Minutes of the Linac4 Diagnostics Working Group Meeting held on 19 January 2009

Present: U.Raich, J.Tan, G.Bellodi, L.Soby, G.Tranquille, C.Dutriat, F.Lenardon, J-J.Gras, A.Lokhovitskiy, R.Scrivens, C.Carli, T.Hermanns, K.Hanke, B.Mikulec.


1. Communications

2. Follow-up of open actions

3. Highlights from the CARE emittance measurement workshop

4. Feschenko monitors (R.Scrivens)

5. Summary of the APL proposal on laser profile monitors (K.Hanke)

6. Measurement precision of current transformers (F.Lenardon)

7. AOB

1. Communications

PSB review: Last week the PSB review with Linac4 took place. K.Hanke mentioned that there has been an ad-hoc discussion on diagnostics after the presentations. The review committee underlined the importance of sufficient beam instrumentation. The following diagnostics were mentioned in particular: a large view screen to visualise both the injected and the circulating beam at once; measurement of the electrical signal from the stripping foil; at least 3 PUs in the ring that can measure turn-by-turn; BLMs; segmented H0/H- dump (foil degradation) with view screens in front; laser emittance measurement (not only after the Linac4 exit, but another one as close as possible to PSB injection). The slides of the committee recommendations can be found here (closeout.pdf).

Diagnostics WG: K.Hanke started compiling an EDMS document summarising the current conclusions of the diagnostics working group before handing over the organisation of the working group to BI (U.Raich and J-J.Gras). L.Soby underlined the importance of having clear written specifications available as soon as possible.

2. Follow-up of open actions

Simulations for emittance meter slit: U.Raich reported that O.Aberle started to work on the slit simulations.

BLMs: One of the upcoming meetings should be dedicated to a status report and discussion on BLMs. In this context it would be good to have G.Bellodi commenting on the loss distribution along the Linac4 line. Will it be possible to simulated the PS fringe field to finalise the loss distribution along this part of the Linac2 transfer line?

Dimensions of BI equipment for diagnostics bench: U.Raich said that the longitudinal dimensions of the BI equipment to be installed on the diagnostics movable bench are known and that they fit with the proposal made by G.Bellodi (see last minutes). He has a meeting this week with the drawing office to discuss how to proceed in order to obtain rapidly the required drawings. One worry is that the French deny to have the drawings of their magnets to be installed on the bench still available. It has to be seen if they can be found back or if enough information can be found in the CATIA drawings.
Link to the planning of the 3 MeV test stand: https://twiki.cern.ch/twiki/bin/view/SPL/TestStand

Wire scanners for 3 MeV test stand: C.Dutriat has found a motor to replace the contaminated motor for one of the 3 MeV test stand wire scanners. He would first like to confirm that the motor is really equivalent and will then proceed to its exchange.

3. Highlights from the CARE emittance measurement workshop

An emittance measurement workshop took place in Bad Kreuznach (Germany) in December 2008 within the CARE framework (http://adweb.desy.de/mdi/CARE/Bad_Kreuznach/ABI_workshop_2008.html). As reported shortly by R.Scrivens, presentations were given on the following basic transverse emittance measurement methods:

  • 3-profile measurements
  • pepper pots: quite a few presentations; nice devices as it is possible to obtain a full 3D image including halo in one shot; but also applicable only at low energies
  • slit-and-grid method
  • systematic studies on different scintillator materials and screens by the GSI group
  • laser detachment: SNS

4. Feschenko monitors

R.Scrivens showed the presentation he gave at the CARE workshop (CAREWorkshopOnBSMs.pdf). The underlying principle is that the beam hits a wire (at -5 kV potential), which produces secondary electrons having the same bunch structure as the primary beam. The electrons pass through a set of slits and a RF deflecting plate (biased to focus electrons onto second slit); only those electrons close to the RF zero crossing are transmitted and measured by a detector. The measurement is therefore done at a defined beam/bunch phase; for the next pulse the RF deflecting phase is shifted.

At CERN 3 different flavours of this device are installed: a bunch shape monitor (Linac2 p at 10 and 30 MeV), a 3D bunch shape monitor (Linac2 p at 50 MeV) and a bunch length and velocity monitor (Linac3 Pb27+ at 4.2 MeV/u).

Bunch shape monitor: measurement of bunch shape, limited halo investigation (wire cannot be used in bunch centre to avoid wire damage) and RF characterisation of RF systems.

Bunch length and velocity monitor: measurement of bunch profile and position; measurement of beam energy and Time of Flight by moving the detector (very reproducible velocity measurement). With the help of a buncher cavity, the bunch centre can be determined (bunch centre as function of cavity phase and amplitude). In addition, the buncher cavity allows for a longitudinal emittance measurement via the bunch rotation technique (relies on RF measurements for the cavity effective voltage).

3D bunch shape monitor:

-- BettinaMikulec - 19 Jan 2009

  • closeout.pdf: Recommendations of PSB with Linac4 review committee.

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf CAREWorkshopOnBSMs.pdf r1 manage 3990.7 K 2009-01-19 - 17:00 BettinaMikulec The Feschenko bunch shape monitor - User experience at CERN
PDFpdf closeout.pdf r1 manage 79.6 K 2009-01-19 - 15:25 BettinaMikulec Recommendations of PSB with Linac4 review committee.
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Topic revision: r3 - 2009-01-19 - BettinaMikulec
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