pei zhang the influence of cooldown conditions at transition temperature on the quality factor of...
TRANSCRIPT
Pei ZhangM. Therasse and W. Venturini Delsolaro
(BE-RF-SRF, CERN)
The influence of cooldown conditions at Tc on the Q0 of niobium sputtered
quarter-wave resonators
*This work received support from a Marie Curie Early Initial Training Network Fellowship of the European Community's 7th Programme under contract number PITN-GA-2010-264330-CATHI.
Outline
Pei Zhang Page 2Oct 7th, 2014Thin film workshop, LNL, Italy
• Brief introduction of HIE-ISOLDE & QWR
• The impact of thermal gradient & cooldown speed
• The impact of ambient magnetic field
• The frequency shift during transition
• The impact of helium processing on low-field Q0
HIE-ISOLDE Linac
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Niobium sputtered on copper
Boost the radioactive beam energy from 3MeV/u to 10MeV/u by using SC linac.
Quarter-wave resonator
Oct 7th, 2014Thin film workshop, LNL, Italy
More on A. Sublet’s talk
High-β QWR
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Frequency 101.28 MHz
Eacc 6 MV/m
βoptimum 10.9%
R/Q 553 Ω
Epeak/Eacc 5.0
Bpeak/Eacc 95.6 G/(MV/m)
G=RsQ 30.7 Ω
U/Eacc2 0.207 J/(MV/m)2
Pc at 6MV/m 10W
|E| field |H| field
Courtesy M. Fraser
Oct 7th, 2014Thin film workshop, LNL, Italy
Cavity production flow
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Cavity reception
Frequency tuning
Surface treatment
Niobium coating
Cryostat preparation
RF cold test
Cavity storage
Niobium Stripping
4-week process
Oct 7th, 2014Thin film workshop, LNL, Italy
More on A. Sublet’s talk
From Feb to Jun 2014
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02.2014
06.2014
Initial cooldown: two full daysThermal cycle: one day
Initial cooldown
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initial cooldown from ~300K
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Initial cooldown & thermal cycle
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initial cooldown from ~300KThermal cycling to ~20K
Oct 7th, 2014Thin film workshop, LNL, Italy
Low-field Q0 improvement
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The reduction of low-field Rs by thermal cycle
12% ~ 55%
Low-field: Eacc = 0.2 MV/m
Thermal gradient
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Thermal gradient [K]: average ΔT from T2=10.5 to 8.5K
Oct 7th, 2014Thin film workshop, LNL, Italy
topbottom TTT
Transition temperature
Error bar: standard deviation of ΔT from T2=10.5 to 8.5K
Cooldown speed
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Cooldown speed [mK/s]: average speed from 10.5K to 8.5K
Oct 7th, 2014Thin film workshop, LNL, Italy
Cooling rates during thermal cycles are normally 10 ~ 20 times faster.
Rs vs. cooldown speed
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Low-field: Eacc = 0.2 MV/m
0
8.30
QRs
No obvious dependence
Rs vs. thermal gradient
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Low-field: Eacc = 0.2 MV/m
0
8.30
QRs
Oct 7th, 2014Thin film workshop, LNL, Italy
Clear dependence on thermal gradient
Decompose Rs
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accERsRsRs 10
Residual resistance
Linear slope
QS1.1 initial cooldown
Rs0 & Rs1 vs. cooldown speed
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accERsRsRs 10
Residual resistance
Linear slope
Rs0 & Rs1 vs. thermal gradient
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accERsRsRs 10
Residual resistance
Linear slope
Ambient magnetic field
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Horizontal plane Vertical plane
Total reduction: 62.5 µT → 18 µT (~70% ↓)
Total enhancement: 62.5 µT → 115.5 µT (~85% ↑)
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Sensitivity to ambient magnetic field
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Ambient magnetic field
0µT 120µT
QP3.2 ~9% ↓ 8% ↑
QS2.1 ~7 % ↓ 6% ↑
• 1.3GHz bulk niobium cavities: 3.5n /Ω µT • Scale to 100MHz bulk niobium: ~1n /Ω µT• Measured 100MHz niobium sputtered QWR
- QP3.2: 0.024 nΩ/µT (1/42 x)
- QS2.1: 0.035 n /µΩ T (1/29 x)
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Reproducible Q0 depression & recovery
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44%
36%20% 17%
39% 33%
Field emission at low E-field region
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During He processing
Summary
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Q0
Thermal gradient
Cooldown speed
Insensitive
Clear dependence
Ambient B-field
0.035 n /µΩ T
Backup slide: Magnetic field
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[Ref] P. Zhang et al., “The Impact of Defects on Q0 for HIE-ISOLDE High-Beta Quarter-Wave Resonators”, CERN-ACC-NOTE-2014-0034, 2014.