Peter McIntosh, PEP-II MAC Review, December PEP-II RF System Status By: Peter McIntosh Klystron Department PEP-II Machine Advisory Committee Review December

Peter McIntosh, PEP-II MAC Review, December Summary RF System Performance RF aborts –RF Problems Encountered –Mitigating these problems! Klystron Status –Limitations RF System Upgrades Conclusions

Peter McIntosh, PEP-II MAC Review, December Cavity Parameter HERLER Jun 2003 Run 3 Jul 2004 Run 4 Jul 2005 Run 5 Maximum Run 5 Jun 2003 Run 3 Jul 2004 Run 4 Jul 2005 Run 5 Maximum Run 5 RF Voltage/Ring (MV) Number of Klystrons Number of Cavities Gap Voltage/Cavity (kV) Dissipated Power/Cavity (kW) Beam Power/Cavity (kW) Total RF Power/Cavity (kW) Klystron Power (kW) Beam Current (A) RF System Performance – Run 4 * Luminosity predictions assuming  y,  y * and n remain fixed. Peak Lumin. (10 33 cm -2 sec -1 ) *16.8* *16.8* Power limited already!Same for Run 5! Linearizers will help!

Peter McIntosh, PEP-II MAC Review, December Run 4 RF Abort Statistics Courtesy: Dan Van Winkle This talk Average of 3.8 Aborts/Day (2.9 Aborts/Day without non-RF events) Compared to 7/Day for Run 3 M Browne’s talk D Teytelman’s talk M Browne’s talk

Peter McIntosh, PEP-II MAC Review, December RF Station Aborts (LER) RF StationNo of AbortsComments LER Stuck combs - software reset implemented and new comb module design initiated Klystron sidebands – focus adjustment did not fix problem LER Klystron Vacuum – increased klystron vacuum trip level Stuck combs – software reset implemented and new comb module design initiated Stuck tuners - replaced tuner actuators Solenoid PSU – PSU replaced LER 4-581Phase drift in new RFP– better control of rack temperature Biasing modifications in RFP module Total224

Peter McIntosh, PEP-II MAC Review, December RF Station Aborts (HER) RF StationNo of AbortsComments HER Not run very much before Dec 2003 RF processed over the Xmas break – has been very reliable since Cavity vacuum – new RF station HER 8-196Cavity arcs – limit station voltage FWDP limitation – focus adjustment improved FWDP, replaced with SLAC tube in March 2004 HER Cavity arcs – under investigation (end of run) HER Clock module – clock module replaced klystron vacuum - klystron vacuum trip level increased Cavity vacuum – needs more processing Stuck tuners - replaced tuner actuators HER Cavity arcs – limit station voltage Klystron arcs – early on in the run, seem to have disappeared Multipacting? – MD and focus adjustment could not replicate problem HER Longitudinal instabilities – most sensitive HER station HVPS arcs - replaced crowbar SCR stacks cavity arcs – under investigation HER HVPS arcs – replaced crowbar SCR stacks Stuck tuners – replaced tuner actuators Cavity vacuum – needs more processing HER Cavity A probe signal drop outs  not real cavity field events – see results HVPS arcs – replaced crowbar SCR stacks Total681

Peter McIntosh, PEP-II MAC Review, December Stuck/Slow Tuners Stuck Tuners: –Number of actuators with sheared pulley pins. –Found carrier lead screw threads stripped (no grease!) –Now re-greased ALL tuners. Slow Tuners: –Readback and control positions drift slowly with time. –Requiring software re-initialization. –Software reset implemented  re- initializes tuner positions at specific time increments. Tuner actuator system being reviewed for possible replacement: –smaller motor. –more compact and robust system. –improved actuator mounting and control.

Peter McIntosh, PEP-II MAC Review, December SCR Stacks All 11 crowbar SCR stacks replaced again this run. Scheduled to not disrupt PEP-II operation. Leaking hermatic seals. Some stacks failed due to Si material defects. SLAC worked closely with EUPEC to overcome apparent QC problems. Faulty SCR’s repaired under warranty at EUPEC. Additional tests implemented to catch faulty units before shipment. It is now believed that the problems have been overcome. EUPEC are the only optically fired SCR vendor available at this time.

Peter McIntosh, PEP-II MAC Review, December Cavity Arcs All HER stations have suffered either cavity arc or vacuum events: –V RF increased by 33% since Run 3 –Average klystron FWDP increased by 29% since Run 3 By far the biggest cavity abort contributor has been HER 12-6 cavity A  ~20 % of all HER RF aborts! Fault files show a rapid (1-2  s) drop in cavity A accelerating field. Much too fast for a breakdown at the RF window. Must be happening in the cavity itself. Installed 8 NLC-type acoustic monitors to the cavity – probe, input coupler, tuners and HOM loads  did not see any pre-cursor events. Also installed video camera looking into the movable tuner  did not see any arcing events either when the station aborts. Have not been able to correlate the station aborts with the cavity operating parameters, although appears to be somewhat sensitive to station voltage. Looking at the raw cavity signals, have been able to localize where the problem may lie.

Peter McIntosh, PEP-II MAC Review, December HER 12-6 Aborts (Fault File) Field Decays in 1- 2  s Large reflected power signal We shouldn’t see similar response signal in Cavity B if an arc occurs in Cavity A !?!? Cavity A Probe Cavity B Probe Cavity A REVP Cavity B REVP Similar responses!

Peter McIntosh, PEP-II MAC Review, December HER 12-6 Aborts (Probe A)

Peter McIntosh, PEP-II MAC Review, December HER 12-6 Aborts (Probe A) No REVP change as Probe Drops out! CAVITY FIELD CANNOT BE DROPPING! Feedback group delay

Peter McIntosh, PEP-II MAC Review, December HER 12-6 Aborts Masked cavity A probe in the LLRF system on 7/22 to ignore such a fast change in signal. Station has not aborted on such a fault since. Signal is dropping out somewhere in the probe signal path and recovers within 10  s – cavity probe, cable or coupler in LLRF rack. Probe signal masked in LLRF

Peter McIntosh, PEP-II MAC Review, December HER 12-6 Downtime Investigation TDR of the probe and cable system revealed no obvious source for possible breakdown. No signs of any breakdown features inside the cavity itself. Internal boroscope of the installed cavity probe showed strange features! Installed second TiN coated probe in auxiliary cavity probe location and will be used as the operational probe for Run 5. Original probe will remain installed and used as a diagnostic tool: –Assess the effect of a solenoid around probe on breakdown frequency.

Peter McIntosh, PEP-II MAC Review, December PEP-II Cavity Probe Assembly Boroscope path

Peter McIntosh, PEP-II MAC Review, December Graticule Marks

Peter McIntosh, PEP-II MAC Review, December Surface Disruptions Graticule Marks

Peter McIntosh, PEP-II MAC Review, December Nose-cone Rework Inspection HER 12-6 cavity A is a cavity received from ACCEL required rework on its nose-cone prior to installation in summer Performed rework at SLAC and RF processed quickly in the test lab. Could have been a possible source for the continuous breakdown, however no evidence observed. Rework feature (Scotchbrite)

Peter McIntosh, PEP-II MAC Review, December HER 8-3 Cavity Arcs Latter part of Run 4  seen a number of cavity D arcs in HER 8-3. Looks more like a real cavity arc signature. REVP increases as (or before) the probe signal drops or saturates. REVP increases without change in klystron signal. Similarly masked cavity D probe signal – yet station still aborts! Appears to be sensitive to FWDP  more aborts when HER I b increased: –Breakdown in coupler box would explain why the REVP increases before the cavity probe reacts. –Does not explain why the cavity probe signal would increase! –More than 1 problem? More investigation required during next startup: –HOMs? – see large 7.1 GHz signal on cavity D probe and need to correlate this with other cavities in 8-3 and other stations in HER. –Longitudinal instabilities? – some of the 8-3 aborts have been associated with longitudinal beam motion – can maybe learn something from the LFB diagnostics? –LLRF anomalies? – closer monitoring of the HER 8-3 LLRF system parameters to rule out self-excitation as a possible cause.

Peter McIntosh, PEP-II MAC Review, December Klystron Status KlystronRF StationHoursComments Philips 01HER Philips 02HER FWDP limited to ~ 850 kW Philips 03LER Philips 04Spare MHz side-bands in HER 8-1 Philips 05LER Repair at CPI Dec 2002 – New Anode Klystron side-bands Philips 06HER Multipactor limited? Philips 07Spare16040Repair CPI Jun 2004 – New Anode Philips 08HER Repair CPI Jul 2002 – New Anode Marconi 01LER Marconi 02Spare4729Vacuum leak – awaiting rebuild Marconi 03SPEAR3Repair at CPI Aug 2003 – New collector Marconi 04LER Repair at CPI Oct 2003 – New collector SLAC 01HER SLAC 02Spare0Repair at SLAC – ready for test early 2005 SLAC 03HER SLAC 04HER SLAC 05HER Ready for high power tests SLAC 06HER SLAC Ready Jun New RF Stations 2004 Power Limited Klystrons Spares

Peter McIntosh, PEP-II MAC Review, December FWDP Klystron Limitations: HER 4-1, 12-1,12-6 and LER 4-3 HER 4-1 (Philips #2) –Klystron saturation in Philips #2, power limited at ~ 850 kW. –Adjusted klystron magnetic field, output match, circulator bias and waveguide length – all to no avail! HER 12-1 (Philips #6) –Klystron saturation in Philips #6, power limited at ~ 750 kW –Evidence of multipacting. LER 4-3 (Philips #5) –Side-bands evident, focus adjustments did not increase power limitation. HER 12-6 (Philips #8) –Power reduced recently in attempt to reduce cavity A arcs. LER 4-5 (Philips #3) –Drive signal spikes in LLRF system  klystron saturation. –Station phase drifts due to LLRF temperature stability. Real limitation

Peter McIntosh, PEP-II MAC Review, December RF System Upgrades More RF stations: –HER10 in –LER5 in –HER11, 12 and 13 possibly beyond Klystron Linearizer: (see Dan van Winkle’s talk) –Artificially linearizes the klystron gain. –Will improve LLRF amplitude and phase stability margins. New Low Group Delay Woofer: (see Dmitry Teytelman’s talk) –Dedicated channel for controlling low frequency modes. –Higher feedback gains  better damping. New Longitudinal Feedback Kickers: –2 over-damped cavity kickers installed in LER to replace LBNL designed drift- tube kickers: Higher kicker voltage transfer efficiency. Reduced HOM power per feedthrough (no directivity). Incorporates new high power feedthrough design. Integrated cooling if required. New Comb-2 module: (see Mike Browne’s talk) –Alleviate overflow faults. –Allow for single side band (asymmetric) functionality.

Peter McIntosh, PEP-II MAC Review, December PEP-II RF Station Evolution HERPresentlyDec 2005Oct 2006+LERPresentlyDec 2005Oct n/a n/a n/a n/a n/a Total26 Total

Peter McIntosh, PEP-II MAC Review, December LFB Kicker Installation and Measurements HFSSMeasured Frequency (GHz) Bandwidth (MHz) Loaded Q L

Peter McIntosh, PEP-II MAC Review, December Conclusions For Run 4: RF abort rate averaged 3.8/day, compared to 7/day for Run 3. 42% of all RF aborts due to high power component problems: –Majority of which being cavity arcs, particularly in HER –As we recovered from one major hardware problem (i.e HER 12-6) another appeared (i.e. HER 8-3). –Ongoing HVPS SCR problems addressed with EUPEC and now hopefully resolved. –Component redesigns in progress  New Comb-2 module and tuner actuators. Beam currents increased by 41% in HER and 63% in LER. For Run 5: Will have 2 operational spare Philips klystrons, plus a repaired SLAC tube by early –More SLAC klystrons being built to replace older, power limited Philips tubes. Currently power limited in the HER, particularly the Philips klystrons  linearizer system hoped to help! New LER RF station and LFB kickers  >30% larger LER beam current. New (split) HER RF station  nominal 13% increase in HER beam current. LLRF system improvements underway to improve system stability and reliability.

Peter McIntosh, PEP-II MAC Review, December Acknowledgements Must go to all members of the PEP-II RF Systems Taskforce, comprising people from many SLAC departments: –ARD-A  LFB Systems –ESD  LLRF and Software Systems –Klystron  High Power RF and TFB Systems –PCD  HVPS Systems