Full Traveling Wave Field Map based on 1D Re and Im data #102
Description
From: jordan.byrne@postgrad.manchester.ac.uk
There is probably a better way to do this but this is what I did.
- So the mathematical equivalence of a TW cavity and two superimposed SW cavities is given in chapter 9 Appendix 2 of the Astra Manual (https://www.desy.de/~mpyflo/). It ultimately comes from the pi/2 relationship between sine and cosine.
- So given the real and imaginary 1D Ez field maps for a TW structure, we can set up two overlapping SW cavities in the input file. One using the real field map and second with the imaginary field map but with a pi/2 phase shift with respect to the real cavity.
Now if autophase is activated, OPAL will (correct me if I am wrong) autophase each cavity independently to find the phase of maximum energy. This will of course not enforce the pi/2 phase shift required to form the TW representation. So I ran my input file with autophase activated just to the point where I could see the autophase values for the two cavities. I then changed my input script to deactivate autophasing with APVETO=TRUE, and manually implemented the phase for the real cavity and then added the pi/2 shift for the imaginary cavity.
OPAL scales all field maps so that the max value is 1 MV/m so it is important to retain the correct combination of real and imaginary parts. In this case I just took the maximum amplitude from each file and set that as the voltage. For scaling the field, a scaling factor will need to be applied to both voltages.
I am not fully sure about my method of phasing the cavity. Moreover, I don't actually know how to calculate the phase of the actual TW cavity or how to do a phase scan. If anyone could give any comments on this, it would be appreciated.