Unexpected values of effective aperture

[Björklund]

Hi,

I'm currently doing some simple scans of the centroid angle of the beam going into a beamline, to get a feeling for the angular acceptance and where charge is lost (which I recently asked some questions about at viewtopic.php?f=15&t=1157&p=4769#p4769). I plot the beam centroids +- beam rms size together with the effective aperture values from the .twiss output file, as given by a series of MAXAMP elements.

I originally did this by changing the centroid offsets in @bunched_beam, but as was suggested in the above linked thread, I inserted a MALIGN element at the start of the beamline to enable parameter scanning. However, when I did this, the previously straight lines of the aperture went "wonky", for lack of a better word. I have attached two plots of this - one with the beam angles set in the @bunched_beam, and one with the angles set in the MALIGN element. The plot of interest is the third from the top, the apertures is drawn with solid, black lines. Clearly, in the MALIGN case, the aperture seems related to the beam.

Is there something I'm misunderstanding about how the effective aperture works here, or what it is actually representing? Is there a better way of extracting just the physical aperture? The aperture plotted in the MALIGN case is clearly small when the charge loss is high, but I would like to just plot the physical aperture...

Best regards,
Jonas

[michael_borland]

Jonas.

Sorry for the late reply. I missed this one.

The "effective aperture" is basically the aperture relative to the central trajectory. Hence, if the beam is steered over to one side to position X, the effective aperture will be A-X, where A is the physical aperture.

--Michael