high power rf system status

High Power RF System Status

By: Peter McIntoshKlystron Department

PEP-II Machine Advisory Committee ReviewOctober 9-11 2003

Peter McIntosh, PEP-II MAC Review, October 9-11 2003

Summary

• PEP-II RF System• Klystron Status• Waveguide and Circulator Status• Cavity System Status• HVPS Status• RF System Trips• Future Plans• Conclusions


PEP-II RF System

1.2 MW Klystron

Circulator

Control Racks

Penetration

Load


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 VRF = 19.5 MV (750kV/cavity)

– 3 LER stations:• All are 2-cavity stations• Max LER VRF = 5.1 MV (850 kV/cavity)

• In 2004 will be installing:– LER4 (2-cavity station) additional 1.7 MV

• Max LER VRF will become 6.8 MV

– HER9 Split existing 4-cavity HER station into 2 x 2-cavity stations

• no overall increase in HER VRF, but more beam power available.


Klystron StatusKlystron Current Location Filament Hours Comments

SLAC S/N 01 HER 12-3 33248SLAC S/N 02 Failed 0 Failed during initial testing, awaiting repairSLAC S/N 03 HER 8-3 689 Installed summer 2003SLAC S/N 04 HER 8-5 122 Installed summer 2003SLAC S/N 05 Construction 0 Ready for install Nov 2003SLAC S/N 06 Construction 0 Ready for install Feb 2004

Philips S/N 01 HER 12-5 28143 Hot spot in output waveguide, minor repair at SLAC Sept 2000Philips S/N 02 HER 4-1 36740Philips S/N 03 LER 4-5 34077Philips S/N 04 HER 8-1 33308Philips S/N 05 LER 4-3 22266 Intermittent heater short, rebuilt CPI Dec 2001Philips S/N 06 HER 12-1 12852 Anode failure, rebuilt at SLAC June 2002Philips S/N 07 Failed 16040 Anode failure, awaiting repairPhilips S/N 08 HER 12-6 21818 Anode failure, rebuilt at CPI July 2002

Marconi S/N 01 LER 4-4 20152Marconi S/N 02 Failed 4729 Vacuum leak, awaiting repairMarconi S/N 03 SPEAR3 1348 Vacuum leak, rebuilt at CPI Aug 2003 - New CollectorMarconi S/N 04 Awaiting Test 4938 Vacuum leak, rebuilt at CPI Aug 2003 - New Collector

7 major operational failures: 3 Philips anode, 3 Marconi vacuum, 1 Philips heaterExpected klystron lifetime ~30k hours have 4 with >33k hours


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.


Philips Klystrons – Side-bands

• The +15 MHz instability:– Philips tubes have their 2

penultimate cavities typically tuned close together:

• C5 = 491.3 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


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.


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.


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.


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.


HER 8-3 Waveguide (Nov 02)Circulator

1st Magic TeeMatching Post

Damaged Bellows

Teflon Barrier


Cavity System Status• Cavities are RF processed individually in a dedicated test facility

up to a higher VRF 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 ParameterHER LER

Nominal Typical* Nominal Typical*

RF Voltage/Ring 19.5 12 5.1 3.6

Number of Klystrons 8 7 3 3

Number of Cavities 26 24 6 6

Gap Voltage/Cavity (kV) 750 500 850 600

Dissipated Power/Cavity (kW) 75 34 97 48

Beam Current (A) 1.5 1.1 3.2 1.8

Beam Power/Cavity (kW) 208 166 386 208

RF Window Power (kW) 283 198 483 256

Klystron Power (kW) 960 738 1021 545

* Parameters for peak and Integrated Luminosity records May-June 2003


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


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.


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


PEP-II Station Arc TripsStationCavity kly circ 1vac 1air 2vac 2air Total kly circ 1vac 1air 2vac 2air Total kly circ 1vac 1air 2vac 2air TotalDec. 0 1 1 0J an. 0 1 1 0Feb. 1 1 1 1 2 0March 0 0 0April 0 1 1 2 1 1May 1 1 1 1 0J une 0 0 0Sept 1 1 2 2 0

Total 1 0 0 2 0 0 0 3 0 0 1 3 3 2 7 0 0 1 0 0 0 1

StationCavity kly circ 1vac 1air 2 3 4 Total kly circ 1 2 3 4 Total kly circ 1 2 3 4 TotalDec. 0 0 0J an. 1 4 1 6 0 1 1 1 3Feb. 1 10 1 12 0 0March 5 5 0 1 1April 6 6 1 1 1 1May 2 2 1 1 1 1J une 0 0 1 1Sept 0 0 0

Total 2 0 27 0 0 1 1 31 1 0 0 1 0 0 2 0 1 2 2 1 1 7

StationCavity kly circ 1vac 1air 2 3 4 Total kly circ 1 2 3 4 TotalDec. 0 1 1J an. 1 1 0Feb. 1 1 1 1 2March 1 1 0April 1 1 2 0May 0 0J une 1 2 3 1 1Sept 5 5 0

Total 1 2 7 0 3 0 0 13 0 0 1 1 0 2 4

StationCavity kly circ 1vac 1air 2vac 2air 4 Total kly circ 1vac 1air 2vac 2air TotalDec. 0 3 3J an. 0 0Feb. 0 1 1March 0 0April 0 0May 0 0J une 1 1 0Sept 0 0

Total 0 1 0 0 0 0 0 1 0 0 0 0 3 1 4

PEP-II Cavity ARC Trips starting Dec. 2003 thru Sept. 2003

HR21 HR23

LR45

During last PEP-II run when the current

Luminosity records were achieved (May-J une), total number of RF system ARCs = 12

HR25 HR26

LR43 LR44

HR81 HR83 HR85


PEP-II Cavity Vacuum TripsPEP-II Cavity VACUUM Trips Dec. thru Sept, 2003

StationCavity 1 2 1 2 1 2Dec.J an. 2 1 1 1Feb. 1 2March 7 15April 2 1 1May 2J une 2Sept 2 1

Total 16 17 3 0 4 1

StationCavity 1 2 3 4 1 2 3 4 1 2 3 4Dec. 3 2 1 1 1J an. 6 1 2 1Feb. 3 1 2 1 1March 3 3 1 2April 2 1 5 1 3 1May 1 2 1 1J une 1 1 2 1 2 2 3 1Sept 2 2 3

Total 18 4 11 1 12 2 4 0 8 3 4 6

StationCavity 1 2 3 4 1 2 3 4 1 2 1 2Dec. 6 40 45J an. 1 4 14 8Feb. 2 1 1 4 1March 3 1April 2 1 18 8May 1 2 12 3J une 3 1 3 2 2 4 4 4 9 2Sept 1 10 9 9

Total 14 1 5 0 4 6 8 4 14 4 105 76

HR21 HR23 HR25 HR26

LR43 LR44 LR45

HR81 HR83

High vacuum activity in HER 12-5 and HER 12-6 which are new stations installed summer 2002. Total operational time so far this year:

HER 12-5 = 19 days and HER 12-6 = 132 days

HR85


Future Plans

• Continue adding more RF stations: higher beam currents in both HER and LER,higher LuminosityHER 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.


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.


Conclusions

• Records for peak and integrated Luminosities have been smashed in the last PEP-II run:– Peak L = 6.582 x 1033 cm-2sec-1 June 19 2003– Intg. L = 2.115 fb-1 May 21-27 2003 (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”).

high power rf system status

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