Completion of the first SSR1 cavity for PXIE

Transcription

1 2013 North American Particle Accelerator Conference Pasadena, CA Completion of the first SSR1 cavity for PXIE Design, Manufacturing and Qualification Leonardo Ristori on behalf of the Fermilab SRF Development Group

2 Project X at Fermilab Page 2

3 Project X and PXIE PXIE SSR1 Project X The Project X Injector Experiment (PXIE) facility is under construction at Fermilab and will serve in the next years as a test bench for key components of Project X to reduce risk One cryomodule with 8 SSR1 resonators is part of PXIE Page 3

4 SSR1 Cryomodule courtesy: T. Nicol, M. Merio Page 4

5 SSR1 325 MHz, 2K SSR1 β Nb-SST Braze Helium Vessel 316L, 6 mm Bellows, 0.6 mm E p /E acc 3.84 B p /E acc 5.81 mt/(mv/m) Aperture 30 mm Diameter 492 mm L EFF (βλ) 205 mm G R/Q 84 Ω 242 Ω Beam Oper. Gradient 12 MV/m Q 0 at E acc > 0.5 Operating B MAX 70 mt Operating E MAX 46 MV/m Tuning constant 40 N/kHz Sensitivity P (RT, CT) < 25 Hz/torr 2 bar, 4 bar SRF Resonator Nb, 3.1 mm Frequency-Tuning Side Page 5

6 Sensitivity to He pressure variations Pressure of L He can vary by ± 0.5 Torr in the cryomodule SSR1 must operate within a small bandwidth ± 20 Hz A self-compensating design was developed allowing low sensitivity Despite non-negligible deformations (see picture), net shift is very low thanks to Slater s Theorem Bare cavity ~ 600 Hz/Torr, with He vessel ~ Hz/torr Ease of tuning 39 N/kHz (bare), 40 N/kHz (with He vessel) courtesy: D. Passarelli Tuning Deformations in high E and B regions balance out resulting in a small frequency shift (Slater s Theorem) Page 6

7 SSR1 Fabrication (Niowave, Roark) SSR1 resonators manufactured in US industry Nb Cu SST Spoke with collars Beam Pipe port 7

8 Brazed transition rings (ANL, Roark) Two different joint designs investigated #1 #2 ANL courtesy: W. Toter (ANL) Cu-Braze Low RRR 316 L High RRR Page 8

9 Issues: Vacuum Flanges SSR1 uses ConFlat-type flanges Sealing unreliable/non-repeatable Rough Machining, Damages Generators of Cu-particulates serrated knife edges able to peel copper pieces from gasket when disassembled Will adopt hex-shaped aluminum seal this seal is widely used in SRF field simple machining of flange, easy to repair courtesy: A. Rowe, C. Crawford ConFlat-type vacuum seal cavity flange blank-off Magnification of a knife edge showing extensive damage Magnification of a copper gasket after disassembly. The imprint left by the knife edge shows rough machining grooves. Aluminum Hex Seal Page 9

10 Issues: Electron-Beam welding Weld blow-throughs observed in 4 resonators no signs of machine faults or power supply issues Extensive studies lead to abatment of events New process parameters developed. Cause attributed to weld bead instability A thinner bead, faster feed-rate and extreme attention to alignment of parts eliminated occurrences in the last 4 cavities. Repairs performed meticulously, cavities tested successfully Typical holes on full-penetration welds Extensive EBW tests on Nb cylinders Machining of plug (top); weld repair from RF-side Page

11 Processing/Testing steps (ANL, FNAL) 1. Inspection RF & Optical 2. BCP µm (flip half-way) 3. HPR C, h (< 5 C/min ramp rate) 5. RF Tuning 6. BCP µm 7. HPR (horiz + vert) 8. Assemble 9. Evacuate C, 48 h. Vertical Test 11. Helium Vessel Dressing 12. HPR 13. BCP µm 14. HPR 13. Assemble 14. Evacuate C, 48 h 15. Horizontal Test 16. Ready for String courtesy: A. Rowe Bare cavity BCP setup FNAL Low-Temp Ovens (<300 C) ANL ANL ANL High-Temp Oven (<00 C) FNAL Page 11

12 VTS Qualification 8 qualified S112 conditionally qualified S114 Q = 2 S113 Repaired S7 76 MV/m 115 mt Q 0, 1-1 Q - solid marker, X-ray - empty marker 0 S1H-NR-5: June 27, 2012 S1H-NR-7: July 30, 2012 S1H-NR-9: November 14, 2012 S1H-NR-8: January 16, 2013 S1H-NR-113: March 7, 2013 S1H-NR-1: April 26, 2013 S1H-NR-112: May 31, 2013 S1H-NR-114: October 2, 2013 PX specifications 1-1 Radiation, mr/h E acc =V acc /βλ, MV/m E pk, MV/m B, mt courtesy: A. Sukhanov -2 Page 12

13 Example of S8 1 st and 2 nd pass Q - solid marker, X-ray - empty marker 0 S1H-NR-8: November 1, 2012 S1H-NR-8: January 16, 2013 (HPR) Q 0, 1-1 PX specifications 1-1 Radiation, mr/h E acc =V acc /βλ, MV/m E pk, MV/m B, mt -2 courtesy: A. Sukhanov Page 13

14 Issues - Multipacting Barriers Two multipacting barriers have been experienced at 4-5 MV/m and 6-7 MV/m Multipacting simulations are in fair agreement with measurements courtesy: A. Sukhanov Page 14

15 Multipacting Processing vs. 120C Bake S1H-NR-5 (no 120C bake): March 27, 2012 (4.4K) S1H-NR-5 (120C bake): April 16, 2012 (2K) S1H-NR-5 (HPR, 120C bake): June 23, 2012 (4.4K) E acc =V acc /βλ, MV/m :00 02:00 04:00 06:00 08:00 :00 courtesy: Time elapsed, h A. Sukhanov Page 15

16 Jacketing Operations (Meyer Tool) Page 16

17 Shifts caused by jacketing < 250 khz courtesy: P. Berrutti Page 17

18 First SSR1 Cavity for PXIE Page 18

19 Measurements of Sensitivity Pressure in He space was cycled between atm using Nitrogen Frequency measurements taken at different pressure increments Dial indicators provided valuable information for calibrating our model Results: + Hz/torr (free) + 4 Hz/torr (with dummy tuner) Requirement is < 25 Hz/torr courtesy: D. Passarelli Page 19

20 The double-lever tuner 2ndArm x2 U bar x2 1stArm x2 Main Probe x2 1stFlex x2 Motor Piezos x2 2ndFlex x2 Motor bracket MAIN ARM U BAR DIFF SCREW 2nd FLEX 2nd ARM NUT PIEZO ASSEMBLY MOTOR BRACKET PLATE PROBE 1st FLEX courtesy: D. Passarelli Cavity Helium Vessel MOTOR Coarse Range 135 khz (0.25 mm) Motor F MAX 1250 N (1:6) Fine Range 1 khz (2 µm) Page 20

21 Summary and Outlook Production SSR1 received (8 needed for 1 st CM) EBW holes repaired, process improved Decision to modify flanges from ConFlat to Aluminum Seal 8 Cavities qualified for PXIE SSR1 Cryomodule First Jacketed cavity received, sensitivity meets requirements Next: Qualification of Jacketed SSR1 s Manufacturing of SSR1 Cryomodule Page 21