Tom Peterson -- Cryomodules Integration of cryomodules into the Project X cryo system -- design comments and issues Tom Peterson 3 Jan 2011

PX Briefing to OHEP Reference design scope PX Briefing to OHEP 2 Warm cw front end (H- ion source, RFQ, MEBT, chopper) 3-GeV cw SCRF linac, 1-mA ave. beam current Transverse beam splitter for 3-GeV experiments 3-8 GeV: pulsed SCRF linac (5% duty cycle) Recycler and MI upgrades Various beam transport lines Pulsed dipole 5% duty cycle

PX Briefing to OHEP 3 Reference design: cw linac Prelim design (preferred) SSR0SSR1SSR2β=0.6β= MHz MeV 650 MHz GeV SectionFreqEnergy (MeV)Cav/mag/CMType SSR0 (  G =0.11) /26/1SSR, solenoid SSR1 (  G =0.22) /18/ 2SSR, solenoid SSR2 (  G =0.4) /24/ 4SSR, solenoid LB 650 (  G =0.61) /24/ 45-cell elliptical, doublet HB 650 (  G =0.9) /34/185-cell elliptical, doublet 180 elliptical cavities From Project X Briefing to DOE/Office of High Energy Physics November 16, 2010, by Sergei Nagaitsev Consider stand-alone cryomodules -- Tom P.

Tom Peterson -- Cryomodules Cryomodule Pipe Sizing Criteria Heat transport from cavity to 2-phase pipe –1 Watt/sq.cm. is a conservative rule for a vertical pipe (less heat flux with horizontal lengths) 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 –Path includes nozzle from helium vessel, 2-phase pipe, may include gas return pipe, and any external vent lines 4

Tom Peterson -- Cryomodules Air inflow heat flux limit Atmospheric air flowing into a vacuum via a round hole –~23 grams/sec per cm2 hole size Heat deposition by air condensing on cold surface –~470 J/g, so 10.8 kW per cm2 hole size Helium heat input per gram ejected for typical ( bar) pressures –~13 J/g Helium mass flow per air inlet area –~830 grams/sec helium per cm2 hole size 5

Tom Peterson -- CryomodulesProject X CW Cryomodules, Tom Peterson For a 3-inch (76 mm) diameter opening, air flow becomes the limiting factor in heat deposition after a few cryomodules. But for one cryomodule, total cavity surface area determines the flow rate. 6 3-inch port

Tom Peterson -- Cryomodules Current lead design Magnets in sub- atmospheric 2 K helium require conductively cooled current leads. 4 leads at 50 A, 2 leads at 200 A Thermal intercepts at 80 K and 5 K Tom Nicol, Valeri Poloubotko, Sergey Cheban

Tom Peterson -- Cryomodules Heat exchanger design 4.5 K - 2 K heat exchanger for 10 grams/sec (~200 W at 2 K, designed by Tom Peterson) in the TTF feedbox assembly 2 K supply flow precooled by 2 K pumped return flow improves 2 K capacity by ~40%. Heat exchanger must be vertically oriented and higher than the liquid in the cryomodule Arkadiy Klebaner, Sergey Cheban, Ben Hansen working on heat exchanger design for Project X

Tom Peterson -- Cryomodules 650 MHz assumptions 2.0 K helium cooling (~30 mbar) 1.5 uncertainty factor for flow estimation and pipe sizing Cavity MAWP = 2.0 bar warm, 4.0 bar cold Heat loads on following slides 9

Tom Peterson -- Cryomodules 2 K heat loads 10

Tom Peterson -- Cryomodules 5 K heat loads 11

Tom Peterson -- Cryomodules 70 K heat loads 12

Tom Peterson -- Cryomodules 650 MHz cryo schematic (“string” probably one CM)

Tom Peterson -- CryomodulesProject X CW Cryomodules, Tom Peterson 2-pipe 2 Kelvin vapor system 650 MHz cryomodule a modified TESLA-type Project X CW Cryomodules, Tom Nicol, Tom Peterson 14

Tom Peterson -- CryomodulesProject X CW Cryomodules, Tom Peterson 650 MHz 2-phase pipe size 33.6 W per cavity -- note the large pipe needed for even just a few cryomodules in series 15 TTF is 72 mm

Tom Peterson -- CryomodulesProject X CW Cryomodules, Tom Peterson 16 Note: a 3-inch air inlet hole results in a mass flow equivalent to ~ 8 beta= MHz cavities. Checking the feasibility of venting a CM string of cavities with a large 2-phase pipe. Looks OK but still need frequent cross-connects to a larger pipe.

Tom Peterson -- CryomodulesProject X CW Cryomodules, Tom Peterson

Tom Peterson -- Cryomodules Stand-alone CM pipe sizes 18

Tom Peterson -- Cryomodules Further considerations Support structure –Stiffness of pipe if used as support backbone –Or other support structure options Emergency venting scenarios drive pipe sizes and influence segmentation –Cold MAWP may be low for 650 MHz, driving up pipe sizes and/or reducing spacing between relief vent ports –Trade-off of pipe size with vent spacing requires further work –Thermal shield pipe may also require frequent venting 5 K has a large surface area for large heat flux 70 K starts at a high pressure Liquid management length needs further work –May want to subdivide strings for liquid management due to large specific liquid flow rate per cavity 19

Tom Peterson -- Cryomodules Liquid management length The 2 K to 4.5 K heat exchanger needs to be divided (not one large heat exchanger) in order to be a practical size, which means distributing multiple heat exchangers in the tunnel. 2 K to 4.5 K heat exchanger size which fits in the Project X tunnel will be roughly grams/sec (about Watts of 2 K heat) With 650 MHz and 1.3 GHz CW heat loads of nearly 200 W per cryomodule, this implies liquid management lengths of one or two cryomodules as limited by JT heat exchanger practical size limits 20

Tom Peterson -- Cryomodules From “Controlling Cavity Detuning for Project X” by Ruben Carcagno, et. al. SNS –Long term pressure regulation to better than 100 ubar (Fabio Casagrande) Regulates flow and maintains constant heat load using bath heaters Distributes He at 4K with a cold box on each cryomodule CEBAF –25 ubar when everything is ‘quiet’ Also regulates flow and uses heaters to maintain constant load Distributes He at 2K –Transients of up to several 1-2 mbar about once a day Identified a control system problem not a cryogenic problem HoBiCaT (BESSY) –15-30 ubar steady state –Large non-gaussian tails in microphonics distribution ~17  fluctuation every one or two hours Origin not completely understood but cryogenic likely a large component Cornell –Heat leak at dead end pipe in cryo system creates gas bubbles which ‘pop’ about once per second

Tom Peterson -- Cryomodules22 Pressure stability Consider short duration pulses (~ a few seconds or less) for which the vapor and liquid are not in equilibrium. –Treat the vapor volume as a closed volume of ideal gas –Heat or vapor flow change results in a direct change of stored gas –Pressure changes in proportion to net mass flow in or out –Pressure changes inversely with total vapor volume –Using total mass flow, if a TTF cryomodule with TTF-sized pipes and 16 W total heat (dynamic plus static), pressure change due to total heat flow into a closed volume is dP/dt =0.023 mbar/sec SSR0 dP/dt = 0.10 mbar/sec SSR1 dP/dt= 0.14 mbar/sec SSR2 dP/dt = 0.33 mbar/sec 650 MHz CW dP/dt = mbar/sec

Tom Peterson -- Cryomodules23 Pressure stability Consider longer duration pulses (many minutes) for which the 2 K liquid and vapor are always in complete thermal equilibrium. –Liquid volume may become a factor (liquid helps to buffer a step change in heat load due to a significant heat capacity with small temperature change) J/g per mK, so J/g for 0.1 mbar pressure change –The process is the addition of heat or transfer of mass (to or from) a closed 2- phase system –Will study the equilibrium (liquid-vapor phase equilibrium) rate of change of pressure with incremental change of heat and flow Various ratios of liquid and vapor Various rates of heat addition Rate of return to vapor-liquid equilibrium is limited by heat transport through the “chimney” as helium condenses (adding heat) or vaporizes (carrying away heat) –Surface area of liquid is a factor to help damp pressure oscillations

Tom Peterson -- Cryomodules24 Pressure stability -- role of liquid surface Consider a 0.1 mbar step change in pressure due to vapor flow –Corresponding temperature change is 1 mK –So surface temperature of the liquid essentially immediately changes by 0.1 mK and heat transport proceeds as vapor evaporates or condenses. –The nominal maximum of 1.4 W/cm 2 corresponding to liquid head reaches to a depth of 0.7 cm for 0.1 mbar. For greater depth, heat transport with 1 mK delta-T is reduced in proportion to length. For a 5 cm chimney height, this becomes 0.2 W/cm 2 for the 1 mbar pressure change. –Corresponding surface mass flux (23.4 J/g latent heat) is g/s per cm 2. –The TESLA 55 mm chimney (24 cm 2 ) can then buffer a vapor flow rate change of up to 24 x = 0.2 gr/sec with a 0.1 mbar pressure change. For the closed 650 MHz dressed cavity, a 110 mm chimney can buffer a 0.1 mbar pressure change with up to 0.8 gr/sec vapor-liquid exchange rate. For an open 650 MHz dressed cavity, the maximum vapor exchange rate with 0.1 mbar delta-P is about 47 gr/sec. Conclusion: there is a significant pressure stability advantage for the large 2.0 K liquid-vapor surface area.

Tom Peterson -- Cryomodules Conclusions Work on cryomodule requirements and configurations is in progress. CW cryomodule piping requirements may be quite different from TESLA/ILC –325 MHz cryomodule 2-phase pipe sizes are overwhelmingly determined by venting requirements –650 MHz and 1.3 GHz CW liquid management lengths may be only one or a few cryomodules Thermal shield piping sizes may be like TTF or smaller Division of 325 MHz cryomodules into shorter sections for emergency venting looks necessary Division of CW 650 MHz and 1.3 GHz cryomodules into short strings or individual cryomodules for liquid management may be necessary A large liquid-vapor surface area is an advantage for pressure stability – This may be an important consideration if we use SNS and Jlab pressure stability experience to set our expectations for Project X 25

Tom Peterson -- Cryomodules References “Project-X, CW Linac (ICD-2+) Lattice Design,” by Nikolay Solyak (presentation to a Project X meeting, March 16, 2010) “Notes about the Limits of Heat Transport from a TESLA Helium Vessel with a Nearly Closed Saturated Bath of Helium II,” by Tom Peterson, TESLA report #94-18 (June, 1994). "Latest Developments on He II Co-current Two-phase Flow Studies," by B. Rousset, A. Gauthier, L. Grimaud, and R. van Weelderen, in Advances in Cryogenic Engineering, Vol 43B (1997 Cryogenic Engineering Conference). "Optical Investigations of He II Two Phase Flow," by E. di Muoio, et. al., in Advances in Cryogenic Engineering, Vol 47B (2001 Cryogenic Engineering Conference). Dynamic RF heat loads from "CAVITY.dat”, Slava Yakovlev (28 Dec 2010) Current lead heat from "Conduction-cooled 60 A Resistive Current Leads for LHC Dipole Correctors", by A. Ballarino and other studies 26