Page 1 Jean Delayen Subashini De Silva Center for Accelerator Science Department of Physics, Old Dominion University and Thomas Jefferson National Accelerator Facility PROOF OF PRINCIPLE CAVITY PREPARATION AND TESTING: ODU/SLAC RF–DIPOLE DESIGN Joint LARP CM20 / HiLumi Meeting – Napa, CA 8-10 April, 2013

Page 2 Proof of Principle Design Design requirements –Frequency = 400 MHz –Beam aperture = 84 mm –Total transverse voltage = 10 MV –Transverse voltage per cavity = 3.4 MV Transverse electric and magnetic fields Surface electric and magnetic fields

Page 3 Basic Properties PropertyValueUnit VT*VT* 0.375MV Ep*Ep* 4.02MV/m Bp*Bp* 7.06mT B p * /E p * 1.76 mT/ (MV/m) U * 0.195J [R/Q] T Ω Geometrical Factor (G) Ω RTRSRTRS 4.04×10 4 Ω2Ω2 At E T * = 1 MV/m 52.8 cm 17 cm 8.4 cm HOM Properties No lower order modes Separation of HOMs from fundamental mode ~ 190 MHz

Page 4 Fabrication Fine grain Nb – RRR Cavity thickness – 3 mm

Page 5 Fabrication End plates with brazed stainless steel flanges Center shell formed in two halves Finished cavity shipped to ODU –March, 2012

Page 6 Bead Pull Study On-axis transverse electric field was measured using a Teflon bead Both on-axis transverse electric and magnetic fields were measured using an Al metallic bead

Page 7 Optical Inspection All the welding seams were inspected ~ 180 images Grain boundaries Weld seam

Page 8 Surface Treatment, Preparation and Testing Bulk BCP – 85 μm Heat treatment – At C for 10 hours Light BCP – ~10 μm High Pressure Rinse – 3 passes Assembly in the clean room RF Tests Performed –2 K high power test –Cavity warmed up to 4 K –4 K high power test –Cavity cooled down to 2 K –2 K high power test RF Test Plan –High power tests at 2 K and 4 K –Rs vs. T –Pressure test –Lorentz detuning –No He processing was done BCP Cabinet HPR Cabinet

Page 9 Chemical Processing Bulk BCP Planned total removal – 120 μm Acid mixture was contaminated with glycol –Reduced etch rate from μm /min to 1.8 μm/min Average removal 85 microns –Average removal in edges > 90 μm –Average removal on flat surfaces < 70 μm Light BCP Removal of 10 μm after heat treatment O1O1 O2O2 O3O3 O4O4 O5O5 O6O6 O7O7 O 10 O 11 O 15 O 16 O 12 O 13 O 14 O8O8 O9O9 81 μm 99 μm 95 μm 108 μm 63 μm 71 μm 68 μm

Page 10 Heat Treatment At C – 10 hours T = CH2H2

Page 11 Assembly Followed by a HPR of 3 passes Ultrasonic degreased hardware Leak tested Assembly in clean room

Page 12 Preparation for Test Cable calibration –Q 1 = 2.76 ×10 9 –Q 2 = 8.62 ×10 10 LLRF control Test with 500 W rf amplifier

Page 13 Design Specifications in Operation Basic PropertiesRequired fields PropertyValueUnit VT*VT* 0.375MV Ep*Ep* 4.02MV/m Bp*Bp* 7.06mT B p * /E p * 1.76 mT/ (MV/m) U * 0.195J [R/Q] T Ω Geometrical Factor (G) Ω RTRSRTRS 4.04×10 4 Ω2Ω2 At E T * = 1 MV/m PropertyValueUnit VTVT MV EpEp MV/m BpBp mT T2.04.2K R BCS nΩnΩ R res 20.0nΩnΩ RsRs nΩnΩ P diss (3.4 MV) W Q0Q ×10 9

Page 14 Multipacting Analysis A multipacting barrier was observed in the first 2 K test at very low fields Increasing the power readily processed the cavity No multipacting was observed in the following 4.2 K and 2 K tests Multipacting analysis was done using the Track3P in SLAC – ACE3P suite

Page 15 Expected Q 0 = 1.6×10 9 –At R S = 90 nΩ –And R res = 20 nΩ Achieved Q 0 = 1.25×10 9 Achieved fields –E T = 11.6 MV/m –V T = 4.35 MV –E P = 47 MV/m –B P = 82 mT Limited by rf power 4.2 K Test Results 3.4

Page 16 R s vs T, Pressure Test, Lorentz Detuning Frequency deviations –Room temperature f : MHz –After bulk BCP : Δ f =  51.1 kHz –After bake : Δ f =  30.2 kHz –Under vacuum : Δ f = kHz –At 2 K : Δ f = kHz R S = 34 nΩ

Page K Test Results Expected Q 0 = 6.7×10 9 –At R S = 22 nΩ –And R res = 20 nΩ Achieved Q 0 = 4.0×10 9 Achieved fields –E T = 18.6 MV/m –V T = 7.0 MV –E P = 75 MV/m –B P = 131 mT Quench

Page 18 Field Emission

Page 19 Summary Proof-of-Principle cavity achieved 7 MV deflecting voltage cw Residual surface resistance a little high (34 nΩ) –Possibly due to contaminated acid, not enough Nb removed –Consistent with losses in stainless steel flanges and copper probes in coupler ports Multipacting quickly processed and did not reoccur Proof-of-Principle cavity has achieved its purpose Ready to move on to the prototype cavity Reasonably confident that 10 MV can be achieved with 2 cavities

Page 20 Acknowledgements ODU –Chris Hopper –Alex Castilla –HyeKyoung Park SLAC –Zenghai Li Niowave –Terry Grimm –Dmitry Gorelov –Chase Boulware –Nick Miller JLab –HyeKyoung Park –Peter Kneisel –Rongli Geng –Joe Preble –Tony Reilly –Tom Powers –Kirk Davis –Pete Kushnick –Danny Forehand and his team –Steve Castagnola and his team –Dave McCay –Casy Apeldoorn