Simulation of LSC in drift and Linac

[Biaobin]

Hi Michael,

Sorry to disturb you again. I am doing microbunching instability study in Linac with elegant. I have two questions about the LSC model in Elegant.

- Does elegant consider about the energy chirp effects to the whole beam?
Physically, the head should be accelerated due to LSC, the tail decelerated.
The following picture is a simple example with 1 meter lscdrift . Only energy modulation due to initial density modulation is seen. I tried increase the beam current and transfer distance, still can not see the chirp effects.


- I want to consider about the LSC in Linac, but keep Linearize=1, which will need to keep N_KICKS=1 to consider LSC. So I divide the cavity to many parts and make sure the single cavity length is small enough. Is this method valid ?

The example file is attached. The input.sdds file seems too large, which is generated using matlab to introduce the density modulation.

Best,
Biaobin

[Biaobin]

Hello,

When I am tracking particles with a linac, the following lattice layout of line0 and line1 will give different energy chirp calculated from the final particles distribution,

Code: Select all

W0: WATCH,FILENAME="W0.out",MODE="COORD"
W1: WATCH,FILENAME="W1.out",MODE="COORD"

CAV0: RFCA,L=15,VOLT="1.553178354259261e+10",PHASE=0.069167595843681,&
 FREQ=1e6,CHANGE_P0=1,END1_FOCUS=1,END2_FOCUS=1,LINEARIZE=0,fiducial=first

!8*CAV0 as a whole linac
CAV1: RFCA,L="15 8 *",VOLT="1.553178354259261e+10 8 *",PHASE=0.069167595843681,&
  FREQ=1e6,CHANGE_P0=1,END1_FOCUS=1,END2_FOCUS=1,LINEARIZE=0,fiducial=first

! using separate cavity
! By particle tracking, the final energy chirp is 10.4517, R65=10.4167 in *.mpr file
! ---------------------
LINE0: LINE=(W0,8*CAV0,W1)

! using a whole cavity
! Particle tracking agree with *.mpr's R65, both are 10.4167, agree with the linear
! theory calculation of energy chirp as: h= ( delta_U * cot(phi) * 2 *pi*f/c ) / (U_0 + delta_U)
! ---------------------
LINE1: LINE=(W0,CAV1,W1)

but R65 in the total transfer matrix of *.mpr file shows the same result in both lines. I can't understand the reasons causing
the differences. Is there a method to make the energy chirp of tracking results with LINE0 same with R65 in *.mpr ?

The elegant files and matlab scripts to get the chirp are attached.

Thanks in advance.
Biaobin