R&D Status and Plan on The Cryostat N. Ohuchi, K. Tsuchiya, A. Terashima, H. Hisamatsu, M. Masuzawa, T. Okamura, H. Hayano 1.STF-Cryostat Design 2.Construction Status of Cryostat 3.R&D Studies of Cryostat Components 4.Summary

Gaining the experience of the long cryostat for the S.C. cavity. R&D of the high performance and the low cost ILC cryostat. Cooling two types of the cavities of 35 MV/m and 45 MV/m down to 2 K in STF, and measuring the thermal characteristics. Starting point of the STF cryostat design: TESLA TYPE III Cryomodule R&D and study items for the STF cryostat –Understanding the TESLA design from the thermal and mechanical points of view. Temperature profile and heat load of the components, and construction errors. –R&D component SUS-Ti joint between the helium vessel and cryogenic lines. –Magnetic shield Measurement of the remnant field in the shield and the magnetic characteristics of the shield material. –Survey of the low cost quadrupole magnet system (conduction cooling) Target of the cryostat R&D in KEK Strategy of the cryostat R&D STF-Cryostat Design (1)

Two cryomodules are connected with bellow tubes. –Four cavities designed for 35 MV/m and 45 MV/m are assembled in the individual cryostat. –The total length of two cryostats is 13.2 m. The vacuum vessel of the TESLA TYPE III cryomodule has the length of 11.4 m including one quadrupole. STF-Cryostat Design (2) Design Overview of STF Cryostat

The design of the cold mass are same as the TESLA TYPE III cryomodule. –Cold mass : support post, gas return pipe, thermal radiation shields (5 K, 80 K), cooling channels –The diameter of the vacuum vessel is mm, same as the TESLA cryomodule. The helium vessels, frequency tuners and input couplers between the cavities of 35 MV/m and 45 MV/m have different configurations. STF-Cryostat Design (3) Cross sections of STF Cryostat 80 K Thermal Radiation Shield 5 K Thermal Radiation Shield Alignment Target Gas Return Pipe (GRP) Input Coupler 35MV/m Cavity45MV/m Cavity

STF-Cryostat Design (4) Cooling scheme and heat loads Cryostat Static 35MV/m Static 35MV/m Dynamic 45MV/m Static 45MV/m Dynamic Total S+D 2K K K STF-Phase-1 Cryogenic system : 20 2K (Cold box : K) Calculated Heat Load for STF-Cryomodule (W) Heat loads via signal wires are not included.

STF-Cryostat Design (5) Calculated pressure distribution Calculation model Q c : 10/8 W or 30/8 W m: evaporated helium gas Pressure drop along the system = 2.27 Pa for 10 W, Pa for 30W Temperature at each cavity = K for 10/8 W, K for 30/8 W

Gas return pipes (GRP) are connected with the support posts which have the alignment targets. The helium vessels for cavities are supported from the GRPs. The surfaces for the connection are processed by a milling machine with the target precision of 0.05 mm. Construction of STF-Cryostat (1) Gas Return Pipe Cryostat Connection Bellows

Thermal radiation shield : aluminum, vacuum vessel : carbon steel (used for magnetic shield) These components have been delivered from the company (Hitachi) on 24th March. Construction of STF-Cryostat (2) Vacuum vessel for 45 MV/m cavities Thermal radiation shield

The four support posts for the STF-cryomodules have been delivered from INFN Milano on March 3 under the research collaboration between INFN and KEK. The support post on the inlet side is fixed to the vacuum vessel, and the other one has a sliding function. –The position change of the sliding support post by thermal contraction is calculated to be 8.4 mm. The cavity helium vessels are hold with sliding supports from the Gas Return Pipes. –The axial positions of the helium vessels are decided by the invar rods. Construction of STF-Cryostat (3) Fixed Slide:8.4mm FixedSlide:1.4mm Fixed Slide:1.4mm Invar rod Support post Sliding cavity support

Material of helium vessel for the 35 MV/m cavity and the TESLA cavity : Ti –The SUS-Ti junction is being studied for the connection between the cooling channel pipes (SUS) and the helium vessels (Ti). Samples of two types (Hot Isostatic Pressure, Friction Pressure Welding) have been manufactured. Mechanical strength tests have been completed. –For both methods, the mechanical strength at the junction was almost same as Ti at room temperature. Helium leak test at 2 K (super-leak) will be performed next week. R&D Studies of Cryostat Components (1) SUS-Ti junction by HIP SUSTi SUS-Ti junction (35 MV/m cavity helium vessel) SUS-pipe Ti helium vessel

The heat losses of the components in the cryomodule will be estimated by the temperature profile and the FEM calculation. –Temperature sensors  2K~ 5K (input coupler, helium vessel etc) : Cernox temperature sensor (54 points)  4K ~ 300 K (support post, thermal radiation shield etc) : PtCo temperature sensor (44 points)  > 80K : Copper-Constantan thermo-couple temperature sensor (58 points) The heat loss of the system at the 2 K region will be measured by the attainable saturated pressure value of the He-II with the pump system. R&D Studies of Cryostat Components (2) Heat Loss Measurement

From the test results of the TESLA cryomodule, the 1st thermal cycle induced the position change of GRP with respect to the original position. Measurement of cavity position during cool-down and warm-up : WPM sensors  Helium vessel : 2 sensors in axial direction 16 sensors for cavity helium vessels  GRP : 5 sensors for one cryostat 10 sensors for GRPs R&D Studies of Cryostat Components (3) Wire Position Monitor GRP Cavity Helium Vessel

The cryomodule design for the STF phase-1 is based on the TESLA type III cryomodule.  Calculated heat loss of the cryostat at 2 K : 12.1 W  Cooling power of cryogenic system at 2 K : 20 W Manufacturing the cryostat components have been completed, and they have been delivered from the company.  The four support post were delivered from INFN under the research collaboration between INFN and KEK.  The assembly of these components and the cavities will start in this summer. R&D studies of the cryostat components;  SUS-Ti junction The junctions have been manufactured by two methods (HIP, friction pressure welding). The helium leak test at 2 K will start next week.  WPM The performance test will start in April. Summary