Thermal simulation and analysis of the STF cryomodule

CPC(HEP & NP), 2009, 33(3): 236- -239Chinese Physics CVol. 33, No. 3, Mar., 2009Thermal simulation and analysis ofthe STF cryomodule'XU Qing Jin(徐庆金)") Ohuchi Norihito2 Kiyosumi Tsuchiya2Tsai Ming-Hsun3ZONG Zhan-Guo(宗占因)4 ZHAI Ji-Yuan(翟纪元) GAO Jie(高杰)'1 (Institute of High Energy Physics, Chinese Academy of Sciences, Beiing 100049, China)2 (High Energy Accelerator Research Organization, Tsukuba, Japan)3 (Synchrotron Radiation Research Center, Hsinchu)4 (Technical Intitute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 10080, China)Abstract STF is a superconducting RF test facility constructed at the high energy accelerator research orga-nization of Japan (KEK), as a main part of a R&D project for the proposed International Linear Collider (LC)in Asia. Thermal study of the STF 1.3 GHz 9-cell cavity cryomodule was carried out within a collaborationbetween China and Japan. Static and dynamic thermal behaviors of the STF cryomodule were simulated andanalyzed with the FEM method, and some simulation results were compared with the available experimentaldata. This paper presents the details.Key words STF cryomodule, thermal simulation, ILCPACS 44.05.+e, 45.10.-b, 41.20.-q1 Introductionstatic and dynamic thermal behaviors of the STF cry-omodule were simulated and analyzed with the FEMAs a main part of the R&D project for the ILCsoftware ANSYS.(International Linear Collider) in Japan and Asia,2 Static thermal analysis of the STFthe construction of a superconducting RF test fa-cility (STF) was decided and carried out at KEK.cryomoduleThis facility includes eight 1.3 GHz 9-cell supercon-ducting cavities, a cryomodule, a power source, a he-The static heat load of the STF cryomodulelium plant, the beam instrumentation, cavity surfacemainly includes: heat conduction through the in-treatment facilities, etc. In STF phase 1, startingput power coupler, support posts, beam tube, sensoron JFY05 (Japanesc Fiscal Year) and to be endcd inwires, RF cables and tuner, and the thermal radia-JFY08, eight 9-cell cavities with two diferent types tion heat through the MLI (Multi-Layer Insulation)(Tesla-like and low loss, four cavities for cach type)system. The radiation heat through the MLI waswill be installed to the STF cryomodule and horizon-calculated with data based on experience: room tem-tally tested. In the fllowing STF phase 2, the nineperature to 80 K with 30 layers MLI- 1 W/m2; 80 Kcavities in onc cryomodule will focus on one typel1.to5 K with 10 layers MLI- 0.05 W/m2; and5K toUnder the support of the Asian region collabo-2 K was ignored. Hcat conduction through the powerration of the ILC R&D project, several Chinese re-coupler and support posts, including temperature dis-searchers started to join the construction of STF fromtributions, were simulated with the FEM 3D model,2006. Thermal study on the STF cryomodule is oneof as shown in Fig. 1 and Fig. 2 (Rclated structure datathe most important parts of this collaboration. Thecomes from Ref. [2).中国煤化工Received 30 June 2008●Supported by National Natural Science Foundation of China.MYHC N M H GScience Foundation(20070410637)1)E-mail: xuqj@ihep.c.cn@2009 Chinese Physical Society and the Institute of High Encrgy Physics of the Chinese Academy of Sciences and the Instituteof Modern Physics of the Chinese Academy of Sciences and IOP Publishing LtdNo. 3XU Qing Jin et al; Thermal simulation and analysis of the STF cryomodule_237AN，四=品Fig, 1. Static temperature field of 35 MV and 45 MV power couplers (Unit: K).281.893 .253.901225.912197.923169.934141.945113.95685.96757.97829. 989“(0.028 0.056 0.084 0112 0.140vertical dretion of the posts/mFig. 2. Static temperature field and temperature distribution along the vertical direction of the fixed post ofthe STF cryomodule (Unit: K).Figure 1 shows the static temperature fields of thepcrature variation along the vertical direction of the35 MV and 45 MV power couplers. For each coupler，posts is shown in Fig. 2.two thermal anchors (separately conncting with twoFigure 3 shows the static temperature distribu-radiation shields of the cryomodule) were added totions of the 5 K and 80 K radiation shields (with 1decrease the heat loads to the cryogenic system. Fopower coupler for each shield). The mass fow rate ofthe 35 MV coupler, the measured data of the roomhelium for the 5 K shield is 1 g/s, and the inlet tem-temperature, first thermal anchor tempcrature, sec-perature is 5 K. With a radiation heat fux of 0.05ond thermal anchor temperature and the cavity tem-W/m2, the simulation results show that the outletperature are 299 K, 83 K, 4.5 K and 2 K, respectively.temperature of the helium is about 5.25 K, and theWith these experimental data, and the ANSYS 3Dhot spot temperature of the shield (around the cou-model, the calculated heat loads of the coupler arepler port) is 5.91 K. For the 80 K shield, the mass2.41 W to the 80 K radiation shield, 1.08 W to the :flow of nitrogen is 1 g/s, and the inlet temperature(5 K) radiation shield and 0.03 W to the 2 K system.is 80 K. With the radiation heat fAux 1 W/m2, theIt is also found from the results that the copper coat-simulation result of the outlet temperature of the ni-ing with a thickness of only several microns at thetrogen is 86.8 K, and the hot spot temperature of theinner surface of the coupler plays a very importantshield (around the coupler port) is about 91.05 K.role in the heat conduction.A vacuum barrier structure was designed and fab-The materials of the support posts are G10 andricated to separate the vacuum of the cryomodule andstainless steel. From the upper side to the lower side,the valve box into two independent parts, to decreasethe posts are connected with the vacuum vessel, thethe vacuum failure possibility of the cryomodule (see80 K radiation shield, the 5 K radiation shield andFig.4). The materials of the barrier are stainless steelthe 2 K system. Fig. 2 shows the simulation results(SS316中国煤化工,5K and 80 Kof the static temperature distributions. The calcu-cryogeiYHCN M H Grere welded withlated heat loads are: 80 K-5.4 W; 5 K-0.81 W andtbe barrier. LU 1uoe ue auutional heat load2 K-0.12 W for the fixed post, and 80 K-5.1 W; 5 K-caused by the barrier, the heat loads to the three pairs0.81 W; 2 K-0.12 W for the sliding post. The tem-of different temperature pipes were optimized consid-238Chincse Physics C (HEP & NP)Vol. 33ering the hcat fux through conduction and radiation.the 5 K helium pipe, as shown in Fig. 4. The opti-Two thermal anchors were added to the SS316 pipemized results of the hcat loads arc 17.32 W to 80 K,which was welded with the 2 K helium pipe, and one2.18Wto5Kand0.057Wto2K.thermal anchor was added to the pipe, welded with |AN..Fig. 3. Static temperature fields of the STF 5 K and 80 K radiation shields (with 1 power coupler, unit: K).2..Fig. 4. Vacuum barrier of the STF cryomodule: (a) design; (b) fabrication (Temperature unit: K).; Dynamic thermal analysis of the| data of the tempcrature rising around the window ofSTF cryomodule35 MV coupler. It shows that the experimental dataapproximately conirm the simulation results. The :During the RF power process, current flow within diference betwcn them should be mainly due to thethe skin depth of the conductor and dielectric loss inmaterial properties crror in the simulation modcl andthe ceramic window will generate joule heat in thethe measuring error in the experiment.coupler. A coupler field (High Frequency magneticThe variation of heat loads of thc 35 MV couplerand thermal) FEM simulation model was buit for with an increase of the input power is also shown inthis dynamic thermal analysis): The HF ficld wasFig. 6. The results show that the dynamic heat loadfirst caculaed; with the HF dstribution, surface ro to the 80 K shield is about 10 times larger than thatsistance of the conductor and delectric loss tangent to the (5 K) shield. The2 K dynamic heat load is .of the ceramic window, the HF heat generation at theabout onc third of the second shicld. The ratio of theinner surface and the window of the coupler was ob-surface loss to the dielectric loss is about 5.tained. Then the thermal simulation was carried outThe dynamic hcat load caused by the cavity canwith the heat generation as a boundary condition.be calculated according to the following equation:Figure 5 shows the input power variation and theE2.*L2electrical field distribution of the STF 35 MV Cou-中国煤化工(1)pler during the experiment. The frequency of the in-put pulse is 5 Hz. At each 0.2 s cycle, the maximumwhere.MYHC N M H G superconductingpower input will last 0.5 ms and then dccrease to 70%cavity; Eacc 一accelerator gradient of the cavity; .during the coming 1 ms. Fig. 6 shows a comparisonL- cavity length: Qo - quality factor of the cavity;between the simulation results and the experimentalR/Q一shunt impedance of the cavity.No.3XU Qing-Jin et al: Thermal simulation and analysis of the STF cryomodule239_14N120f 10言4喜2(a)(b12:43:00 12:3:00 13:03:00 13:13:00time (007-11-20)Fig. 5. (a) The input power of the STF 35 MV coupler; (b) The electrical field distribution with the maximuminput power 193 kW (Electrical field unit: V/m).113.51.58●experimenal data13.0， FEM simulaition resuts2.2 t1.56; 112.5.0 t1.54112.8 t111.51.611.0，)1.4812:43:00 12:5.00 13:03:00 13:13:00time (00711-20)Fig. 6. (a) Temperature rising around the window of the STF 35 MV coupler caused by RF heat; (b) Variationof the heat loads of the 35 MV coupler.4 Summarydata. A vacuum barrier structure was designed andfabricated, to separate the vacuum of the cryomoduleKey components of the STF cryomodule wereand the valve box into two independent parts, so thatstudied by thermal simulation and analysis with thethe vacuum failure possibility of the cryomodule wasFEM software ANSYS. Part of the simulation resultsdecreased. A thermal analysis of this part was alsohave been compared with the available experimentalcarried out. The preliminary summary of the heatload of the STF cryomodule (35 MV part) is shownTable 1. Heat load summary of the STF cry-in Table 1.omodule (35 MV part, *data from Ref. [4]).stati/WThis work was mainly carried out at KEK, underheat Bource80K5K2K80K5K2Kcollaboration with the STF cryomodule group. Manyradiation0.6thanks go to Professor Hayano, Professor Noguchi,support posts10.5 1.62 0.24 /Professor Saito, Dr. Kako, Dr. Yamamoto, Dr.input coupler (one)2.41 1.08 0.03 2.5 0.2 0.06Saeki, for providing u8 with the necessary materialscavity (one)0.47 0.06 0for the thermal simulation, and Professor Yamamotoinstrumentation cables* 1.25 1.64 0.05for his techrical support.vacuum barrier17.32 2.18 0.06Thanks to M8. Tongming Huang of IHEP, forother0.30.2 /46.95 7.48 0.58 2.5 0.2 0.46the very helpful discussion on the Ansys multi _physicssimulation.References2 Eng|中国煤化Idule. KEK, Jepan, .1 Hitoshi Hayano. Superconducting RF Test Facility (STF)3 ANS200-HCNMHGfor ILC. Proceedings of the 2nd Anual Meeting of Particle4 Tsal Mingnsun. Heat LoSS Calculation of STF Cryomodule.Accelerator Society of Japan and the 30th Linear Acceler-Internal Report in KEK, 2007.7.13ator Meeting in Japan. July 20- -22, 2005, Tosu Japan