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26.02.2018 HL-LHC WP13 BI Meeting 2018 #2
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Europe/Zurich
892/1-D20 (CERN)
BI WP13 meeting #2
Monday 26 February 2018
(https://indico.cern.ch/event/702541/)
AGENDA
14:00 Approval of minutes and Highlights from Chamonix 30m (Rhodri)
14:30 E/O BPM status & plans for 2018 30m (Stephen/Thibaut)
15:00 AOB
Actions/minutes from last meeting
Gas Jet Monitor:
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Cooling of the photomultiplier installation completed, maybe a leak.
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Camera not delivered before end of YETS: will be installed in May shut down.
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E-gun ordered and delivered in May.
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Collaboration Meeting Workshop 19-20th March (close to GSI). Giuseppe Bregliozzi will also participate, vacuum group helpful and keen to find solutions for the BGC to work.
IP4 optics discussed on 6th of March @14h. Invitation circulated.
RJ: cost and schedule review tomorrow with HL WP leaders:
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Re-profiling:
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CryoBLM out of scope, final BGV in (same money as Cryo BLM ?). ECR ongoing.
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Review on instrumentation mid or end of next year to have clear direction on which kind of technology we should concentrate on.
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Present also what synchrotron light can do, IPM, BGI, quad-BPM (or moveable electrodes?) and movable Schottky monitor. We should have a working design approved by end 2019 with impedance sorted.
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We should make a distinction between EM monitors that are not direct measurement of beam size and profile monitors.
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BPM slightly behind schedule, but still in line with string test (late by one year). 1 or 2 prototypes to be ready for string test.
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BGC and EO/BMP are part of UK contract, and they are on schedule. To be seen if they deliver what promised.
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Luminosity monitoring getting along. Spending ok.
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BLM: rad-hard electronics after LS2.
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HEL instrumentation: discussion with Diego and Stefano. Ok with 1 BGC in the centre of the main magnet (better to split magnet in 2 for mechanical reasons, imaging better because not affected by the bent deformation)
S.Gibson:
E/O BPM status & plans for 2018
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Concept: Replace pick-ups in a button BPM with electro-optic crystals.
Transverse displacement through bunch looking at polarisation at crystal
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Timeline: slide 5 - as at the review - shows what has been done. Plan to make balanced pick-up A&B types, and make a compact one. But could already do H test and V compaction.
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The current design (shown in slide 7) is good for tests but not compact for LHC installation
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Pick-Up variants: PU0 not giving strong enough signal, PU1 could (and is now installed)
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Slide 9 shows progress and history of modifications. Recent shut-down optics changed in box A and ??. Bottom flange not easily accessible. Concentrate on H balance.
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Slide 10 shows the compact design. 6D reflective collimators, not automatically controlled but more compact and fits all optics. This design has been physically realised using 3D printing in plastic to test concept.
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The metal version tested at RHUL (with high voltage on electrodes) and sent at CERN (7th Feb installed at CERN in SPS).
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In slides 13-15 one can see how compact is new design
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2 fibre splitters to split light between crystal and fibre to get on the other side interference signal to check if there are coupling losses through the crystal.
Very good coupling through crystal was measured. One could think of doing balance detection using both outputs. This setup is tolerant to drift in power through the crystal.
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Alignment check results are shown in slide 18. Amplitude of fringes gives an idea of the amplitude of signal we are going to see. Some imbalance between 2 arms. Stable to vibration. More power with compact setup.
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Main purpose to see if it is possible to make compact optics. At SPS we have CC tests, we will see if have any sensitivity to those tests, even if not expected.
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The new dual-crystal pick-up was manufacture at RHUL with Mach - Zehnder interferometer. When e-field applied, signal should be opposite in each crystal if they are right opposite in position: push-pull will give double the signal.
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In slide 21: quite good/large signal with this setup (10% modulation w.r.t. 0 value - previously 1%), but optical power reduced (could be due to sampling rate). Up scope image = sin V applied, sin signal out, square pulse applied.
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Plan to install pick-up at CLEAR (no time for installation in Califfe). Bunch structure different but interesting. Head-tail instability to be tested at SPS. In CLEAR we can tune the type of signal we want to test (tests in slide 25).
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Tests should be simulated, including with other design (etalon interferometer promising)
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Milestone M3.2 (kind of ) done for SPS but for LHC will need more time (6 month) because need more tests at CERN.
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Potential lab at CERN next to Sofie's office ???. Equipment decommissioned from ATLAS could be acquired and used in a lab. Tuneable laser amplifier compatible with our fibre. High power delivered (>300mW against now 30mW now, which should improve S/N) .
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S29: 2018 plans
Manfred: To verify crabbing: what time and special resolution is required and where are you at the moment? Stephen/Thibaut: crabbing should be larger than LHC (several mm within ns), even poor resolution will do, still to be seen.
Rhodri: with 2 interferometers you can take difference than recombine: can you use both path for the interferometric measurements?
Length with free space optics would bring too a long fibre interferometers ??? Done now in stages, may be possible with compact design??
Manfred: electro-optical modulator as pick-up signal, is it true? S/T: Yes you can create a differentiate signal, but do not observe direct e-fill with electro-optical pick-ups. Ongoing programme, because electro-optical modulator on the market: time resolution, dynamic range, other limitations? To be put in another review.
Rhodri/Tom: Crabbing gives constant offset difficult but taking a shot without offset should give good reference. Manfred: Strip-line development to time-gate reflected part completely could be an option.
Rhodri: idea of ultimate limits of current system. 10% modulation of intensity signal: this could be improved subtracting fringe DC signal and combining left-right.
S: 5mW coming back to detector to have enough sensitivity to measure motion we are looking at. What should we optimise? Specification of final system for HL would be good.
Rhodri: we may need 2 different types of monitor with 2 time-resolutions.
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