Minutes of the LIS Section meeting held on 17^th September 2007.

Present: M. Aiba, G. Arduini, S. Aumon, O. Berrig, R. Calaga, C. Carli, M. Chanel, A. Franchi, S. Gilardoni, M. Juchno, M. Martini, S. Maury, E. Métral, G. Rumolo.

General information (G. Arduini)

The issue of the RF fingers in the LHC is still under investigation. It seems that all the buckled RF fingers in the arcs are systematically localized on on side of the short straight sections.

G. Arduini reminded that the "habilitation electrique" is valid for 3 years. No access to the machines will be possible if this delay is expired.

The Radiation Protection course must be attended every 5 years.

G. Arduini reminded that S. Baird is collecting the information concerning the drawings that should be scanned for the systems in the PS-SPS complex.

A meeting on SPS impedance took place on Friday 14/9. The outcome is summarized below.

-         a high frequency signal is visible on the longitudinal profile of the beam (to be verified that this is not a feature of the HT monitor: Benoit will send the picture to Elena to see whether a similar observation was done in the faraday cage on the same MD (27/8). Giovanni will ask Giulia to verify whether a similar structure was observed form the bunch length measurements in the Faraday Cage on 2/8. Benoit will check whether the same high frequency structure was observed in 2006.

-         The measurements of the threshold of the TMCI instability are not comparable with those taken in 2003 and 2006 as the beam conditions were different (different voltage and longitudinal emittance as most of the measurements were taken at 1.8x10^11 p/bunch).

-         Simulations with HEADTAIL show very clear coupling between modes when increasing the intensity when a broad-band impedance (Z/n=10 Ohm and fres=1 GHz) is assumed. Benoit will look whether the longitudinal profiles of the bunch as simulated by HEADTAIL shows the modulation (at ~1 GHz) measured with HEADTAIL. Very nice results!!!. Elias suggested to compare the simulation of bunch lengthening with intensity with the measurements.

-         The measurements of the phase advance variations with intensity show a large scatter and the precision is not sufficient to draw any conclusion on the impedance distribution. The measurements were taken with a large injection voltage (2MV). Some of the BPMs do not provide useful data and careful adjusting of the gates is required for any new measurement

It was concluded that:

We need to repeat the measurement of the detuning of the quadrupole synchrotron frequency vs. intensity in the intensity range 0.1-1.2 x10^11 p and for a longitudinal emittance of 0.2 eV.s (making sure to record the intensity in the PS and SPS). Which voltage programme should we apply? Can we run with matched voltage (it was 0.57 in 2003 – measured in the faraday cage) during the whole plateau?. WE should vary the intensity in the PSBooster by vertical scraping.

Measure the bunch lengthening vs. intensity in the same range of intensities. Same voltage programme as above? The longitudinal emitance of the beam should be 0.2 eV.s. The intensity in the PSB should be varied by vertical scraping.

Shall we measure also the stable phase shift vs. intensity?

The measurement of the threshold for the TMCI and the measurement of the mode coupling vs. intensity should be repeated in the same conditions as in 2003. Longitudinal emittance close to 0.2 eV.s. Intensities ranging from 0.1 to 1.2 x10^11p. Matched voltage at injection and along the injection plateau. The measurements should be performed at injection. The chromaticity should be kept low (0.05). Keeping the voltage matched all along the flat bottom should help in minimizing the longitudinal emittance blow-up due to mismatch and could be the only way to study mode coupling experimentally.

The measurement of the phase advance vs. intensity should be repeated by extending the intensity range in particular at low intensity. We should try to have matched voltage at injection and adiabatic voltage increase to shorten the bunch. Verification of the BPM gating should be performed before starting the measurements. Longitudinal emittance should be 0.2 eV.s. We should verify that the transverse and longitudinal measurements can be done in parallel (i.e. with the same settings) and the beam should be carefully checked in the PSB/PS before the MD.

Status of the machines

SPS (E. Métral) - Week 36 - Week 37

Machine studies (E. Métral) - summary

PS (S. Gilardoni)

The slow extraction is now working with the configuration using the sextupole in 1 (instead of that in 1). OP is happy with this configuration. We should review that at the APC to take a final decision on the removal of the sextupole in 3.

We will continue to run the CT extraction with the QKE in 25 and 73. This has been agreed with RP and the RSO. During the shut-down the fork of WS75 will be moved to SS65 in the tank of the measurement target.

No tune measurement is possible at larger radial offsets. M. Gasior claims that this is due to the filters that have been installed to filter-out low frequencies. It was suggested to verify that the problem occurs at low energy when a local bump is created at the location of the tune measurement pick-up. Action: S. Gilardoni.

The islands for the MTE could be recreated for a bunch intensity of 3×10^12 p but no fine tuning is possible (equalization of the population and losses during capture) because the non-linear chromaticity cannot be measured.

The new doublet power supplies for the gamma jump in the PS (to be installed during the next shut-down) have a ripple of ~4×10^-3. The effect of that is being studied by S. Gilardoni and S. Aumon.

PSBooster (M. Chanel)

M. Chanel is going to discuss with M. Gasior concerning the PSB tune measurement in the afternoon.

There is a problem with the C04 cavity in Ring 1. This is preventing operation at high intensity.

G. Arduini asked whether the studies on the behaviour of the beam at 160 MeV in the PSBooster have been continued (effect of the second harmonic and of the working point, study of the effect of the different ramp rates). M. Chanel replied in the negative.

Ions (C. Carli, M. Chanel, M. Martini)

The SEM wires in the ETL line are working now. Measurements need to be taken in the ETL line to understand the large mismatch observed in the horizontal plane.

The Ionization Profile Monitor is now working in LEIR

A large mismatch has been observed in the TT2 transfer line. This can be reduced by reducing to zero the current in QFO205 and QDE207. It was suggested to verify that no cabling error occurred during the shut-down. According to C. Lacroix no work has been done on QDE207 while the QDE207 power supply has been exchanged.

G. Arduini noted that the current delivered by the PS is marginal and 50 % losses are still observed. 

Next meeting

Monday, 1^st October 2007 at 09:00 in room 354-1-001

Agenda

General information (G. Arduini)

Comparison of simulations and measurements for the PS losses (J. Barranco)

Highlights from ECOOL07 (C. Carli)

Status of the machines (supervisors)

Status of Machine Studies (E. Métral)

A.O.B.

Back to Minutes