Setting of bmp_noise and force specific position in &correct

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Joined: 25 Jun 2019, 07:53

Setting of bmp_noise and force specific position in &correct

Post by richtmann » 23 Jul 2019, 15:30


I would like to use the &correct command with bpm noise. The BPMs are assumed to have a noise of 50 microns with gaussian distribution and the cutoff should be 3 sigmas, both in both planes.
I tried to use
bpm_noise[0] = 50e-6, 50e-6
bpm_noise_cutoff[0] = 3,3
bpm_noise_distribution[0] = "gaussian", "gaussian"

I'm wondering if this is the correct way to use it as I don't see that the correction is affected at all by this setting.
Could you explain how the index in square brackets has to be set? I thought it should be 2 as I'm setting values in two planes, but it only works when I'm setting it to 0.

Furthermore, is there a way in the &correct command to force a specific position at some elements even with the cost that the beam is more offset at other positions? I'm thinking about a bump, where an offset of for example 1mm should be achieved within a specific region. The goal is to really have this offset of 1mm in this region, even if the payoff is that the beam takes longer to return to (0,0) after the bump.

Thank you very much for your help!

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Joined: 19 May 2008, 09:33
Location: Argonne National Laboratory

Re: Setting of bmp_noise and force specific position in &correct

Post by michael_borland » 07 Aug 2019, 08:40


The values you provided for BPM noise should produce the desired effect of 50 micron noise. However, it is important to appreciate that this noise varies from reading to reading of the same BPM. Hence, it will manifest itself in poor convergence of the trajectory, even for large numbers of iterations. See the attachment for an example of this.
The syntax for array entries can take several forms. The index always gives the location of the first entry to be set. E.g.,

Code: Select all

bpm_noise[0] = 75e-6
bpm_noise[1] = 50e-6
would set the noise for the x plane ([0]) to 75 microns and for the y plane ([1]) to 50 microns. This could also be entered as a list, starting from the first location:

Code: Select all

bpm_noise[0] = 75e-6, 50e-6,
In this case, the first element (75e-6) goes into slot 0, the second into slot 1.

If you want to make a trajectory bump, you can use the XSETPOINT and YSETPOINT parameters on the MONI element to change the zero point of steering. For this to work, you must carefully consider the setpoints of nearby BPMs that might be within the bump.

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