RF potential by double RF system

[xhs05]

To whom it may concern,

Hi! It's Haisheng Xu who is using elegant in the study of double RF system. There was a problem in using double RF system to generate 'ideal-flat' RF potential. Wish to get your help! The details were described as follows:

I first calculated analytically the voltage and phase of both the fundamental RF cavity and the third harmonic cavity for achieving the so-called 'ideal-flat' RF potential condition. Then, the voltage and phase of both cavities were set in the elegant tracking. The ILMATRIX element was used to represent the one-turn map. SREFFECTS element was used to represent the synchrotron radiation effects.

However, when I turn on the radiation damping and quantum excitation in SREEFFECTS by setting 'DAMPING=1,QEXCITATION=1', I didn't get 'flat' distribution after tracking enough turns, as shown in the attached figure. The SREFFECTS was written in the .lte file in the following way:

Code: Select all

SR1: SREFFECTS,include_offsets=0,losses=0,damping=1,qexcitation=1, coupling=0.0

distribution when turning on the damping and excitation

If I turn off the radiation damping and quantum excitation in SREEFFECTS by setting 'DAMPING=0,QEXCITATION=0' (all the other settings were kept unchanged), The 'flat' distribution after tracking enough turns can be seen, as shown in the attached figure. The SREFFECTS was written in the .lte file in the following way:

Code: Select all

SR1: SREFFECTS,include_offsets=0,losses=0,damping=0,qexcitation=0, coupling=0.0

distribution when turning off the damping and excitation

It's very confusing. It seems to me that the radiation damping and quantum excitation introduce extra energy loss, which leading to the distortion of hte bunch distribution in the longitudinal phase space and the shift of the bunch centroid.

The scripts were attached. The folder 'Off' indicated the case without radiation damping and quantum excitation. The script 'Run_Me.sh' can be used to run the tracking.

Look forward to getting your kind help!

Regards,
Haisheng

[michael_borland]

Haisheng,

Sorry for the delayed reply. Without digging into all the details in your files, I think the reason is that you set all the cavity parameters the same in both cases. However, when you add synchrotron radiation, the phase of the main rf cavity must change. The phase of the harmonic cavity should not change, but its voltage must.

My TAPAs Android app (from the Google store) can calculate this for you.

--Michael

[xhs05]

Hi Michael,

First thanks a lot for your kind reply! I'll try to vary the phase of the main RF cavity and the voltage of the harmonic cavity following your kind suggestions.

However, In still don't understand why the RF settings should be different. In the two test ("damping=1,qexcitation=1" or "damping=0,qexcitation=0"), I always set the "losses=0". According to the manual, my understanding was that the energy loss due to synchrotron radiation should be ignored in both cases. Is this understanding correct?

Thanks!
Haisheng