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 Post subject: ALICE solenoid peeks
 Post Posted: Sat Apr 30, 2011 3:39 pm 
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Joined: Tue Mar 02, 2010 2:35 pm
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Location: Prague, Czech Republic
Hi everybody,
does enybody know, why Alice solenoid has regular current peeks, as it is visible on http://meltronx.com/lhclite/lhcexpmag.html?

The peeks are only -0.4 Amps (which is only 0.00133% of the magnet current 30 000 Amps), but they seem to me very regular on the time axis (with interval aproximately 3.6 minutes) so I don't think it is only the noise.

Jakub


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 Post subject: Re: ALICE solenoid peeks
 Post Posted: Sat Apr 30, 2011 9:49 pm 
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Hi Jakub,

I can answer this as my software controls the current in the Alice magnet (and all the other "slow" magnets in the LHC and LHC experiments). The spikes on the current are due to cross talk from the SPS extraction kickers which are near by to the Alice magnet powering system (I've not been to see exactly how close these systems are, but obviously a bit too close). The frequency varies according to the cycles being run in the SPS. If the stop pulsing the SPS then the spikes disappear.

So the spikes are simply noise on the measurement, but of course they cause the current controller to react very slight to fight the spike which then does perturb the current very slightly. Fortunately the magnitude of the effect is completely insignificant for the Alice experiment, which is why it has not been a priority to resolve the issue. The fact that it's visible at all is due to the very high resolution of the current measurement system.

Hope that answers your question.

All the best, Quentin


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 Post subject: Re: ALICE solenoid peeks
 Post Posted: Wed Oct 12, 2011 4:44 am 
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Well, I have to agree with Q king there because as far as I know, the software’s does control current inside the Alice Magnet and for that matter, we can ascertain that the spikes or fluctuations on the current are thereby a resultant of the cross talk that comes from the extraction of the SPS kickers. Although, we can conclude the increase in fluctuations to be noise in the instrument, it nevertheless controls current to a great deal.
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