Minutes of the July 15, 2005 Tevatron Dept Meeting

* Five stores have been started this week with luminosities ranging from
69 to 80 E30 cm^-2 s^-1.  Lack of pbars was the main reason for lower
luminosities.  Three stores ended intentionally, one with a quench caused by
longitudinal instability for proton (#4271), one still in progress.  A problem
with the Accumulator main bend bus allowed two shifts of study time spent on
investigating possible new working points in the Tev (near 0.5 or near 2/3),
tune tracking, attempting to use crystal collimator, exercising octupoles at
low beta, and measuring tunes without the downstream pair of Schottky plates
at A17.  The Tev suffered for two days from longitudinal instabilities (see
below).

* Ever since the 4th of July weekend, the proton RF phase noise was larger
than usual causing small bunch length blow-ups, but reducing the longitudinal
damper (mode 1) gain was helpful.  However, in store 4269, phase noise was 
very bad, and neither raising nor decreasing damper gain helped.  Eventually, 
there was a large instability that dumped lots of protons out of the buckets.
The store survived, but luminosity dropped 20%, and Xiaolong needed to come in
to sweep the TEL in the abort gaps to remove excess beam.  Experts checked out
the RF and damper system after the store, but no obvious problem was 
identified.  The problem worsened for the following store (#4271), and ended 
in a quench after only 1.5 hours.  Experts spent another extended period 
investigating.  It was found serendipitously that adding an open cable to a 
longitudinal damper output improved the phase noise, although the reason isn't
immediately obvious.  In addition, the PA on station #5 (pbar cavity) was 
replaced, and the resonant frequency of cavities 5 and 7 were changed slightly.
A mode 0 damper can be made to work and incorporated in less than a shift, 
if needed.  No instabilites were observed in the subsequent 36x0 and HEP
stores.

* Aisha provided a status on the Longitudinal Phase Meter (LPM).  The LPM
can measure the longitudinal phase of the 36 proton bunches.  Currently, only
the phase of P1 is available via ACNET (and it was very valuable 
for investigating the longitudinal instability problem mentioned above!), but
it is possible to extract data for all bunches from two internal circular
buffers that can be started and stopped on TCLK events.  There was some 
discussion about why the reported phase is not zero for fixed energy, and why
there is a ~2 deg difference between the phases reported at 150 and 980 GeV.
The Tev Dept should request additional features, e.g., getting the data
for all 36 bunches into ACNET, devices for setting the clock events for 
starting, stopping the circular buffers.

* Alex showed results of doing closed orbit bumps to confirm the discrete 
coupling sources observed near D16 and A38 in differential orbit measurements.
He did a series of 3-bumps near those locations and looked at the cross-plane
response.  The largest cross-plane oscillations (~1 mm) were observed in
VD17 and HA38 bumps.  TD reported their records indicate that survey lugs on 
the D16 and A39 quads were rotated.  Alex's measurements agree with the roll
direction and are not far off from the TD measurements.  We can realign those
quads during a shutdown period.

* Alex also showed progress on modeling the optics for the 28 cm beta* and 
new working point tunes near 0.5.  For the 28 cm beta*, the horz beta beating
is better overall. The vertical beta beating is larger in the short arc and 
smaller in the long arc, but better overall.  The dispersion at the IP is 
smaller, too.  All the quad magnet current changes are OK, but a couple of 
trim quads are close to the 50 A limit. He is simulating beam-beam effects 
with new optics now. Regarding the half-integer working point, Alex showed a 
plot illustrating how the beam-beam tune shift decreases as the tune 
approaches 0.5 for a constant xi parameter.  Near 0.5, the beta-beating is 
about twice larger than for the current lattice, but the Q39 circuit can be 
used to reduce the horz beta-beating.  The existing quads can be used reduce 
the beta-beating by a lesser amount.

* Eliana showed results from TBT data taken for a working point tunes near 2/3
(150 GeV) and near 1/2 (150 GeV and low beta).  The fast decoherence
at low beta allowed Eliana to use only the first 256 turns of data, rather
than the 1024 turns used for the 150 GeV analysis. For the 1/2 point, the 
measured beta-beating was up to 40-50% compared to the current model.  She was
able to correct the low beta beta-beating substantially by changing only 2
quads, but her solution would require an additional power supply and cables
to split the B0Q2D trim circuit.  The beta* would likely change, too.  
Analysis will continue offlien.

* Study topics being planned for the next week: 28 cm beta*; additional 
TBT measurements at low beta for 1/2 working point; measuring momentum
aperture for 1/2 working pt; differential orbit measurements at 150 GeV; using 
the C100 application to measure coupling.

Minutes recorded by R. Moore