RF System Status and Upgrades

RF System Status and Upgrades By: Peter McIntosh Klystron Department Klystron Ron Akre RF system components and electronics Transverse Feedback System Diagnostics and Operational Support ARD-A John Fox Longitudinal Feedback System Diagnostics and Operational Support ESD Mike Browne LLRF System Upgrades Diagnostics and Operational Support PEP-II Machine Advisory Committee Review April 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 Control Racks Load Circulator Penetration 1.2 MW Klystron

PEP-II Station Configuration

Klystron Status Original tube life expectancy was ~ 30k hours!

Calculated Measured System Operation From June 2003 to April 2004 Peak Luminosity increased by 21% HER Beam Current increased by 15% LER Beam Current increased by 14%

HER 8-1 and 12-1 Cavity Arcs 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 days over the xmas break, station has run routinely at high voltage since Jan 2004 without any major problems.

HER 12-1 Multipacting? 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.

Power Limitation Example – HER 8-1 Dec 9 2003

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! High Power Component Aborts – HER 12-6 Field decay time ~ 2s

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

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! Beam Induced 12kW 14kW LFB Kicker Design

Boron Nitride Boron Nitride To To Amplifier Amplifier or Load or Load Vacuum Interface Vacuum Interface VSWR = 1.3 7/8” EIA Connector 7/8” EIA Connector To Kicker To Kicker Glass Vacuum Seal Alumina RF Seal Back-to-back Feedthroughs New High Power RF Feedthrough

Port p3 (Output) Circulator (S/N 970762/2002) Port p1 (Input) Port p2 (High Power Load) Circulator (S/N 970759/2002) Port p4 (High Power Load) ) 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(seeBrowne’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