[PPT] - Ultraefficient superconducting RF cavities for FCC Alexander PowerPoint Presentation

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Ultraefficient superconducting RF cavities for FCC

Alexander Romanenko FCC Week 2015, Washington, DC 24 Mar 2015

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Summary

Recent breakthroughs at Fermilab allow record Qs at

gradients of interest to FCC in bulk Nb cavities

– Nitrogen doping => record low BCS surface resistance, reduced non-flux residual – Tuning Meissner effect => no/low contribution from trapped magnetic flux => record low residual resistance

Cryo cost savings (capital and operating) is the main

advantage

Thanks to LCLS-II at SLAC nitrogen doping has received a

strong technological push to make it production-ready

– Q and Eacc statistics on 9-cells

Doping of lower frequencies cavities shows a proof-or-

principle for FCC

– 650 MHz for PIP-II

3/24/15 Alexander Romanenko | FCC Week 2015 2

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Q0 Eacc (MV/m)

T= 2K

Nitrogen doping: a breakthrough in Q

3/24/15 Alexander Romanenko | FCC Week 2015 3

Standard state-of-the art preparation

This was the highest Q possible up to 2012 Record after nitrogen doping – up to 4 times higher Q!

A. Grassellino et al, 2013 Supercond. Sci. Technol. 26

102001 (Rapid Communication) – highlights of 2013

1.3 GHz Since the discovery -> developed to production- ready for LCLS-II within the context of high Q collaboration (FNAL/Cornell/Jlab)

SLIDE 4

N Doping – small deviation from standard ILC treatment

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Example from FNAL 2/6 doping process:

Bulk EP
800 C anneal for 2 hours in vacuum
2 minutes @ 800C nitrogen diffusion
800 C for 6 minutes in vacuum
Vacuum cooling
5 microns EP

Cavity after Equator Welding EP 140 um Ethanol Rinse External 20 um BCP Short HPR 800C HT Bake RF Tuning EP 40 um Ethanol Rinse Long HPR Final Assembly Long HPR Helium Tank Welding Procedure VT Assembly HPR HOM Tuning Ship to DESY Leak Check 120C bake

XFEL

X

A. Grassellino et al, 2013 Supercond. Sci. Technol. 26 102001 (Rapid

Communication)

3/24/15 Alexander Romanenko | FCC Week 2015

SLIDE 5

“Production” recipe for LCLS-II – 9-cells for prototype cryomodule(s)

3/24/15 Alexander Romanenko | FCC Week 2015 5

Work in collaboration with Jlab and Cornell to demonstrate transfer and validation of best recipe

A. Crawford et al, IPAC’14, WEPRI062

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Data from Cornell/Jlab/FNAL

16 MV/m 2.7e10

Recipe 2/6 Recipe 20/30

<Q>=3.24e10 <Emax>=16.3 MV/m Emaxmedian=16.5MV/m

Statistics for two doping recipes on 1.3 GHz 9-cells

Data from FNAL/JLab

<Q>=3.6e10 <Emax>=22.2 MV/m Emaxmedian=22.8MV/m

3/24/15 Alexander Romanenko | FCC Week 2015 6

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Minimizing residual resistance (maximize Q) by avoiding the ambient magnetic flux to be trapped

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#1: First fast from 300K #2: Slow from 15K #3: Fast from 15K

Q0 Eacc (MV/m)

Flux expelled efficiently Flux mostly trapped Same cavity, just cooled differently through 9.2K 2K, 1.3 GHz

SLIDE 8

Magnetic probes reveal the new physics

Full expulsion of the magnetic field should give ~2x higher field at the equator in superconducting state

Fluxgate magnetometers

Efficient flux expulsion Poor flux expulsion

H

It turns out the expulsion efficiency can be controlled by the cooldown procedure (fast/slow, uniform or not)

A. Romanenko, A. Grassellino, O. Melnychuk, D. A. Sergatskov, J. Appl. Phys. 115, 184903 (2014)

3/24/15 Alexander Romanenko | FCC Week 2015 8

SLIDE 9

Experimental proof that thermogradient at NC/SC interface is key parameter for flux expulsion

3/24/15 Alexander Romanenko | FCC Week 2015 9

Temperature difference at the phase front (dT/dx)

A. Romanenko, A. Grassellino, A. C. Crawford, D. A. Sergatskov, and O. Melnychuk, Appl. Phys. Lett. 105, 234103 (2014)

SLIDE 10

Differences between fast/slow

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A. Romanenko, A. Grassellino, O. Melnychuk, D. A. Sergatskov, J. Appl. Phys. 115, 184903 (2014)

Difference in geometry of transition

SLIDE 11

Observing fast and slow cooldown dynamics

3/24/15 Alexander Romanenko | FCC Week 2015 11

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Fast and slow cooldown dynamics captured

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Fast from 300K Slow from 12K

M. Martinello, M. Checchin - PhD work

Top Bottom

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Fast cooldown

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1 4 7 10 13 16 36 29 22 15 8 1

Thermometer Number Board Number

9.250 10.03 10.80 11.57 12.35 13.13 13.90 14.68 15.45 16.23 17.00

Equator Iris Sx Iris Dx

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1 4 7 10 13 16 36 29 22 15 8 1

Thermometer Number Board Number

9.250 10.03 10.80 11.57 12.35 13.13 13.90 14.68 15.45 16.23 17.00

Equator Iris Sx Iris Dx

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1 4 7 10 13 16 36 29 22 15 8 1

Thermometer Number Board Number

9.250 10.03 10.80 11.57 12.35 13.13 13.90 14.68 15.45 16.23 17.00

Equator Iris Sx Iris Dx

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1 4 7 10 13 16 36 29 22 15 8 1

Thermometer Number Board Number

9.250 10.03 10.80 11.57 12.35 13.13 13.90 14.68 15.45 16.23 17.00

Equator Iris Sx Iris Dx

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1 4 7 10 13 16 36 29 22 15 8 1

Thermometer Number Board Number

9.250 10.03 10.80 11.57 12.35 13.13 13.90 14.68 15.45 16.23 17.00

Equator Iris Sx Iris Dx

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1 4 7 10 13 16 36 29 22 15 8 1

Thermometer Number Board Number

9.250 10.03 10.80 11.57 12.35 13.13 13.90 14.68 15.45 16.23 17.00

Equator Iris Sx Iris Dx

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1 4 7 10 13 16 36 29 22 15 8 1

Thermometer Number Board Number

9.250 10.03 10.80 11.57 12.35 13.13 13.90 14.68 15.45 16.23 17.00

Equator Iris Sx Iris Dx

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1 4 7 10 13 16 36 29 22 15 8 1

Thermometer Number Board Number

9.250 9.825 10.40 10.98 11.55 12.13 12.70 13.27 13.85 14.43 15.00

Equator Iris Sx Iris Dx

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Slow cooldown – encircling normal areas

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