Outline

1. PEP-II LER RF High Current MDReportDan Van Winkle, Claudio Rivetta, Kirk Bertsche, Themis Mastorides

2. Outline • High Current Plan Review • Goals for MD • RF Operating Points • Grow Damps • Results • Summary and Plans • Asymmetric Comb Filters and Comb Rotation

3. Plan Review • 3 Blocks of Increases • Block 1 2600-2800 mA • Redistribute power balance • Tune RF stations • Take G/D HOM and LOM • Block 2 2800-3000 mA • Increase drive power 1W • Tune RF stations • Take G/D HOM and LOM • Block 3 3000mA+ • Increase drive powers 1 more Watt • Tune RF stations • Take G/D HOM and LOM

4. Goals • Determine potential limiting points in RF systems (reflected power, collector power etc) • Measure longitudinal growth and damping rates at high currents to validate model and new preamps. • Check Asymmetric comb filter feasibility and learn impacts of changing comb filters with beam in machine. Also check extreme (-25 degrees) comb rotation.

5. Day 1 Thursday August 30

6. Block 1 Results • We changed power balance feedback to put higher load on LR4-3 (SLAC tube). Settings were: • LR4-2 98% • LR4-3 120% SLAC Tube • LR4-4 78% Slated for replacement • LR4-5 100% This worked very well.

7. Block 1 Results • Pushed currents easily up to 2800 mA • Collector powers were well below the 1.1 MW we chose for drive power changes • Transfer functions were easily tuned with only very minor changes HER Klixon Trip

8. Block 2 Results • We were so successful that we decided to push on that same day. Per plan increased klystron drive level 1W. At 2860 mA we were pushed into a reflected energy trip point on LR4-3 (twice). • Investigations showed significant errors in the diode signal vs. the IQ detector signal. (IQ read back 80kW Diode read back 180kW)

9. Block 2 Results • IQ vs. Diode Errors Significant HOM signals in reflected power signal cause erroneous readings on diode detector. Adding a Low Pass Filter on all inputs for all cavities will be necessary for next run

10. Block 2 Results • We added low pass filters to LR4-3’s reflected power cables but were out of time on Thursday to continue pushing .(Access for cooling issue in HER) Significant Finding of the Day Reflected energy signals from cavites contain significant amounts of HOMs which contaminate the diode detector reading. We had reported on this before, but has not been a limiting factor up to now…

11. Day 2 Friday August 31

12. Block 2 Results • Resumed where we left off and rapidly climbed to 3000mA • Abort with LR4-2 Cavity 2 vacuum/arc • Plagued with BaBar radiation aborts (tune mgmt) • Finally ended up with LR4-3 crowbar at 2950 mA • Luckily we had stopped at 2900 mA to get significant grow damp data and station transfer function data.

13. Block 2 results Raw Grow Damp Data

14. Block 2 results Processed Grow Damp Data High Order Modes -------------------------------------------------------------------------------------------------------------------------------- Mode# G.rate G.freq D.rate D.freq -------------------------------------------------------------------------------------------------------------------------------- 806 0.449+/-0.008 4063+/-1 -1.1+/-0.04 4057+/-8 807 0.321+/-0.01 4041+/-2 -1.67+/-0.2 3881+/-2e+01 809 0.365+/-0.009 4071+/-1 -0.905+/-0.04 3976+/-6 -------------------------------------------------------------------------------------------------------------------------------- Low Order Modes (71=-1, 70=-2; ....) -------------------------------------------------------------------------------------------------------------------------------- Mode# G.rate G.freq D.rate D.freq ------------------------------------------------------------------------------------------------------------------------------- 67 1.86+/-0.02 4043+/-4 -1.77+/-0.04 4158+/-1e+01 69 1.64+/-0.008 3994+/-1 -2.07+/-0.03 4038+/-6 70 1.25+/-0.03 3869+/-4 -2.42+/-0.07 3896+/-2e+01 71 1.18+/-0.02 3861+/-4 -2.5+/-0.1 3749+/-2e+01

15. Block 2 results Gap Transient in LER front end is approaching the +/- 128 Limit

16. Block 2 Results • No Real breakthroughs on Friday • Grow damp data shows good margins for LOM and HOM control • New LER current record (barely) • RF stations tuned and ready to run at 3A. • RF station transfer functions show good loop stability at this comb rotation (10 degrees)

17. Block 2 Conclusions • Cavity reflected energy will be an issue at these higher currents from actual power and calibration errors. • Filters will need to be installed in every station on the cavity reflected power detector • The phase transient is pushing towards the limit of +/- 128 Counts. For higher current operation, a small attenuator should be added to the LER LFB beam comb signal.

18. Day 3 Saturday September 1

19. Block 3 - Saturday • An extra 2dB was added in front of the LFB front end and the gains adjusted accordingly.

20. Block 3 - Saturday • Saturday was spent trying to again push the current in the LER. We were limited unexpected HER beam losses. (HR12-1 cavity vacuum) HR12-1 was finally parked. • Record Current reached 3026mA • High HER current appeared to be important for maintaining high LER and when HR12-2 finally had to be parked due to HVPS oil temperature, we threw in the towel.

21. Summary • We were able to reach record current (just barely) in the LER. • We did not find a LER limit due to RF power, damping rates or station stability, but the overall machine reliability came into play. • All stations will need low pass filters in front of the reflected power inputs in the IQ&A modules • We did not evaluate overall heating or other current related effects. • Damping rates seem sufficient to go higher in current

22. Plans • RF Meeting on Monday to discuss downtime issues. • Preliminary List: • Filters on reflected power signals for all stations • Calibration of IQA and Diode signals on IQA modules • Discussion of running Tune Cavities and Make Poly's routinely during the next run • Removal and storage of old pre-amplifiers • New monitoring equipment for finding HV power dips? • Cavity Vacuum problems in HR12-1 • Software Development (Add diode power to RF panels? EPICS changes…who will support us?) • HR4-6 Power Supply Plan • LFB phase fault file recorder (Another Gage board?) • Oscillating Tuner Loops • HVPS Oil Tank Temp • Limiter set point for LLRF (R Akre) • Gap Transient Issues (FJD)

23. Brief report on Asymmetric Combs and Comb Rotation Comb rotation and asymmetric combs are techniques to improve impedance control • Ran combs at +25 degrees comb rotation to look for peaking • Also ran asymmetric comb filter to evaluate transfer function and comparison to model predictions

24. Brief report on Asymmetric Combs and Comb Rotation Second, Rotate 25 degrees First, Tuned Optimally Finally, Asymmetric Combs

25. Brief report on Asymmetric Combs and Comb Rotation • Comb rotation worked perfectly and thanks to new pre-amps, no excessive peaking in transfer function. • We used to see +10 dB of peaking • Asymmetric combs look weird, but they should. Comparisons with model underway. • Full affect for both items will be evaluated with additional grow/damp studies at current.