Minutes of the Linac4 Diagnostics Working Group Meeting held on 1 September 2008

Present: U.Raich, G.Bellodi, G.Tranquille, M.Pasini, A. Lokhovitskiy, C.Dutriat, M.Eshraqi, T.Lefevre, R.Scrivens, K.Hanke, B.Mikulec.


1. Communications

2. Follow-up of open actions

3. Studies of the spectrometer line (G.Bellodi)

4. Test report of the new CERN ADC card (U.Raich)

5. Sum-up of diagnostics for the new transfer line (B.Mikulec)

6. AOB

1. Communications

On October 14th a presentation of the Linac4 work package 'Beam Instrumentation' is scheduled. U. Raich will give an overview on the contents of this work package and send around a draft to this working group beforehand.

K.Hanke informs everybody that beginning of 2009 a review is planned about the Booster operation with Linac4.

2. Follow-up of open actions

Emittance meter: G.Tranquille tells us that Caburn had difficulties to deliver all the parts for the emittance meter; in addition the motor drive part had to be sent back as it arrived very dirty. Hopefully the assembly can be started beginning of October. G.Tranquille also expressed his worries about the slit cooling even at source energies as practically the full beam power is deposited in the slit. Currently nobody is available to perform simulations on this subject.

Beam losses in Linac4: G.Bellodi agreed to present the beam loss studies performed by E.Sargsyan in one of the upcoming meetings. With this information the BLM locations in the Linac4 line can be finalised and 2 actions closed.

Spectrometer magnet: T.Zickler can only identify a suitable magnet with the input of the simulations. U.Raich promised to transmit the simulation results presented in this meeting by G.Bellodi to T.Zickler.

Assigned to Start date Description State Result
U.Raich 2008-09-01 Contact T.Zickler to communicate the specifications for the spectrometer magnet for the movable bench and try to identify a suitable magnet. closed 18/12/08, not completed at this date; negotiations to get a spectrometer from CEA under way edit

Feshenko monitor: U.Raich should get into contact as not much information is available on this subject.

3. Studies of the spectrometer line

G.Bellodi presented the results of her simulations of the spectrometer line that should be installed as part of the movable bench (see spectro.pdf).

This proposal foresees 2.3 m space between the center of the spectrometer dipole and the SEMgrid; max. 0.8 m are available behind the SEMgrid for the dump and anything else. 2 new quadrupoles are required (1 before the slit to obtain a parallel beam and the second one after the slit before the bending); for tanks 1 and 2 the EMQs could be used, but their standard gradients should be doubled (check with C.DeAlmeida if new power supplies would be needed!). The aperture before the slit is 10 mm (radius) and should be increased to 50 mm radius after the slit to avoid beam losses above the 1 W/m limit.

The slit should be placed as close as possible to the end of the tank to avoid energy spread growth due to space charge effects. The slit itself has an assumed aperture of 0.2 mm, which will cut 96-97% of the beam. Cooling needs, slit thickness and activation have to be further assessed with simulations.

Up to 50 MeV (after tank 3) the spectrometer dipole has to fulfill the following specifications: l=0.8 m, rho=1 m, alpha=45 deg, B=0.5-1 T. U.Raich will send this information to T.Zickler. A NMR probe is required for magnetic field calibrations.

With these parameters the following energy spread values (90%), beam sizes on the SEMgrid (90%; full current) and energy resolutions are obtained:

  1. tank 1: 83 keV / 7.7 mm / 11 keV/mm
  2. tank 2: 150 keV / 4 mm / 37.5 keV/mm
  3. tank 3: 165 keV / 2.7 mm / 61 keV/mm
  4. CCDTL: 165 keV / 1.4 mm / 118 keV/mm
The measurement after the CCDTL seems not very realistic. For the other cases a wire spacing of <0.5 mm is requested; this should be feasible, but BI has yet to propose a concrete technical solution.

It might be possible to use this spectrometer line for RF tuning, but the energy shift is comparable to the measurement resolution. Nevertheless this could be useful as a relative measurement should be feasible as the measurement of the profile shift has a resolution < wire distance.

Due to the very limited space for this spectrometer the system performance is also limited. Moreover the spectrometer line will be quite bulky (is it still 'movable'?) and not cheap - do the pro's stand for it's construction?

Dump design: 2 dumps will be needed - one at the end of the movable bench and the other one at the end of the spectrometer. None of them has been designed yet and therefore the section of Y.Kadi should be contacted with the specifications. The 2 dumps should also be included in the work package. The dumps are required for the tank 1 commissioning (12.2 MeV) probably in 2011.

Assigned to Start date Description State Result
U.Raich 2008-09-01 Contact the section of Y.Kadi to communicate the specifications for the 2 dumps required for the movable bench and to find out the time scale for their design. Done. No design effort can be provided before the end of 2008. edit
U.Raich confirmed that it is still planned to use the French diagnostics bench for the 3 MeV test stand.

4. Test report of the new CERN ADC card

U.Raich reported on the test results of the new CERN ADC card (see ADCTest.pdf). The new card is hardware-compatible with the old one. There are 6 ADCs at the input with 6 channels each, yielding effectively a 36-channel ADC. The card can be accessed either via VME or via a microprocessor. For the tests the serial port was used to control the card and read out the data with a PC under a MatLab application. A second card was designed for test purposes to inject either a DC signal or a sine-wave signal into the ADC card inputs. As parallel input into several ADC channels is possible, cross-talk can be checked as well. For the moment only the 8k internal FPGA memory was used, but even in this configuration one can store enough signals to sample a 200 us pulse.

Measurements showed an effective resolution (noise deduced) between 13-14 bits. A few issues remain: an error in the ordering of the channels (can be fixed with a mapping table) and a problem in accessing via VME 2-3 registers (but this problem might also be a driver software issue).
Timing resolution: 4 us (250 MHz).

Hopefully by end of October 50 modules should be available. The cost of each card is around 1 kCHF, cheaper than the INCAA solution (and more channels). The card will be used for all profile measurements.

5. Sum-up of diagnostics for the new transfer line

B. Mikulec summed up the diagnostics needs for the transfer line between Linac4 and Linac2 (see BI_transferline_L4diagnWG.pdf).

After the PIMS until the Linac4 dump the following equipment will be installed: 1 'diagnostics box' directly after the PIMS (1 BCT, 1 SEMgrid, 1 PU), 1 Feshenko monitor, 2 PUs, an emittance measurement unit (to be defined) and another BCT in front of the dump.
In the new transfer line, between the horizontal bending and the existing LT-LTB line, there will be 5 BLMs, at least 2 SEMgrids (one after the horizontal and the other one after the vertical bending), max. 10 PUs (some PUs could be replaced by SEMgrids if allowed by budget), 6 BCTs and 1-2 MTVs (mainly for commissioning).
The radius of the transfer line vacuum chamber amounts to 50 mm. The approximate positions of the BI equipment are marked in the Excel sheet provided by A.Lombardi (see slide 3 of presentation).

It should be clarified if the PU in the 'diagnostics box' is really needed as there will be 2 PUs installed a bit further along the line; once this detail is sorted out, ABP should check this region as it might be required to move the first quadrupole to leave space for this box. The PIMS drawing should also be modified in this case as it currently includes the complete 'diagnostics box'.

R.Scrivens recalled that the Feshenko monitor has to be placed as far away from magnetic fields (in particular from pulsed magnets) as possible.

Now the requirements and approximate positions are known, work can continue on the definition of details. Before the designs and the positions can be frozen the magnet dimensions have to be known (T. Zickler will try to communicate approximate dimensions before the end of this year). There is a Pakistani team at CERN starting this month; they will work on the integration of the transfer line and are keen to obtain this information.

The start of the installation of the transfer line is planned for October 2011; the equipment to be installed is required for March 2011.

6. AOB

Emittance scanner application: R.Scrivens questioned the status of the emittance scanner application that is linked to the use of the CERN ADC card. A FESA class has to be written for the ADC, but this requires a working driver version. Moreover the BI software developers need a setup to advance. A.Lokhovitskiy proposed the following strategy:
In order not to waste time, a first step should be to provide a simplified version of the FESA class to deal with the data transfer alone without any specific calculations. This allows to work in parallel on the LabView application. As a second step Arkady will take care of the full FESA class version (work load around 2 months). In addition, once a test setup will be available with a PLC control card, work can also start on the stepping motor controls.

Drawings: K.Hanke has contacted P.Bourquin who informed him that no manpower will be available before June 2009. Klaus will send him the priority list to deposit our needs. The highest priority has the drawing of the movable bench, followed by the line at the end of Linac4 going to the dump and then the LBE/LBS lines.

Assigned to Start date Description State Result
K.Hanke 2008-09-01 Send a priority list for drawing jobs to P.Bourquin. Done. edit
LT/LTB line: The suitability of the installed BI equipment in the LT/LTB line (after LT.BHZ20) with Linac4 operation has to be checked.
Transformers: 2 transformers in LT line (TRA30, TRA40) and 3 in LTB line (TRA50, TRA55, TRA60); in addition there are transformers installed in the LTB line (TRA49, TRA59) to measure ions.
SEMgrids: 2 SEMgrids in LTB line (position 20, 40).
PUs: 2 PUs in LT line (UMA40, UMA50) and 3 PUs in LTB line (UMA10, UMA20, UMA30). It has to be clarified with L.Soby whether these pickups are able to deal with the different bunch length, but it seems more likely that they have to be replaced.
In addition, cables have to be pulled to the Linac4 building connecting all BI equipment in the old Linac2 line that will be used with Linac4 operation. This should be added to the budget estimate and into the BI work package.
Assigned to Start date Description State Result
L.Soby 2008-09-01 Check whether the PUs in the LT and LTB line have to be replaced to operate with Linac4. The PUs will all be replaced (avoid normalisation with transformer measurement), but the design of the new pickups is still pending. edit
U.Raich 2008-09-01 Add installation of cables for BI equipment in LT/LTB line to BI work package. closed 18/12/08, not completed at this date; BI responsibility to complete the work package description; not followed up by this working group edit

-- BettinaMikulec - 01 Sep 2008

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