simulation with a (time-depended) bumper

[li.chao]

Hi,

I am trying to simulate a fan-out kicker model by bumper.

In the attached file. I set up a bunch train uniformly occupying the ring.

1. The initial bunch distribution is 80b_1MP_even.sdds

2. The Bumper file is set up as fan_kick.wf following a sine function, and inserted in the lattice.

When the bunch train passes through the bumper for the first time.
I expect the head-bunch to experience delta_xp=0. And the following bunches with delta_xp follow the strength set-up in the bumper (fan_kick.wf).

By checking data (s,xp) in FANKICKWATCH_2.WC file (exactly after the bumper), I found two things expected:
1. not all bunches experience the kick from the bumper.
2. head-bunches experience stronger kick than following bunches.

Can anyone help me to check how to set-up the simulation correctly?
Many thanks

[michael_borland]

The problem is related to the way the BUMPER element aligns the time coordinates of the beam to the time coordinates of the waveform. In particular, it computes <t> for the particles and aligns that to t=0 in the waveform file. If you center your waveform t data about t=0, you should get the results you expect.

--Michael

[li.chao]

Hi Michael,
Thanks a lot for you quick reply.

Following your suggestion, I set up a new bumper as shown in the attached file.
To clearly show how bumper kick different bunches.
I set 2 watch element before and after the bumper and calculated the delta_Px and compare with
the kicker strength set up in bumper.

The results is show as

Still there are two things those confuse me.

1. in the file "tracking.ele" , I insert the bumper as

&insert_elements name = BPM_SWL_7, type= "MONI",
element_def="Fanout_KICKER:BUMPER,L=0.0,WAVEFORM=\"fan_kick.wf=t+Waveform\",ANGLE=2E-3,tilt=0,FIRE_ON_PASS=1,TIME_OFFSET=3.77E-6"
&end

As you noticed, I set TIME_OFFSET=3.77E-6. With this value, I can align the bunch_train with the bumper.
I put the BUMPER at 530m, then the time offset_should be 1.77E-6. Why is there a 2E-6 time shift?

2. As shown in the plot. The delta_px (difference before and after bumper) experienced by bunches.
The bunches along the ring occupy a time window of 1 unit. To generate this plot，20 turns are tracked.
From left to right is the pass time of pass turns.
My question is: within a bunch train, which bunch is the head bunch and which is the tail bunch?
It seems like the time convention is t_{head} < t_{tail}, is it?

For example in the plot,
take the time window from 11 to 12. I expect the head bunch to experience zero kick and the tail to experience 1.4E-3 rad kick ,

Could you clarify it?

Many thanks
Chao

[li.chao]

The problem is related to the way the BUMPER element aligns the time coordinates of the beam to the time coordinates of the waveform. In particular, it computes <t> for the particles and aligns that to t=0 in the waveform file. If you center your waveform t data about t=0, you should get the results you expect.

--Michael

Hi, Michael,

Sorry for keeping asking the same questions on Bumper simulation.

In the past few days, I tried to run the bumper simulation again. The Elegant script can be found in the attached bumper.zip.
Scripte can be run "elegant tracking.ele -macro=root=test"

Two output files will be generated: FanKickWatch1.WC and FanKickWatch2.WC, which are particle coordinates before and after the bumper.
Then comparing the xp in these two files can tell me how particles are kicked by the bumper element.

I assume that the ring is occupied uniformly by 80 bunches, (I set 1 particle per bunch).
Since the bumper is set to a sine curve, I expect the head bunch to experience a 0 kick and the tail bunch to experience a larger kick when the bunch train passes through the bumper element for the first time.

Again, the following plot shows the comparison between delta_xp and bumper setups.

Two questions.

1. I have to set TIME_OFFSET=3.77E-6 in bumper. With this value, I can align the bunch_train with the bumper.
In the ring, I put the BUMPER at 530m, then it should be TIME_OFFSET=530/3E+8 = 1.77E-6, isn;t it?

2. As shown in the plot. The bunches along the ring occupy a time window of 1 unit and the bumper is turned on at the 8th turn.
Within turns 8 to 9, I expect that the head is not kicked and the tailing bunches experience larger kicks.
Whereas the simulation shows the opposite: the tail bunches are not kicked, and the head is kicked by a large angle.

Could you please help me? How can I set up the simulation with such a bumper correctly?
Many thanks
Chao