Spoke Resonators at Fermilab TTC 2011, Milan L. Ristori Serena Barbanotti, Evgueni Borissov, Ivan Gonin, Timergali Khabiboulline, Robyn Madrak, Frank McConologue, Tom Nicol, Joe Ozelis, Ronak Patel, Youriy Pischalnikov, Warren Schappert, Robert Wagner, Robert Webber, et al.
325 MHz SSR1 1st prototype Zanon, Italy 2nd prototype Roark, USA Quantity Original Values CW machine Beampipe, shell ID 30 mm, 492 mm Epeak/Eacc 2.56 Bpeak/Eacc 3.87 mT/(MV/m) G, R/Q0 , βg 84 , 242 , 0.21 RF structure 1 ms, 9 mA CW, 1 mA Loaded BW 388 Hz 43 Hz He temp, pressure 4.4 K, 900 torr 2.0 K, 20 torr He press variation 12.9 torr .25 torr Accel. Grad., Eacc 10 MV/m 12 MV/m Q0 at Eacc > 0.5x109 >1x1010? LFD co. (jacketed) 3.8 Hz/(MV/m)2 Non-issue df/dp (jacketed) -210 Hz/torr 25 Hz/torr 1st prototype Zanon, Italy 2nd prototype Roark, USA FNAL & ANL: Eacc = Tot acc voltage /Leff Leff = Liris = (2/3) = 135 mm If using: Leff *= = 202.5 mm Eacc* = 0.67 Eacc L. Ristori - TTC 2011, Milan
RF design of SSR1 The dimensions were varied in MWS to optimize the RF design. Surface electric (left) and magnetic (right) fields in SSR1. The field strength increases as the color changes from green to yellow to red. L. Ristori - TTC 2011, Milan
SSR1 Fabrication (Niowave & Roark, USA) Beam Pipe port SST Cu Nb 10 resonators currently in production Spoke with collars Power Coupler port L. Ristori - TTC 2011, Milan
SSR1 trimming & tuning F trims weld tune 324.8 Goal before processing 50.4 324.8 gaps F trims tune weld Goal before processing Chemistry +100 kHz Cool down +500 kHz Tune – 150 kHz Preload – 150 kHz L. Ristori - TTC 2011, Milan
Chemistry and HPR of unjacketed cavities at ANL G150 BCP: two 80 minute sessions Between sessions, flip top to bottom and replace acid. Remove 120 microns at 15-16C Frequency shifts +300 and +70 kHz HPR: 6 ultra-pure water jets, two each at +40, 90, and -40 2 hrs water time with cavity in 6 different orientations. L. Ristori - TTC 2011, Milan
CW tests bare cavities Cavity 1 – 4th test Cavity 2 – 1st test During cool down, a 7 hr hold at 100 K produced a large Q0 drop, confirming Q disease. Subsequently baked SSR1-01 at 600 C for 10 hours at Jlab. Cavity 2 – 1st test Effects of Q disease should not appear on first cooldown. X-rays increase at MP barriers, then disappear after punch through. L. Ristori - TTC 2011, Milan
Jacketing of SSR1-01 and preparation for CW and Pulsed tests in cryostat 10 hr, 600 C vacuum bake for hydrogen degassing at Jlab Adjust cavity tune at room temperature: fixture to inelastically stretch or compress at beam pipes (capable of 250 kHz). Weld on the helium vessel: argon purge and temperature and frequency monitoring. Degreasing, flash BCP (20 min at 13 C) and HPR. L. Ristori - TTC 2011, Milan
Prototype tuner Two piezo actuators “in series” with slow tuner arms (pivot with 5:1 mech. advantage). Stepping motor with harmonic drive,1:100 ratio (0.9 Hz/step). Present tests with a tuner on each end. Low profile along beam required due to close proximity to solenoid. dF/dL ~ 540 Hz/um Max stroke 3 mm L. Ristori - TTC 2011, Milan
Commissioning 325 MHz Spoke Cavity Test Facility(SCTF) Cooling to 4.5 K. (2 K upgrade is planned). Primary (secondary) pressure relief of 10 (5) psig. Operation near 5 psig. 200 W solid state supply for CW. 2MW Klystron for pulsed tests (used only 50kW). Digital LLRF with GUI interface screens . Locks to cavity frequency for CW operation. Room temp B shield just inside cryostat wall. 80 K thermal shield. Robyn (runs the place). Jacketed cavity with tuner. Test magnets. X-ray detectors along beam line: Diodes ~10 cm from beampipe flanges Foxes and Chipmunks ~50 cm outside cryostat. CW: Drive antenna with Qext = 1.5 x 108 L. Ristori - TTC 2011, Milan
Q0 .vs. Eacc scan in first cooldown and Q disease test Scan in first cooldown compares well with first cooldown of bare SSR1-02 in VTS at 4.4 K. Maximum Eacc of 27 MV/m is a bit higher. Within 5% measurement uncertainty, scan was unchanged after a second 3 hour cooldown. Third cooldown of 11 hours through sensitive region (150 K to 70 K): Much milder case of Q disease than before degassing: At 10 MV/m, Q0 decrease of 20% versus 87% for 7 hour hold at 100 K in last VTS test of bare SSR1-01. However, 20% decrease at ~4.5 K is about a factor of three decrease at 2 K L. Ristori - TTC 2011, Milan
SSR1 Pulsed Tests at SCTF These are the first cold tests of the SSR1 with a Power Coupler suitable for accelerator operations. Cold section with antenna was installed onto cavity port at the MP9 clean room. Warm section attached through the cryomodule port at the SCTF cave. The warm section has its own vacuum pump. 36.5 MV/m with a 1.5 ms flat top without quenching. measured how high one could run as a function of flat top length. It looks like it may level out at about 36 MV/m for CW operation, but this is obviously a large extrapolation. peak surface B field at Eacc = 36 MV/m is 139 mT (from Ivan's simulation). L. Ristori - TTC 2011, Milan
Tuner tests on jacketed SSR1-01 Microphonics (He pressure fluctuation) compensation dF/dP Pressure, torr SSR1 Static Lorentz Force Detuning Coefficient LF detuning coefficient KLF (DF=-KLF*Eac2); KLF[Hz/(MV/m)2] = -1,5 (Predicted -3.8) DF,Hz L. Ristori - TTC 2011, Milan
SSR1 RF Pulse Mode Operation Lorentz Force Detuning Compensation Fill=1ms Flat-Top=1ms LFD during Flat-Top Eacc Piezo OFF Piezo On (ApiezoV) 20MV/m 450Hz 30Hz 35V(18%) 34MV/m 1450Hz 75Hz 80V(40%) Piezo On Detuning, Hz 20MV/m 2000Hz Piezo OFF DF=-kEacc2 LFD during 1ms Flat-Top Time 27-34MV/m K~1,2Hz/(MV/m)2 Detuning, Hz Piezo On 2000Hz Piezo OFF L. Ristori - TTC 2011, Milan
Round end walls proposed to avoid “donut rib” SSR0 SST/Nb braze joints SSR0 parameters Aperture 30 mm F(MHz) 325 βoptimal 0.115 Dcavity,mm 406.84 R/Q, Ω 109.2 G, Ω 51 Emax/Eacc 5.66 Hmax/Eacc (mT/MV/m) 6.83 Deff(2*βoptλ/2),mm 106 Bolted Nb/SST connections SST He vessel E fields B fields Round end walls proposed to avoid “donut rib” One bellow L. Ristori - TTC 2011, Milan
Df/dP, free and locked at beam pipe dF/dP ~ 14 Hz/torr Locked dF/dP ~ -26.4 Hz/torr Total deformation: between 0 and 55 µm Deformation @ BP: below 10 µm The actual df/dp of cavity + tuner will fall in this range with average of -6 Hz/torr L. Ristori - TTC 2011, Milan
Range of Piezos 100 N on ½ piezo surface (diameter 10 mm) Max deformation 23 µm Max stresses 24 MPa (very localized) Frequency shift ~ 1 kHz for 4 piezo Frequency shift ~ 250 Hz for 200 N applied by 1 piezo L. Ristori - TTC 2011, Milan