Date March 9, 2000
Attendees S. Danilov, J. Galambos, J. Holmes, D. Jeon,  S.H. Kim, J.G. Wang, J. Wei
 
Summary The purpose of this meeting was to report on the status of ongoing work.
 


J. Galambos summarized the activity regarding the SC linac in the last several
weeks, leading to the present design point. The previous design point of 6 
cavities/ klystron with a vector sum control suffered from a vulnerability to 
microphonics, and a waste of usable cavity gradient, if sorting is not 
possible. 

J. Holmes, S. Danilov and S. Kim developed a simple model for scoping 
transient analysis issues such as feedforward correction of cavity Q errors. 
Even for the present design there is concern on the specified microphonic 
noise distribution (presently specified as guassian with sigma = 25 Hz, and 
truncated at 6 sigma). The seriousness of this level  on pulse-to-pulse 
energy jitter and on emittance growth needs to be evaluated. The T3D code 
will be used to analyze the impact on emittance growth due to these 
microphonic errors.

J Holmes noted that he and S. Danilov had looked into the issue of retarded 
potentials on space charge, and concluded in was negigilbe for SNS. The status 
of the SNS code  suite was discussed. Benchmarking of space charge models to 
AGS Booster and PSR was discussed. The preliminary booster results need to be 
modeled, and revisiting PSR may be possible. Also, the idea of trying 
different proposed SNS working points on the booster was raised.

D. Jeon noted he encountered a problem modeling the HEBT bend with the linac 
code. The possibility of using the last linac cavity for focusing instead of 
acceleration was discussed (to reduce energy jitter). It was agreed to try 
and model this. 

J. G. Wang is the interface person with the target group. Among the concerns 
raised on this topic is the difficulty of meeting all the target 
specifications. Especially worrisome is the criteria that the last quad 
misalignment be < 0.1 mrad. 

S. Kim discussed superconducting cavity design optimization. He finds shapes 
capable of higher accelerating gradients, for the same peak surface field as 
LANL, and with acceptable magnetic fields. He has shown the work to JLab, 
and will forward it to LANL for comment too.

S. Danilov discussed the collimator impedance calculation. There is only a 
small dependence on the angle of the collimator leading edge. This will 
be checked by other calculations. 


5) action items
 
a) Galambos / Jeon - calculate the gross beam emittance growth due to 
microphonic errors, using T3D
b) Jeon - with multiparticle tracking, look at replaceing the last 
superconducting cavity as a focusing element, rather than an accelerating 
element.