High Power RF System Status By: Peter McIntosh Klystron Department PEP-II Machine Advisory Committee Review October

Peter McIntosh, PEP-II MAC Review, October Summary PEP-II RF System Klystron Status Waveguide and Circulator Status Cavity System Status HVPS Status RF System Trips Future Plans Conclusions

Peter McIntosh, PEP-II MAC Review, October PEP-II RF System 1.2 MW Klystron Circulator Control Racks Penetration Load

Peter McIntosh, PEP-II MAC Review, October PEP-II RF System Currently have on PEP-II: –8 HER stations: 5 x 4-cavity stations 3 x 2-cavity stations –HER 4-1 installed summer 2003 Max HER V RF = 19.5 MV (750kV/cavity) –3 LER stations: All are 2-cavity stations Max LER V RF = 5.1 MV (850 kV/cavity) In 2004 will be installing: –LER4 (2-cavity station)  additional 1.7 MV Max LER V RF will become 6.8 MV –HER9  Split existing 4-cavity HER station into 2 x 2-cavity stations no overall increase in HER V RF, but more beam power available.

Peter McIntosh, PEP-II MAC Review, October Klystron Status 7 major operational failures: 3 Philips anode, 3 Marconi vacuum, 1 Philips heater Expected klystron lifetime ~30k hours  have 4 with >33k hours

Peter McIntosh, PEP-II MAC Review, October Philips Klystrons - Anodes The anodes on the Philips klystrons are designed to run hot  minimize the deposition of barium from the cathode. A heat trap or ring is employed around the anode to ensure the anode runs at an elevated temperature. Suspect that the anode rings got too hot and the for 3 of the Philips klystrons became detached under normal operating conditions. The filament power was subsequently reduced in Aug 2001 on ALL Philips klystrons (maintaining the correct beam perveance) to protect against further anode ring failures.

Peter McIntosh, PEP-II MAC Review, October Philips Klystrons – Side-bands The +15 MHz instability: –Philips tubes have their 2 penultimate cavities typically tuned close together: C5 = MHz C6 = 493 MHz –Generates Gain at these frequencies if excited. –These cavities have no frequency adjustment mechanism and so are difficult to re-tune. –Theory: Returning electrons from the collector excite either/both these cavity resonances  significant gain at +15 MHz HER 8-3 (Philips S/N 01) Feb 2002 HER 12-1 (Philips S/N 06) Oct 2000

Peter McIntosh, PEP-II MAC Review, October Philips Klystrons – Side-bands Power at +15 MHz is outside the BW of the circulator and is reflected back to the klystron  driving the instability further. Counteracting measures used: 1.Adjust the output match of the klystron  reduces the amount of returning electrons, but also reduces klystron gain at 476 MHz! 2.Alter the waveguide length between klystron and circulator  adjusts the phase of the reflected power. 3.Adjust the circulator bias  change its match characteristics at +15 MHz with marginal affect at 476 MHz. Combination of all 3 employed to successfully overcome this instability for the Philips klystrons. HER 12-1 (Philips tube S/N 06) is much more sensitive to this phenomena than all other Philips klystrons (C5 and C6 tuned much closer together!) and has required frequent attention.

Peter McIntosh, PEP-II MAC Review, October Marconi Klystron (Oct 2002) Vacuum leak identified at the collector braze joint on each of the 3 failed Marconi klystrons. When trying to find the, found each of the collector bodies had deformed. Deformation occurred in approximately the same location for all 3 klystrons. Excessive heating of the collector the primary cause. Marconi S/N 02 and 03 rebuilt at CPI with an improved collector design: –has longitudinal cooling channels as opposed to radial channels. –Baffled water circulation to specifically direct water around the collector braze joint.

Peter McIntosh, PEP-II MAC Review, October SLAC Built 1.2 MW Klystrons SLAC S/N 01 installed March 1997 in HER 12-3 and has operated without any problems. Failure problems with the Philips and Marconi tubes have been rectified without impact to PEP-II operations. It is expected that more Philips tubes will fail in the near future: –will be replaced by SLAC built units currently being manufactured.

Peter McIntosh, PEP-II MAC Review, October Waveguide/Circulator Status 11 x 1.2 MW AFT circulators installed – No failures during PEP-II history. 32 x 1.2 MW Dielectric loads installed – 1 failure during PEP-II history. 562 x WR2100 MEGA waveguide components installed: –In the last 2 years only 1 incident in Nov 2002 on HER 8-3: Matching post on the first Magic Tee failed resulting in a ruptured bellows near the circulator.

Peter McIntosh, PEP-II MAC Review, October HER 8-3 Waveguide (Nov 02) Circulator 1 st Magic Tee Matching Post Damaged Bellows Teflon Barrier

Peter McIntosh, PEP-II MAC Review, October Cavity System Status Cavities are RF processed individually in a dedicated test facility up to a higher V RF than is typically run on PEP-II  up to 850 kV/cavity. Cavities are also RF processed in-situ at this higher level when installed (1.7 MV for each 2-cavity station and 3.4 MV for each 4- cavity station). Cavity operating parameters on PEP-II: Cavity Parameter HERLER NominalTypical*NominalTypical* RF Voltage/Ring Number of Klystrons8733 Number of Cavities Gap Voltage/Cavity (kV) Dissipated Power/Cavity (kW) Beam Current (A) Beam Power/Cavity (kW) RF Window Power (kW) Klystron Power (kW) * Parameters for peak and Integrated Luminosity records May-June 2003

Peter McIntosh, PEP-II MAC Review, October Cavity System Status 26 HOM-damped cavities installed in the HER. 6 installed in the LER. Only 1 major component failure in last 2 years: –a broken HOM-load water fitting on cavity HER 12-1A in Oct 2002 which could not be repaired in-situ, required replacement of the HOM-load. No cavities, coupling networks or RF windows have needed to be replaced once installed. RF Cavity Support Raft Tuners HOM loads Coupling Network RF Window Vacuum Pump

Peter McIntosh, PEP-II MAC Review, October Crowbar SCR Upgrade In summer 2002, the HVPS crowbar SCR stacks were replaced with optical-fired SCRs to improve station reliability. Found in early 2003 that the new SCRs were failing due to broken hermatic seals which leaked oil leading to high current leakage in the devices. Found a large number of new units which had high current leakage, but also a number which were electrically faulty but without the high leakage characteristics. ALL 10 crowbar SCR stacks, containing a total of 240 SCRs replaced ‘again’ with functional SCRs. Voltage divider networks installed on all station crowbar stacks to limit the load at the individual SCRs.

Peter McIntosh, PEP-II MAC Review, October RF System Trips Klystron –Klystron failures (anode failure and collector vacuum leaks) –Side-band instabilities –Arcs Cavity –Vacuum – predominantly HER 12-1 and 8-1  synchrotron radiation from upstream bending arcs also from newly installed stations. –Arcs at the RF window (majority on the vacuum-side, but also some air- side trips) –Reflected power aborts: when beam is lost always get Reflected Energy (RE) interlock at the RF stations  cause not always originating in the RF system! HVPS –SCR stack failures –Current and Voltage regulation (complicated system requiring regular maintenance). –Over Temperature, particularly during the summer months: Additional cooling and protection from sun exposure has successfully limited the number of Over Temp trips in the last 2 years. Waveguide –Component failures: bellows and loads

Peter McIntosh, PEP-II MAC Review, October PEP-II Station Arc Trips

Peter McIntosh, PEP-II MAC Review, October PEP-II Cavity Vacuum Trips

Peter McIntosh, PEP-II MAC Review, October Future Plans Continue adding more RF stations:  higher beam currents in both HER and LER,  higher Luminosity  HER 8-1 and 12-1 will split into 4 x 2-cavity stations:  Allowing more efficient use of available klystron power. Improve RF system diagnostics to more accurately diagnose RF system trips. Convert HVPS rectifiers to optical SCRs (similar to the new crowbar SCRs) to further improve reliability.

Peter McIntosh, PEP-II MAC Review, October Conclusions Of the 15 klystrons installed on PEP-II, 7 have required a major re-build in 6.5 years of PEP-II operation – ~ 1 repair/year! 32 HOM-damped cavity systems now installed, with only 1 major component failure to date. The waveguide feeder and circulator isolation systems have an excellent performance record – only 1 load and 2 waveguide component failures to date. The crowbar SCR upgrade for the HVPS’s, although problematic, was successful! When HER 8-1 and 12-1 are split into 2-cavity stations, it is hoped the number of arcing trips/station reduces. As HER 12-5 and 12-6 accumulate more ‘active’ running time, the number of cavity vacuum trips is expected to reduce.

Peter McIntosh, PEP-II MAC Review, October Conclusions Records for peak and integrated Luminosities have been smashed in the last PEP-II run: –Peak L = x cm -2 sec -1  June –Intg. L = fb -1  May (7 days) Which is testament in no small part to the capability and reliability of the PEP-II RF system. System upgrades are planned to increase further the RF system capability  more stations. With better diagnostics and upgraded LLRF systems, RF reliability should also be improved upon (see Breakout Session: “RF and Feedback”).