Minutes of the Linac4 Diagnostics Working Group Meeting held on 7 April 2008

Present: E.Bravin, U.Raich, K.Hanke, E.Sargsyan, M.Eshraqi, L.Soby, A.Lokhovitskiy, M. Jones, M. Pasini, B.Mikulec.


1. Communications

2. Follow-up of open actions

3. Design of D-plate

4. Alignment strategy for Linac4

5. AOB

2. Follow-up of open actions

-. Emittance meter and slit tolerances: Work ongoing.

-. EVM document and budget breakdown per year: Work has been started.

-. CEA/CERN cost comparison for D-plate: There has been a meeting last week with representatives of CEA. The outcome of this meeting was that it seems more reasonable to leave the fabrication of the D-plate under CERN responsibility as practically all the elements of the movable bench will be standard Linac4 equipment. One possible collaboration would be to hand over to CEA the fabrication of the readout electronics for the pickups.

-. Development of Linac4 software applications: The message from CO is that OP should provide software applications for beam diagnostics. For the 3 MeV test stand an application for the emittance meter should already be available by the end of this year. K. Hanke will try to find a solution, but most probably this will consist of using an 'expert tool' until a new application can be provided. He will contact R. Scrivens to discuss the details.

Assigned to Start date Description State Result
K.Hanke 2008-04-07 Contact R. Scrivens to make sure that a solution can be found to control and read out the emittance meter needed for source characterisation at the 3 MeV test stand. See minutes 09/06/2008. edit

-. Beam loss distribution along Linac4 to PSB transfer line: M. Eshraqi presented a plot showing the ratio between the aperture and the rms beam size (see plot). The critical regions are where this ratio is small; the biggest restriction is in the vertical plane at the location of the septum. With this input and taking into account the regions of high dispersion it should be possible to get an idea of the number of BLMs required for the transfer line. The final location of these BLMs can be determined later once the optics of the line will be frozen.

Assigned to Start date Description State Result
B.Mikulec 2008-04-07 Determine the approximate number of BLMs to be installed in the Linac4 to PSB transfer line. See minutes 09/06/2008. edit

3. Design of D-plate

U. Raich presented the design status of the movable bench (see file).
Instruments on the movable bench:

  • 2 or rather 3 BPMs: position and time-of-flight measurement for beam steering, phase measurement and determination of beam energy.
  • 1 BCT: measures the absolute intensity and together with the BCT in front of the tank the transmission
  • Slit + SEMgrid: transverse emittance measurement; use SEMgrid of emittance meter for profile measurement
  • Feschenko-type monitor: longitudinal profile measurement
  • Energy degrader + Faraday Cup (change degrader thickness for different energies)
Moreover there will be 2 quadrupoles and 1 steerer on the movable bench.

A check of the proton penetration depth in graphite yielded about 1.5 cm for 50 MeV protons and >10 cm for 160 MeV protons; this already excludes the use of a slit for the latter case.

U. Raich showed calculations of the expected resolution for the ToF measurement using the SNS configuration (pickups 30 cm apart) and the Linac4 parameters. SNS claims 26 keV energy resolution with +/-2 deg. phase resolution, which corresponds to the calculations. In the case of Linac4 at 12.1 MeV one obtains about 62 keV energy resolution. In case this would be not acceptable, either the phase resolution must be improved or the distance between the pickups could be increased.

An estimation for the Linac4 beam power was also given in the presentation.

The remark was made that a spectrometer (+SEMgrid) was needed for the range 3 to 50 MeV. Once the magnet parameters will be evaluated, it was proposed to look around whether there would be a suitable magnet available.

Following a question of A. Lokhovitskiy, it was clarified that all the required applications for the movable test bench will be standard Linac4 applications; the only new application will be the one for the Feschenko-type monitor.

4. Alignment strategy for Linac4

M. Jones explained the alignment strategy for Linac4 modules and module elements in his presentation. Module elements that require measurement or alignment need 2 survey reference points and 1 tilt reference surface. For the measurement laser tracking is proposed and yields a measurement precision of 0.03-0.04 mm.
The alignment of module elements will be performed with a mechanical key system ('clavette') leading to an alignment precision of 0.1-0.2 mm. In case this precision is not acceptable, one would have to use laser tracking where a measurement precision of ~0.05 mm between two objects could be obtained. It is assumed that only quadrupoles need alignment and it should be clarified what diagnostic elements need alignment/measurement (foresee reference points and surface).

All quadrupoles will be aligned to the common (mechanical) axis. If a module has several quadrupoles, each quadrupole needs a positioning alignment system. The quadrupole+pickup system at the end of each tank is fixed to the tank, but it has to be kept in mind that the quadrupole needs to be alignable. The pickup will be aligned beforehand with respect to the quadrupole mechanical axis.

The modules (tanks) themselves will be aligned as an ensemble in the tunnel; rigidity of the module support is assumed. For the alignment the module reference sockets and the tilt reference will be used and the position of the individual elements then deduced from the previous measurements. Alignment precisions reached for the modules in the tunnel will be ~0.1 mm as for the other current machines.

Concerning the diagnostics elements, the BPMs need their position to be measured as well as the SEMgrid that is part of the spectrometer to be able to obtain an absolute energy measurement. Therefore reference targets have to be included in the design. The question was again raised if it is acceptable to have no measurement for the wire scanners.

For the SPL a permanently installed measurement system for the modules will possibly be provided.

-- BettinaMikulec - 10 Apr 2008

  • Apr-to-RMS.pdf: Aperture to rms beam size along Linac4 to PSB transfer line.

Topic attachments
I Attachment History Action Size Date Who Comment
PDFpdf Apr-to-RMS.pdf r1 manage 58.4 K 2008-04-10 - 16:51 BettinaMikulec Aperture to rms beam size along Linac4 to PSB transfer line.
PDFpdf LINAC4AlignmentStrategy.pdf r1 manage 863.3 K 2008-04-10 - 17:57 BettinaMikulec LINAC4 Alignment Strategy
PDFpdf movableBench.pdf r1 manage 173.2 K 2008-04-10 - 17:08 BettinaMikulec Movable beam diagnostics bench for Linac4.
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Topic revision: r6 - 2008-06-30 - FrankGerigk
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