Error using RFCW with LSC

[lewellen]

When attempting to use the RFCW element with longitudinal space charge enabled, I am getting the following error:

tracking through L01.KSN.TN
Error: distance between LSC kicks for L01.KSN.TN at z=3.148100e+001 is too large.
Suggest reducing distance between kicks by factor 2.924681e+000

Here is the lattice fragment showing this element's definition:

L01.KSn.Tn: RFCW, L="sTankLength", cell_length="sTWcellLen", &
volt="90775805.502607062", freq="sFreq", phase="36.9529639842", &
change_P0=1, end1_focus=0, end2_focus=0, &
zwake=1, trwake=1, tcolumn="t", &
wxcolumn="W", wycolumn="W", wzcolumn="W", &
zwakefile="wakes\LCLS\longitudinal\sz_5um_10mm.sdds", &
trwakefile="wakes\LCLS\transverse\sx_5um_10mm.sdds", &
interpolate=1, N_kicks=0, smoothing=1, LSC=1, &
LSC_bins=1024

Given this is a "normal" 84-cell SLAC-type S-band linac tank, it looks like the required minimum kick distance is 1 meter, and N_kicks should reduce the distance between kicks to just under one meter. However, I still get the error, with a smaller suggested reduction factor. I have to increase N_kicks to ~ 10 to stop the error from reappearing.

Is there a recommended value for N_kicks (or equivalently, spacing between kicks) when using LSC?

Thanks,

- John L.

[michael_borland]

John,

The requirement is that dL = 0.1/kSC, where kSC=2/(R*sqrt(Ipk/IA/gamma^3)), where R is the beam radius, Ipk=peak current, Ia=Alfen current.

Unfortunately, I can't give a simple recommendation for how to set N_KICKS beyond using this formula.

--Michael

[lewellen]

Michael,

Thanks; that's great.

Cheers,

- John L.