hie isolde cavity developments
DESCRIPTION
HIE ISOLDE Cavity Developments. Walter Venturini Delsolaro On behalf of - PowerPoint PPT PresentationTRANSCRIPT
Walter Venturini DelsolaroOn behalf of
L. Alberty, G. Arnau Izquierdo, O. Brunner, S. Calatroni, O. Capatina, B. Delaup, A. D’Elia, P. Garritty, N. Jecklin, P. Maesen, M. Malabaila, I. Mondino, E. Montesinos, M. Gourragne,
G. Pechaud, T. Renaglia, K. M. Schirm, A. Sublet, M. Therasse, D. Valuch
HIE ISOLDE Cavity Developments
ISOLDE Workshop, 19 December 2012
Overview
• Cavity specifications and design• Prototype cavity developments in 2012• Strategy and actions taken• Test cavities and results • Q switch issues• Last two prototype cavity results• Remaining issues and next steps
HIE ISOLDE accelerating cavities
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.60
0.2
0.4
0.6
0.8
1
V CLI
L~/4
L~/4
HIE ISOLDE cavities
High Q (low power dissipation) for several MV/m accelerating fieldOnly achievable with a superconducting structure
Technologies for SC QWR • Bulk Nb with high RRR and EB welds
– Available from industry: – High gradients at low dissipated power are easier– Difficulties in operation (microphonics, high RF power
needs)
• Superconducting coatings (mechanical and thermal stability, lower cost)
– Electroplating of Pb on Copper (limited to few MV/m due to low Bc of lead)
– Nb sputtering on copper
– Higher performance than lead plating, competitive with bulk Nb at these frequencies and temperatures
– Multidisciplinary technology (surface science, vacuum, sputtering, clean room, superconductivity, RF engineering Never industrialized on the QWR shape
– Several LINAC projects after HIE ISOLDE could profit from an industrialization
• 4 units “old design”: Q1-Q2-Q3-Q5(rolling, EB welding, deep-drawing)
• 1 new design: QP1+ 2 more in pipeline(3D machining in bulk copper, EB welding)
6
• 1 cavity (Q4) manufactured for sputtering tests on samples
Cavity prototypes designed and built at CERN
Note: Q3 and QP1 were left longer to reduce B on RF contact with tuning plate
QP1: sensitivity to He pressureQP1 (new design)Q2 (old design)
1.140 1.160 1.180 1.200 1.220 1.240 1.260101270500
101270520
101270540
101270560
101270580
101270600
101270620
101270640
101270660
101270680
f(x) = − 851.651263820066 x + 101271636.229103R² = 0.913741478893653
He pressure (bar)
Reso
nanc
e fr
eque
ncy
(Hz)
1.1401.1601.1801.2001.2201.2401.2601.2801.3001.3201.340101369659
101369661
101369663
101369665
101369667
101369669
101369671
101369673
101369675
f(x) = 10.8581832289356 x + 101369654.221436R² = 0.198094747891516
He pressure (bar)
Reso
nanc
e fr
eque
ncy
(Hz)
~ 1 Hz/mbar ~ 0.01 Hz/mbar
• RF cavities (5 or 6)• SC (Nb3Sn) solenoid (1 or 2)
Up to 600 A• Supporting frame• Alignment / monitoring system
0.15 mm at cold !• Cryogenics reservoir and piping• Vacuum system (valves, pumps)• Thermal shield (50-80 K)• Vacuum vessel
HIE ISOLDE Cryomodule Side view
Optics Compactness Common vacuum
Common vacuum
risk of cavity contamination
Cleanliness
Surface treatment (dummy and real cavity)
Sputtering system
Diode sputtering
Niobium sputter coatings: 9 test cavities produced in 2012Focusing on the DC bias sputtering method (INFN-LNL)
Hardware modifications to the system were required to approach the desired sputtering parameters:
– Cavity support in coating chamber redesigned– Infra red lamps baking system inside chamber with radiation shields– Discharge power increased from 2 kW to 10 kW : new power supplies
Substrate preparation Tumbling, EP then SUBURinsing water pressure 100 barBake out temperature 600 ᵒ C (higher than sputtering T)Sputtering temperature 300-500 ᵒ C Heating system IR lamps inside vacuum chamber and QWRNumber of layers 12-20 layersSputtering Power 5 kW for 160 MHz structure 12.5 KW assumed from scaling of areasAuxiliary electrode 4 cm diameter, rounded, bias potentialFilm minimum thickness 2 µmCathode edge profile sharpenedSputtering gas ArgonVenting gas Nitrogen
QWR workflow, tests in 2012Stripping
metrology
Chemistry
Clean Room Assembly
Coating
Rinsing & Clean Room Assembly
Insertion in cryostat
Cool Down
RF Conditioning, RF Measurements
Warm Up, Venting
Jan-12 Feb-12 Mar-12 Apr-12 May-12 Jun-12 Jul-12 Aug-12 Sep-12
Coating system Design and procurement of SS cavity support Resistive heating inside the antenna Copper screens, IR lamps, 8 kW Power supply 12 kW PSCoatings Q1_9 Hlicoflex Q1_10 Q2_6 Q3_1 tests of new baking Q1_11 QP1_2 Q3_2
RF tests Q2_5 Q1_9 Q2_5 LNL coupler+ In Q1_10 LNL couplerQ1_10 CERN couplerQ2_6 Q3_1 Cryo SM18 downQ3_1 + Magnet Q1_11 QP1_2
Effective turnaround for cold RF tests: 3 weeks
Increasing test rate at end 2012Aug-12 Sep-12 Oct-12 Nov-12
12 kW PSQP1_2 Q3_2 Q2_7 Q3_3
Q1_11 QP1_2 Q2_7 Q3_3
CRYO OK 37Tests RF 12
3.083 Weeks/test
2Weeks/cavity demonstrated
0 1 2 3 4 5 6 71E+07
1E+08
1E+09
HIE-ISOLDE specification
Q1_9 (February 2012)
Q1_10 (April 2012)
Q2_6 (May 2012)
Q3_1 June 2012
10 W
Q1_11 after He processing
Q1_11 after 2nd He processing
QP1_2
Eacc(MV/m)
Qua
lity
Fact
orTest cavity performances in 2012
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 21E+07
1E+08
1E+09
Q1_11 10 W
Eacc(MV/m)
Qua
lity
Fact
orQ1_11 first test results at 4.5 K
Most likely field emission from the tip of the inner conductor (tuning plate heating, exponential Q drop) Was eliminated with He processing
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 21E+07
1E+08
1E+09
1E+10
Q1_1110 WQ1_11 after He processingQ1_11 after 2nd He processing
Eacc(MV/m)
Qua
lity
Fact
orQ1_11 test results after He processing: Q switches
QP1 test results: before He processing, similar behaviour as Q1_11 after He processing. Onset al lower fields. Slight gain in field at 3 K
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 21E+07
1E+08
1E+09
1E+10
10 W QP1_2
Eacc(MV/m)
Qua
lity
Fact
or
Observations on “Q switches”
Happen at a determined value of field, not correlated with direct power (checked by changing coupling)Associated with temperature increase at tuning plate Deterministic hysteresis paths in Q-E planeCan jump on upper branch by switching off and on RF (very fast recovery if power is switched off and restored at a level below onset threshold)Very low Q slopes (contrary to classical field emission)
Actions taken after Q1_11 and QP1_2 Electrical heater installed on the bottom plateDouble check RF contact at the bottom plateIncrease the thickness of the Nb film by 25%Plan incremental stripping on the cavities with Q switchPlan systematic thickness measurements on cavity and on samples
First measurement at 4.5 K before He processingQ0 is of the order of 1.2 109 and on the first powering the cavity reached 5 MV/m at 10 WThe curve very much resembles that of Q1_11 but it does not have any Q switch.
Onset of field emission
Sudden Q drop and x rays burst
0 1 2 3 4 5 6 71.00E+07
1.00E+08
1.00E+09
2nd calibration pointQ1_11 after He ProcQP1_2 after He processingQ2_7 first meas10W
Eacc (MV/m)
Qua
lity
Fact
or
Measurement at 4.5 K when heating the tuning plate
0 0.5 1 1.5 2 2.5 31.00E+07
1.00E+08
1.00E+09
QP1_2 after He processing Q2_7 heating the tuning plate 10W
Eacc (MV/m)
Qua
lity
Fact
or
increasing T tuning plate
11.6 K
Q vs tuning plate temperature
4.5 5.5 6.5 7.5 8.5 9.5 10.5 11.5 12.51.00E+08
1.00E+09
Q2_7 heating the tuning plate
TT845 (K)
Qua
lity
Fact
or
Power dissipation of normal conducting bottom plate
0 1 2 3 4 5 61.00E+07
1.00E+08
1.00E+09
QP1_2 after He processing
Q2_7 with SC tuning plate
Q2_7 heating the tuning plate
Eacc (MV/m)
Qua
lity
Fact
or
ΔPcav Q2_7
ΔPcav QP1_2
Power dissipation due to a normal conducting bottom plate (flat plate Tipgap70)@0.55MV/m: calculated value Δ[email protected]/m= 0.11455W*
[email protected]/m = 0.041W before the QswitchPcav @0.55MV/m = 0.45Wafter the QswitchΔ[email protected]/m= 0.409W
[email protected]/m = 0.035Wbefore the QswitchPcav @0.55MV/m = 0.15W after the Qswitch due to NC tuning plateΔ[email protected]/m= 0.115W
The power dissipated during the experiment on Q2_7 matches with the simulated value, while the one dissipated in QP1_2 Qswitch is 4 times bigger. * A.D`Elia
0 1 2 3 4 5 6 7 80.00E+00
5.00E-08
1.00E-07
1.50E-07
2.00E-07
2.50E-07
3.00E-07
3.50E-07
4.00E-07Q3_3
Q2_7
Q3_2
QP1_2
Q1_11
Q3_1
Q2_6
Q1_10
HIE ISOLDE SPEC
Eacc (MV/m)
Rs (O
hm)
Conclusions and outlook• HIE ISOLDE cavities performances greatly progressed in 2012• Q2_7 reached 5 MV/m at 10 W 5.3 MeV/u for A/q=4.5• Cavity optimization will continue in the first half of 2013• Cavity review requested by IAP will be held on 21 January 2013