View
229
Download
6
Category
Tags:
Preview:
Citation preview
S. Keckert, R. Kleindienst, J. Knobloch, O. Kugeler
Status of the HZB Quadrupole Resonator*
* work partly funded by EuCARD2
Overview
RF characterization of superconducting thin films
• CW operation at high currents & turn-key systems• Detailed understanding of cavity loss mechanisms required
• Aim: Measurement of surface resistance• Parameters: Frequency, field strength, temperature
• Ideal tool: Quadrupole Resonator (QPR)• Wide phase space quickly available• sub-nΩ resolution ↔
• Comissioning of a QPR at HZB• Based on a system built at CERN
• E. Brigant, E. Haebel, E. Mahner, „The quadrupole resonator, design considerations and layout of a new instrument for the RF characterization of superconducting surface samples“, EPAC 98
• E. Chiaveri, E. Haebel, E. Mahner, J. M. Tessier, „The quadrupole resonator, construction, RF system, field calculations and first applications”, EPAC 98
2
The Quadrupole Resonator (QPR)
• Resonator cavity andquadrupole rods madeof Nb RRR 300
• Pole shoes focusmagnetic fieldon sample
• Sample thermallydecoupled viacoaxial structure
3
Pumping portsCoupler ports
Calorimetry chamber(large domain Nb)
Hollow quadrupolerods (Nb)
LHe
Resonator body (Nb)
Frame(SS, Ti)
Coaxial gap
Sample
Pole shoes
HeaterT-Sensor
Gap
Optimization of HZB design
• Optimization criteria• Phase space: Frequency, field strength, temperature• High resolution
• Full parameterization with CST• Maximizing figures of merit
4
Baseline(CERN QPR)
Optimized
Operating frequencies 400 / 800 / 1200 MHz 433 / 866 / 1300 MHz (TESLA)
Focussing factor*
Risk of field emissionBSample/Epk
4.68 mT/(MV/m) 7.44 mT/(MV/m)
Operating rangeBSample/BPk
0.81 0.89
Microphonics1st mechanical mode 69 Hz 172 Hz
* fraction of field exposure between sample and resonator
[R. Kleindienst, „Developmentof an Optimized QuadrupoleResonator at HZB“, SRF 2013]
• Radius of rods increased8 mm → 13 mm
• Gap reduced(pole shoes ↔ sample)1 mm → 0.5 mm
Surface resistance measurement
RF-DC compensation technique
• High precision: calorimetric measurement• Resolution: sub-nΩ
• Wide temperature range: 1.8 K up to • Operating at low frequency (433 MHz)
• Low BCS resistance → sensitivity to Rres
5
[S. Aull, „High Resolution Surface Resistance Studies“, SRF 2013]
QPR preparation at JLab
• QPR manufactured by Niowave• Resonator shipped to JLab for surface treatment and first RF tests
6
BCP
600 °C bakeoutfor 12 hours
Ultrasonic rinsing
[Photos: A. Burrill, HZB]
Pole shoes – view from below
First RF test at Jlab (433 MHz)
Emitted power measurement
• Strongly coupled antenna• microphonics expected
• Forward power: step function
•
achieved on sample
Limited by quench
• Significant improvement
7
Alternative calorimetry chamber
8
Matching surfaces
M2.5 Helicoil
Double sided CF100 flange
Indium wire
Central heaterM4 threat
Cernox sensorsMotivation
Risks
• Cleanliness• Vacua possibly connected• Indium wire gaskets• Additional risk: low quench field
• Impact on RF
• Flat sample for coatingh = 12 mm
• No welding required• Height adjustment possible
→ sensitivity of resonator on
distance rods ↔ sample
RF simulations
• Impact of removable sample on RF?• Simulations using COMSOL 4.4
• Worst case: circumferential gap• Height: 0.5 mm• Position: 5 mm below sample
9
• Color plot:• Magnetic field [mT]
(Different scales for sample and coax)• RF surface currents (red arrows)
→ Separated gaps of several millimeters are acceptable
Sample
5 mm
0.5 mm
Indium
Current status
• 433 MHz RF system ready• Data acquisition
• Hardware set up• Software in progress
• Heater with minimized magneticfield built and tested
10
• Helium bath cryostat delivered andinstallation finished soon
• First RF test at JLab succesful• QPR is currently being shipped to HZB
• New sample holder in production• Indium seal tested successfully
(Al-prototype, room temperature)
Outlook
• QPR installation in October• First measurements with uncoated sample (Nb RRR 300)• Better understanding of unexpected microphonics
• New sample holder arrives next week• First test at CERN in November
• coating: ANR/DFG project (waiting for approval)• Universiät Siegen: coating, characterization of surface state• CEA-Irfu, Saclay: , RRR• Université Paris Sud, Orsay: thermal properties• HZB: RF properties, flux trapping
Always looking for collaboration partners whoare able to make films / prepare samples
11
B A C K U P S L I D E S
12
First RF test at JLab
Microphonics
• Frequency shift ≈ 4 kHz• Major contribution at 40 Hz• Mechanical oscillations
expected • Thicker rods included in design
to lower effect of microphonics
13
First RF test at JLab
Quench observed
• Quick drop of transmitted power•
(on rods)
• Note • Significant improvement
14
Antenna and Coupling
Power coupler @ 45 deg
microphonics expected
Field probe @ -90 deg
15
CST simulation by Raphael Kleindienst
Electric and magnetic fields in QPR
16
Electric Magnetic
CST simulation by Raphael Kleindienst
Recommended