radiation damping from tracking
Posted: 03 Apr 2017, 03:42
Hi everybody,
for demonstration of synchrotron radiation effects I tracked a bunch of electrons with large initial energy spread and observed the longitudinal radiation damping. Then I determined the damping time from an exponential fit, but the value is 40-50% smaller than expected.
Here is what I did:
- use CSBEND dipoles with use_rad_dist=1
- define a bunched_beam: gaussian with 50 particles, sigma_dp larger than equilibrium
- define a watch element in parameter mode to get energy spread Sdelta
- track 2-3 times the expected damping time using Pelegant (2-3e4 turns)
- plot Sdelta as a function of Pass (or Pass times revolution time, here 548e-9 s)
- fit f(x)=a*exp(-x/tau)+offset via a,tau and offset
-> tau is only 50-60% of the expected value (taudelta from .twi output)
Find the files attached.
It seems not to be a problem of statistics or the fit. I tried with more particles and different seeds. The fit errors are about 1%. Any ideas?
Thanks in advance!
Jan
for demonstration of synchrotron radiation effects I tracked a bunch of electrons with large initial energy spread and observed the longitudinal radiation damping. Then I determined the damping time from an exponential fit, but the value is 40-50% smaller than expected.
Here is what I did:
- use CSBEND dipoles with use_rad_dist=1
- define a bunched_beam: gaussian with 50 particles, sigma_dp larger than equilibrium
- define a watch element in parameter mode to get energy spread Sdelta
- track 2-3 times the expected damping time using Pelegant (2-3e4 turns)
- plot Sdelta as a function of Pass (or Pass times revolution time, here 548e-9 s)
- fit f(x)=a*exp(-x/tau)+offset via a,tau and offset
-> tau is only 50-60% of the expected value (taudelta from .twi output)
Find the files attached.
It seems not to be a problem of statistics or the fit. I tried with more particles and different seeds. The fit errors are about 1%. Any ideas?
Thanks in advance!
Jan