Overview on Recent Development of Conduction Cooling Cavities

SRF’21 - Virtual

G. CiovatiWednesday, June 30, 2021

Outline

Development of conduction-cooled SRF at:• Fermilab

－Development of conduction-cooled 650 MHz cavity－Ongoing activities

• Euclid BeamLabs－Development of 1.6 MeV conduction-cooled

cryomodule• Cornell University

－Investigation of conduction-cooled 2.6 GHz cavity• Jefferson Lab

－Conduction cooling tests on 1.5 GHz and 1.3 GHz cavities

－Ongoing activities

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R. Dhuley

R. Kostin

N. Stilin

THANK YOU:

Underlying theme…

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Cryocooler & Nb3Sn

650 MHz conduction-cooled cavity at Fermilab

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5N

650 MHz Nb/Nb3Sn cavity with thermal links

R. Dhuley et al., IEEE Trans. Appl. Supercond. 29, 0500205 (2019)

Conduction cooling setup at Fermilab

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Cryocooler• Cryomech PT420

(2 W @ 4.2 K with 55 W @ 45 K)

Thermal shield• Cooled by cryocooler stage-1

Vacuum vessel• SS304, 5 feet tall

Magnetic shield• <10 mG total field at the

cavity location

SRF cavity (650 MHz, Nb3Sn)• Cooled by cryocooler stage-2

R. Dhuley et al., IOP Conf. Ser.: Mater. Sci. Eng. 755, 012136 (2020)

650 MHz conduction cooled cavity test results

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Bp ≈ 36.5 mT

See talk by S. Posen on Friday

R. Dhuley et al.,Supercond. Sci. Technol. 33, 06LT01 (2020)

Ongoing activities at Fermilab

• Design of a 10 MeV, 1 MW, conduction-cooled e- accelerator

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• Design and production of a 1.6 MeV, 20 kW, conduction-cooled SRF e- accelerator

1.3 GHz conduction-cooled SRF gun cavity at Euclid BeamLabs

• Development of conduction-cooled cryomodule for ultra-fast electron microscopy (UEM)

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1.8 W @ 4 K GM cryocooler

5N Aluminum buses Nb rings EBWedto the cavity

Thermal analysis to find stable points of operation at Eacc=10 MV/m, CW

Poster: MOPTEV001

Conduction-cooled cryomodule at Euclid BeamLabs

• The cryomodule (without cavity) was assembled and the cryocooler 2nd stage achieved the base temperature of 2.5 K

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Ongoing activities at Euclid BeamLabs

• The Nb cavity will be coated with Nb3Sn at FermiLab• The Nb/Nb3Sn cavity will be tested in the conduction cooling

cryomodule－Aim at Eacc = 10 MV/m for 1.6 MeV beam

• The cryomodule will be delivered to BNL to produce the beam and beam quality studies

• Development of high thermal conductivity coatings by cold-spray for conduction-cooled cavity applications

Talk Title Here 10

Poster: SUPTEV010

Conduction cooling setup at Cornell University

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2.6 GHz Nb3Sn cavity (ILC design)

Cryocooler 2nd stage cold head

Copper thermal strap

Copper beam-tube clamp

• Focus on compact design (2.6 GHz)

• Uses Cryomech PT420-RM cryocooler

• 1.8 W @ 4.2 K with 55 W @ 45 K

• Copper thermal straps & beam-tube clamps connect cold head to cavity

Poster: SUPTEV008

N. Stilin et al., arXiv:2002.11755 (2020)

Test results

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• Key result: first demonstration of stable CW operation at 10 MV/m• Reaches Eacc relevant to industrial applications

• < 1 W dissipated heat at max fields• Q0 approaching 4.2 K vertical test• Key Finding: cavity performance improved via temperature cycling / better

cooldown!

Test results

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• Thermal gradient across Nb/Nb3Sn produces thermoelectric currents, leading to trapped flux

• Demonstrated two improved cooldown methods:1) Passive gradient reduction via temperature cycling2) Active gradient reduction via beam-tube clamp heaters

Lower thermal gradient Lower residual resistance Improved performance

Thermal analysis

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• Agreement between ANSYS Simulation and Experiment temperatures－Simulation heat load & cold head temperature set to 10 MV/m values

• Extracted thermal conductivity for niobium cavity also shows good agreement

Numerical simulations accurately predict thermal behavior

3.35

3.45

3.91

(fixed at experimental temperature)

Design of 1 MeV, 1 MW conduction cooled cryomodule at JLab

• Designed for a CW e- accelerator for environmental remediation

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750 MHz, β=0.5, Cu/Nb/Nb3Sn CAVITY

COAXIAL FPCs

& T. Schultheiss, J. Rathke

G. Ciovati et al., Phys. Rev. Accel. Beams 21, 091601 (2018)

Conduction-cooled cryomodule thermal analysis

• “Ingredients” for FEA steady-state thermal analysis:－Rs(T) of Nb3Sn (10 nΩ at 4.3 K)－Bpk = 40.5 mT－κ(T) of Cu, Nb, SS, Ti45Nb－Cryocoolers’ capacity map－600 kW RF in each FPC－Thermal radiation

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Converged solution:

Conduction cooling of 1.5 GHz cavity at JLab

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• 1.5 GHz single-cell Nb cavity with Nb3Sn thin film• ≥5 mm thick Cu layer deposited by cold-spray (~76 µm) and electroplating• Apiezon N grease and an estimated 46 MPa contact pressure at the equator ring

interface.

Poster: SUPTEV010

1.8 W @ 4 K GM

G. Ciovati, G. Cheng, U. Pudasaini, R. Rimmer, Supercond. Sci. Technol. 33, 07LT01 (2020)

1.5 GHz conduction cooled cavity test results at JLab

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• Cool-down across Tc controlled by switching the cryocooler on & off

Avg. temperature measured at the equator (~7.5 K) consistent with ANSYS analysis for 5 W RF heat load (0.18 W radiation heat load, 0.58 W static heat load, 0.7 W/K contact thermal conductance)

• Amplitude of microphonics at Bp = 10 mT: 13.8 Hz pk-to-pk• Maximum Bp = 29 mT (Eacc = 6.5 MV/m)

“Clamp-cooling” of 1.3 GHz SRF cavity

Talk Title Here 19

• ~2 K T-difference between 2nd stage and cell • Amplitude of microphonics at Bp = 2 mT: 3.6 Hz pk-to-pk• Will check for damage to Nb3Sn film due to clamping at equator

Ongoing activities at JLab

• Development of a multi-metallic Cu/Nb/Nb3Sn 952 MHz single-cell cavity

• The cavity will be tested in a horizontal test cryostat at General Atomics with 3 cryocoolers, aiming at Bp = 45 mT

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T. Schultheiss, J. Rathke

Conclusions

• A lot of development and ideas over the last 3 years!－4 different cavity frequencies－3 different conduction-cooling schemes－2 different types of cryocoolers

• A CW accelerating gradient of 10 MV/m has been achieved at 650 MHz and 2.6 GHz

• Beam from a conduction-cooled SRF cryomodule may soon be a reality!

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