Minutes of the Jan 12, 2007 Tevatron Dept Meeting

https://indico.fnal.gov/conferenceDisplay.py?confId=524

* Operations Summary (Dan Bollinger) - It was another good week for the 
accelerator complex - a record 44.9 pb^-1 were delivered to each experiment
over the official Monday-to-Monday reporting period.  Over the past 7 days,
there have been 6 stores with initial luminosities between 187 and 251 E30
cm^-2 s^-1 (new record).  Four of those stores were in the top 5 highest
initial luminosities.  The record store aborted after less than 3 hrs when 
T:SF (focussing sextupole supply) tripped off; all other store terminations 
were intentional.  The aborted store had another record - most pbars ever 
aborted during HEP = 2476 E9; that's not one to boast, but at least it was a 
clean abort (no quench).  TRF8 has tripped off during 3 stores this week, but
experts have not discovered the reason yet.

* Update on Pbar Injection Closure (Jerry Annala) - Ever since the MI BPM
electronics were updated, there has been large pbar injection steering errors
that cause significant emittance dilution (few pi mm mmrad) on the first
pbar transfer.  The Tevatron injection closure algorithm corrects the
steering errors well for subsequent transfers, but the A150 line trim settings 
from reverse injection tune-up (with protons) must get us closer to the 
desired trajectory.  After analyzing a series of shots, Jerry determined that 
subtracting 1 amp from the HT902, HT904 and VT901 settings derived from 
reverse injection tune-up should be sufficient.  Since those changes were
implemented in the sequencer (store 5166), the emittance dilution on the first
pbar transfer has been reduced greatly.  Still, it would be good to understand
why reverse injection tune-up does not provide good trim settings.

* Proton Scraping @ 150 GeV (Dean Still) - We want to investigate proton
scraping @ 150 GeV (especially longitudinally) to: 1) remove beam that would 
be lost up the ramp and through the squeeze anyway and 2) attempt to inject 
even more protons and then scrape them to get "brighter" protons without 
additional loss on the way to HEP.  The challenge is scraping a lot of beam 
(~10%) quickly and reliably without quenching.  After trying the D172 
collimator (at high dispersion location) to scrape just a few %, it was
estimated that scraping ~10% would require the nearby cold magnets to take
> 100 Rad - very likely too much.  Using the E01 "proton-removal" collimator
with the dogleg turned on worked quite well - the downstream magnets saw little
beam loss.  For store 5172, 10% of the protons were scraped (on central orbit)
in ~3 minutes, reducing the RMS bunch length from 2.88 to 2.79 ns.  During
pbar injections, the proton bunch length actually grew a little bit, whereas
protons are normally momentum-shaved by beam-bean effects.  The proton
lifetime during pbar injections was better (~factor 2) even with similar 
pbar intensities.  Proton losses up the ramp and through the squeeze were 
similar to typical values. We need to repeat this exercise for several shots 
to get a better understanding of the benefits.  There is a little work to do
to automate the process for operations.  It was suggested that scraping first
with E01 (lower dispersion) and then scrape with D172 (high dispersion) may
be helpful, too.

* New Pbar Cogging for Acceleration (Ron Moore) - In order to get pbars out
of the abort gap during acceleration, we tried a new pbar cogging value 
suggested by Yuri (see last week's meeting slides).  The value (VQCOG3=69.96
buckets) is only +2 buckets from the collision cogging (VQCOG3=67.96 buckets).
One command was added to the sequencer to do the cogging after pbar injection
is completed; the cog for collisions is still done after reaching flattop. The
new cogging worked fine - there were no expected beam losses at 150 GeV or up
the ramp.  As we cog during pbar injections, one sees peaks and valleys in 
the CDF proton halo - perhaps the valleys indicate better cogging values to use
while we wait between pbar injections.  We could develop more complicated 
cogging schemes to take advantage of possible proton lifetime improvements;
more investigation is needed. 

* Plans for Next Week (All)

   - Continue our recent record performances for CDF and D0!
   - Keep using the new pbar cogging scheme for HEP shots.
   - Try proton scraping @ 150 GeV again (Dean & Jerry, shot-setup)
   - TEL-2 studies (the usual crew, during HEP stores)
   - Crystal collimator (Dean, end-of-store)
   - Electron cloud (Xiaolong, proton-only)
   - Transfer line mismatch measurements with IPM (Andreas, shot-setup)
   - ...plus several others...