Tracking with Broad-band Impedances

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Akhyani
Posts: 16
Joined: 26 Jun 2018, 08:09

Tracking with Broad-band Impedances

Post by Akhyani » 23 Oct 2018, 04:04

Dear Michael and all,

I want to use broad-band impedance model for ring tracking. I set BROAD_BAND=1 in ZTRANSVERSE command and specified the resonators but I couldn't realize how to determine the plane (x/y) they belong to. Also, how can I figure out the appropriate bin size in this case?
Any help would be appreciated.

Regards,
Mina

michael_borland
Posts: 1927
Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory
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Re: Tracking with Broad-band Impedances

Post by michael_borland » 23 Oct 2018, 08:59

Mina,

By default, ZTRANSVERSE applies the same impedance in both planes. You can change this using the XFACTOR and YFACTOR parameters. E.g., if you set YFACTOR=0, then the impedance will only apply in the horizontal plane.

The number of bins nBins should be a power of 2. The bin width binSize must be such that nBins*binSize>2*(fullBunchDuration). The frequency spacing is computed as df = 1/(nBins*binSize). Setting the number of bins and the bin size is a bit of an art. In particular, you'll want enough bins to resolve the resonance (df<<fRes/Q) but not so many that you have excessive binning noise.

Here's my suggestion:
  1. Compute df = fRes/Q/M, with M~10 so that the resonance is well resolved.
  2. Compute binSize = fullBunchDuration/N, with N~50 so that the bunch distribution is well resolved. Use the nearest power of 2.
  3. Compute nBins = 1/(df*binSize)
  4. Choose number of particles np = P*nBins, with P~100.
This is just a rough guide. It's important to vary M, N, and P to ensure that the results have converged. If you find the number of bins and number of particles are excessive, it may be best to switch to the RFMODE or TRFMODE elements, which simulate resonators in a more direct fashion.

--Michael

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