ILC : Type IV Cryomodule Design Meeting Main cryogenic issues, L. Tavian, AT-ACR C ryostat issues, V.Parma, AT-CRI CERN, January 2006

2 Content Design pressure of cavity cold mass structure Minimum diameter requirement of distribution lines Cool-down and warm-up principle

3 Design pressure of cavity cold-mass structure

4 The spacing of safety device needed to protect the cavities depends strongly on the design pressure of the cold-mass structure: »“High” design pressure (~ bar) Discharge of helium during technical incident (break of beam vacuum with air) can be done via the pumping line (DN300) with safety relief valves located close to access shaft. »“Low” design pressure (< bar) Safety relief valves must be periodically installed in the tunnel on the pumping line, i.e. ODH issues in the tunnel or large additional header to collect the valve discharge.

5 Design pressure of cavity cold-mass structure Design pressure level AdvantageDrawback “High” - No helium discharge in the tunnel - Cost of safety devices - Cavity design “Low”- Cavity design - ODH issue (personnel safety) - Additional header (space + cost) - Larger safety device number (cost and reliability)

6 Minimum diameter of distribution lines Line Minimum diameter [mm] Line A60 Line B300 Line C70 Line D70 Line E100 Line F100

7 Cool-down and warm-up principle Tesla TDR principle

8 Cool-down and warm-up principle ILC principle proposal

9 Cool-down and warm-up principle PrincipleAdvantageDrawback Tesla TDR No change W/r to the TTF type III cryomodule. - Need of additional valve - Additional temperature measurement - Need of hydraulic restriction to share the CD WU flow (risk of plugging) - Risk of unbalanced and uncontrollable CD/WU operation of cryo-string elements (// cooling). ILC proposal - CD/WU operation fully controllable (series cooling). - Saving of 1 valve per cryo-string (128 valves in total) - Saving of ~15000 temp. sensors and corresponding acquisition (~10 MEuro). Change w/r to the TTF III cryomodule design.

10 Main cryostat design issues Real-estate gradient: inter-cavity and cryomodule interconnection space optimization [1][1] Cryomodule length? [2][2] Thermal performance. review of static heat loads: table 1 of bcd:main_linac:ilc_bcd_cryogenic_chapter_v3.doc [3] bcd:main_linac:ilc_bcd_cryogenic_chapter_v3.doc[3] Design of thermal shielding feed-throughs and thermalisations (couplers, tuners, etc.): strong impact on cryostat thermal performance. [4][4] Cryomodule interconnection design: Length optimization, thermal design, interconnection bellows stability. [5] [5] Cryo-string extremity modules (Technical Service module in LHC jargon) housing cryo equipment: 2 out of 15 cryomodules in a cryo-string. [6][6] Cryogenics flow (and vacuum pumps) induced vibrations. Performance limiting? bcd:main_linac:ilc_bcd_cryogenic_chapter_v3.doc [7] bcd:main_linac:ilc_bcd_cryogenic_chapter_v3.doc[7] Materials and assembly technologies: »Ti helium vessel and weldability to Ni. [8][8] »Ti-to-st.steel transitions leak-tightness at cryo T (13 units per cryomodule!). [9][9] External support system (ground support vs. hanging) and re-alignment strategy  impact on tunnel integration

11 Inter-cavity space optimisation ~283mm Space optimisation is a must! (1 cm gain  ~100m gain per linac)

12 Cryo-module length Impact of cryo-module length: »Increasing length: »< No.of interconnections:  < No.componets (bellows) and installation cost saving »So > real estate gradient:  tunnel length cost saving »< No. critical components (bellows)  higher reliability  All desirable effects Practical limits: »Weight increase. (TTF~8 tons?). Longer Cryo-modules will remain “light” objects (below 15 tons). »Road transport: from ~11 m to ~ 15 m cryomodule still transportable (according to European regulations). LHC cryo- dipoles are ~15 m long. »Handling: no major limitation, but…wider tunnel shafts:  cost increase  Increase length to about 15 m or longer?

13 Interconnections…often forgotten Optimise compactness  > real estate gradient Specific design of compensation systems: »Mechanical stability of pressurised lines (Al extruded thermal shields for LHC) »Low stiffness/compact optimised bellows (plastic domain for LHC bellows) Do not forget thermal performance: »Appropriate (active) thermal shielding with MLI »Beware of thermal contraction gaps in thermal shields (radiation multi-reflection paths). »Cryo-module extremities need specific features LHC interconnection Experience gained in the past! 

14 Thermalisations Welded Al thermal shields (50-65 K) Al welded shrink-fit thermalisation of pumping tubes (SSS) (50-65 K) Avoid bolted braid assemblies and st.steel brazing whenever possible All-welded or shrink-fitted solutions preferable  Proper interface must be foreseen on components for effective thermalsations Thermalisation weld of support post / bottom tray (50-65 K) A few LHC solutions

15 Estimated heat loads Table 1. Estimated values of distributed heat loads in steady operation [W/m] (without contingency) Temperature level K5 - 8 K2 K Static heat inleaks Dynamic loads at initial energy Couplers, absorbers… RF load Total at initial energy Dynamic loads at final energy Couplers, absorbers… RF load Total at final energy

16 Vibrations Table 4. Maximum vibration level (integrated RMS of vertical displacement) FrequenciesMaximum vibration level [nm] f >= 0.5 Hz80 f >= 1 Hz70 f >= 5 Hz20 f >= 10 Hz5