Set up for LER RF stations

 

(BTW: Chimera isn’t as pretty for web pages as Explorer or Netscape)

Modified Last Updated Friday, 21-Sept-2005 17:00:00 PST

Please send e-mail to kkubler@slac.stanford.edu if there are any updates needed.

 

PROCEDURE:

 

  1. Reconfigure the LFB (If changing the total gap voltage)
  2. Reconfigure the Low Group Delay Woofer  (If changing the total gap voltage)
  3. Change Comb Filter Settings (if change total gap voltage) and Enter Station Gap Voltages (by hand or with loading EPICS configs)
  4. May need to change the woofer setup
  5. May need to change the Power Balance Feedback Setup   
  6. Check collision phase for luminosity
  7. May need to alter the bucket pattern to keep charge/bucket similar for luminosity

 

SUMMARY OF SETTINGS for 3 or 4 LER RF stations:

 

A table of optimized configurations is no longer maintained given the dynamic nature of the RF setup.  Rather, “snapshots” of the RF setup can be taken from the SCP with “PEP_RF_SNAPSHOT.edl” from PEP-II Tune Panel à EPICS Display Panel à PEP RF Setup.  These snapshots of relevant parameters are then regularly saved to the MCC elog for reference.   

 

1. RECONFIGURE THE LFB if you are changing the total gap voltage.

 

MANUAL OPTION:

 

EPICS CONFIG LOAD: There is no such option at this time.

 

2. RECONFIGURE THE LOW GROUP DELAY WOOFER (LGDW) if you are changing the total gap voltage. 

 

MANUAL OPTION:

·         From LER LFB panel, select LGDW.  

·         Select “LER SETUP”

·         Select “LER SAVE/RESTORE”

·         In text field enter the appropriate file and press RETURN while the mouse is in the text field.

·         Select “RESTORE” to load file

(You should not need to STOP and RUN the LFB to pick up LGDW changes?)

 

EPICS CONFIG LOAD: There is no such option at this time.

 

3. COMB FILTER SETTING (if you are changing the total gap voltage) and STATION GAP VOLTAGES. 

 

There are only three possible comb filter setups available at a time.  For each different gap voltage, a new comb filter coefficient file is made.  

 

** LER RF 4-5 is an exception ** It is running a “new” type of comb filter module.

 

The comb filter setting and station gap voltage may be entered either manually (i.e. you type it in one station at a time) or with loading an EPICS config.

 

MANUAL OPTION for OLD TYPE COMB FILTER MODULES:

Load the appropriate filter set.  In order to activate these one has to do the following on each of the 16 comb filter control panels (Module Diagnostics --> CFM1 and CFM2):

·         Place module in "Load" mode (set of buttons labeled "state" at the bottom of the panel)

·         Push "IIR" button (to the right of the IMCF file name).  Make sure the status line on the top reports success.

·         Select desired comb set (0, 1, or 2).

·         Return the module to the "run mode"

 

Load the appropriate gap voltages.

 

EPICS CONFIG LOAD for OLD TYPE COMB FILTER MODULES:

William Colocho and Nancy Spencer have made SCP config files for use in the parking of a given LER RF station.  The configuration region is called LER_GAPV (SCP path INDEX -> CONFIG -> MISC CONFIG -> EPICS CONFIG -> LER GAP VOLT) and the NORMAL directory has setups for parking each station for the 2004 PEP-II run.  Configs for 2005 are still in the works.

 

These new configuration files save the following parameters for each RF station in LER:

1.                  Desired gap voltage

2.                  LFB woofer link state (ON/OFF); meaning woofer is turned on or off.  This does not load LFB configs.

3.                  Comb filter set value (0, 1, or 2)

 

MANUAL OPTION for NEW TYPE COMB FILTER MODULE for station 4-5:

 

http://mccelog.slac.stanford.edu/elog/wbin/elog_item.php?elog_id=17297  (Dmitry’s latest filenames & instructions)

http://mccelog.slac.stanford.edu/elog/wbin/elog_item.php?elog_id=16167  (More general help about the new CFM Type 2).

 

BACKGROUND COMB FILTER INFO: 

My Q: What do comb filters do? 

Dmitry A: "Comb filters provide feedback gain at the synchrotron sidebands so that the effective impedance of the RF cavity is reduced.  These filters are adjusted to peak at the synchrotron frequency using several coefficients.  If the gap voltage changes, the synchrotron frequency moves.  Then the comb filter does not peak at the right frequency and the feedback gain at Fs is reduced."  (Fs = synchrotron frequency)

 

4. MAY NEED TO CHANGE THE WOOFER SETUP (EPICS “FEEDBACK” PANEL FOR EACH STATION).

 

MANUAL OPTION:

When changing the woofer complement, keep in mind that not all stations may have been set up for woofing, and if too many stations are woofing, the system may become longitudinally unstable and abort.

 

EPICS CONFIG LOAD:

This step is handled by the EPICS config load of the gap voltages, comb filter set, and LFB woofer link ON/OFF in the previous step.

 

BACKGROUND WOOFER INFO:

My Q: What does a woofer really do?  My guess: Since the LFB system has a limited bandwidth and is setup to handle higher-frequency, higher order modes, the woofer somehow removes lower frequency noise from the RF stations.  Without any woofing, would I see longitudinal motion aborts? 

 

Dmitry A: "Pretty close.  LFB is actually quite wideband and handles both high and low frequency modes.  However the growth rates of the low frequency modes (close to RF frequency and driven by the RF cavity impedance) are very high.  Without woofer, LFB would not have enough gain to stabilize the machine at high currents.  We send the low-frequency part of the feedback signal to the RF stations which act as a high-gain kicker."

 

5.  MAY NEED TO CHANGE THE POWER BALANCE FEEDBACK SETUP

 

MANUAL OPTION:

If the parked station was the reference station for the feedback loop, either turn off the loop or select a new reference station.  See http://www.slac.stanford.edu/grp/ad/op/PowerBalance/ for further help.

 

EPICS CONFIG LOAD: There is no such option at this time.

 

6.  CHECK COLLISION PHASE FOR LUMINOSITY

 

7.  MAY NEED TO ALTER THE BUCKET PATTERN TO KEEP CHARGE/BUCKET SIMILAR FOR LUMINOSITY IF OPERATING AT REDUCED CURRENTS.