Minutes of the Linac4 Technical Design Committee

meeting no. 2

date: 02 May 2006


AB/RF F. Gerigk, M. Pasini, J. Broere, R. Wegner, M. Vretenar
AB/ABP G. Bellodi, A. Lombardi, E. Sargsyan, R. Scrivens, D. Kuchler, Th. Meinschad
AB/BI L. Soby
AB/CO I. Kozsar
AB/PO C. De Almeida, J.P. Royer
TS/SU M. Jones
AT/VAC E. Mahner
AT/MEL W. Kalbreier
SC/RP M. Silari, M. Magistris

excused: K. Hanke, C. Rossi, A.L. Hernandez, O. Brunner, W. Weterings


1. Introduction and Linac4 Parameter List (M. Vretenar)
2. Status of the H- RF source for Linac4 (Th. Meinschad)
3. Low Energy Beam Transport design (R. Scrivens)
4. Solid state long pulse klystron modulator: development of a prototype (C. De Almeida)
6. next meeting

1. Introduction and Linac4 Parameter List (M. Vretenar)

The Linac4 web site (http://project-spl.web.cern.ch/project-spl/linac4.htm) has been updated with the most recent parameter list, the minutes of the last meeting with link to the slides, and the structure of the Technical Design Report. It is recalled that the deadline for contribution to the Linac4 Technical Design Report is END OF MAY, i.e. about a month from now. Only for the technical services will be accepted an extended deadline (end of July), because they are dependent on the machine layout, which will be frozen only at the end of May.

2. Status of the H- RF source for Linac4 (Th. Meinschad)

The source considered for Linac4 is an RF driven volume source, where a solenoidal RF antenna produces a 2 MHz RF electric and magnetic field that excites a plasma confined by a multicusp magnetic field. The excited H2 molecules are then dissociated by the capture of a slow electron, to form H- and H0 ions. The source is based on the DESY design, where the RF antenna is outside of the Alumina plasma chamber. CERN is starting a collaboration with DESY, and the drawings of the source should be available in July. Work is going on in optimizing the position of the vacuum pumps and defining the RF generator. The source for the test stand is supposed to deliver only >40 mA, to be then slowly improved in order to reach the 80 mA required for Linac4. Commissioning is foreseen from June 2007.


  • The 40 mA from the source for the test stand is the minimum for beam measurements (space charge). Improvement to the 80 mA for Linac4 will require a lot of work on the source.
  • It was stressed the importance of having the vacuum pumps outside of the high voltage. As far as the pumping speed is concerned, the present installation at DESY is clearly oversized, and the source can probably operate with a lower speed.

3. Low Energy Beam Transport design (R. Scrivens)

Beam simulations from the source to the RFQ are in progress. A standard 2 solenoid LEBT has been chosen, assuming a high degree (90%) of neutralization. Four different types of solenoids have been compared in terms of emittance growth. For the source beam considered in the simulations the smaller emittance growth (6-7%) corresponds to Linac3 or LIL type of solenoids, while Linac2 solenoids give a 20% emittance growth but are less expensive (magnet and power supply).


  • For the TDR, one should present the best solution, i.e. the one with Linac3 type solenoids. For the tests, one can still decide whether to start with one Linac2 solenoid and measure the actual beam properties, or to start directly with the Linac3 solenoids.
  • The vacuum group is worried for the gas injection in the LEBT required to control neutralization. This is nowhere done in our machines, and presents some risks from the operational point of view.

4. Solid state long pulse klystron modulator: development of a prototype (C. De Almeida)

Traditional pulsed power modulators (PFN based) are bulky and expensive, especially for long pulses, and rely upon cathode tubes used as switching devices. Modern modulators designs instead prefer solid state switches at lower voltage, usually followed by a transformer stage, and a capacitor bank for energy storage. The design can be basically different in case the klystron is equipped with a modulating anode. The solution proposed for the test stand and for Linac4 is based on the Fermilab-TESLA pulsed cathode modulator. Commercial components are available, and some LEP HV connectors could be reused. The prototype could be built in Fall 2006, and first pulses should be available at end 2006.


  • The same basic pulsed modulator design could be used for the 700 MHz klystrons, delivering 4 times more RF power than the LEP ones, and which are not equipped with a modulating anode. As well, this principle could be followed for a 50 Hz version for SPL.

next meeting:

Tuesday June 13th, 14:00, room 354 1-001

-- MaurizioVretenar -

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