Minutes of the LIS Section meeting held on 9th May 2011

Present: G. Arduini, H. Bartosik, C. Carli, A. Lachaize, M. Martini, G. Prior

General Information (Gianluigi)

LHC: Injected up to 768 bunches. Luminosities in excess of 8x1032 cm-2 s-1. The LHC has now exceeded the maximum Tevatron peak luminosity and detains the record luminosity for a hadron collider. MDs have been performed during the past week showing that head-on beam-beam limits of 0.03 (2 head-on collision per bunch) can be achieved. The so called ATS (Achromatic Telescopic Squeezing) optics for the upgrade has been successfully tested at injection and during the ramp.

IPAC11: the scientific programme has been finalized with the selection of the contributed oral presentations.

A Group Meeting followed by a barbecue will take place on 28th June.

 

Round Table (Gianluigi)

Hannes: Low gamma-t optics setting-up: (so-called Q20 cycle) preparation started 2 weeks ago. A longitudinal instability has been observed for negative momentum offsets (for approximately -1.5x10-3) both for the nominal and low gamma-t optics. No transverse instability is observed at the same time.

The studies of the electron cloud instability with Q20 have been postponed. Measurement of blow-up at injection and during the low energy plateau will be performed first (this week). Simone warned that the measurement of the emittance with the wire scanners in the PS is not working well. Wire scanners are not reliable. OTRs in the TT2-TT10 transfer line could be used. The application has been tested yesterday..

The matching of the transfer line for the low gamma transition optics has been performed by Hannes with Elena Benedetto. No large difference has been observed in the tail population before and after matching

The dependence of the electron cloud instability on gamma transition is going to be studied with HEADTAIL. Preliminary results seems to indicate  a slower rise time although the threshold remains the same.

An unknown external excitation has been observed in the SPS. This is a new feature. The excitation frequency changes during the ramp and crosses the tune frequency during the ramp for LHC beam. The excitation frequency is 1.7 kHz at flat top. Gianluigi suggested to verify whether there is a correlation of the external excitation frequency swing with the RF frequency swing. Gianluigi suggested to verify whether the excitation is occurring at high frequency (close to high harmonics of the revolution frequency). For that multi-bunch measurements with 25 or 50 ns spacing would be required.

Christian:

The optics of the LINAC4 to PS-Booster line is being reviewed in order to match the power supplies (already ordered) specifications to those of the magnets which have been recently finalized.  A longer vertical chicane is now required to reduce the strength requirements compatibly with the power supplies specifications. The issues related to integration for this new layout are being studied.

PS ions to East area for radiobiological studies: Slow extraction tests have been performed at injection energy (OP) in the PS but they were not conclusive. The beam was extracted but likely it was lost in the extraction channel. Gianluigi asked whether this could be the result of the non-linear fields present at injection that could significantly alter the topology of the separatrices at the extraction point. Christian will verify with Rende.

Etienne Forest and Alexander Molodozentzev are at CERN to set-up ORBIT-PTC.  Discussions are ongoing with them to see how the longitudinal dynamics and temporal evolution of parameters are implemented in ORBIT-PTC. A tutorial on the use of ORBIT-PTC could be very useful. This should take place on week before the departure of Etienne and Alexander. The effect of the magnetic.imperfections, in particular those of the injection chicane, should be included. Gianluigi will talk to Elias so that such seminar is organized as an ABP forum.

The RCS option with a circumference corresponding to 4/21 of the PS circumference is being studied. Space charge effects should be stronger for that solution as compared to those for a machine 1/7 of the PS circumference.

Gersende

A discrepancy is still observed when comparing ICOOL results with MARS results. ECFA review took place in the UK. Beta beams studies should be further pursued.

Simone

The setting-up of the multi-turn extraction with electrostatic septum has not been successful so far. Studies are ongoing to understand the variation in the performance of the extraction.

The measurements of the beam phase space at extraction seem to indicate that the trajectory of the beamlets is not reproducible. The use of the turn-by-turn beam position monitor data is not straightforward and some instrumental problems need to be fixed before any conclusion can be drawn based on the observations done.

The 50 ns beam double batch injection form PSB to PS is available up to 1.9 x 1011 p/bunch. Wire scanners are not working reliably to allow a comparison of the emittances all through the injector chain.

 Next meeting

Monday, 23rd May 2011 at 10:30 in room 6-R-012

Agenda

 

 

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