Date July 20, 2001
Attendees  P. Chu, S. Cousineau, M. Doleans, J. Galambos, J. Holmes, S. Danilov, S. Kim
D. Jeon, W. Wan
 
1) J. Galambos reported activities at Snowmass 2001. He noted that the SNS plays a 
prominent role in the proton driver working group discussions.
 

2) M. Doleans is working on an analytic treatment of the beam transport through an RF
cavity.

3) Sarah is benchmarking the K2 code and the ORBIT collimation routines. There is a large sensitivity
to small changes in collimator placement.

4) Paul Chu is creating an interface between trace3d and a Java application programing
architecture. The input file is being prepared through an XML interface.

5) Dong O Jeon is doing multiparticle studies of the phase scans for the DTL
and CCL. These results are slightly different from the previous single particle 
results found previously.

6) Sang ho Kim reported on the static Lorentz detuning results from JLab for the
medium beta cavity (k = 8 MH/MV/m^2). The actual detuning (including dynamic) 
will be very sensitive to precise mechanical boundary conditions, that are difficult to predict.

7) Slava Danilov has prepared an analytic model for the impedance of a finite
length kicker, including the effects of a ceramic chamber and ferrite. This
will be useful for estimating the injection kicker magnet impedance / film thickness.

8) Jeff Holmes has finished coding the 3D FFT space charge model with conducting wall 
BCs in ORBIT. He is now debugging it.














2) On RFQ/MEBT halo It is not obvious whether one can still claim that RFQ is
a good filter. It is better to plan for collimation in MEBT. It is likely that scraper is needed,
and it is possible that the halo pattern is systematic caused by FE characteristics as reported 
by Rod. However, the actual halo pattern may vary depending on tuning. Sasha suggests that
a good place is at the chopper location since it is upstream near RFQ. The phase advance between 
scraper and scraper target is pi/2, and between chopper and anti-chopper pi. It can be useful
to have two pairs of scrapers located pi/2 apart but it may not be necessary. 
 
3) Note that at Snowmass ESS reported that their design require a MEBT chopper rise time
less than 2 ns in order to eliminate anti-chopper (50% more space). Sasha quotes that
the space due to anti-chopper is about 25%.
 
4) On Lorentz detuning of SRF cavity
Ron reported exceedingly high analyzed Lorentz detuning K value (K~8) as comparing to
expected (K=2+/-1). This corresponds to about 1kHz frequency detuning, and significant
loss of RF power, although fortunately medium beta has larger power reserve. A efficient way
is to have active tuning using e.g. piezo sensor but Ron called in video that it is difficult
to retro-fit. Sang-ho talked with Yung and Marion on possible capacitive tuning in the
waveguide for better matching but the practice can be costly. 
 
5) On achievable SRF cavity gradient 
Thomas Roser reported at Snowmass BNL's proton driver plan using SNS frequency 
cavity but also 1.6 GHz cavity in order to achieve a accelerating gradient of 22 MV/m.
Sang-ho noted that given the time and possibility (polishing, Nb scanning) it is 
possible to reach 20-30 (up to 40 per TTF) MV/m accelerating gradient. The key is probably
not be in gradient itself but instead in magnetization (below 150 - 160 mT) before quench. 
 
6) Slava asserted the correlation between transverse instability threshold and halo generation in 
Slava's ORBIT simulation and prediction.
 
7) On ring collimation Jie reported that JHF quote their overall transverse collimation efficiency
of 99% and momentum collimation efficiency 95%, comparing with Nuria's one-pass efficiency
of 95% for doublet lattice and near 80% for FODO lattice. There seem to be a need to
calibrate in more detail the relation between one-pass and multi-pass efficiency (multi-pass
has to be much higher than one-pass efficiency?) to reconcile/understand the difference.
Sarah will contact Nuria on it.
 
8) We should have a plan to wind weak solenoid on ring vacuum chamber in the section
of collimation where the chamber is not under magnets. One needs to evaluate the solenoid
field needed to suppress secondary electron production without introducing magnetic 
field perturbation on the beam
 
9) With Slava's help, Sarah is considering modifying ORBIT to model electron accumulation
for a full e-p simulation. 
 
10) On ring injection kicker ceramic pipe coating Slava reviewed Piwenski's paper and 
noted the difference and possible typos. The newly derived result shows that the ceramic
wall thickness does not enter, but the conclusion seems the same a thin coat of 
material with conductivity (e.g. gold, under TiN), together with ceramic/ferrite reflection, 
can effectively shield otherwise large impedance by forcing current through the thin
layer of e.g. gold (much thinner than skin depth). According to Chen-Pi's mechanical
analysis, heating is ok. Kicker field penetration should also be no problem since it only
depends on skin depth. Slava still needs to check transverse impedance but it
it follows Panofsky-Wensel theorem, then it is also ok. 
 
11) permeability budget There is a need to evaluate and maintain a "permeability budget"
to monitor anything that can be magnetic. Such problem occurred on many machines
including FNAL recycler and CESR. There will be an estimate of all possible
contributions and then an estimate on the tolerance. Yannis will be on ring, Deepak on lines,
Sasha and Eugene on FE and linac. Stuart volunteered to collect everything. 
 
12) post meeting Jim Stovall reported that Ken Crandall propose to have a fast feed-forward to
adjust the phase of the HEBT energy corrector cavity so that the beam always arrive at
a zero crossing, thus eliminating inefficiency from phase error.
 
13) continued debate on the need and definition of magnet/power supply polarity convention
and local coordinate convention. The key is in (1) avoiding later confusion in engineering,
installation, and maintenance and (2) consistency in applications for commission/operations.
It is hard to believe that such a practice is not needed. 
 
14) Travel this week Eugene/Dong-o at LANL on CCL testing and next week Sasha at
LANL on two reviews. This week John/Jeff/Stuart at Snowmass and next week Jie at
Snowmass. Sarah plan to visit BNL early August. 
 
15) Ken Reece brought proposal for protection against exceedingly high beam density on target
and dumps. The three identified "critical" devices are (1) 8 injection painting kickers (2) 
monitor transfer matrices in each beam line and (3) in-beam harps