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RFQ2 update
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Europe/Zurich
Present: G Bellodi, S Chicarella, A Grudiev, J-B Lallement, E Marchetti, L Millar, S Ramberger, R Scrivens
LM showed some slides proving that RFQ2 frequency tuning looks possible with differential temperature control on the RFQ body/vanes.
There is little effect however on the field profile:
dipole/quad amplitude effect of changing body temperature is small (0.1% or less), not enough to recover the field profile deviations.
AG comments that a local frequency change is needed in the RFQ to correct the field flatness ( i.e. individual temperature control of the 3 modules)
SR replies that it would be costly to revert to such a water distribution control.
Given the holiday period, no conditioning will be possible for the next 3-4 weeks.
It is also not clear if we have the correct antenna measurements, since the seals were changed in the meantime.
Repeating beadpull measurements would hence be quite useful and top priority.
AG comments that half of frequency shift is due to vacuum and is reversible, the other half is not understood, probably an
effect of plastic deformation. We cannot be sure that this field flatness will be the final one.
SR replies that the auxiliary support will no longer be used and that a new lifting girder is being produced and is due by October.
Final RFQ tuning might have to wait until then, and RFQ manipulations should be tested in advance for precaution.
In-situ tuning was done on RFQ1 back in 2013 but required to move equipment out of the way, with limited or
no source operation during that time.
A possible strategy is to retune with a limited set of tuners just after taking the beadpull measurements, having an estimate of the required correction.
The expected change in tuner length is relatively small , so the favoured solution at the moment is to remachine flanges.
One spare prototype tuner is available, and a possibility would be to do one by one changes for measurements.
As mitigation measure, RS will ask the price of producing 4 new tuners from the workshop.
RFQ2 beam measurements are most likely excluded this year.
The period required for conditioning depends on the maximum number of breakdowns set to be achieved, it may vary from 1 month to 3 months, but
can be done offline.
At the test stand the RF pulse length is limited by the modulator at 300us, with a direct effect/limitations on conditioning.
Overconditioning by increasing the field would not achieve the same effect as increasing the RF pulse length.
RS will check with D Aguglia (EPC) if a different modulator could be installed at the test stand, allowing for longer pulses.
The next meeting is scheduled on 09 August at 14h00.
-GB 17/07/2024
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