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Minutes of E-Beam Meeting #7 (draft)

The meeting was held at CERN (864/2-B14) on 06/11/2019 - See indico

Participants

D. Gamba, L. Ponce, A. Rossi, S. Sadovic, O. Sedlacek, G. Tranquille

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Those minutes are incomplete!

Actions

  • A. Frassier, D. Gamba: understand why the head amplifiers of AD e-cooler have been removed.
  • D. Gamba: Verify with A. Latina if RFTrack model of e-cooler (and/or e-lenses) dynamics is possible and of any use.

Simulation of e- beam with WARP (O. Sedlacek)

[...]

G. Tranquille suggested to concentrate on the model of benders instead of the gun, as this is a missing ingredient, for example, in CST simulations.

E-Lens test stand (S. Sadovich)

CERN

The Hollow Electron Lens (HEL) test stand at CERN aims to test HL-LHC HEL components, diagnostics for electron (and hadron) beams, and it is also meant to contribute to the WP16 of ARIES project for space-charge compensation e^- gun design.

So far the Test Stand is composed by two tunable solenoids, an e^- gun and a passively cooled collector. The collector cooling capabilities and the present HV system only allow to work in pulsed mode (10 \mus long pulses of 5 A at 10 Hz). A diagnostic section installed in between the two solenoids consists of: - YAG:Ce screen - Movable pin-hole Faraday Cup (FC).

From simulations, it should be possible to measure the beam profile as a function of solenoid currents and gun parameters.

Presently, the cathode of the gun is being conditioned. This is an extremely slow process, expected to take of the order of one or two months. This triggered some discussion: - Some un-expected variations of filament current have been observed, which still need to be understood even though they are not worrying at the moment. - The process is limited by the acceptable outgassing that one is expected to tolerate. Too poor pressure could lead to contamination of the cathode and therefore loss of e^- yield. S. Sadovich mentioned that the design of the present cathode is different from previous. It seems like there could be wiring problems which will need to be debugged with the HV once the cathode is conditioned.

A second stage for the test facility is foreseen with the installation of an additional solenoids and more room for instrumentation, for example for a Gas Curtain Monitor. At this point, the powering circuits could also be updated to allow for more flexibility on the settings of the gun electrode voltages.

A. Rossi mentioned that such a test stand could at some point (1-2 years ahead) be an additional test stand for e-cooler gun tests.

RHIC

At RHIC two tests stand are available: one with a full system including benders, and one straight. Attempts to simulate both systems with CST have been made. This were done by dividing the device in small units to be simulated. Currently the agreement between simulations and measurements is not perfect and is worst for the bended system. Possible explanation, still to be verified with sensitivity studies, is that the misalignment and imperfection of the real system could heavily affect the obtained beams.

S. Sadovich stressed that each simulation can take up to 4 days. D. Gamba asked if WARP is meant to be a replacement for CST simulations in the future, and if this could be faster. S. Sadovich and O. Sedlacek replied that the main challenge for both codes is the choice of the mesh for the simulation, and that one does not gain in time with WARP, but just gains in understanding of the actual models being used for the simulation.

Status of e- beam orbit measurement (in ELENA cooler) (A. Frassier, B. Galante, L. V. Joergensen, D. Gamba)

This was a quick update on e^- orbit acquisition for the different e-coolers at CERN: - LEIR: a test of measurement was already done at the end of 2018. Signal was visible, but no attempt to reconstruct an orbit was made. - AD: the head amplifiers of the BPMs inside the e-cooler are missing, and cables disconnected. To be understood the reason why the amplifier were removed - ELENA: two methods to obtain a beam position signal on the BPMs have been tested by acting on the grid voltage: - HV step: this allows to see a signal, but might be difficult to calibrate it in mm. - HV modulation: a clean sinusoidal signal could be observed and converted into mm. This is what was already used in past tests, and seems to be the most promising methods. More details on the work done on ELENA will be presented at a later working group meeting.

AoB (A. Rossi)

  • The budget for a new AD cooler seems to be granted.
  • An hollow e- lenses agreement done, but needs final approval during cost and schedule review (Nov 2019).