Minutes of the Feb 28, 2003 Tevatron Dept Meeting

1. Jerry reviewed three stores we had since last Friday: lumi bounced from
18.3e30 to 31.7 - store to store variations were due to stack size and in
#2271 we had scalloped pbar emittances again (emittances blown in the first
15 min at the start of HEP). Base H and V tunes bumped down for the next
store in order to fix scallops. Proton intensity is as before shutdown
(6300-6700e9 total).  There was a question: do we believe the CDF
luminosity ('cause CDF-D0 difference is now bigger than before shutdown)?
Answer(Ron): they (CDF) claim that they recalibrate their PMT gain often
enough so everytime they report correct luminosity.

2. Mike Syphers discussed results of recent coupling studies (JA, TJ, DE):
it is clearly seen in "flash" BPM readings that coupling being acquired
almost uniformly along the Tevatron. About 1 unit (10^-4 at 1 inch) of a_1
(skew quad) B-field component in each of 774 Tev dipoles is needed to
explain observed phenomena. And that is exactly what TD guys conclude from
recent measurements of the cold mass positions in several Tev dipoles
(measured "smart bolt" positions show that SC coils are moved down by 150
micron with respect to the iron yoke, that should give exactly 1 unit of
a_1). Alvin (being concerned of emm growth) asked how stable are skew
cuircuit PSs ? Answer was that they are probably 10 times more stable than
dipole corrector PSs.

3. Jim S reported that the longitudinal damper electronics are slightly
modified (new notch filters installed) and the damper is re-commissioned.
They see much less "leakage" at revolution harmonics than before (less
mode-to-mode or bunch-to-bunch cross talk is expected). Dampers
were tested in 36x0 and are going to be employed at 150 and 980-LB in the
next store. Damping time of beam phase oscillations is minute(s) - as
before.

4. Jim also summarized unsuccessful efforts to remove longitudinal line
from transverse Tev 1.7GHz Schottky signals: narrower (50-100MHz)
band-pass filter were installed in the tunnel, weird lines in spectra
disappeared but no betatron lines seen (Transv-spectrum contains only huge,
 70dB above noise floor, revolution harmonic line). AT 150 GeV, tiny
betatron lines were observed at right frequencies (<10dB above floor, and
again much smaller than Nxf_0 line amplitude). There is no idea why we
have strong longitudinal line in transverse Schottky (cooperative motion
in the bunch?). In order to understand the phenomena some 6MHz band pass
filter and/or Nxf_0 notch filter (similar to what is used in transverse
b-b-bunch damper)  will be installed. Transverse and/or longitudinal
tickling can be tried later as well.

5. Andreas borrowed a longitudinal tomography code from CERN (originally
proposed by Gerry Jackson) which uses ART algorithm, compiled it and used
data from Ron's Digital Mountain Range(DMR) display. He was able to
correct the DMR data for the trigger errors and cable dispersion to get
really nice and sharp 2D images - which show holes in the long phase space
distribution, "blubs", etc (esp at 150 GeV). From the reconstruction he
derived rms dP/P and found that dp/p variations are quite small (few% at
2xf_s), and, thus, can not explain "jumping" H-emittances at 150. That
looks to be quite useful tool, we need it in the MCR, and Andreas thinks
that can be done fast. Tan asked can the tomography be used to determine
RF voltage distortion due to wake-fields - Answer was:  not clear yet how,
but probably yes. Then there was discussion - do we want the SBD scope to
be placed in the tunnel: opponents (Jerry and JimS) are afraid of rad
levels at F-sector and think that dispersion correction can be taken in
the data processing; Vladimir (and Alvin?) just do not see much progress
with that correction in the SBD and are afraid that details (e.g. tails) of
the longitudinal distribution function will not be seen even after the
numerical correction.

6. Valery tried to measure P1/A1 optics but failed (twice) because
corresponding BPMs had errors of about 1.5 mm (due to wrong timing?) -
so, no progress.

7. Peter & Co found that stability threshold after the shutdown is quite
different compared to pre-shutdown era: a) now vertical instability
sometimes does not take place even with negative v-chromaticity (-3) while
before it occured even at small positive values; b) instability boundary
on C_v/C_h plane moved down by 3-5 units on both central orbit and p-helix
(for 230-250e9 single p-bunch at 150 GeV). Impedance estimates are coming
(need to analyse tons of data saved by head-tail monitor). He proposes to
use octupoles and keep C_v,h near zero as p-losses (inverse lifetime) are
proportional to |C_v,h|. He also plans to compare mutibunch and single
bunch stability thresholds. Jerry asked how well coupling was controlled
(as it matters for stability, too) - XL thinks it was not worse or better
than usual, though couple times over few hours they needed to decouple the
Tev. Another Q: can we employ more protons/bunch? - yes, if chromaticity
reduced, dampers or octupoles work and pbars will survive well.

8. Finally, Vahid made quite encouraging communication: he and Vic
Scarpine were able to ping the beam (1 mm hor), measure differential
motion of different parts inside single coalesced bunch (spaced by 0.8 ns)
and, from there, derive chromaticity - very close to C_h measured by a
standard method (df/f), within less then a unit. Eventually, we'd love to
have such a tool in the MCR - it's fast, can be used on the ramp, etc.
Next steps include - ping and measure vertical motion, C_v; determine
minimum kick still useful for analysis, etc.


Minutes recorded by V. Shiltsev, edited by R. Moore