequent experiments the setting corresponds to 346 A in the first solenoid and 351 A in the second solenoid.
FIG. 4. Scan result: beam intensity at the slit cup as a function of solenoids currents.
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02A712-3
Peng et al.
FIG. 5. Current measurements: currents obtained at FC1, ACCT, and slit cup under the same conditions.
Rev. Sci. Instrum. 85, 02A712 (2014)
FIG. 6. Three ion fractions in the scan through the magnetic field strength of the dipole.
IV. CONCLUSIONS B. Beam currents and LEBT transport efficiency
There are three beam current measurement points along the beam line including faraday cup 1 (FC1) behind the extraction system, the ACCT prior to the 4-QD, and the slit cup of HIBEMU behind the 4-QD. The three beam currents measured are shown in Fig. 5. All 3 pulses have flat tops with short rise and fall time. These characteristics indicate good injector performance in beam production and transport. The peak currents at FC1, ACCT and slit cup are 15.7 mA, 13.7 mA, and 13 mA, respectively. Based on these numbers, the LEBT transport efficiency is 87.5%. Approximately 0.7 mA ion beam is lost at the 4-quadrant diaphragm and tube wall.
C. Emittance and ion fraction
The result of the emittance measurement of the helium beam is 0.16 π mm mrad. Considering and correcting the errors introduced by the misalignment and deformation of the slit molybdenum plate in the slit cup, the real emittance is reconstructed to be 0.14 π mm mrad. The Twiss parameters satisfy the requirements in Table I. The ion fraction is measured by scanning through the DAM current to manipulate the magnetic field of the vacuum box. During the scan three current pulse peaks were observed at the faraday cup located at the end of the vacuum box at magnet currents of 1.41 A, 2.68 A, or 5.17 A, respectively. As Fig. 6 shows, these three peaks can be identified as H+ , He+ , and other ions. The ion fraction of He+ is 99.6%.
With the purpose of injecting a qualified beam into the CRS cavity to study this new type of accelerating structure, a helium injector was designed at PKU. The design, manufacturing, and assembly were completed in early 2013. A beam measurement system was designed to measure the beam current, the emittance, and the ion fraction. All experiments were completed in June and showed positive results. The presented helium injector satisfies or even surpasses all design requirements. The on-site test of this injector will be carried out once the assembly of the CRS cavity is completed. ACKNOWLEDGMENTS
This work is supported by NSFC, Grant Nos. 11075008 and 11175009. 1 W.
J. Starling and D. A. Swenson, Nucl. Instrum. Methods Phys. Res. B 261, 21–24 (2007). 2 P. N. Ostroumov, A. A. Kolomiets, S. Sharma, N. E. Vinogradov, and G. P. Zinkann, Nucl. Instrum. Methods Phys. Res. A 547, 259–269 (2005). 3 J. E. Chen, J. X. Fang, W. G. Li, Y. Wu, and X. Q. Yan, Prog. Nat. Sci. 23, 12 (2002). 4 X. Q. Yan, C. E. Chen, J. X. Fang, Z. Y. Guo, and Y. R. Lu, Nucl. Instrum. Methods Phys. Res. A 539, 606–612 (2005). 5 Z. Wang, J. E. Chen et al., Nucl. Instrum. Methods Phys. Res. A 607, 522– 526 (2009). 6 Z. Wang, J. E. Chen et al., Phys. Rev. ST Accel. Beams 15, 050101 (2012). 7 W. L. Xia, Z. Wang et al., in Proceedings of 4th International Particle Accelerator Conference, TUPWA023, Shanghai, 2013. 8 H. T. Ren, S. X. Peng et al., Rev. Sci. Instrum. 81, 02B714 (2010). 9 H. T. Ren, J. Zhao et al., “Handling radiation generated during an ion source commissioning,” Rev. Sci. Instrum. (these proceedings). 10 Jia Chen, Shixiang Peng et al., in Proceedings of 4th International Particle Accelerator Conference, MOPFI033, Shanghai, 2013. 11 P. N. Lu, S. X. Peng, Z. X. Yuan, J. Zhao, H. T. Ren, Z. Y. Guo, and Y. R. Lu, in Proceedings of DIPAC2011, TUPD65, Hamburg, 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: 129.174.21.5 On: Tue, 23 Dec 2014 23:32:36
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: 129.174.21.5 On: Tue, 23 Dec 2014 23:32:36
REVIEW OF SCIENTIFIC INSTRUMENTS 85, 02A712 (2014)
Commissioning of helium injector for coupled radio frequency quadrupole and separated function radio frequency quadrupole acceleratora) Shixiang Peng,1,b) Jia Chen,1 Haitao Ren,1 Jie Zhao,1 Yuan Xu,1 Tao Zhang,1 Ailing Zhang,1,2 Wenlong Xia,1 Shuli Gao,1 Zhi Wang,1 Yuting Luo,1 Zhiyu Guo,1 and Jia’er Chen1,2 1 2
SKLNPT and IHIP, School of Physics, Peking University, Beijing 100871, People’s Republic of China University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
(Presented 12 September 2013; received 6 September 2013; accepted 10 October 2013; published online 15 November 2013) A project to study a new type of acceleration structure has been launched at Peking University, in which a traditional radio frequency quadrupole (RFQ) and a separated function radio frequency quadrupole are coupled in one cavity to accelerate the He+ beam. A helium injector for this project is developed. The injector consists of a 2.45 GHz permanent magnet electron cyclotron resonance ion source and a 1.16 m long low energy beam transport (LEBT). The commissioning of this injector was carried out and an onsite test was held in June 2013. A 14 mA He+ beam with the energy of 30 keV has been delivered to the end of the LEBT, where a diaphragm with the diameter of 7 mm is located. The position of the diaphragm corresponds to the entrance of the RFQ electrodes. The beam emittance and fraction were measured after the 7 mm diaphragm. Its rms emittance is about 0.14 π mm mrad and the fraction of He+ is about 99%. © 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4828375] I. INTRODUCTION
The traditional radio frequency quadrupole (RFQ) is widely used all over the world due to its capability of doing transversal beam focusing, longitudinal beam accelerating, and bunching synchronically. However, due to the constraint for the accelerating factor A and the focusing factor F of A + F = 1, the RF efficiency of RFQs is limited when beam is accelerated to relatively high energy, while the post RFQ structure like Draft Tube Linac (DTL) is restricted to accelerate these MeV beams with relatively low efficiency. To solve this dilemma, many post-RFQ and ante-DTL structures are proposed, such as Rf-Focused Interdigital (RFI) or hybrid RFQ.1, 2 With the same purpose, a structure called separated function radio frequency quadrupole (SFRFQ) was proposed in Peking University (PKU).3 This structure separates the focusing and accelerating functions of an RFQ by means of eliminating the RFQ surface modulation and adding accelerating diaphragms.4 Previous SFRFQ prototype experiments demonstrate higher RF efficiency and more compact accelerating length.5, 6 In order to combine both advantages of the RFQ and the SFRFQ, a coupled RFQ and SFRFQ (CRS) cavity is proposed in PKU to integrate these two structures into one cavity.6 This cavity is designed to accelerate He+ from 7.5 keV/u to 201.2 keV/u with a current of 5 mA, which would be used to do radiation research in PKU.7 The linac length is reduced from 3.25 m to 2.5 m. For the sake of producing and transporting qualified beam for this CRS cavity, a helium injector a) Contributed paper, published as part of the Proceedings of the 15th Interna-
tional Conference on Ion Sources, Chiba, Japan, September 2013. b) Author to whom correspondence should be addressed. Electronic mail:
with particular parameters, which are shown in Table I, was designed. In this paper, besides a brief introduction in Sec. I, the design and assembly of the injector and its measurement system will be presented in Sec. II, which is followed by the commissioning results in Sec. III and a discussion at the end. II. SYSTEM AND DIAGNOSTIC METHODS A. He+ injector
The helium injector for the CRS cavity was developed based on previous design experience accumulated at the Peking University neutron imaging facility (PKUNIFTY).8 Given the compact framework and the beam manipulating convenience, the helium injector was designed to consist of a permanent magnet electron cyclotron resonance ion source (PMECRIS) and a 1.16 m long low energy beam transport (LEBT) containing two solenoids. As Fig. 1 shows, the limited LEBT length of 1.16 m contains the following elements: a 20 mm gap for RFQ electrode safety, a 20 mm space occupied by the RFQ cavity front flange, a tri-electrode TABLE I. Injector design parameters. Parameters He+ beam current Energy Macro-pulse frequency Pulse length Emittance (norm rms) α β
Unit
Value
mA keV Hz ms π mm mrad cm/rad
10 30 166 or CW 1 0.15 1.447 7.7064
[email protected] 0034-6748/2014/85(2)/02A712/3/$30.00
85, 02A712-1
© 2013 AIP Publishing LLC
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: 129.174.21.5 On: Tue, 23 Dec 2014 23:32:36
02A712-2
Peng et al.
Rev. Sci. Instrum. 85, 02A712 (2014)
FIG. 3. The helium injector and the beam measurement system. FIG. 1. Mechanical view of the helium injector.
system, a faraday cup (FC), 2 solenoids, 2 steering magnets, a heavy ion collimator (HIC), a beam intensity tuning aperture (BITA), an alternating-current current transformer (ACCT), an electron trap, and 2 valves. For the ion source and first drift part, we kept our matryoshka structure that first developed for PKUNIFTY.9 Compared with PKUNIFTY, four improvements were adopted for the helium injector: a front compensation gas inlet, a kicker installation position, a BITA which was named as 4-quadrant diaphragm in the referred paper, and the LEBT length optimization.10
B. Beam measurement system
For the purpose of measuring the beam parameters of the beam coming from the injector, a beam measurement system was designed and manufactured. The schematic drawing of this measurement system is depicted in the box in Fig. 2. As it is shown, the measurement system consists of a 4-quadrant diaphragm (4-QD), a high intensity beam emittance measurement unit (HIBEMU) with its slit cup (FC2) and a dipole analysis magnet (DAM).11 The 4QD simulates the entrance of the RFQ poles, and has the same aperture diameter as the RFQ, i.e., 7 mm. The four sections of diaphragms are isolated to each other and each connected to ampere meters so that the trajectory deviation of the helium beam can be observed. The HIBEMU is used to measure the beam emittance and the Twiss parameters. The slit cup (FC2)
FIG. 2. The beam measurement system.
can also be used to measure the beam current. Figure 3 shows a complete view of the helium injector and its beam measurement system. III. COMMISSIONING RESULTS A. Optimized operational parameters
After the assembly of the helium injector and the beam measurement system had been completed, preliminary tests were performed yielding positive results.9 The ECR ion source is capable of ionizing helium gas and over 10 mA helium ion beam current was extracted at 30 keV. In order to inject a qualified ion beam into the CRS cavity, many operational parameters can be adjusted to manipulate the beam, among which the setting of the focus currents of the 2 solenoids are crucial. A two-dimensional scan of the currents of the 2 solenoids was performed, and the slit cup current was recorded as a function of the 2 solenoid currents. The scanning result is shown in Fig. 4. The red plateau in Fig. 4 indicates an area of effective solenoid current settings for which a relatively high beam current was delivered to the slit cup of HIBEMU. According to the scan results, the effective plateau is located in the range of 310 A–360 A for the first solenoid and 345 A–360 A for the second solenoid. For the subsequent experiments the setting corresponds to 346 A in the first solenoid and 351 A in the second solenoid.
FIG. 4. Scan result: beam intensity at the slit cup as a function of solenoids currents.
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02A712-3
Peng et al.
FIG. 5. Current measurements: currents obtained at FC1, ACCT, and slit cup under the same conditions.
Rev. Sci. Instrum. 85, 02A712 (2014)
FIG. 6. Three ion fractions in the scan through the magnetic field strength of the dipole.
IV. CONCLUSIONS B. Beam currents and LEBT transport efficiency
There are three beam current measurement points along the beam line including faraday cup 1 (FC1) behind the extraction system, the ACCT prior to the 4-QD, and the slit cup of HIBEMU behind the 4-QD. The three beam currents measured are shown in Fig. 5. All 3 pulses have flat tops with short rise and fall time. These characteristics indicate good injector performance in beam production and transport. The peak currents at FC1, ACCT and slit cup are 15.7 mA, 13.7 mA, and 13 mA, respectively. Based on these numbers, the LEBT transport efficiency is 87.5%. Approximately 0.7 mA ion beam is lost at the 4-quadrant diaphragm and tube wall.
C. Emittance and ion fraction
The result of the emittance measurement of the helium beam is 0.16 π mm mrad. Considering and correcting the errors introduced by the misalignment and deformation of the slit molybdenum plate in the slit cup, the real emittance is reconstructed to be 0.14 π mm mrad. The Twiss parameters satisfy the requirements in Table I. The ion fraction is measured by scanning through the DAM current to manipulate the magnetic field of the vacuum box. During the scan three current pulse peaks were observed at the faraday cup located at the end of the vacuum box at magnet currents of 1.41 A, 2.68 A, or 5.17 A, respectively. As Fig. 6 shows, these three peaks can be identified as H+ , He+ , and other ions. The ion fraction of He+ is 99.6%.
With the purpose of injecting a qualified beam into the CRS cavity to study this new type of accelerating structure, a helium injector was designed at PKU. The design, manufacturing, and assembly were completed in early 2013. A beam measurement system was designed to measure the beam current, the emittance, and the ion fraction. All experiments were completed in June and showed positive results. The presented helium injector satisfies or even surpasses all design requirements. The on-site test of this injector will be carried out once the assembly of the CRS cavity is completed. ACKNOWLEDGMENTS
This work is supported by NSFC, Grant Nos. 11075008 and 11175009. 1 W.
J. Starling and D. A. Swenson, Nucl. Instrum. Methods Phys. Res. B 261, 21–24 (2007). 2 P. N. Ostroumov, A. A. Kolomiets, S. Sharma, N. E. Vinogradov, and G. P. Zinkann, Nucl. Instrum. Methods Phys. Res. A 547, 259–269 (2005). 3 J. E. Chen, J. X. Fang, W. G. Li, Y. Wu, and X. Q. Yan, Prog. Nat. Sci. 23, 12 (2002). 4 X. Q. Yan, C. E. Chen, J. X. Fang, Z. Y. Guo, and Y. R. Lu, Nucl. Instrum. Methods Phys. Res. A 539, 606–612 (2005). 5 Z. Wang, J. E. Chen et al., Nucl. Instrum. Methods Phys. Res. A 607, 522– 526 (2009). 6 Z. Wang, J. E. Chen et al., Phys. Rev. ST Accel. Beams 15, 050101 (2012). 7 W. L. Xia, Z. Wang et al., in Proceedings of 4th International Particle Accelerator Conference, TUPWA023, Shanghai, 2013. 8 H. T. Ren, S. X. Peng et al., Rev. Sci. Instrum. 81, 02B714 (2010). 9 H. T. Ren, J. Zhao et al., “Handling radiation generated during an ion source commissioning,” Rev. Sci. Instrum. (these proceedings). 10 Jia Chen, Shixiang Peng et al., in Proceedings of 4th International Particle Accelerator Conference, MOPFI033, Shanghai, 2013. 11 P. N. Lu, S. X. Peng, Z. X. Yuan, J. Zhao, H. T. Ren, Z. Y. Guo, and Y. R. Lu, in Proceedings of DIPAC2011, TUPD65, Hamburg, 2011.
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