### Beam loading simulation of two active cavity system by RFMODE

Posted:

**26 Aug 2021, 12:05**HI Michael,

I am studying the transient beam loading with gaps. I made the progress in semianalytic method to compute the bunch profiles which varies over the train of bunches with beam loading effect included. Now I like to simulate the beam loading with RFMODE and I have encountered the difficulties to correct them.

I am able to control the cavity voltage and its phase by using AMPLITUDE_FILTER and PHASE_FILTER which comes with elegant/examples.

case 1) But I couldn't control both voltage and phase in the desired value when I use both the fundamental and harmonic cavity in active mode as RFMODE elements.

case 2) So I set the main cavity as RFCA element and the harmonic cavity as RFMODE element. It does control the voltage and phase to the desired value. But the resulting bunch length is far too small.

I expect the bunch length 40 ps with the nominal setting that V1=10 MV, phis1="180 3.86e6 10e6 / dasin -" , V3=3.1 MV, phis3=0.0 (360 works in RFMODE).

For case1) the system is unstable.

For case2) it damps to 10ps (instead of 40 ps) even if V1 and V3 are 10MV (RFCA) and 3.1MV (RFMODE), respectively.

I need your help in both case1) and case2) to simulate two active rf system. For this I attached the bunch file(prepared by makeBunchTrains, elegant files, result files.

You can produce the results by:

for case1:

elegant p4time.ele macro=Ib=0.1,root=rfhm_N3k_Ramp10k_PRELOAD_360_3.1MV_960,Npass=20000,Nparticle=3000,Nslot=6000,Vrf1=10e6,Vrf3=3.1e6

for case2:

elegant p4time3.ele macro=Ib=0.1,root=rfhm3_N3k_Ramp10k_PRELOAD_360_3.1MV_960,Npass=20000,Nparticle=3000,Nslot=6000,Vrf1=10e6,Vrf3=3.1e6

In both cases, I am using 80-trains of bunches (10-bunches+2-buckets)*80=800-bunches out of 960-buckets with hrf=3840; each bunch has 3000 particles. And the rf-system is

! RF System - fundmental

! Harmonic number = 3840, Ncavity=24, Q=29000, beta=3.0, R/Q=3.4e6/29000

! RF System - 3rd harmonic

! Harmonic number = 3840*3, Ncavity=24, Q=17000, beta=5.3, R/Q=1.5e6/17000

I also attached the element-by-element lattice file so that you can compute the lattice characteristics.

Your help will be highly appreciated.

Best,

Yong-Chul

I am studying the transient beam loading with gaps. I made the progress in semianalytic method to compute the bunch profiles which varies over the train of bunches with beam loading effect included. Now I like to simulate the beam loading with RFMODE and I have encountered the difficulties to correct them.

I am able to control the cavity voltage and its phase by using AMPLITUDE_FILTER and PHASE_FILTER which comes with elegant/examples.

case 1) But I couldn't control both voltage and phase in the desired value when I use both the fundamental and harmonic cavity in active mode as RFMODE elements.

case 2) So I set the main cavity as RFCA element and the harmonic cavity as RFMODE element. It does control the voltage and phase to the desired value. But the resulting bunch length is far too small.

I expect the bunch length 40 ps with the nominal setting that V1=10 MV, phis1="180 3.86e6 10e6 / dasin -" , V3=3.1 MV, phis3=0.0 (360 works in RFMODE).

For case1) the system is unstable.

For case2) it damps to 10ps (instead of 40 ps) even if V1 and V3 are 10MV (RFCA) and 3.1MV (RFMODE), respectively.

I need your help in both case1) and case2) to simulate two active rf system. For this I attached the bunch file(prepared by makeBunchTrains, elegant files, result files.

You can produce the results by:

for case1:

elegant p4time.ele macro=Ib=0.1,root=rfhm_N3k_Ramp10k_PRELOAD_360_3.1MV_960,Npass=20000,Nparticle=3000,Nslot=6000,Vrf1=10e6,Vrf3=3.1e6

for case2:

elegant p4time3.ele macro=Ib=0.1,root=rfhm3_N3k_Ramp10k_PRELOAD_360_3.1MV_960,Npass=20000,Nparticle=3000,Nslot=6000,Vrf1=10e6,Vrf3=3.1e6

In both cases, I am using 80-trains of bunches (10-bunches+2-buckets)*80=800-bunches out of 960-buckets with hrf=3840; each bunch has 3000 particles. And the rf-system is

! RF System - fundmental

! Harmonic number = 3840, Ncavity=24, Q=29000, beta=3.0, R/Q=3.4e6/29000

! RF System - 3rd harmonic

! Harmonic number = 3840*3, Ncavity=24, Q=17000, beta=5.3, R/Q=1.5e6/17000

I also attached the element-by-element lattice file so that you can compute the lattice characteristics.

Your help will be highly appreciated.

Best,

Yong-Chul