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Crab Cavity Cryostat Fabrication and Challenges

Crab Cavity Cryostat Fabrication and Challenges. Tom Peterson (FNAL) FNAL-LHC Crab Cavity Engineering Meeting 14 Dec 2012. Crab cavity cryostat discussion. Fabrication of the different types of cryostat and their advantage and disadvantages should be reviewed.

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Crab Cavity Cryostat Fabrication and Challenges

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  1. Crab Cavity Cryostat Fabrication and Challenges Tom Peterson (FNAL)FNAL-LHC Crab Cavity Engineering Meeting14 Dec 2012

  2. Crab cavity cryostat discussion Fabrication of the different types of cryostat and their advantage and disadvantages should be reviewed. Challenges in the design choice, fabrication steps, integration along with feasibility of a two cavity cryostat within the specified scheduled should be reviewed and mitigation should be discussed. LHC Crab Cavity Cryostat, 14 Dec 2012

  3. Final crab cavity system requirements • Definition of requirements is still in progress • Elements of these requirements include: • Interfaces to the LHC accelerator system, cryogenic system, and tunnel infrastructure • Thermal conditions, cavity temperature, intercept temperatures, heat loads • Cavity arrangement, supporting structure and possibility for alignment, beam-beam spacing and allowance for two beams, how many cavities per cryostat? 2 • Constraints from vertical and horizontal crabbing schemes RF coupler and HOM/LOM configurations and constraints • Tuner configurations and constraints • Instrumentation requirements • Cryostat, piping, and helium vessel safety, code compliance requirementsfrom final design. LHC Crab Cavity Cryostat, 14 Dec 2012

  4. Given the final system requirements above, how may the prototype differ from the final design? Cavity support structure, same as final design? YES Arrangement of multiple cavities. Same total number of cavities? NO Provisions in the prototype for one beam only? PERHAPS Cryostat vacuum vessel differences SIGNIFICANT RF couplers and HOM/LOM configuration and orientation through the cryostat SIMILAR to final design Special instrumentation not in the final cryostat Cryogenic connections, interfaces to infrastructure may differ YES, but not yet defined LHC Crab Cavity Cryostat, 14 Dec 2012

  5. Peak warm pressure ILC presentation – Tom Peterson • Compressor suction set pressure • 1.2 bar (to avoid subatmospheric excursions) • Control margin • +/- 0.2 bar • Relief set pressure margin • + 0.3 bar above control excursions (a judgment here, would like 0.5 bar) • Suction relief set pressure • 1.7 bar (from 1.2 + 0.2 + 0.3 bar above) • Pressure drop from far helium vessel to relief • + 0.1 bar (needs to be determined for specific system, but probably low for the low flow in the warm situations) • Peak warm pressure • 1.8 bar (note that 0.5 bar set pressure margin, which would be better ==> 2.0 bar peak warm pressure) • Conclusion: 2.0 bar warm MAWP is a practical lower limit LHC Crab Cavity Cryostat, 14 Dec 2012

  6. Cold peak pressures - 1 ILC presentation – Tom Peterson • Loss of vacuum to air • “Safety Aspects for the LHe Cryostats and LHe Containers,” by W. Lehman and G. Zahn, ICEC7, London, 1978 • “3.8 W/sq.cm. for an uninsulated tank of a bath cryostat” • “0.6 W/sq.cm. for the superinsulated tank of a bath cryostat” • “Loss of cavity vacuum experiment at CEBAF,” by M. Wiseman, et. al., 1993 CEC, Advances Vol. 39A, pg 997. • Maximum sustained heat flux of 2.0 W/sq.cm. • LEP tests and others have given comparable (2.0 to 3.8 W/sq.cm.) or lower heat fluxes • Film boiling of helium with 60 K surface is about 2.5 W/sq.cm. LHC Crab Cavity Cryostat, 14 Dec 2012

  7. Cold peak pressures - 2 ILC presentation – Tom Peterson • Input parameters • Heat flux as limited by • Rate of air inleak • Surface heat transfer • Total surface area involved • Can be limited by vacuum breaks, fast valves • Initial conditions • Note that 4.5 K just after filling (as opposed to 2 K when the large, low pressure volume acts as a buffer) is the worst case! • Pipe diameters out to the helium vent • Overall distances and pipe lengths out to the helium vent • A finer degree of segmentation can reduce pipe diameter requirements LHC Crab Cavity Cryostat, 14 Dec 2012

  8. Cold peak pressures - 3 ILC presentation – Tom Peterson • Relief pressure will be suction relief set pressure (for example, 1.7 bar) • Heat flux of 10’s of KW to liquid helium • Mass flows of many kg/sec • Pressure drops to vent may result in peak pressures of 2.5 bar to 4 bar locally • Maintaining a low peak pressure (e.g., 2.5 bar) requires larger piping and/or shorter vent path lengths LHC Crab Cavity Cryostat, 14 Dec 2012

  9. Conclusion for MAWP ILC presentation – Tom Peterson • “Maximum Allowable Working Pressure” (MAWP) • The pressure which we declare on our engineering notes will be the maximum the vessel will see • Relief valves and vent piping are sized to prevent pressure exceeding this value • 2 bar differential pressure warm (minimum!) • Helium space to cavity vacuum • Helium space to insulating vacuum • 2.5 bar to 4 bar differential pressure cold • Helium space to cavity vacuum • Helium space to insulating vacuum • Higher (closer to 4 bar) is better in allowing smaller diameter and longer pipes to vent valves LHC Crab Cavity Cryostat, 14 Dec 2012

  10. Presentation to DOE, 21 Sep 2011 Safety/compliance issue • In the U.S., Europe, and Japan, these helium containers and part or all of the RF cavity fall under the scope of the local and national pressure vessel rules. • Thus, while used for its superconducting properties, niobium ends up also being treated as a material for pressure vessels. • For various reasons, it is not possible to completely follow all the rules of the pressure vessel codes for most of these SRF helium vessel designs LHC Crab Cavity Cryostat, 14 Dec 2012

  11. Presentation to DOE, 21 Sep 2011 Issues for code compliance • Cavity design that satisfies level of safety equivalent to that of a consensus pressure vessel code is affected by • use of the non-code material (niobium), • complex forming and joining processes, • a shape that is determined entirely by cavity RF performance, • a thickness driven by the cost and availability of niobium sheet, • and a possibly complex series of chemical and thermal treatments. • Difficulties emerge pressure vessel code compliance in various areas • Material not approved by the pressure vessel code • Loadings other than pressure • Thermal contraction • Tuning • Geometries not covered by rules • Weld configurations difficult to inspect LHC Crab Cavity Cryostat, 14 Dec 2012

  12. Presentation to DOE, 21 Sep 2011 General solution • In applying ASME code procedures, key elements demonstrating the required level of design safety are • the establishment of a maximum allowable stress • And for external pressure design, an accurate approximation to the true stress strain curve • Apply the ASME Boiler and Pressure Vessel Code as completely as practical • Exceptions to the code may remain • We have to show the risk is minimal • Satisfy the requirement for a level of safety greater than or equal to that afforded by ASME code. • Fermilab, Brookhaven, Jefferson Lab, Argonne Lab, and others in the U.S. have taken a similar approach LHC Crab Cavity Cryostat, 14 Dec 2012

  13. Presentation to DOE, 21 Sep 2011 Conclusions • Niobium, niobium-titanium, electron beam welding, and other features required for the proper function of superconducting RF cavities create problems with respect to pressure vessel codes in all regions of the world • With significant effort, laboratories have found various ways to provide levels of safety equivalent to the applicable code rules • These methods involvetaking some very conservatively low values for niobium yield strength due to heat treatments and uncertainty, and doing analysis and quality assurance inspections in accordance with code rules as much as possible • Treating the vacuum vessel as the primary containment volume or excluding the niobium material from the pressure boundary definition may be feasible in some cases LHC Crab Cavity Cryostat, 14 Dec 2012

  14. Cryomodule requirements -- major components • Dressed RF cavities • RF power input couplers • One intermediate temperature thermal shield • Cryogenic valves • 2.0 K liquid level control valve • Cool-down/warm-up valve • 5 K thermal intercept flow control valve • Pipe and cavity support structure • Instrumentation -- RF, pressure, temperature, etc. • Heat exchanger for 4.5 K to 2.2 K precooling of the liquid supply flow LHC Crab Cavity Cryostat, 14 Dec 2012

  15. Cryomodule requirements -- major interfaces • Bayonet (or other style) connections for helium supply and return • Vacuum vessel support structure • Beam tube connections at the cryomodule ends • Double vacuum valves • Guard vacuum pumping • Thermal intercepts • Allowance for thermal contraction • RF waveguide to input couplers • Instrumentation connectors on the vacuum shell • Alignment fiducials on the vacuum shell with reference to cavity positions. • Vacuum system for pumping insulating vacuum LHC Crab Cavity Cryostat, 14 Dec 2012

  16. Design considerations • Cooling arrangement for integration into cryo system • Pipe sizes for steady-state and emergency venting • Pressure stability factors • Liquid volume, vapor volume, liquid-vapor surface area as buffers for pressure change • Evaporation or condensation rates with pressure change • Updated heat load estimates • Options for handling 4.5 K (or perhaps 5 K - 8 K) thermal intercept flow • Alignment and support stability • Thermal contraction and fixed points with closed ends LHC Crab Cavity Cryostat, 14 Dec 2012

  17. Cryomodule Pipe Sizing Criteria • Heat transport from cavity to 2-phase pipe • 1 - 1.4 Watt/sq.cm. is a conservative rule for a vertical pipe (less heat flux with non-vertical connection to helium vessel, analysis for tight spaces) • Two phase pipe size • 5 meters/sec vapor “speed limit” over liquid • Not smaller than nozzle from helium vessel • Gas return pipe (also serves as the support pipe in TESLA-style CM) • Pressure drop < 10% of total pressure in normal operation • Support structure considerations • Loss of vacuum venting P < cold MAWP at cavity • Heat flux as much as 4 W/cm2 on low-T bare metal surfaces • Path includes nozzle from helium vessel, 2-phase pipe, may include gas return pipe, and any external vent lines LHC Crab Cavity Cryostat, 14 Dec 2012

  18. Cryostat design options • Use existing designs to the extent possible • Two cavities, R&D nature of test • Provide relatively easy access to cavities, tuner, input coupler, HOM couplers • Several examples of such cryostats exist • 1 – capture cavity • 2 – horizontal test cryostats • 3 – various top-loading designs LHC Crab Cavity Cryostat, 14 Dec 2012

  19. Cryostat design option examples – 1 • Capture Cavity • Single cavity in a cryostat • Tension rod support • Flanged vacuum shell heads • Short cryostat allows attachment of tension rods to vacuum shell and transfer of load to the rods after insertion of cavity on simple tooling • Similar to what we saw from Niowave LHC Crab Cavity Cryostat, 14 Dec 2012

  20. Saclay/Fermilab Capture Cavity LHC Crab Cavity Cryostat, 14 Dec 2012

  21. Cryostat design option examples – 2 • Horizontal test cryostat (similar to “Chechia” at DESY) • Single cavity in a cryostat • Support post and frame beneath cavity • Cavity rolls into position for ease of frequent changes • Flanged and hinged vacuum shell heads LHC Crab Cavity Cryostat, 14 Dec 2012

  22. Horizontal Test Cryostat LHC Crab Cavity Cryostat, 14 Dec 2012

  23. Horizontal test cryostat LHC Crab Cavity Cryostat, 14 Dec 2012

  24. Cryostat design option examples – 3 • Top-loading cryostat • Argonne, Triumf, Daresbury, and others • Rectangular sides • Structures hung from top plate • This design has some attractive features given the physical constraints of the SPS tunnel location and the R&D nature of these first tests LHC Crab Cavity Cryostat, 14 Dec 2012

  25. LHC Crab Cavity Cryostat, 14 Dec 2012

  26. 4K GHe RETURN Design Approach – CryomoduleSchematic 2K (GHe) RETURN 4K (LHe) SUPPLY 40 K FORWARD ShrikantPattalwar 60 K RETURN 2K HEX and a valve box could be a part of the module ?? 4K PRE-COOL THERMAL SHIELD 40K TO 60K Outer Vacuum Chamber Magnetic shield TWO PHASE LINE 5K THERMAL INTERCEPTS Shrikant Pattalwar Hi-Lumi Crab Cavity Engineering Meeting Dec 13-14, 2012 Fermi Lab LHC Crab Cavity Cryostat, 14 Dec 2012

  27. Design Approach – Conceptual Model ShrikantPattalwar 1000mm 2160mm 420mm 413mm 1000mm 194 mm Triple tube cavity support system RF input coupler Low order mode coupler High order mode coupler SPS by-pass line Shrikant Pattalwar Hi-Lumi Crab Cavity Engineering Meeting Dec 13-14, 2012 Fermi Lab LHC Crab Cavity Cryostat, 14 Dec 2012

  28. Schedule • Design process for new cryostat or cryogenic box is typically 2 to 3 years • After a complete definition of requirements, details of associated components (e.g., tuner, input coupler) are known, conceptual design (first year or more) . . . • ~1 yr engineering and design/drafting • ~1 yr procurement and fabrication LHC Crab Cavity Cryostat, 14 Dec 2012

  29. LHC Crab Cavity Cryostat, 14 Dec 2012 Schedule Eric Montesinos • Cavities to be installed in SPS in December 2015 • Cryostat fully tested Q3-2015 • Cryostat fully dressed Q2-015 • Couplers available for cryostat Q1-2015 • Couplers RF processed 50 kW SW cw all phases Q4-2014 • Couplers assembled in clean room Q2-2014 onto test box • Special processes FPC + Test Box (Cleaning, Brazing, EB welding, Gold plating, Ti coating) completed Q1-2014 • All couplers + Test Box parts machined Q4-2013 • All raw material delivered Q2-2013 • All raw material ordered Q1-2013 • (common) Coupler design completed February 2013 (+ Test Box !) 2013 2014 2015 2016 February

  30. SM18 tests • Important to verify as much as possible before installation in SPS • Leak tight cold • Heat loads • RF performance of power couplers and cavities • Compatibility for cryogenic connections between SM18 and SPS • 2 K – 4 K heat exchanger, valves • Opportunity also to verify SPS flexible connections LHC Crab Cavity Cryostat, 14 Dec 2012

  31. Conclusions • Three cryostats, one for each cavity type • Each will contain two cavities of the same type • Tight thermal constraints for SPS operation • Tight mechanical constraints for SPS installation • Plus motion requirement • Vertical cavity tests • Cryostat test at SM18 before tunnel installation • Verify thermal performance within SM18 constraints • Verify, as-installed in cryomodule, coupler and cavity RF performance at SM18 LHC Crab Cavity Cryostat, 14 Dec 2012

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