LIU-SPS ZS Electrostatic Septum Upgrade Review held on 20.02.2013

M.J. Barnes & T. Kramer

Contributions and acknowledgements- Thanks to the speakers for clear, complete and concise presentations.- Thanks to all who attended and participated in the lively discussions.- Thanks also to Julia and Cecile for the excellent organisation

Present limitations

The ZS has sparked since introducing LHC type beam. During 2009 ZS

outgassing was an important limiting factor. Outgassing depends strongly

on beam parameters, in particular the bunch length.

In 2011 sparking problems with bright beams: –100kV on cathode was set

to avoid sparking (due to long-time constants full voltage modulations,

cycle to cycle, are not possible).

Maximum intensity seen by ZS, during operation to date, is with 25ns beam

1.2x1011 (i.e. OK for nominal LHC but is about half the intensity required for

the HL-LHC).

Worst pressure rise is in ZS5 – the reason for this is not understood:

maybe ecloud occurs in nearby equipment?

Pressure rise occurs when beam is extracted from SPS (but not in ZSTF) –

the reason for beam induced sparking is not understood.

ZS is not presently an important factor in the overall SPS impedance – but

could become so in the future.

Conclusions and recommendations

• Bench measurements of beam coupling impedance of a ZS, with and without electrical circuit, to understand effect of circuit. Compare measurements with suitable predictions to validate impedance model. Damping, e.g. lossy material such as cable with ferrite loaded rubber, to be studied for electrical circuit in tank.

• Bench measurements to understand if wire versus foil make a difference to beam coupling impedance (bench measurements on a short model?).

• Determine contribution of pumping ports, in ZS interconnects, to SPS impedance.

• Carry out a feasibility study for moving of pumps from interconnects to ZS tanks.

• Ecloud simulations with electrical field map (considering effect of A-K field leakage between the wires) – with and without ion trap voltages.

• Cost benefit analysis of having an individual power supply for each ZS.

• The ZS test facility (ZSTF), although not totally representative of the installation, is invaluable for testing ideas (e.g. connection box modifications) and thus MUST be retained.

• All potential “solutions” must be tested in ZSTF before being deployed.

Actions• Investigations shall be made re improving of the powering and measurement circuits – TE-ABT

• E-cloud simulations with improved model (anode wires/ main field) – field map needed – BE-ABP

• Investigate if measurements concerning beam induced voltage in the ZSTF are feasible – TE-ABT

• Follow up meeting concerning damping of high a Q impedance resonance at 44MHz – TE-ABT & BE-ABP

• Investigate construction of a short model to understand if wire vs. foil make a difference to beam coupling impedance – TE-ABT

• Define bench measurement campaign – TE-ABT & BE-ABP

• Determine contribution of pumping ports, in ZS interconnects, to SPS impedance – TE-ABT & BE-ABP

• Check if NEG coating keeps low SEY during cathode installation – TE-ABT. Done: NEG coating will only keep its low SEY under special atmosphere when not exposed to oxygen. Exposure to oxygen (air) will lead to a loss of the advantageous SEY.

• Improve understanding of dynamic behaviour of the ion trap – beam induced effects maybe modulating voltage and therefore possibly reducing efficiency (ABT +impedance team) – TE-ABT & BE-ABP

• Explore possibilities to reduce e-cloud in ZS anode on ion traps (longitudinal grooves, coating?) – TE-ABT, BE-ABP & TE-VSC

• Study the possibility to make improvements to the ion trap box, in particular reduce resistance – TE-ABT

• Investigate improvements on ZS pumping and individual tank sectorisation including failure analysis – TE-ABT & TE-VSC

• Assess the need for the Anode current measurement. If not needed, put the anodes directly to ground (RF screen?) – TE-ABT