Review of Diamond SR RF Operation and Upgrades Morten Jensen on behalf of Diamond Storage Ring RF Group
Agenda Stats X-ray and LN2 pressure results Cavity Failure Conditioning in the RFTF Cavity Simulations IOT Upgrade Helium Refrigerator update
MTBF and Number of trips MTBF and Number of trips 180.0 160.0 140.0 120.0 100.0 80.0 60.0 40.0 20.0 0.0 38 RF MTBF of beam loss and Number of beam trips per run 18 21 26 18 6 21 20 12 36 c 13 15 6 3 6 6 11 19 24 7 37 19 1 Cavity 1 only 1.8 MV typical Many trips in Run 1 to find acceptable voltage Cavity 3 Installed 2008-1 2008-3 2008-5 2008-7 2008-9 2009-2 2009-4 Run Number 2009-6 MTBF complete RF System (beam loss only) Beam dumps MTBF year to date 2008 MTBF year to date 2009 MTBF year to date 2010 Overall MTBF STILL dominated by Cavity trips 2009-8 2010-1 2010-3 120 100 2010-5 80 60 40 20 0 2010-1? 2010-2 2010-3 2010-4 2010-5 Partial Run
X-ray count /msv/hr or Power / kw X-ray count / msv/hr Power / kw X-ray count / msv/hr x-ray count / (msv/hr) X-ray measurements on the cavities X-ray count vs Ib 120 100 80 60 40 20 0 X-ray intensity vs Voltage Intensity increases exponentially with voltage 0 0.5 1 1.5 2 2.5 Cavity Voltage (Ib=0)/ MV 30 25 20 15 10 5 0 Intensity varies linearly with power to beam! Fiddled with voltage 0 20 40 60 80 100 120 Beam current / ma X-ray and Power vs Detune (100 ma, 1.4 MV) 140 120 100 80 60 40 20 0-30 -20-10 0 10 20 30 40 Detune angle / (deg) X-ray count Pfor Detuning (i.e. increasing power for constant beam does not change intensity Total intensity is varies with both 140 power and 120 voltage 100 80 60 40 20 0 X-ray count vs Vcav with stored beam @ (100 ma) 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1 Vcav / MV 135 130 125 120 115 110 105 100
LN2 supply pressure stability improved LN2 Supply pressure Peak to peak reduced from ~ 1.5 bar to 0.25 bar Further optimisation likely Tuner position reduced but most noticeable on cavity 1 LN2 Pressure stability improved by the installation of pressure and level control valves on the LN2 supply tank Ongoing investigation to determine residual perturbation
Cavity 2 Failure Cavities 1 and 2 installed and being warmed up over Christmas. Warming up the cavities requires the use of electrical heaters. Procedure and Manual did not include turning off heaters. Heaters were not interlocked. Heaters were left on! First sign: Leak from helium can to insulation vacuum 500 K 400 K 515ºC 460ºC Estimate of max heater temperature 200 K 0 K Maximum EPICS value Heaters OFF CLTS on Cavity 2 Fail
Cavity 2 Failure Investigation revealed: Both Helium level sensors not functioning Main pickup and waveguide coax cables have short circuit (both in helium can). Some of the temperature sensors on the niobium cell have been unsoldered. Helium level probes with blue plastic insulation which has melted Vacuum seal has failed and indium has melted
Cavity 2 Failure Additional observations not related to the increase in temperature Bellow section has distorted. Radial groove from original BCP etch
Copper Plating Problems Peeling copper plating on most pickups and missing plating inside the cups Marks on copper plating in the waveguide. Staining or tracking marks? Damaged plating in waveguide section
Copper Plating Problems Discolouration of waveguide components and of the gasket Staining or damaged plating in the corners of the waveguide
5-8 January: Cavity 2 removed from tunnel and make up vessel installed. 9-10 January: Cavity 1 cooled down noticed that no level sensors were usable and RF pickup cables short circuited. 10 January (Sunday night): Controlling level by controlling total inventory. RF control via spare RF cable on the beam pipe. 11 January: Machine start-up Then move on to Radiofrequency Test Facility commissioning, cavity installation and conditioning in RFTF.
Conditioning of cavity 3 inside RFTF Initial conditioning in February 2010. Gradual increase in cavity voltage and power dips caused by fast vacuum protection during conditioning can be seen. Power dips caused by fast vacuum protection Cavity voltage Forward power Vacuum spikes during conditioning
Soak test in April. Time scale is kept the same as last slide. Improvement in long term performance can be seen clearly. Cavity voltage RBT taper vacuum Forward power Pump out box vacuum ~ 3 days
Infrared pictures of RF window during conditioning 84KW forward power, cavity on resonance 55KW forward power, detune angle -60degree RF Window 28 degree Window heated up to 30 degree Waveguide walls
Q0 (10^9) Q0 (1e9) 2 Q0 measurement showing Q0 drop at low voltage Q0 measurement 1.2 1 Q0 drop possibly caused by field emission 0.8 0.6 0.4 0.2 Original Specification 0 1.1798135 1.3633327 1.5249236 1.6880237 1.8632531 2.0574732 2.2585668 2.4448395 2.6412452 Cavity voltage (MV) Q0 measurement 1.2 1 0.8 0.6 0.4 0.2 Original Specification 0 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 Cavity voltage (MV)
Cavity partial warm up experiment Partial warm up to 28K to release hydrogen. Warm up can help with the vacuum but not necessary the long term performance of the cavity Out gassing during partial warm up Vacuum is better after partial warm up. But many vacuum spikes appeared. Some spikes triggered protection.
PMT signal during conditioning PMT signal showing probe blip PMT Probe Forward power X-ray during the pulse Probe Forward power PMT X-ray spike PMT X-ray starts around 1.5MV. Probe Beam trip X-ray spike and probe blip during a trip Forward power
Probe problem 1. Main probe and e- pickup have failed. 2. Cavity 2 and 3 both suffer probe blips. Cavity 1 under investigation. 3. Probe blips happen with and without beam. 4. Probes don t have blips at the same time. 5. Probe blips don t always trip the beam. 6. Very high amplitude. 7. Not successful to filter it out. (Band pass filter, DC block) 8. Not successful with bias voltage. Cavity Signal Spare pickup Another spare pickup
Observed probe blips kicked off wake field simulation of the RF probes DLS Pickup Pin 6 mm CLS Pickup Pin 1 mm 240 mm beam pipe Port-1 Port-2
Snapshot E-Field at t=1.05 ns for 10 & 3 mm bunches, yz-plane s = 10 mm 10 mm bunch The maximum field value is clamped at 100 V/m in both cases. The field at the DLS pick-up has decayed by the time the bunch passes the CLS pickup and therefore appears to be lower. s = 3 mm 3 mm bunch
DLS Pick-up Thin lines 10 mm bunch The EM signal induced by the beam propagates in many modes through the pick-ups. CLS Pick-up Thick lines For 10 mm bunch the voltage induced between the conductors is very low at 0.003 V for DLS pickup and lower still for CLS design DLS Pick-up 3 mm bunch CLS Pick-up DLS CLS 3 mm bunch ~ 7 V between conductors for 250 ma 600 bunches. DLS probe has 4 x CLS voltage
Frequency content of Voltage Signal s = 10 mm DLS CLS Summary: Diamond beam (σ =3 mm) excites stronger signal in the pick-ups compared to the CLS and CESR (σ=10mm) beams for the same charge. s = 3 mm The DLS Pick-ups have larger diameters and so the signal induced will be stronger. Risk of breakdown and wakefield effects are greater for the DLS pickup but unlikely to be the main reason for our beam trips.
Multipactor simulation of the DLS Cavity & Waveguide Nb RF Window Cu (Plating) Al
To establish TW fields in the waveguide Transmitted Reflected Input Monochromatic Excitation with f = 499.654 MHz
Development of Multipactor, P = 200 kw PIC Solver t = 42 ns t = 122 ns t = 2 ns Exponential growth of number of particles indicate multipactor t = 250 ns t = 498 ns
CST model for Multipactor study near Coupling tongue Coupling tongue Electron Source definition TM010 E field from Eigen mode solver near coupling tongue
Preliminary tracking solver Results Eigen mode field scaled to 1 MV across cavity No exponential growth!
DLS IOT Upgrade from TED to E2V IOTs TED IOT E2V IOT
DLS IOT Upgrade from TED to E2V IOTs Successfully upgraded Systems 1 and 2 from TED to e2v IOTs during Christmas 2009 shutdown Advantages Reduced IOT trips Simple tuning and setup with indexed settings Built in radiation shields no lead required Ion Pump readily recovers vacuum during initial filament start up Differences Cavities built around IOT Cathode at the top inside the input cavity Network analyser not required for tuning
e2v S/N Hrs in user operation IOT11 224-0711 2467 IOT12 290-0939 996 IOT13 211-0647 18976 IOT14 212-0647 18839 Current IOT Operating Hours Hrs (Spares) Hrs (Failed) Status Notes IOT31 289-0938 4269 IOT32 287-0931 4264 IOT33 273-0907 5624 IOT34 288-0935 4265 IOT22 223-0710 15327 Grid emmission Waiting for grid outgassing 210-0647 14853 Suspect Under investigation for tripping IOT21 268-0851 1040 Spare 205-0639 1219 Failed During initial commissioning 222-0710 Spare Unused 269-0904 Spare Unused 277-0909 510 Spare 2009: 19 trips during 4300 operational hours (mostly TED IOTs) 2010: 9 x ISCs: 5 during initial run with new tubes 4 in a quick succession on single IOT
1710 2030 3040 3860 5380 8100 10500 12500 15300 20500 25600 30300 35400 40900 46000 50100 50900 55800 57200 60400 61100 61200 62000 62000 62300 65400 66000 67000 67200 67300 67500 67600 68600 71400 71900 72700 73500 73900 82000 Efficiency (%) HV (kv) Typical Operating Conditions (S/N 268-0851) Pin Pout I b Eff Gain (W) (kw) (A) (%) (db) -35 159 35 2.0 50 23.5-35 234 50 2.6 55 23.31-35 352 80 3.29 67 23.4 80.00 Efficiency During Initial Tune/Set Up (S/N 268-0851) 70.00 60.00 50.00 40.00 30.00 20.00 10.00 Note jagged curve due to changes in tuning during initial set up 0.00 Output Power (W)
Current measurement board affected by change from TED to E2V IOTs Original e2v configuration HVPS Curren Total Body I IOT 1-4 Collector Current Collector cable not connected PSU 0V PSU -36kV Not connected IOT Body I -36kV return Now through IOT Body and HVPS I input
Current measurement board affected by change from TED to E2V IOTs All collector inputs are connected Total IOT current transducer Earth current directed through IOT current transducers Body current components removed
Problem: Speed sensing of the warm turbine has occasionally become erratic without prior warning. Repair: After ensuring that the fibre optic cable was properly mounted, part of the signal conditioning box was changed. The problem reoccurred. The frequency to analogue converter was then replaced. There has been no reoccurrence. Frequency to analogue converter Signal conditioner Fibre optic input
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