rf system status and upgrades

Peter McIntosh, PEP-II MAC Review, April 15-17 20041

RF System Status and Upgrades

By: Peter McIntoshKlystron Department

Klystron Ron Akre RF system components and electronicsTransverse Feedback SystemDiagnostics and Operational Support

ARD-A John Fox Longitudinal Feedback SystemDiagnostics and Operational Support

ESD Mike Browne LLRF System UpgradesDiagnostics and Operational Support

PEP-II Machine Advisory Committee ReviewApril 15-17 2004


Summary

• PEP-II RF Systems– Configuration Inventory

• Klystron Status• RF System Operation

– Limitations– High Power Component Aborts

• Upgrades– New RF Stations

• Splitting a HER 4-cavity Station!– New LFB Kickers in LER

• LLRF System Issues • Conclusions


A Typical PEP-II RF System

1.2 MW Klystron

Circulator

Control Racks

Penetration

Load


PEP-II Station Configuration

Number of Cavities per RF Station

HER Presently

Oct 2004

Dec 2005

Oct 2006+

LER Presently

Oct 2004

Dec 2005

4-1 2 2 2 2 4-1 0 0 2

8-1 4 4 4 2 4-2 0 2 2

8-2 0 0 0 2 4-3 2 2 2

8-3 4 4 4 2 4-4 2 2 2

8-4 0 0 0 2 4-5 2 2 2

8-5 4 4 4 2

8-6 0 0 0 2

12-1 4 2 2 2

12-2 0 2 2 2

12-3 4 4 2 2

12-4 0 0 2 2

12-5 2 2 2 2

12-6 2 2 2 2

Total 26 26 26 26 Total 6 8 10


Klystron Location Filament Hours Comments

SLAC S/N 01 HER 12-3 37,504

SLAC S/N 02 Rebuild 0 Gun ceramic failure - rebuilding at SLAC - expected Sept 2004

SLAC S/N 03 HER 8-3 4,952

SLAC S/N 04 HER 8-5 4,382

SLAC S/N 05 HER 8-1 312 Installed March 2004

SLAC S/N 06 Construction 0 Expected May 2004

Philips S/N 01 HER 12-5 32,704 Hot spot in output waveguide, minor repair at SLAC Sept 2000

Philips S/N 02 HER 4-1 41,298

Philips S/N 03 LER 4-5 38,877

Philips S/N 04 SPARE 34,146 Removed from HER 8-1 March 2004

Philips S/N 05 LER 4-3 26,529 Intermittent heater short, rebuilt CPI Dec 2001

Philips S/N 06 HER 12-1 20,029 Anode failure, rebuilt at SLAC June 2002

Philips S/N 07 Rebuild 16,040 Anode failure currently at CPI - expected May 2004

Philips S/N 08 HER 12-6 26,379 Anode failure, rebuilt at CPI July 2002

Marconi S/N 01 LER 4-4 24,414

Marconi S/N 02 Failed 4,729 Vacuum leak, awaiting repair

Marconi S/N 03 SPEAR3 1,348 Vacuum leak, rebuilt at CPI Aug 2003 - New Collector

Marconi S/N 04 SPARE 4,938 Vacuum leak, rebuilt at CPI Aug 2003 - New Collector

Klystron Status

Original tube life expectancy was ~ 30k hours!


Cavity ParameterHER LER

Limit Jun 2003 Apr 2004 Apr 2005 Limit Jun 2003 Apr 2004 Apr 2005

RF Voltage/Ring (MV) 19.5 12 16 16 6.8 3.6 3.8 5.05

Number of Klystrons 9 7 8 9 4 3 3 4

Number of Cavities 26 24 26 26 8 6 6 8

Gap Voltage/Cavity (kV) 750 500 615 615 850 600 633 631

Dissipated Power/Cavity (kW) 75 34 51 51 97 48 54 53

Beam Power/Cavity (kW) 243 166 191 219 356 208 261 261

Total RF Power/Cavity (kW) 319 198 244 270 453 256 315 314

Klystron Power (kW) 957 738 826 829 951 545 683 683

Beam Current (A) 1.75 1.1 1.38 1.58 3.85 1.8 2.23 2.91

From June 2003 to April 2004Peak Luminosity increased by 21%

HER Beam Current increased by 15%LER Beam Current increased by 14%

Cal

cula

ted

Mea

sure

d

Peak Lumin. (1033 cm-2sec-1) 6.582 8.339 >10? 6.582 8.339 >10?

System Operation

HER Station Gap Voltage (kV) Klystron (kW)

4-1 720 730

8-1 500 830

8-3 630 920

8-5 630 890

12-1 510 680

12-3 650 900

12-5 690 830

12-6 670 680

Average 609 808

LER Station Gap Voltage (kV) Klystron (kW)

4-3 630 680

4-4 630 740

4-5 635 660

Average 632 693


HER 8-1 and 12-1 Cavity ArcsStationCavity kly circ 1vac 1air 2 3 4 Total kly circ 1 2 3 4 Total kly circ 1 2 3 4 Total kly circ 1vac 1air 2vac 2air TotalJ an. 1 4 1 6 0 1 1 1 3 0Feb. 1 10 1 12 0 0 0March 5 5 0 1 1 0April 6 6 1 1 1 1 1 1May 2 2 1 1 1 1 0J une 0 0 1 1 0Sept 0 4 4 0 0Oct 2 2 1 12 13 1 1 0Nov 2 2 1 1 1 3 1 1 0Dec. 1 1 0 1 1 0J an. 0 0 0 0Feb. 6 6 1 1 0 1 1March 0 4 4 1 1 2 3 3April 0 2 2 0 0Total 2 0 37 0 1 1 1 42 7 0 1 14 0 7 29 3 1 3 2 1 2 12 0 0 4 0 1 0 5

StationCavity kly circ 1vac 1air 2 3 4 Total kly circ 1 2 3 4 TotalJ 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 0Oct 1 1 2 0Nov 1 1 1 1Dec. 1 1 1 3 0J an. 2 2 0Feb. 3 3 0March 3 1 4 1 9 2 2April 2 2 1 1Total 10 3 11 0 4 5 2 35 0 0 3 3 0 1 7

Station HR25 HR26Cavity kly circ 1vac 1air 2vac 2air Total kly circ 1vac 1air 2vac 2air TotalJ an. 0 0Feb. 0 1 1March 0 0April 0 0May 0 0J une 1 1 0Sept 1 1 2 4 6Oct 0 8 8Nov 1 1 1 14 1 16Dec. 0 1 4 2 7J an. 0 3 3Feb. 0 13 1 14March 1 1 1 10 11April 0 2 9 11

Total 1 1 2 0 0 0 4 7 0 65 0 4 1 77

HR83 HR85 HR41

HR21 HR23

HR81

Jan 2003 – April 2004

HER 8-1 and 12-1 cavity arcing due to increased SR from upstream HER and LER injection.

HER 4-1 not operated before Dec 2003.

RF processed the station for 10 daysover the xmas break, station has run routinely at high voltage since Jan 2004 without any major problems.


HER 4-1, 12-1,12-6 and LER 4-5 Power Limits

• 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.

• 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.

Multipacting?

HER 12-1


Power Limitation Example – HER 8-1

Dec 9 2003


High Power Component Aborts – HER 12-6

• 12-6 Cavity A arcs• If an arc occurs at

the window, have seen in the test lab that the field takes 25 – 30 s to decay.

• The breakdown event must therefore be occurring in the cavity itself.

• About to install acoustic and video monitoring of this cavity to identify the breakdown source suspect movable tuner!

Field decay time ~ 2s


High Power Component Aborts - HVPS Issues

• SCR crowbar stacks:– HER 4-1, 8-1, 12-5 and 12-3 had a number of

transformer arcs since Dec 2003.– Number of SCR components have failed following

replacement in early 2003 oil leakage and breakdown.

– Leaking SCR stacks have been replaced again!– Power Conversion Group working closely with Eupec

to replace faulty units under warranty.

• SCR stack voltage dividers:– Dividers limit the voltage to each SCR device.– A number of dividers have also been defective and

replaced.


HER 12-1HER 12-1HER 12-2

RF System Upgrades – HER 12-2


RF System Upgrades - New LFB Kickers

• As VRF in LER increased bunch length reduces.• HOM heating damage of LFB kicker feedthroughs and

cables, which has limited LER currents:

• In collaboration with INFN-Frascati and KEK, a new LFB cavity kicker has been designed and fabricated at SLAC.

• A new high power, broadband feedthrough has also been designed at SLAC and manufactured by industry.

• 2 kickers will be installed in summer 2004.


LFB Kicker Design

• Existing drift-tube kickers have directivity HOM power extracted via the 2 load ports

• New cavity-kicker has no directivity HOM power extracted via all 4 coupling ports, less power/feedthrough

• New cavity-kicker has twice the shunt impedance of drift-tube kicker more efficient!

12kW 14kW

Beam Induced


New High Power RF Feedthrough

7/8” EIA Connector

Alumina RF Seal

Boron Nitride

Vacuum Interface

To Kicker

To Amplifier

or Load

7/8” EIA Connector

Glass Vacuum Seal

Boron Nitride

Vacuum Interface

To Kicker

To Amplifier

or Load

VSWR = 1.3

Back-to-back Feedthroughs


Port p1 (Input) Port p2

(High Power Load)

Port p3(Outpu

t)

Port p4 (High Power

Load))

Circulator(S/N

970759/2002)

Circulator(S/N

970762/2002)

LFB Kicker Cold Testing


LLRF System Issues and Upgrades• PowerPC Implementation:

– Older NI IOC CPU saturation. – Newer Motorola PPC IOC reduced CPU usage from >95% (typical) to

~10%.• Clock Module Failures:

– A number of modules replaced since Dec 2003.– Connector failures and module overheating.

• Stuck Comb modules:– Large number of aborts due to stuck combs (27 since Sept 2003).– New comb module will alleviate these problems.

• Module Upgrades:– New modules required VXI firmware revisions to work with PPC IOC.– Needed to retroactively update older modules also.– Development of a single side-band comb module (see Dmitry’s Talk).– New low group delay woofer (see Dmitry’s Talk).

• Temperature Stabilisation:– New RFP modules have shown increased sensitivity to operating rack

temperature variations slow station phase drifts (see Browne’s Talk).– Currently investigating improvements in stabilizing internal RFP

components as well as rack cooling circulation and regulation (see Browne’s Talk).


Conclusions

• During this last PEP-II run, beam currents in both HER and LER increased by 15%.

• New HER 4-1 station operated routinely since Dec 2003.• Installed Philips klystrons are currently limiting the RF power available

in the HER.• Systematically replacing ageing Philips klystrons with new SLAC built

tubes.• Cavity voltages being limited in HER 8-1 and 12-1 due to synchrotron

radiation from upstream injection locations:– Splitting 12-1 this summer will help!

• HER 12-6 cavity A arcs many aborts since Dec 2003:– New diagnostics will hope to identify the problem.

• HVPS SCR’s are still failing and SLAC’s Power Conversion Group working closely with Eupec to have units replaced/repaired under warranty – now in progress.

• New LFB kickers will allow higher beam currents in LER.• LLRF module upgrades and improvements continue to increase the

various feedback operating margins: – achieve more stable and reliable LLRF system.

rf system status and upgrades

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