SESSION 3

1. SESSION 3 Cryogenic and Vacuum issues affecting Beam Commissioning N. Hilleret L. Serio Session 3

2. Origin: In-situ welds ~ 150000 ! Imported leaks Thermal cycles Faulty o-rings Damaged sealing surfaces Etc… Peculiarities: Cryopumping (for He) He: 1/10 monoC, 1.9K, 8x10-11Pa Long time constant (He) Size of tolerable leaks (He) Large (very) leaks could be tolerated Tolerable size determined by time between warming up (20 hours cycle) W/O pumping Cryomagnet (200 days) : 3x10-6 Pa.m3.s-1 QRL: 10-6 Pa.m3/s With Pumping (MLI transparency): Cryomagnet : ~10-3 Pa.m3.s-1 QRL restricted axial cond. ~ 10-4 Pa.m3.s-1?? Cryogenic and Vacuum issues affecting Beam CommissioningImpact of leaks in QRL and Insulation VacuumP. Cruikshank/G. Riddone 24hours 10-4 Pa.m3.s-1 Session 3

3. Air leaks: 5ppm He in air, 200 days =>0.1 Pa.m3.s-1 Detection and localisation Delicate : sticking + limited diagnostics Remotely: within a vacuum sub- sector Fine localisation if repair needed after warming up more difficult (Possible?) in QRL (Longitudinal conductance) Repair : Short:13 days ( fast warm up + short mechanical intervention) Long: 38 days Cryogenic and Vacuum issues affecting Beam CommissioningImpact of leaks in QRL and Insulation VacuumP. Cruikshank/G. Riddone Session 3

4. Consequences of leaks Local accumulation of gas (desorption yield, secondary electron yield) Pressure Bumps/Transients Enhanced radiation (local electronic) Enhanced background (experiments) Heat deposition in cryomagnets: Quench ( 1m at 5x10-5Pa (300K), Inom) Air leaks Where? Vicinity of cold/warm transitions: LSS Limited extension : 10-7 Pa.m3.s-1 =>30 monolayers condensed over 0.2 m, 1 week Transients E cloud enhancement (H2O, N2 ?) => E.I.D. (large yields) Gas migration: transient effect after significant period without beam Repair: Classic Cryogenic and Vacuum issues affecting Beam CommissioningHow to Deal with Leaks in the LHC Beam VacuumV. Baglin 1015 N2/m2 ,1.5W/m, 100 eV Session 3

5. Helium leaks He Front Speed of the He front: 7x10-8 Pa.m3.s-1 ~ 2 cm.h-1 Quench after~ 150 days with leak If front width< 1/2 sensor spacing: quench before any detection At Inom leaks < 1x10-7 Pa.m3.s-1 can be detected before quench Diagnostics Cryo measurements: power in the cold mass, Magnet temperature BLM and Rad. Monitors (could be mobile and installed when/where needed) Some vacuum gauges/valves for mobile equipment: identification of He in the rest gas tactic 1 Cold mass cryo powerincrease=>cryo cell 2 Localisation by mobile BLM or rad monitors 3 RGA Identification of excessive He pressure(not all loses are due to a leak) Repair If leak < 1x10-7 Pa.m3.s-1: no problem 1.3x10-7 Pa.m3.s-1 Warm up 4K each 30 days Leak>5x10-7 Pa.m3.s-1 => Warm up Cryogenic and Vacuum issues affecting Beam CommissioningHow to Deal with Leaks in the LHC Beam VacuumV. Baglin Session 3

6. Refrigerator system All tests foreseen can be done without impact on the installation and test of the magnet system Valuable experience will be gained through these tests and LHC commissioning time would be minimized Operational resources can be spared by skipping test, but valuable experience and training will be lost DFBs and DSL Cold test in SM18: Type test to be done in parallel with installation, No impact on schedule QRL He leaktightness of the sub-sector should be kept (no schedule impact on the QRL installation) => Stimulated a discussion Combined pressure and leak test: cannot be skipped, can be postponed with large risks Cryogenic and Vacuum issues affecting Beam CommissioningShortcuts during installation and commissioning: risk and benefit H. Gruehagen, G. Riddone Session 3

7. Cryogenic and Vacuum issues affecting Beam CommissioningShortcuts during installation and commissioning: risk and benefit H. Gruehagen, G. Riddone • Cooldown/thermal cycles: • At least one thermal cycle per sector (quick test) • Several thermal cycles (6-7) recommended for sectors with “old” production and might be skipped for sectors with only “new production” • Heat inleaks measurements • First sector (8-1): the full sector will be measured (old and new production) • Sector 7-8: heat inleaks will be measured on a portion of QRL (subsectors A, B,…) • Other sectors: measurement of at least one full sector with only new production is highly recommended • If measurements are skipped: • Critical headers: B and F (contribution from headers C and D are negligible with respect to the dynamic loads) : • Header F (41% of total heat load): cold spots might be a reason for higher heat inleaks • Header B (89 % of total heat load, factor 2 margin in ultimate operation): measurements are still possible with magnets. Session 3

8. Cryogenic and Vacuum issues affecting Beam CommissioningCommissioning the DFB’sA. Perin, V. Benda • MAIN CHARACTERISTICS OF THE DFB’s • Cryogenics • Current leads operation in 4.5 K saturated LHe bath • Controls: liquid helium and helium gas flow for the current leads • Max. pressure for DFBs 0.35 Mpa => specific cooling procedure • DFBA supply/exit of GHe for E line • Electrical • Concentration of all types of busbars in very small space • Significant quantity of electrical interconnects: 900 current leads to busbars, 1400 busbar to busbar, ranging from 120A to 13’000A • Insulation vacuum • No vacuum barrier: DFB share the vacuum of the magnets they power • Beam vacuum (DFBAs only) • Actively cooled beam pipes with beam screens • Cold-warm transitions • Extensive testing at room temperature is required before installation • All delay in DFBs will have a direct impact on LHC commissioning • DFBs must be installed to pump/cool down arcs and MS magnets • DFBs must be fully operational to power the magnets Session 3

9. Cryogenic and Vacuum issues affecting Beam CommissioningCommissioning the DFB’sA. Perin, V. Benda • Commissioning • In order to reduce the commissioning time in the LHC tunnel, all ancillary equipment will be installed on the DFBs and tested before tunnel installation • Data gathered during a cold test of one DFB (“type test”) can minimize the LHC commissioning time • Beam commissioning cannot be performed with non working DFBs • The DFBs must be commissioned together with the magnets they are powering • The specific pressure requirements of the DFBs imply a specific cool down sequence • Without cold test, displacement of the beam pipes can only be validated with a circulating beam • Failures • Each DFB is unique: no spare DFB will be available. • The current leads can be replaced in situ with a moderate effort • The splices are accessible in situ with moderate effort • Any access, except to splices, to the internal components will most probably require the disconnection of the DFB with a minimum downtime of several months Session 3

10. Characteristics of the SC-RF cryo system The RF: a low pressure (2bar max) equipment connected to a high pressure line (quench recovery :15bar) Pressure stability :1.35bar±15 mbar Alternative cooling schemes studied to provide the possibility to discharge helium gas at a lower pressure than nominal 1.350 bar, increasing availability of sc cavities operation To keep availability at least as it is now Cryogenic and Vacuum issues affecting Beam CommissioningCryogenic System in Pt4 Possible Options S. Claudet , U. Wagner • While reviewing possible options, why not giving the possibility to operate the sc cavities independently from the sectors • The reference solution works and needs to be implemented, with simple adaptations (control & check valves) to prevent perturbation due to back pressure from line D Session 3

11. SM18 experience shows that the pressure stability requirements are and will be fulfilled with present configuration (line D plus control valve) A back-up return via the warm recovery line (sol.1) is a minor modification and would prevent from major pressure excursions above 1.5 bar and therefore minimize helium losses Any alternative cooling scheme (sol 2->5) requires a modification of the corresponding cryogenic distribution line; this option requires an ECR from the RF group Additional capacity does not appear to be necessary and would only be triggered by needs for ultimate beams or (bad!) operational experience Cryogenic and Vacuum issues affecting Beam CommissioningCryogenic System in Pt4 Possible Options S. Claudet , U. Wagner Session 3

12. The cryogenic system should have a very low impact (except on sector 2-3) on the beam commissioning because of: Built in redundancy of systems Available spare cooling capacity for low intensity beam Reliability of components and instrumentation Availability of first installed refrigerator (pt1.8) during the first few years of operation is above 99% The reliability strongly depends On maintenance management and organization ->Resources are urgently needed Reliability of the control system -> still requires improvement Maintenance policy Baseline: 13 weeks campaign during each shut-down Spare parts: 2.2% cryoplant cost (criticity analysis) Strategy for Shut downs: Full maintenance/ floating temperature (200K):Thermal cycle/stresses Maintenance on 1 cryoplant/point (not possible for sector 2-3 (80K) : No thermal cycle(good and bad) Warm up could be needed (magnet exchange,…...) Cryogenic and Vacuum issues affecting Beam CommissioningIssues concerning the Reliability of the Cryogenic System M. Sanmartí Session 3

13. Failures: Failure of sub-systems and components would only result in several hours delays Worst failure would be the loss of insulation vacuum on the QUI or QRL (no redundancy) the refrigerator in point 2 or DFB’s for magnet powering Most likely failure would be filters blockage on the QUI during or after the first cool down and magnets quench due to accumulation of impurities (consolidation under study) Recovery time after major failure (utility, cryo or controls) : 6 hours plus 3 times the stop length (15 times if bad vacuum/QRV leaks) Cryogenic and Vacuum issues affecting Beam CommissioningIssues concerning the Reliability of the Cryogenic System M. Sanmartí Session 3