RFCW Wake field current binning

[Benedikt]

Hi,

I try to simulate a passive c band cavity streaking experiment.
The beam has a strongly asymmetric current distribution: Narrow peak in the head (few 10 fs) followed by long tail (few ps) obtained from non-linear compression.

How does auto-binning (N_BINS = 0) calculate the number of bins?
If I set N_BINS to: 300 = (distance of first to last particle) / (point separation in wake file), I get a different result than for N_BINS = 0.

In our case the length of the current peak in the head is in the order of the point separation in the wake file.
Therefore, I expect auto binning is not adequate, as the current peak will not be resolved.
I expect not to get precise results for the wake in the head, as the spacing in the wake file is too large, but I expect a good consistent result for the tail, if the binning approximates the current appropriately.

The result for N_BINS = 300 and 3000 are very similar, whereas N_BINS = 0 gives a very different result.

If I set N_BINS manually I get warnings:
warning: only 0 of 100084 particles where binned (TRWAKE)
consider setting n_bins=0 in TRWAKE definition to invoke autoscaling
warning: only 84350 of 100084 particles were binned (WAKE)
consider setting n_bins=0 in WAKE definition to invoke autoscaling

Thank you very much for you support.
In case you need more information, just let me know.

Best,
Benedikt

[michael_borland]

Benedikt,

The number of bins is set to (max(t) - min(t)/dt+3, where max(t) and min(t) are the extremal values of the arrival time at the wake element and dt is the time spacing in the wakefield file. This is the optimal choice, since it encompasses all the particles. If you set the number of bins manually, you will either leave out some particles (n_bins too small) or include empty bins at the ends (n_bins too large).

If you are concerned about resolving a very short feature in your bunch, you need to decrease the time spacing of the data in your wake input file.

--Michael