C=Fermilab Managed by Fermi Research Alliance, LLC for the U.S. - PowerPoint PPT Presentation

FERMILAB-SLIDES-19-044-AD-DI-LDRD-TD C=Fermilab Managed by Fermi Research Alliance, LLC for the U.S. Department of Energy Office of Science A conduction-cooled SRF cavity: Apparatus and first results R. C. Dhuley 1 , M. I. Geelhoed 1 , Y. Zhao 2 , I. Terechkine 1 , M. Alvarez 1 , O. Prokofiev 1 , J. C. T. Thangaraj 1 1 Fermi National Accelerator Laboratory, Batavia, Illinois 2 Euclid Techlabs LLC, Bolingbrook, Illinois 2019 Cryogenic Engineering Conference, Hartford, Connecticut This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.

Goal: To demonstrate cryogen-free SRF cavity operation Take out liquid helium Cool SRF cavities conductively with (and its complexities) 4 K cryocoolers Port He Fill Port https://upload.wikimedia.org/wikipedia/ Vacuum In su lation commons/c/c4/SRF_Cavity_Diagram_1.png Key thermal design criterion • SRF cavities dissipate heat during operation (dynamic heat load) • Cryocoolers have limited 4 K cooling capacity • Need a high thermal conductance link to extract this dynamic load and transport to the cryocooler. C=Fermilab 2 Dhuley| Conduction cooled SRF cavity 7/18/2019

~ Cavity-cooler thermal link: Our design approach Surface magnetic fields dissipate E-beam weld niobium rings most heat near the equator around the equator to attach a thermal link 1  = - DI 2 P R H ds diss s s 2 . · 1n . ~ ' H s O. Prokofiev ---------------------- 0 Fermilab 3 Dhuley| Conduction cooled SRF cavity 7/18/2019

Cavity-cooler thermal link: Our design approach 0 Use high purity (5N) aluminum as the thermal link material Measure and design low thermal resistance pressed niobium-aluminum contacts H en ter bl oc k Construct a thermal link for distributed cooling around the cavity equator R. C. Dhuley et al., Cryogenics 93, 86-93, 2018 R. C. Dhuley et al., IEEE TAS 29(5), 0500205, 2019 C=Fermilab 4 Dhuley| Conduction cooled SRF cavity 7/18/2019

Conduction cooled cavity test setup Vacuum vessel Cryocooler • SS304 • Cryomech PT420 • 5 feet tall (2 W @ 4.2 K with M. Alvarez 55 W @ 45 K) Magnetic shield • MuMetal Cavity and shield • Room temperature supports • <10 mG total field at the cavity location • Ti64 rods I. Terechkine SRF cavity MLI wrapped • Cooled by cryocooler stage-2 thermal shield • Elliptical single cell, 650 MHz • Cooled by cryocooler stage-1 • Niobium or Nb 3 Sn coated • Copper 101 top plate • Aluminum 1100 shell 5 Dhuley| Conduction cooled SRF cavity 7/18/2019

Conduction cooled cavity test setup RF driver with feedback for PLL F r--, I RFL RF Monitor r: - - "'"" - - J NIPXIND FWD __ R _ F_ Mon _ itor ., _________________ '---' 14 Detector Detector - - - - PXle Crate Control computer r--- 1 / 0demod Cavity Field monitor I - - - ., ,------ a NI PXleFPGA FNAL 10MHz Ref Y. Zhao 630MHz Carrier OCXO PLL Freq . Source •••••••••••••••••••••• C=Fermilab 6 Dhuley| Conduction cooled SRF cavity 7/18/2019

Conduction cooled cavity test setup ------------------------0 Fermilab 7 Dhuley| Conduction cooled SRF cavity 7/18/2019

Cool down characteristics The cryostat cooled to its base temperature within 24 hours - Cryocooler stage I < 30 K, thermal shield top plate ≈ 32 K - Cryocooler stage II ≈ 2.95 K - Cavity cell ≈ 5 - 5.8 K (measured at multiple locations) A possible reason for the significant 4 K stage cryocooler-cavity Δ T T - The estimated heat leak to cryocooler 4 K stage is ≈ 450 mW, mostly coming via the RF cables - This heat flows through the cavity body (4 mm thick niobium), then through the thermal link, and into the cryocooler Thermal shield ------------------------0 Fermilab 8 Dhuley| Conduction cooled SRF cavity 7/18/2019

~ ~ First results: Accelerating gradient > 1.5 MV/m • First measurements used a single cell, 650 MHz, niobium cavity • Cryocooler had available ~ 1.55 W @ 4.2 K after accounting for the static leaks 4.E+8 ± 10% Uncertainty = ·- 0 Cl Limit of RF ~" .8 3.E+8 power supply Q - 0 -~- E>-c -~ • ~e ~ ::s No load on cryocooler cr- 0 2.E+8 stage 1 -~ 55 W on cryocooler stage 1 u 1.E+8 0.0 0.5 1.0 1.5 2.0 Accelerating gradient, Eacc [MV I m] ------------------------0 Fermilab 9 Dhuley| Conduction cooled SRF cavity 7/18/2019

.,♦., ■- Projections for a Nb 3 Sn coated cavity with the existing link Need to know the cavity RF surface and cryocooler temperatures • T cavity,RF is estimated from Q 0 , T cryocooler is measured 6.0 T cavity,RF = f(Q0) ≈ 5.7 K -·--• - -- - \ ~EJ-fr r---, ≈ 5.1 K ~5.0 .,,, ..... ........ T cryocooler (measured) .... .,, 3.0 0.5 1.0 1 .5 0.0 2.0 Accelerating gradient, Eacc [MV I m] ------------------------0 (a measure of heat dissipation in the cavity) Fermilab 10 Dhuley| Conduction cooled SRF cavity 7/18/2019

~ ✓ Projections for a Nb 3 Sn coated cavity with the existing link Assume no changes to the link I Niobium R BCS (T) ] 1000 I • T cavity,RF = 5.7 K 0 I .......... I • Nb 3 Sn T cryocooler = 5.1 K R BCS (T) + 100 n Ω Q) u - 100 ······ ········ ····· ············ 1 ····· ····· g ------- _. __ _ ------ - ----- r --- R BCS (T) + 50 n Ω · - f/l f/l R BCS (T) + 10 n Ω Q) 1 .....  1 Q) 10 E R BCS (T) u c.s acc + I R ( ) T R 3 I BCS residual r/J. / 1 5.3 5.5 5.7 5.9 Nb 3 Sn << Niobium Nb 3 Sn has demonstrated Temperature [K] (see plot) as low as 10 n Ω R BCS (T) computed using https://www.classe.cornell.edu/~liepe/webpage/researchsrimp.html Surface resistance E acc [MV/m] with the existing in Nb 3 Sn [n Ω ] conduction-cooling link Projected E acc for Nb 3 Sn with different 20 (residual = 10) 11.5 residuals 60 (residual = 50) 6.5 110 (residual = 100) 5.0 -----------------------0 Fermilab 11 Dhuley| Conduction cooled SRF cavity 7/18/2019

Summary and outlook First ever demonstration of accelerating gradients on a cryogen-free, cryocooler conduction-cooled SRF cavity • Niobium cavity produced >1.5 MV/m with a 2 W @ 4.2 K cryocooler • There is considerable scope for improving the thermal management in our setup • Ongoing: mitigation of static heat leak • An Nb 3 Sn coated cavity is projected to yield >10 MV/m accelerating gradients on our existing setup • Tests are planned for the near future ------------------------0 Fermilab 12 Dhuley| Conduction cooled SRF cavity 7/18/2019

This presentation has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics. ------------------------0 Fermilab 13 Dhuley| Conduction cooled SRF cavity 7/18/2019

Thank you. ------------------------0 Fermilab 14 Dhuley| Conduction cooled SRF cavity 7/18/2019