[esa-t474] Energy resolution for the ESA spectrometer

[Alexey Lyapin]

On 03/16/2010 05:04 PM, Yury Kolomensky wrote:
> 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
>

Hello Yury and Michele,

Well, shame on me, I never learned how to run the data processing for 
the ESA data, as there used to be quite a few people able to do that, 
but I believe that Bino did some optimization for the data in question. 
I'll ask him anyway, all his codes are still there so I should be able 
to run them, hopefully with minor tweaks.

For now I tried fixing BPM24's phase issue simply rotating one of the 
states to match the other (fix24.pdf), which makes the IQ plot look a 
lot better, but a small correction to the amplitude may still be 
necessary. Regardless of the correction, the rms of BPM24 still seems to 
be much worse than of BPM12 (about 3 times, energyBpmRawResolution.pdf), 
so maybe it makes sense to use BPM12 only.

Anyway, I decided to estimate the resolution of BPMs 12 and 24: I took 
the scan data and calibrated BPM12, correlated the raw energy from both, 
took the residual and multiplied it with the calibration scale to get it 
in MeV (energyBpmResolution.pdf). The result is about 6.4 MeV or ~2.2e-4 
at 28.5 GeV. Assuming that the raw resolution values are dominated by 
noise, resolution12:resolution24 = 1:3. Then resolution12 = 6.4 
MeV/sqrt(10) = 2.0 MeV or 7.1e-5, which is again pretty close to 
Michele's 4.2e-5...

I'll probably be busy with other stuff for a week or so, but if you have 
any suggestions, please, let me know and I will try them when I get back 
to this.

Cheers,
Alex


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