Beam loading simulation with feeder current modulation

[Skamarokha]

Hello

Is there a way to simulate beam loading effect for bunch train with a gap with special modulation of generator current. Modulation is supposed to simulate loading with bunches in the gap.

Also, do you have any tips on how to setup AMPLITUDE_FILTER and PHASE_FILTER? For a test run I've tried to use a file from examples, but I see distirbances to bunches in the middle of a train. I don't know whether it happens because I have ILMATRIX instead of a lattice or due to incorrect RF feedback filter coefficients.

[michael_borland]

Mikhail,

I don't quite understand what you are asking to do for the simulation of bunches in a gap. If you set up a multi-bunch beam that has the gap and those bunches, RFMODE will simulate the transient beam loading and the response of the feedback system to that pattern.

I can't offer much help with the feedback setup, since that was done by my colleague Tim Berenc. Without more details, it is hard to diagnose what might be going wrong. However, I wouldn't think that the ILMATRIX element would cause an issue. If you can upload your input files, I'll have a look and get Tim's help if needed.

--Michael

[Skamarokha]

The problem with a bunch train with a gap is that bunches will have different RF acceptance, lifetime and length. We want to avoid that by changing the behavior of generator - if we introduce special modulation to generator current at the moments when there is no beam loading (gap, empty separatrices), we might be able to create a condition when beam loading effect shows itself for a bunch train with a gap as if there is no gap. The question is - is it possible to set via sdds file or by other means special behaviour for RF generator current?

[michael_borland]

Mikhail,

That's an interesting idea. We plan to deal with this problem by making the bunches on either side of the gap higher in intensity. It seems to work well in simulations, but of course the high-intensity bunches will have shorter lifetime.

The rf feedback model diagram

(which is supposed to appear in the manual on line but doesn't for some reason) shows how "noise" can be injected into the loops. In reality, this feature allows injection of signals of any type at various points in the loops. I think you could use this to modulate the generator current, generator phase, voltage setpoint, and phase setpoint. Since you need to do this bunch-by-bunch, the feedback update interval should be equal to the bunch interval.

--Michael