[esa-t474] Energy resolution for the ESA spectrometer

[Yury Kolomensky]

	Hi Alexey and Michele,

On Mar 16, 2010, at 7:42 AM, Alexey Lyapin wrote:
>
> Thanks Michele! That was exactly my mistake - I did not check the  
> energy BPMs first. Now actually looking at the same energy scan  
> data I am getting about 20 MeV or 7e-4 resolution, which is  
> consistent with your results. There is some room for improvement  
> (fix bpm24 and include into the analysis, include the NMR data,  
> maybe include bpms 31/32, zygo data...), but we shall see if we can  
> get any closer to the 1e-4 level...
>

Did you try to optimize BPM processing parameters (filter bandwidth,  
etc) and did you try to look at a different run ? One can start with  
trying to maximize the bpm4 resolution with field off, then bpm12/24  
resolution, and then look at the residuals with field on.

Other possible improvements:

- BPMs 12 and 24 are positioned at the opposite betatron phases. So  
when subtracting the energy fluctuation, it's better to subtract the  
average (bpm12x+bpm24x)/2 which cancels out position jitter to first  
order (in reality, this works well only if the resolution of the two  
BPMs is comparable). In Alexey's approach of regressing against  
position BPMs and BPM12 this probably does not matter, but may make a  
difference in Michele's numbers.

- It would be good to look at the correlation between the energy  
residual and the NMR data. At least see if there is something to be  
gained by including the data

- Same with zygo

Yury