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真空稳定性问题是粒子加速器设计中的关键问题之一, 对高能量的超级质子-质子对撞机而言更是如此. 质子束流在弯转区产生的同步辐射将会引起束屏壁面吸附的气体分子发生解吸和裂解, 从而引发真空不稳定问题, 导致束流品质和寿命的降低, 甚至引起束流的崩溃. 本文通过建立超级质子-质子对撞机束屏内的气体动态模型, 首次计算分析了束屏内气体密度随束流运行时间的演化规律, 并探究了将非蒸散型吸气剂涂层应用于束屏设计的优化方案. 结果表明: H2是束屏内的主要解吸气体, 其次是CO, 而CO2和CH4分子密度被分子裂解所限制. 束屏内最高气体密度出现在运行初期, 气体密度随时间呈下降趋势. 考虑到非蒸散型吸气剂涂层具有强化吸附降低解吸的特性, 讨论了不锈钢镀TiZrV涂层的束屏方案, 计算得到最高等效H2密度相比不锈钢镀铜降低接近两个数量级. 计算结果定性地反映束流运行过程中束屏内的动态真空演化情况, 可为真空系统设计提供参考.
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关键词:
- 超级质子-质子对撞机 /
- 动态真空 /
- 光子致解吸 /
- 束屏
Vacuum stability is one of the key issues in the design of particle accelerators, especially high-energy super proton-proton colliders. The synchrotron radiation generated by proton beams in the bending area will desorb and crack the gas molecules which have adsorbed on the wall of the cold bore. The collision or scattering between the proton beam and the desorbed gas molecules may result in the degradation of the beam quality and the reduction of beam life time, and even the collapse of the beam. Usually a copper coated stainless steel beam screen is installed in the cold bore to intercept synchrotron radiation and reduce gas desorption. Based on the design parameters of the Super Proton-Proton Collider, in this paper the source of gas in the beam screen is analyzed. By considering the photon-induced desorption process and the gas molecule cracking process, the gas dynamic model in the beam screen is established. Moreover, the calculation of the evolution of the gas density in the beam screen with the beam operating time is carried out, and the effect of TiZrV non-evaporable getter film coated beam screen on the dynamic gas density is explored. The results show that H2 is the main desorption gas in the beam, the next is CO, while the molecular density of CO2 and CH4 are limited by molecular cracking. The maximum gas density in the beam screen appears at the initial stage of operation, and the gas density decreases with time going by. In order to strengthen adsorption and reduce desorption, TiZrV coated beam screen is discussed in this paper. In the case of TiZrV coated stainless steel beam screen, the maximum equivalent H2 density is about two order of magnitude lower than in the case of copper coated stainless steel beam screen. The non-evaporable getter(NEG) for beam screen material can significantly improve vacuum performance. The calculation results can qualitatively reflect the dynamic vacuum evolution in the beam screen during the beam operation and provide a reference for designing vacuum systems.-
Keywords:
- super proton-proton collider /
- dynamic vacuum /
- photon stimulated desorption /
- beam screen
[1] Aad G, Abajyan T, Abbott B, Abdallah J, Khalek S A, Abdelalim A A, Abdinov O, Aben R, Abi B, Abolins M 2012 Phys. Lett. B 716 1
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[8] Brüning O S, Collier P, Lebrun P, Myers S, Ostojic R, Poole J, Proudlock P 2004 LHC Design Report (Geneva, CERN, CERN-2004-003-V-1 [R])
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[12] Baglin V, Tavian L, Lebrun P, van Weelderen R 2013 Cryogenic Beam Screens for High-energy Particle Accelerators (Geneva, CERN, CERN-ATS-2013-006 [R])
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Google Scholar
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Google Scholar
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Google Scholar
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[21] Gan P P, Fu Q, Li H P, Liu Y D, Lu Y R, Tang J Y, Xu Q J, Zhu K 2017 the 8th International Particle Accelerator Conference (IPAC'17) Copenhagen, Denmark, May 14−19, 2017 p2974
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Google Scholar
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Google Scholar
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Google Scholar
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Google Scholar
[29] Gröbner O, Calder R 1973 IEEE Trans. Nucl. Sci. 20 760
Google Scholar
[30] Malyshev O B, Rossi A 1999 Ion desorption stability in the LHC (Geneva, CERN, VACUUM-TECHNICAL-NOTE-99-20 [R])
[31] Anashin V V, Malyshev O B, Calder R, Gröbner O, Mathewson A G 1998 Nucl. Instrum. Methods Phys. Res., Sect. A 405 258
Google Scholar
[32] Bellafont I, Mether L, Kersevan R 2019 the 10th International Particle Accelerator Conference (IPAC'19) Melbourne, Australia, May 19−24, 2019 TUPMP038
[33] Baglin V, Grünhagel C, Collins I R, Gröbner O, Jenninger B 2002 Synchrotron Radiation Studies of the LHC Dipole Beam Screen with COLDEX (Geneva, CERN, LHC-Project-Report-584 [R])
[34] Baglin V, Collins I R, Grünhagel C, Gröbner O, Jenninger B 2000 First Results from COLDEX Applicable to the LHC Cryogenic Vacuum System (Geneva, CERN, LHC-Project-Report-435 [R])
[35] Baglin V, Bregliozzi G, Lanza G, Jimenez J M 2011 Synchrotron Radiation in the LHC Vacuum System (Geneva, CERN, CERN-ATS-2011-245 [R])
[36] Rathjen C 2002 Mechanical Behaviour of Vacuum Chambers and Beam Screens under Quench Conditions in Dipole and Quadrupole Fields (Geneva, CERN, LHC-Project-Report-582 [R])
[37] Malyshev O B, Scott D, Bailey I, Barber D, Baynham E, Bradshaw T, Brummitt A, Carr S, Clarke J, Cooke P 2007 J. Vac. Sci. Technol., A 25 791
Google Scholar
[38] Calder R, Gröbner O, Mathewson A G, Anashin V, Dranichnikov A, Malyshev O B 1996 J. Vac. Sci. Technol., A 14 2618
Google Scholar
[39] Spallino L, Angelucci M, Larciprete R, Cimino R 2019 Appl. Phys. Lett. 114 153103
Google Scholar
[40] Anashin V V, Derevyankin G, Dudnikov V, Malyshev O B, Osipov V, Foerster C, Jacobsen F, Ruckman M, Strongin M, Kersevan R 1994 J. Vac. Sci. Technol., A 12 1663
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[41] La Francesca E, Angelucci M, Liedl A, Spallino L, Gonzalez L A, Bellafont I, Siewert F, Sertsu M G, Sokolov A, Schäfers F, Cimino R 2020 Phys. Rev. Accel. Beams 23 083101
Google Scholar
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Google Scholar
[43] Anashin V V, Collins I R, Dostovalov R V, Fedorov N V, Krasnov A A, Malyshev O B, Ruzinov V L 2004 Vacuum 75 155
Google Scholar
[44] Širvinskaitė R, Malyshev O B, Valizadeh R, Hannah A, Cropper M D 2020 Vacuum 179 109510
Google Scholar
[45] Ady M 2016 Monte Carlo Simulations of ultra High Vacuum and Synchrotron Radiation for Particle Accelerators (Lausanne, EPFL, BEL-EPFL-Thesis7063-7 [R])
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Google Scholar
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Google Scholar
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图 1 COLDEX束屏内气体分压的实验测试结果与计算结果对比 (a) 实验测试结果; (b)计算结果
Fig. 1. Comparisons of experimental results and calculated results of gas partial pressure in COLDEX beam screen: (a) Experimental test results; (b) calculated results.
图 4 镀铜涂层的不锈钢束屏内 (a) 气体体密度n; (b) 一次解吸产额 η; (c) 二次解吸产额
$\eta '$ 随光子累积剂量D演化的规律Fig. 4. (a) The gas density n, (b) primary photodesorption yieldη and (c) secondary photodesorption yield
$\eta '$ as function of accumulated photon dose D in a copper coated stainless steel beam screen.
图 5 镀TiZrV涂层的不锈钢束屏内 (a) 气体体密度n; (b) 一次解吸产额η; (c) 二次解吸产额
$\eta '$ 随光子累积剂量D演化的规律Fig. 5. (a) The gas density n, (b) primary photodesorption yield η and (c) secondary photodesorption yield
$\eta '$ as function of accumulated photon dose D in a TiZrV coated stainless steel beam screen.气体种类 H2 CH4 CO CO2 O2 $\eta ' _{ {\rm{r} }\;{\rm{max} } }$ 0.55 0.4 0.04 0.45 0.04 $\eta '_{\rm{max} }$ 0.55 0.04 0.04 0.04 0.04 $ {\kappa }_{\rm{max}} $ — $ {\kappa }_{{{\rm{C}}{\rm{H}}}_{4}\stackrel{}{\to }2{{\rm{H}}}_{2}+{\rm{C}}}\approx 0.36 $ — $ {\kappa }_{{{\rm{C}}{\rm{O}}}_{2}\stackrel{}{\to }{\rm{C}}{\rm{O}}+{\rm{O}}}\approx 0.41 $ — $ {\chi }_{\rm{max}} $ $ {\chi }_{{{\rm{H}}}_{2}}\left({s}_{{{\rm{C}}{\rm{H}}}_{4}}\right)\approx 0.72 $ — $ {\rm{\chi }}_{{\rm{C}}{\rm{O}}}\left({s}_{{{\rm{C}}{\rm{O}}}_{2}}+{s}_{{{\rm{C}}{\rm{H}}}_{4}}\right)\approx 0.41+0.36 $ — $ {\chi }_{{{\rm{O}}}_{2}}\left({s}_{{{\rm{C}}{\rm{O}}}_{2}}\right)\approx 0.2 $ 
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表 3 LHC型铜样品、锯齿形铜样品及激光刻蚀铜样品的光子反射率及光电子产额[41]
Table 3. Photon reflectivity and photoelectron yield of LHC type samples, sawtooth copper samples and laser treated copper samples[41]
样品类型 反射率R 光电子产额${Y_{{\rm{pe}}}}$ LHC型铜样品(LHC) 0.75 0.25 锯齿形铜样品(ST) 0.07 0.08 激光刻蚀铜样品(LASE) 0.006 0.09
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术语 A (cm2) 真空腔室轴向单位长度壁面面积 $u = {A_{\rm{c}}}{D_{\rm{k}}}$(cm4/s) 轴向单位长度真空流导 ${A_{\rm{c}}}$(cm2) 真空腔室横截面积 V (cm3) 真空腔室体积 $C = \rho {k_{\rm{t}}}S$ (cm3/s) 束屏孔的抽气速率 v (cm/s) 平均分子速率 ${D_{\rm{k}}}$(cm2/s) 努森扩散系数 α 分子在壁面的黏附系数 ${k_{\rm{t}}}$ 束屏开孔率(束屏抽气孔面积与束屏表面积之比) Γ (photons/(s·m)) 光子通量密度 n (molecules/cm3) 气体体密度 η (molecules/photon) 一次解吸产额 $S = Av/4$(cm3/s) 壁面理想抽气速率 $\eta '$(molecules/photon) 二次解吸产额 s (molecules/cm2) 气体表面密度 ρ 束屏孔的克劳辛系数
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[1] Aad G, Abajyan T, Abbott B, Abdallah J, Khalek S A, Abdelalim A A, Abdinov O, Aben R, Abi B, Abolins M 2012 Phys. Lett. B 716 1
Google Scholar
[2] Chatrchyan S, Khachatryan V, Sirunyan A M, Tumasyan A, Adam W, Aguilo E, Bergauer T, Dragicevic M, Erö J, Fabjan C 2012 Phys. Lett. B 716 30
Google Scholar
[3] Chatrchyan S, Khachatryan V, Sirunyan A, Tumasyan A, Adam W, Bergauer T, Dragicevic M, Erö J, Fabjan C, Friedl M 2013 J. High Energy Phys. 2013 81
Google Scholar
[4] Behnke T, Brau J E, Foster B, Fuster J, Harrison M, Paterson J M, Peskin M, Stanitzki M, Walker N, Yamamoto H 2013 arXiv: 1306.6327 [physics.acc-ph]
[5] Mangano M, Azzi P, Benedikt M, Blondel A, Britzger D, Dainese A 2019 Eur. Phys. J. C 79 474
Google Scholar
[6] CEPC Study Group 2018 arXiv: 1809.00285 [ap-ph]
[7] FCC collaboration 2019 Eur. Phys. J. Spec. Top. 228 755
Google Scholar
[8] Brüning O S, Collier P, Lebrun P, Myers S, Ostojic R, Poole J, Proudlock P 2004 LHC Design Report (Geneva, CERN, CERN-2004-003-V-1 [R])
[9] Bellafont I, Morrone M, Mether L, Fernández J, Kersevan R, Garion C, Baglin V, Chiggiato P, Pérez F 2020 Phys. Rev. Accel. Beams 23 033201
Google Scholar
[10] Anashin V V, Malyshev O B, Calder R, Gröbner O, Mathewson A G 1997 Vacuum 48 785
Google Scholar
[11] Malyshev O B, Anashin V V, Collins I, Gröbner O 1999 Photon Stimulated Desorption Processes including Cracking of Molecules in a Vacuum Chamber at Cryogenic Temperatures (Geneva, CERN, VACUUM-TECHNICAL-NOTE-99-13 [R])
[12] Baglin V, Tavian L, Lebrun P, van Weelderen R 2013 Cryogenic Beam Screens for High-energy Particle Accelerators (Geneva, CERN, CERN-ATS-2013-006 [R])
[13] Mathewson A G, Gröbner O, Strubin P, Marin P, Souchet R 1991 AIP Conf. Proc. 236 313
Google Scholar
[14] Foerster C, Halama H, Lanni C 1990 J. Vac. Sci. Technol., A 8 2856
Google Scholar
[15] Hseuh H, Cui X 1989 J. Vac. Sci. Technol., A 7 2418
Google Scholar
[16] Gröbner O 1999 CAS-CERN Accelerator School: Vacuum Technology Snekersten, Denmark, May 28–Jun 3, 1999 p127
[17] Baglin V, Collins I R, Gröbner O, Grünhagel C, Jenninger B 2002 Vacuum 67 421
Google Scholar
[18] Malyshev O B 2012 Vacuum 86 1669
Google Scholar
[19] Bellafont I, Mether L, Kersevan R, Malyshev O B, Baglin V, Chiggiato P, Pérez F 2020 Phys. Rev. Accel. Beams 23 043201
Google Scholar
[20] Perez Rodriguez F J, Garion C, Chiggiato P, Fernandez Topham J 2017 Preliminary Beam Screen and Beam Pipe Engineering Design: Deliverable D4.3 (Geneva, CERN, CERN-ACC-2019-0023 [R])
[21] Gan P P, Fu Q, Li H P, Liu Y D, Lu Y R, Tang J Y, Xu Q J, Zhu K 2017 the 8th International Particle Accelerator Conference (IPAC'17) Copenhagen, Denmark, May 14−19, 2017 p2974
[22] 范佳锟, 王洁, 高勇, 游志明, 严涛, 张静, 王盛, 许章炼 2019 原子能科学技术 53 1670
Google Scholar
Fan J K, Wang J, Gao Y, You Z M, Yan T, Zhang J, Wang S, Xu Z L 2019 Atom. Energ. Sci. Technol. 53 1670
Google Scholar
[23] Anashin V V, Malyshev O B, Collins I R, Gröbner O 2001 Vacuum 60 15
Google Scholar
[24] Collins I R, Malyshev O 2001 Dynamic Gas Density in the LHC Interaction Regions 1&5 and 2&8 for Optics version 6.3 (Geneva, CERN, LHC-PROJECT-NOTE-274 [R])
[25] Anashin V V, Malyshev O B, Osipov V N, Maslennikov I L, Turner W C 1994 J. Vac. Sci. Technol., A 12 2917
Google Scholar
[26] Malyshev O B 2020 Vacuum in Particle Accelerators: Modelling, Design and Operation of Beam Vacuum Systems (USA: John Wiley & Sons) p96
[27] Billy J C, Bojon J P, Henrist B, Hilleret N, Jimenez M J, Laugier I, Strubin P 2001 Vacuum 60 183
Google Scholar
[28] Andritschky M, Gröbner O, Mathewson A, Schumann F, Strubin P, Souchet R 1988 Vacuum 38 933
Google Scholar
[29] Gröbner O, Calder R 1973 IEEE Trans. Nucl. Sci. 20 760
Google Scholar
[30] Malyshev O B, Rossi A 1999 Ion desorption stability in the LHC (Geneva, CERN, VACUUM-TECHNICAL-NOTE-99-20 [R])
[31] Anashin V V, Malyshev O B, Calder R, Gröbner O, Mathewson A G 1998 Nucl. Instrum. Methods Phys. Res., Sect. A 405 258
Google Scholar
[32] Bellafont I, Mether L, Kersevan R 2019 the 10th International Particle Accelerator Conference (IPAC'19) Melbourne, Australia, May 19−24, 2019 TUPMP038
[33] Baglin V, Grünhagel C, Collins I R, Gröbner O, Jenninger B 2002 Synchrotron Radiation Studies of the LHC Dipole Beam Screen with COLDEX (Geneva, CERN, LHC-Project-Report-584 [R])
[34] Baglin V, Collins I R, Grünhagel C, Gröbner O, Jenninger B 2000 First Results from COLDEX Applicable to the LHC Cryogenic Vacuum System (Geneva, CERN, LHC-Project-Report-435 [R])
[35] Baglin V, Bregliozzi G, Lanza G, Jimenez J M 2011 Synchrotron Radiation in the LHC Vacuum System (Geneva, CERN, CERN-ATS-2011-245 [R])
[36] Rathjen C 2002 Mechanical Behaviour of Vacuum Chambers and Beam Screens under Quench Conditions in Dipole and Quadrupole Fields (Geneva, CERN, LHC-Project-Report-582 [R])
[37] Malyshev O B, Scott D, Bailey I, Barber D, Baynham E, Bradshaw T, Brummitt A, Carr S, Clarke J, Cooke P 2007 J. Vac. Sci. Technol., A 25 791
Google Scholar
[38] Calder R, Gröbner O, Mathewson A G, Anashin V, Dranichnikov A, Malyshev O B 1996 J. Vac. Sci. Technol., A 14 2618
Google Scholar
[39] Spallino L, Angelucci M, Larciprete R, Cimino R 2019 Appl. Phys. Lett. 114 153103
Google Scholar
[40] Anashin V V, Derevyankin G, Dudnikov V, Malyshev O B, Osipov V, Foerster C, Jacobsen F, Ruckman M, Strongin M, Kersevan R 1994 J. Vac. Sci. Technol., A 12 1663
Google Scholar
[41] La Francesca E, Angelucci M, Liedl A, Spallino L, Gonzalez L A, Bellafont I, Siewert F, Sertsu M G, Sokolov A, Schäfers F, Cimino R 2020 Phys. Rev. Accel. Beams 23 083101
Google Scholar
[42] Alamgir M K, Ikram M, Mughal G H, Asghar G, ur Rehman S, Qaseem S, Kamran M, Ullah A, Khan S 2019 J. Korean Phys. Soc. 75 373
Google Scholar
[43] Anashin V V, Collins I R, Dostovalov R V, Fedorov N V, Krasnov A A, Malyshev O B, Ruzinov V L 2004 Vacuum 75 155
Google Scholar
[44] Širvinskaitė R, Malyshev O B, Valizadeh R, Hannah A, Cropper M D 2020 Vacuum 179 109510
Google Scholar
[45] Ady M 2016 Monte Carlo Simulations of ultra High Vacuum and Synchrotron Radiation for Particle Accelerators (Lausanne, EPFL, BEL-EPFL-Thesis7063-7 [R])
[46] Malyshev O B, Smith A, Valizadeh R, Hannah A 2010 J. Vac. Sci. Technol., A 28 1215
Google Scholar
[47] Chiggiato P, Costa Pinto P 2006 Thin Solid Films 515 382
Google Scholar
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