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Improvement of ionization chamber for tritium measurements in in-pile tritium extraction experiments
Fusion Engineering and Design 147 (2019) 111222
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Improvement of ionization chamber for tritium measurements in in-pile tritium extraction experiments
T
⁎
Zhilin Chen , Shuming Peng, Ping Chen, Ruiming Chang, Guanyin Wu, Yu Li Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, 621900, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Tritium measurement Ionization chamber Fusion Tritium breeding
Ionization chamber with gold plated wire-wall based on flange structure has been developed for tritium measurements in in-pile tritium extraction experiments. Performance of the improved ionization chamber on airtight and memory effect was greatly enhanced. Gas leakage rate of the chamber was lower than 1.0*10−13 Pa. m3/s with the flange structure. Both tritiated water vapor and tritium in gaseous form have been used in experiments to examine the influence of memory effect caused by tritium absorption on chamber wall. Results indicate that with the design of gold plated wire wall, output signal of the ionization chamber can recover to background level within 1 min after 1 h exposure in tritiated water vapor at 3.0*108 Bq/m3 created by bubbling. While recovery time is less than 20 s after being exposed to tritium in gaseous form at 3.9*1010 Bq/m3 for 7 days.
1. Introduction
memory effect of the improved ionization chamber.
Real time and in-line tritium measurement is very important to obtain the release behavior of tritium breeding materials for both inpile and out-pile tritium extraction experiments which is one of the key issues to support tritium self-sufficiency in a fusion reactor [1–5]. In the Institute of Nuclear Physics and Chemistry (INPC) lots of out-pile experiments have been carried out to examine tritium release behavior of Li4SiO4 pellets, and ionization chambers were used to measure tritium concentration in-line [6–10]. Although the inner surface of ionization chamber used in out-pile experiments was gold plated to weaken the influence of memory effect caused by tritium absorption on inner surface, it was contaminated after several runs due to the absorption of both HTO and HT released by tritium breeder, and decontamination treatment was necessary to deal with the chamber. Recently a new inpile tritium extraction test facility is under construction in INPC which will be operated in continuous mode, and each run might last more than one week. Therefore ionization chambers with low memory effect are very important to obtain the exact tritium concentration in-line. Furthermore, better airtight performance is also essential to prevent tritium leakage especially when high level tritium presents in in-pile tritium extraction experiments. To improve the performance of the current used ionization chamber on both memory effect and airtight ability, an improved kind of ionization chamber with gold plated wirewall based on flange structure has been developed. Experiments with both HTO and HT have been carried out separately to investigate the
2. Design of the ionization chamber
⁎
For an ionization chamber of cylinder shape, theoretically the saturation ionization current (Is ) can be denoted as:
Is =
E ⋅e E ⋅e ¯ ⋅C⋅V ⋅η1⋅ξ + ⋅D⋅S⋅η2⋅ξ W W
(1)
E is the average energy of beta ray from tritium, eV. e is elementary charge, 1.602*10−19 C. C is tritium concentration in the chamber, Bq/cm3. V is the sensitive volume of the chamber, cm3. η1 is energy deposition rate of beta rays emitted by tritium in the sensitive region of the chamber. ξ is the charge collection rate of an ionization chamber. W is the average ionization energy of carrier gas in the chamber, eV. D¯ is average tritium contamination level on the surface around the sensitive region of the chamber, Bq/cm2. S is the total surface area around the sensitive region of the chamber, cm2. η2 is energy deposition rate of beta rays emitted by tritium absorbed on the surface around the sensitive region of the chamber. Generally most beta rays emitted by tritium in the sensitive region of the chamber will deposit all their energy into the sensitive region of the chamber and devote to final signal output, and the values of η1 and ξ
Corresponding author. E-mail address: [email protected] (Z. Chen).
https://doi.org/10.1016/j.fusengdes.2019.05.041 Received 9 October 2018; Received in revised form 28 May 2019; Accepted 29 May 2019 0920-3796/ © 2019 Elsevier B.V. All rights reserved.
Fusion Engineering and Design 147 (2019) 111222
Z. Chen, et al.
PV = nRT with a standard container of given volume. Relationship between the measured current (Im ) of the ionization chamber and tritium concentration (CTS ) derived from the given tritium gas standard can be expressed as, Im = CTS⋅k
(2)
where k is the response factor of the ionization chamber. Then the response factor k can be obtained,
k=
Im CTS
(3)
Three runs were carried out in calibration experiments, and tritium concentration (CTS ) in each run was different. Gas pressure in the ionization chamber during calibration was 95 kPa, while temperature in laboratory was 21 ℃. Results are shown in Table 1. In Table 1, tritium measurement uncertainty is denoted by μk = δ I2m + μC2TS , where Im is the measured current, and δ Im is the uncertainty of Im . μCTS is the uncertainty of tritium standard gas, which is determined by the uncertainty of both tritium source ( μS ) and the volume ( μ V ),
Fig. 1. 3D view of the ionization chamber.
μCTS = μS2 + μV2 . Results in Table 1 show that response factor (k) of the ionization chamber is around 1.10*10−21 A/(Bq/m3), and the relative deviation (Dk = ∑ (|ki − k |)/ k ) is smaller than 2.0%. The measured uncertainty ( μk ) is 3.3% at 4.62*108 Bq/m3, while it is 7.2% at 1.25*107 Bq/m3.
will be nearly 1.0 [11]. While the value of η2 is around 0.5 in common conditions [12]. The second part of Eq. (1) is contributed by memory effect and it is directly determined by the total amount of tritium absorbed on the surface of components around the sensitive region of the chamber. It’s obvious that decrease of inner surface area (S) is an effective way to reduce the output signal caused by memory effect. Therefore wire wall composed of gold plated tungsten wire of 0.05 mm in radius is used instead of sealed wall in the chamber, and wall surface area is reduced to about 1% of the previous chamber with the same size. Furthermore, 316 L stainless steel is chosen as the main body material and the inner part of the whole chamber is gold plated to reduce the absorption of tritium. The chamber is constructed based on flange structure. Both connectors and pipes are welded onto the flange to ensure the airtight performance. The sensitive volume of the ionization chamber is 50 mL. The 3D view of the ionization chamber is shown in Fig. 1.
3.2. Memory effect Comparing with HT, tritium in HTO form is much easier to be absorbed on the inner surface of an ionization chamber and results in serious memory effect. As depicted in Ref.6, part of tritium released by tritium breeder Li4SiO4 is in HTO form. Therefore, the influence of HTO vapor on tritium measurements must be checked before the developed ionization chamber is used in the in-pile experiments. To test the performance of the developed ionization chamber on memory effect, both tritiated water vapor and tritium in gaseous form were used in experiments. Tritiated water vapor was obtained by bubbling with dry air in tritiated water. Experimental setup of bubbling system is shown in Fig. 3. In Fig. 3, three bubblers were used in experiments. Firstly, dry air was pumped into bubbler-1 by a micro-pump, and a bottle filled with dryer (CaCl2) was used to absorb water vapor in the air before it entering bubbler-1. A flow meter was employed to control the gas flow rate. After passing through the ionization chamber, gas with tritiated vapor was washed in both bubbler-2 and bubbler-3 before it was discharged into fuming hood. In experiments, the ionization chamber was exposed to HTO vapor of 3.0*108 Bq/m3 about 1 h, then flushed with fresh dry air. Gas flow rate in experiments was set to be 0.6 L/min. Tritium concentration is obtained by CT = Im/ k , where k is 1.35*10−21 A/(Bq/m3) for tritium in air. Results are shown in Fig. 4. In Fig. 4, it shows that output signal of the improved ionization chamber can recover to background level within 1 min after flushing with fresh dry air. Furthermore, the ionization chamber was also tested with tritium in gaseous form. In experiments, tritium concentration of 3.9*1010 Bq/m3 was kept in the ionization chamber for about 7 days to examine the influence of memory effect. And after that, tritium gas was pumped out and the ionization chamber was flushed with fresh dry air. Results are shown in Fig. 5. In Fig. 5, it's obvious that output signal of the improved ionization chamber decreases greatly just after tritium gas being pumped out, and it can recover to background level (7.4*106 Bq/m3) within 20 s. Results depicted in Figs. 4 and 5 show that with structure of wire wall and gold plated treatment, the influence of memory effect on output signal of the ionization chamber is effectively reduced to the level lower than the LOD of the chamber. In addition, the electric field
3. Experimental tests and discussions Experiments have been carried out to examine the performance of the developed ionization chamber before it can be applied to the in-pile tritium extraction experiments. Firstly, tritium standard gas is used to test the response of the chamber. Secondly, both tritiated water vapor and high level tritium in gaseous form were used to check the memory effect of the improved ionization chamber. Tritiated water vapor was generated by bubbling in tritiated water. The limit of detection (LOD) of the improved ionization chamber is 7.4*106 Bq/m3 (for air). Before tritium was introduced into the chamber, the airtight performance was examined by mass spectrometer, and it turned out that leakage rate of the improved chamber was lower than 1.0*10−13 Pa. m3/s. In experiments, current meter model 6517 B (Keithley company, USA) was used to measure the signal output of the ionization chamber. 100 V was applied to the wire wall to ensure the ionization chamber be operated in saturation mode. 3.1. Calibration of the ionization chamber Tritium standard gas set modeled TRITON CL-1 made by Johnston company was used in the calibration. Tritium concentration is 5.994 × 109 Bq/m3 by April 27th, 2017, and the accuracy of the tritium concentration is 2.0%. The calibration system based on TRITON CL-1 is shown in Fig. 2. In experiments, tritium standard gas was firstly introduced into volume I and then into ionization chamber. Volume II is used to determine the amount of helium gas filled into the ionization chamber. The volume of both volume I and volume II was determined by 2
Fusion Engineering and Design 147 (2019) 111222
Z. Chen, et al.
Fig. 2. The calibration setup with tritium standard gas. Table 1 Calibration results with tritium standard gas. T, ℃ 21 21 21
CTS , Bq/m3 7
1.25*10 5.20*107 4.62*108
Im , pA 0.0137 0.0564 0.5122
δ Im 6.5% 5.6% 0.8%
k, A/(Bq/m3) −21
1.10*10 1.11*10−21 1.08*10−21
μk 7.2% 6.6% 3.3%
μS = 2.0% , μV = 2.5% .
between the wire wall and chamber wall can also effectively prevent the ions generated outside entering the sensitive region of the chamber.
4. Conclusion The improved ionization chamber was designed based on flange structure to obtain high airtight performance, and the leakage rate lower than 1.0*10−13 Pa. m3/s was achieved. Tritium exposure was carried out with tritium in form of both HTO and HT to examine the effect of memory effect and results indicated that the wire wall and gold plated treatment could effectively weaken the influence of memory effect caused by tritium absorption. Output signal of the ionization chamber can recover to background level within 20 s even after being filled with tritium in gaseous form at 3.9*1010 Bq/m3. While less than 1 min is taken to recover to background level of the ionization chamber after exposing in tritium in HTO form at 3.0*108 Bq/m3 about 1 h. Therefore, the improved ionization chamber is suitable for tritium inline measurements inpile tritium extraction experiments which might last several days one round.
Fig. 4. Results of memory effect test with tratiated water vapor.
Acknowledgement This research is supported by National Natural Science Foundation of China, No. 11505165.
Fig. 5. Results of memory effect test with tritium in gaseous form.
Fig. 3. Experimental setup for memory effect test by HTO vapor. 3
Fusion Engineering and Design 147 (2019) 111222
Z. Chen, et al.
References [1] [2] [3] [4] [5]
[6] [7] [8] [9] [10] [11] [12]
H. Yoshida, et al., Fusion Eng. Des. 61–62 (2002) 513–523. M. Glugla, et al., Fusion Eng. Des. 82 (2007) 472–487. T. Tanae, J. Nucl. Mater. 438 (2013) S19–S26. D. Demange, et al., Fusion Eng. Des. 87 (2012) 1206–1213. M. Abdou, et al., Fusion Eng. Des. 100 (2015) 2–43.
4
K. K. C. C. C. C. C.
Chunmei, et al., Fusion Eng. Des. 88 (2013) 113–117. Chunmei, et al., J. Nucl. Mater. 432 (2013) 455–459. Zhilin, et al., Nucl. Instr. Meth. A 762 (2014) 7–10. Zhilin, et al., Fusion Eng. Des. 101 (2015) 52–55. Zhilin, et al., Nucl. Instr. Meth. A 806 (2016) 267–270. Zhilin, et al., Rev. Sci. Instr. 84 (103302) (2013) 103302-1–103302-6. Zhilin, et al., Nucl. Instr. Meth. A 622 (2010) 136–138.
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Improvement of ionization chamber for tritium measurements in in-pile tritium extraction experiments
T
⁎
Zhilin Chen , Shuming Peng, Ping Chen, Ruiming Chang, Guanyin Wu, Yu Li Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, 621900, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Tritium measurement Ionization chamber Fusion Tritium breeding
Ionization chamber with gold plated wire-wall based on flange structure has been developed for tritium measurements in in-pile tritium extraction experiments. Performance of the improved ionization chamber on airtight and memory effect was greatly enhanced. Gas leakage rate of the chamber was lower than 1.0*10−13 Pa. m3/s with the flange structure. Both tritiated water vapor and tritium in gaseous form have been used in experiments to examine the influence of memory effect caused by tritium absorption on chamber wall. Results indicate that with the design of gold plated wire wall, output signal of the ionization chamber can recover to background level within 1 min after 1 h exposure in tritiated water vapor at 3.0*108 Bq/m3 created by bubbling. While recovery time is less than 20 s after being exposed to tritium in gaseous form at 3.9*1010 Bq/m3 for 7 days.
1. Introduction
memory effect of the improved ionization chamber.
Real time and in-line tritium measurement is very important to obtain the release behavior of tritium breeding materials for both inpile and out-pile tritium extraction experiments which is one of the key issues to support tritium self-sufficiency in a fusion reactor [1–5]. In the Institute of Nuclear Physics and Chemistry (INPC) lots of out-pile experiments have been carried out to examine tritium release behavior of Li4SiO4 pellets, and ionization chambers were used to measure tritium concentration in-line [6–10]. Although the inner surface of ionization chamber used in out-pile experiments was gold plated to weaken the influence of memory effect caused by tritium absorption on inner surface, it was contaminated after several runs due to the absorption of both HTO and HT released by tritium breeder, and decontamination treatment was necessary to deal with the chamber. Recently a new inpile tritium extraction test facility is under construction in INPC which will be operated in continuous mode, and each run might last more than one week. Therefore ionization chambers with low memory effect are very important to obtain the exact tritium concentration in-line. Furthermore, better airtight performance is also essential to prevent tritium leakage especially when high level tritium presents in in-pile tritium extraction experiments. To improve the performance of the current used ionization chamber on both memory effect and airtight ability, an improved kind of ionization chamber with gold plated wirewall based on flange structure has been developed. Experiments with both HTO and HT have been carried out separately to investigate the
2. Design of the ionization chamber
⁎
For an ionization chamber of cylinder shape, theoretically the saturation ionization current (Is ) can be denoted as:
Is =
E ⋅e E ⋅e ¯ ⋅C⋅V ⋅η1⋅ξ + ⋅D⋅S⋅η2⋅ξ W W
(1)
E is the average energy of beta ray from tritium, eV. e is elementary charge, 1.602*10−19 C. C is tritium concentration in the chamber, Bq/cm3. V is the sensitive volume of the chamber, cm3. η1 is energy deposition rate of beta rays emitted by tritium in the sensitive region of the chamber. ξ is the charge collection rate of an ionization chamber. W is the average ionization energy of carrier gas in the chamber, eV. D¯ is average tritium contamination level on the surface around the sensitive region of the chamber, Bq/cm2. S is the total surface area around the sensitive region of the chamber, cm2. η2 is energy deposition rate of beta rays emitted by tritium absorbed on the surface around the sensitive region of the chamber. Generally most beta rays emitted by tritium in the sensitive region of the chamber will deposit all their energy into the sensitive region of the chamber and devote to final signal output, and the values of η1 and ξ
Corresponding author. E-mail address: [email protected] (Z. Chen).
https://doi.org/10.1016/j.fusengdes.2019.05.041 Received 9 October 2018; Received in revised form 28 May 2019; Accepted 29 May 2019 0920-3796/ © 2019 Elsevier B.V. All rights reserved.
Fusion Engineering and Design 147 (2019) 111222
Z. Chen, et al.
PV = nRT with a standard container of given volume. Relationship between the measured current (Im ) of the ionization chamber and tritium concentration (CTS ) derived from the given tritium gas standard can be expressed as, Im = CTS⋅k
(2)
where k is the response factor of the ionization chamber. Then the response factor k can be obtained,
k=
Im CTS
(3)
Three runs were carried out in calibration experiments, and tritium concentration (CTS ) in each run was different. Gas pressure in the ionization chamber during calibration was 95 kPa, while temperature in laboratory was 21 ℃. Results are shown in Table 1. In Table 1, tritium measurement uncertainty is denoted by μk = δ I2m + μC2TS , where Im is the measured current, and δ Im is the uncertainty of Im . μCTS is the uncertainty of tritium standard gas, which is determined by the uncertainty of both tritium source ( μS ) and the volume ( μ V ),
Fig. 1. 3D view of the ionization chamber.
μCTS = μS2 + μV2 . Results in Table 1 show that response factor (k) of the ionization chamber is around 1.10*10−21 A/(Bq/m3), and the relative deviation (Dk = ∑ (|ki − k |)/ k ) is smaller than 2.0%. The measured uncertainty ( μk ) is 3.3% at 4.62*108 Bq/m3, while it is 7.2% at 1.25*107 Bq/m3.
will be nearly 1.0 [11]. While the value of η2 is around 0.5 in common conditions [12]. The second part of Eq. (1) is contributed by memory effect and it is directly determined by the total amount of tritium absorbed on the surface of components around the sensitive region of the chamber. It’s obvious that decrease of inner surface area (S) is an effective way to reduce the output signal caused by memory effect. Therefore wire wall composed of gold plated tungsten wire of 0.05 mm in radius is used instead of sealed wall in the chamber, and wall surface area is reduced to about 1% of the previous chamber with the same size. Furthermore, 316 L stainless steel is chosen as the main body material and the inner part of the whole chamber is gold plated to reduce the absorption of tritium. The chamber is constructed based on flange structure. Both connectors and pipes are welded onto the flange to ensure the airtight performance. The sensitive volume of the ionization chamber is 50 mL. The 3D view of the ionization chamber is shown in Fig. 1.
3.2. Memory effect Comparing with HT, tritium in HTO form is much easier to be absorbed on the inner surface of an ionization chamber and results in serious memory effect. As depicted in Ref.6, part of tritium released by tritium breeder Li4SiO4 is in HTO form. Therefore, the influence of HTO vapor on tritium measurements must be checked before the developed ionization chamber is used in the in-pile experiments. To test the performance of the developed ionization chamber on memory effect, both tritiated water vapor and tritium in gaseous form were used in experiments. Tritiated water vapor was obtained by bubbling with dry air in tritiated water. Experimental setup of bubbling system is shown in Fig. 3. In Fig. 3, three bubblers were used in experiments. Firstly, dry air was pumped into bubbler-1 by a micro-pump, and a bottle filled with dryer (CaCl2) was used to absorb water vapor in the air before it entering bubbler-1. A flow meter was employed to control the gas flow rate. After passing through the ionization chamber, gas with tritiated vapor was washed in both bubbler-2 and bubbler-3 before it was discharged into fuming hood. In experiments, the ionization chamber was exposed to HTO vapor of 3.0*108 Bq/m3 about 1 h, then flushed with fresh dry air. Gas flow rate in experiments was set to be 0.6 L/min. Tritium concentration is obtained by CT = Im/ k , where k is 1.35*10−21 A/(Bq/m3) for tritium in air. Results are shown in Fig. 4. In Fig. 4, it shows that output signal of the improved ionization chamber can recover to background level within 1 min after flushing with fresh dry air. Furthermore, the ionization chamber was also tested with tritium in gaseous form. In experiments, tritium concentration of 3.9*1010 Bq/m3 was kept in the ionization chamber for about 7 days to examine the influence of memory effect. And after that, tritium gas was pumped out and the ionization chamber was flushed with fresh dry air. Results are shown in Fig. 5. In Fig. 5, it's obvious that output signal of the improved ionization chamber decreases greatly just after tritium gas being pumped out, and it can recover to background level (7.4*106 Bq/m3) within 20 s. Results depicted in Figs. 4 and 5 show that with structure of wire wall and gold plated treatment, the influence of memory effect on output signal of the ionization chamber is effectively reduced to the level lower than the LOD of the chamber. In addition, the electric field
3. Experimental tests and discussions Experiments have been carried out to examine the performance of the developed ionization chamber before it can be applied to the in-pile tritium extraction experiments. Firstly, tritium standard gas is used to test the response of the chamber. Secondly, both tritiated water vapor and high level tritium in gaseous form were used to check the memory effect of the improved ionization chamber. Tritiated water vapor was generated by bubbling in tritiated water. The limit of detection (LOD) of the improved ionization chamber is 7.4*106 Bq/m3 (for air). Before tritium was introduced into the chamber, the airtight performance was examined by mass spectrometer, and it turned out that leakage rate of the improved chamber was lower than 1.0*10−13 Pa. m3/s. In experiments, current meter model 6517 B (Keithley company, USA) was used to measure the signal output of the ionization chamber. 100 V was applied to the wire wall to ensure the ionization chamber be operated in saturation mode. 3.1. Calibration of the ionization chamber Tritium standard gas set modeled TRITON CL-1 made by Johnston company was used in the calibration. Tritium concentration is 5.994 × 109 Bq/m3 by April 27th, 2017, and the accuracy of the tritium concentration is 2.0%. The calibration system based on TRITON CL-1 is shown in Fig. 2. In experiments, tritium standard gas was firstly introduced into volume I and then into ionization chamber. Volume II is used to determine the amount of helium gas filled into the ionization chamber. The volume of both volume I and volume II was determined by 2
Fusion Engineering and Design 147 (2019) 111222
Z. Chen, et al.
Fig. 2. The calibration setup with tritium standard gas. Table 1 Calibration results with tritium standard gas. T, ℃ 21 21 21
CTS , Bq/m3 7
1.25*10 5.20*107 4.62*108
Im , pA 0.0137 0.0564 0.5122
δ Im 6.5% 5.6% 0.8%
k, A/(Bq/m3) −21
1.10*10 1.11*10−21 1.08*10−21
μk 7.2% 6.6% 3.3%
μS = 2.0% , μV = 2.5% .
between the wire wall and chamber wall can also effectively prevent the ions generated outside entering the sensitive region of the chamber.
4. Conclusion The improved ionization chamber was designed based on flange structure to obtain high airtight performance, and the leakage rate lower than 1.0*10−13 Pa. m3/s was achieved. Tritium exposure was carried out with tritium in form of both HTO and HT to examine the effect of memory effect and results indicated that the wire wall and gold plated treatment could effectively weaken the influence of memory effect caused by tritium absorption. Output signal of the ionization chamber can recover to background level within 20 s even after being filled with tritium in gaseous form at 3.9*1010 Bq/m3. While less than 1 min is taken to recover to background level of the ionization chamber after exposing in tritium in HTO form at 3.0*108 Bq/m3 about 1 h. Therefore, the improved ionization chamber is suitable for tritium inline measurements inpile tritium extraction experiments which might last several days one round.
Fig. 4. Results of memory effect test with tratiated water vapor.
Acknowledgement This research is supported by National Natural Science Foundation of China, No. 11505165.
Fig. 5. Results of memory effect test with tritium in gaseous form.
Fig. 3. Experimental setup for memory effect test by HTO vapor. 3
Fusion Engineering and Design 147 (2019) 111222
Z. Chen, et al.
References [1] [2] [3] [4] [5]
[6] [7] [8] [9] [10] [11] [12]
H. Yoshida, et al., Fusion Eng. Des. 61–62 (2002) 513–523. M. Glugla, et al., Fusion Eng. Des. 82 (2007) 472–487. T. Tanae, J. Nucl. Mater. 438 (2013) S19–S26. D. Demange, et al., Fusion Eng. Des. 87 (2012) 1206–1213. M. Abdou, et al., Fusion Eng. Des. 100 (2015) 2–43.
4
K. K. C. C. C. C. C.
Chunmei, et al., Fusion Eng. Des. 88 (2013) 113–117. Chunmei, et al., J. Nucl. Mater. 432 (2013) 455–459. Zhilin, et al., Nucl. Instr. Meth. A 762 (2014) 7–10. Zhilin, et al., Fusion Eng. Des. 101 (2015) 52–55. Zhilin, et al., Nucl. Instr. Meth. A 806 (2016) 267–270. Zhilin, et al., Rev. Sci. Instr. 84 (103302) (2013) 103302-1–103302-6. Zhilin, et al., Nucl. Instr. Meth. A 622 (2010) 136–138.