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Reviewed IR3 specifications and impedance discussion

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https://cern.zoom.us/j/4980957494?pwd=K3JvSFVOdXFPQ25jVzBPWDgrQVo3QT09#success

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Present: S. Redaelli (SR), N. Neri (NN), M. Ferro-luzzi (MFL), K. Dewhurst (KD), L. Esposito (LE), P. Hermes (PH), F. Vidal (FV), D. Mirarchi (DM), M. Di Castro (MDC), E. Matheson (EM), C. Antuoni (CA), Q. Demassiaux (QD), O. Aberle (OA), Jinlin Fu (JF), C. Zannini (CZ), G. Arduini (GA), S. Cesare (CS), A. Merli (AMe)

Excused: A. Mazzolari (AM), M. Zanetti (MZ)


Comments to the previous minutes and follow up of actions:

  • No comment to the minutes.
  • SR informed MZ about the upcoming beam tests.
  • NN contacted the team Milano-Bicocca (H8 measurements) and Padova (H8 telescope support) who confirmed their interest to support the H8 tests for TWOCRYST as well as to join the whole study. They pointed out that they have previous commitments with Ferrara to test other crystals, so we should exclude that the measurement weeks clash with this. Action for NN and SR to follow this up in the planning and to inform AM.
  • Beam time allocation from LHCb is still under discussion.

Update specifications for the IR3 layouts (P. Hermes)

PH showed an updated version of the IR3 functional specification document following internal discussions with the CERN groups involved, when it was decided (EDMS 2811718) that the construction of two new goniometers compatible with high intensity is not feasible for beam tests before the end of Run 3. For the TCCS will use the design of the IR7 TCPC (featuring a replacement chamber) and in fact plan to recuperate one device from the pool of those removed from IR7, with a new crystal produced for TWOCRYST. The new version of the specs will be circulated soon.

  • QD asked about the parameters to be considered. PH replied that the MD case outlined in the previous specs remains the same (top energy intensity limit = 3x1011p). SR stressed that for TCCP design considerations, calculations should still be done for the nominal Run 4 parameters as this remains the design target for the studies.
  • MFL asked about the TCCP gonio: can this also be recuperated fro IR7? This is not the case: it will have to be built new as the specs for the long crystal and target are not compatible with the present TCPC design.
  • It was agreed that a new version of the specs will be circulated in EDMS (Action PH).

Review of goniometer impedance considerations (C. Antuono)

CA reviewed the present status of impedance calculations for TCCS and TCCP and discussed some suggestions for improvements. See details in the slides. 

  • MFL asked if power loads are computed for the perfect resonance modes seen in simulations. CA replied that this is the case. In reality, the resonance can be slightly off compared to the simulation values however we need to assume a certain span in frequencies of the simulated modes in this design phase, assuming that the simulated peak will be hit.
  • NN asked a confirmation of beam parameters: calculations are done for the HL-LHC case in Run 4 however the MD figures will be much lower (total intensity will be about 2000 times lower).
  • QD stressed that according to simulations one might not need the replacement chamber concept for the TCCP, as power loads are small at parking positions. SR welcomed this news: if confirmed, it could significantly simplify the new designs. It would also leave the possibility to study crystal insertions at intermediate intensities (not allowed with the replacement-chamber design: the chamber must be in beam with unsafe intensities).
  • PH pointed out that the quoted crystal/beam distance of about 6~mm is ok for the TCCP but not for the TCCS that is closer. Action: to check this offline (PH, CA).
  • MFL asked if tungsten is considered as alternative material for the holder. CZ replied that it is a priori excluded because it is conductive.
  • MFL stressed that it would be useful to add as many temperature measurements as possible. QD commented that this was done for the IR7 TCPC however we cannot easily access the parts that are expected to become hottest. SR recalled that a monitoring of the IR7 devices is planned during the intensity ramp up of ion beams in 2023.
  • MFL suggested to study different shapes of the holder and of the element protruding into the beam pipe to identify potential reductions of the impedance: even if not feasible in reality, such simulations could indicate a path forward to design improvements. Action: more simulation changing holder design and hard edges (CA). QD comments that smooth geometries are in general more complex to achieve, however it was agreed that an exploratory study in simulations would be useful.
  • SR asked if we could consider ferrites to dump the observed modes. CZ replied that this solution is not excluded a priori however it is not favoured and it has not been used recently in any design of new elements in the LHC.
  • MFL asked the target power loads. QD comments that anything above about 1 W risks to create problems as in vacuum it is difficult to evacuate it. CZ asked if detailed field maps are useful to simulate in more detail the thermo-mechanical response. QD confirms that this can be done when the design is more mature.

Goniometer design considerations (Q. Demassiaux)

  • QD comments that, given the choice to recuperate an IR7-TCPC as TCCS, the effort on this front is mainly from BE/CEM side to assess the specs/performance of the available devices. SR asked what specs are in doubt and EM replied that some goniometers have lost the full range of +/-10mrad. This of course must be assessed and validated for the available devices.
  • QD comments that they are still missing the model of the long crystal from INFN-FE. NN asked what are the specs of the crystal given to CERN (as reported at last meeting by AM). SR recalled that this is just for setting up the x-ray measurements. EM shared the specs of this crystal (see below), which are indeed not suitable for usage as TCCP. Action: SR/PH to contact AM and see if updated drawings are available for the crystal that will be delivered in April.
  • SR asked clarification on the two goniometer technologies introduced by QD: "virtual pivot" vs "mecartex". QD clarified that both are going to use interferometers however the latter might not be suitable for heavier crystals. He commented that tests are ongoing in the BE/CEM team: we would use the mecartex solution if it was demonstrated that it is compatible with the long-crystal weight. To be followed up. Action: EM's team.
             
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