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EMMA Bunch Charge Monitoring Set-up

EMMA Bunch Charge Monitoring Set-up. A. Kalinin EMMA tasks, experiments, and procedures 09 November 2011. The Current Situation.

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EMMA Bunch Charge Monitoring Set-up

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  1. EMMA Bunch Charge Monitoring Set-up A. Kalinin EMMA tasks, experiments, and procedures 09 November 2011

  2. The Current Situation. • The EPICS BPMs have a charge threshold <3nC (bunch on the centre). It is easy to check/measure that threshold atInjection Line BPMs (which are able to measure each bunch in the ALICE train) againstthe Faraday Cup. • Usually, a nominal bunch charge 40pC from ALICE is set on a train plateau. The first bunch(es) charge is often lower than on the plateau. • From the last EMMA run, it looks that the injected bunch is clipped in the Septum or immediately after. As a result, the circulating bunch has lower charge. Besides, the charge is strongly jittering as the loss is highly sensitive to small trajectory deviation. • All above together make the EMMA bunch charge lower than the BPM threshold for most of the injections. On a successful injection, due to a typically outrageously big bunch oscillation on first turns, one of the button signals passes through low values. This aggravates the low charge condition for the BPMs. • I suggest the following set-up for a cradle-to-grave bunch charge monitoring. I’ll assemble it for the next EMMA run. • Note a similar monitoring can be realised with use of EPICS BPMs and some addition to Shinji’s BPM Python script (see the slides attached).

  3. IL BPM1 Cable to MCR BPM Scope Combiner Ring/Ext BPM Front-Ends A pair of verticalbuttons is used. The Front-Ends are modifiedto sum up two button signals. To see bunch charge in the ALICE train (+FC), the first bunch in particular. To compare the EMMA bunch charge to the ALICE bunch charge. To have a turn-by-turn charge picture not obscured by bunch oscillation. To see a charge at the extraction.

  4. BPM signal range monitoring/setting. For a single pass bunch each BPM channel CH1, CH2 gives four voltages (1-1) where is a DC pedestal (typically about +0.92V), are the opposite button signals, are the button signal tails. Check either of (1-2) If (1-2) is not met at least for one signal, ignore this button pair as the ADC is over-ranged, and show a red flag “over range”. For the next shots, set the CH attenuator (default is 0dB, settings are by 1dB in a range up to 31dB). For the condition (1-2) met, check either of (1-3) If (1-3) is not met at least for one signal, show a flag “low signal”, and if other signal is (1-4) at the next shot move the bunch closer to the pickup centre, if other signal is (1-5) either reduce the attenuator, or increase the injected bunch charge.

  5. IV. Bunch charge calculation in a BPM. • In the pickup centre vicinity, the bunch charge expressed in pickup voltage units, is (4-1) • For a BPM of number write the channel gains as (4-2) Re-write (4-1): (4-3) • Express (4-3) in BPM output voltage units: (4-4) Neglecting as finally the bunch charge in the centre vicinity is: (4-5)

  6. (continued) • Do mapping: (4-6) where (4-7) and the button polynomials are found on some mesh as (4-8) with normalisation at the pickup centre as (4-9) Note that the polynomials are individual for a pickup type, circular or rectangular. For circular pickups, the polynomials are the same for any pickup radius provided that the button angle size is the same.

  7. V. Bunch charge in all BPMs. For a lossless turn, calculate for BPMs: (5-1) For each BPM, calculate the BPM individual gain (5-2) The gain-normalised bunch charge in any BPM is: (5-3)

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