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 Δpcav@0.55MV/m= 0.11455W*

QP1_2Pcav@0.55MV/m = 0.041W before the QswitchPcav @0.55MV/m = 0.45Wafter the QswitchΔpcav@0.55MV/m= 0.409W

Q2_7Pcav@0.55MV/m = 0.035Wbefore the QswitchPcav @0.55MV/m = 0.15W after the Qswitch due to NC tuning plateΔpcav@0.55MV/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