IPAC2012 - List of Authors (Valuch, D.)

Paper

Title

Page

LHC Abort Gap Cleaning Studies during Luminosity Operation

496

E. Gianfelice-Wendt
Fermilab, Batavia, USA
W. Bartmann, A. Boccardi, C. Bracco, E. Bravin, B. Goddard, W. Höfle, D. Jacquet, A. Jeff, V. Kain, M. Meddahi, F. Roncarolo, J.A. Uythoven, D. Valuch
CERN, Geneva, Switzerland

The presence of significant intensities of un-bunched beam is a potentially serious issue in the LHC. Procedures using damper kickers for cleaning both Abort Gap (AG) and buckets targeted for injection, are currently in operation at flat bottom. Recent observations of relatively high population of the AG during physics runs brought up the need for AG cleaning during luminosity operation as well. In this paper the results of experimental studies performed in October 2011 are presented.

THPPD056

Performance of the Crowbar of the LHC High Power RF System

3641

G. Ravida, O. Brunner, D. Valuch
CERN, Geneva, Switzerland

During operation, the LHC high power RF equipment such as klystrons, circulators, waveguides and couplers have to be protected from damage caused by electromagnetic discharges. Once ignited, these arcs grow over the full height of the waveguide and travel towards the RF source. The burning plasma can cause serious damage to the metal surfaces or ferrite materials. The "crowbar" protection system consists of an arc current detector coupled with a fast high voltage switch in order to rapidly discharge the main high voltage components such as cables and capacitors and to shut down the high voltage source. The existing protection system, which uses a thyratron for grounding the high voltage circuit, has been installed in the LHC about 20 years ago. The problem of "faulty shots" appears due to the higher energy of LHC compared to LEP, which may lead to unnecessary stops of the LHC due to the crowbar system. This paper presents two approaches under consideration to improve the thyratron’s performance and to use a solid state thyristor in high energy environment. The main objectives will be dissipate as little energy as possible in the arc and avoid "faulty shots".

Poster THPPD056 [0.703 MB]

THPPR039

Controlled Transverse Blow-Up of High-energy Proton Beams for Aperture Measurements and Loss Maps

4059

W. Höfle, R.W. Assmann, S. Redaelli, R. Schmidt, D. Valuch, D. Wollmann, M. Zerlauth
CERN, Geneva, Switzerland

A technique was developed to blow-up transversely in a controlled way high energy proton beams in the LHC. The technique is based on band limited white noise excitation that is injected into the transverse damper feedback loop. The injected signal can be gated to selectively blow-up individual trains of bunches. The speed of transverse blow-up can be precisely controlled. This opens the possibility to perform safely and efficiently aperture measurements and loss maps with high intensity bunch trains well above stored beam energies that are considered to be safe. In particular, lengthy procedures for measurements at top energy, otherwise requiring multiple fills of individual bunches, can be avoided. In this paper, the method is presented and results from beam measurements are discussed and compared with alternative blow-up methods.

WEPPR069

Measurements and Simulations of Transverse Coupled-Bunch Instability Rise Times in the LHC

3087

N. Mounet, R. Alemany-Fernandez, W. Höfle, D. Jacquet, V. Kain, E. Métral, L. Ponce, S. Redaelli, G. Rumolo, R. Suykerbuyk, D. Valuch
CERN, Geneva, Switzerland

In the current configuration of the LHC, multibunch instabilities due to the beam-coupling impedance would be in principle a critical limitation if they were not damped by the transverse feedback. For the future operation of the machine, in particular at higher bunch intensities and/or higher number of bunches, one needs to make sure the coupled-bunch instability rise times are still manageable by the feedback system. Therefore, in May 2011 experiments were performed to measure those rise times and compare them with the results obtained from the LHC impedance model and the HEADTAIL wake fields simulation code. At injection energy, agreement turns out to be very good, while a larger discrepancy appears at top energy.

Paper	Title	Page
MOPPD058	LHC Abort Gap Cleaning Studies during Luminosity Operation	496
	E. Gianfelice-Wendt Fermilab, Batavia, USA W. Bartmann, A. Boccardi, C. Bracco, E. Bravin, B. Goddard, W. Höfle, D. Jacquet, A. Jeff, V. Kain, M. Meddahi, F. Roncarolo, J.A. Uythoven, D. Valuch CERN, Geneva, Switzerland
	The presence of significant intensities of un-bunched beam is a potentially serious issue in the LHC. Procedures using damper kickers for cleaning both Abort Gap (AG) and buckets targeted for injection, are currently in operation at flat bottom. Recent observations of relatively high population of the AG during physics runs brought up the need for AG cleaning during luminosity operation as well. In this paper the results of experimental studies performed in October 2011 are presented.

THPPD056	Performance of the Crowbar of the LHC High Power RF System	3641
	G. Ravida, O. Brunner, D. Valuch CERN, Geneva, Switzerland
	During operation, the LHC high power RF equipment such as klystrons, circulators, waveguides and couplers have to be protected from damage caused by electromagnetic discharges. Once ignited, these arcs grow over the full height of the waveguide and travel towards the RF source. The burning plasma can cause serious damage to the metal surfaces or ferrite materials. The "crowbar" protection system consists of an arc current detector coupled with a fast high voltage switch in order to rapidly discharge the main high voltage components such as cables and capacitors and to shut down the high voltage source. The existing protection system, which uses a thyratron for grounding the high voltage circuit, has been installed in the LHC about 20 years ago. The problem of "faulty shots" appears due to the higher energy of LHC compared to LEP, which may lead to unnecessary stops of the LHC due to the crowbar system. This paper presents two approaches under consideration to improve the thyratron’s performance and to use a solid state thyristor in high energy environment. The main objectives will be dissipate as little energy as possible in the arc and avoid "faulty shots".
	Poster THPPD056 [0.703 MB]

THPPR039	Controlled Transverse Blow-Up of High-energy Proton Beams for Aperture Measurements and Loss Maps	4059
	W. Höfle, R.W. Assmann, S. Redaelli, R. Schmidt, D. Valuch, D. Wollmann, M. Zerlauth CERN, Geneva, Switzerland
	A technique was developed to blow-up transversely in a controlled way high energy proton beams in the LHC. The technique is based on band limited white noise excitation that is injected into the transverse damper feedback loop. The injected signal can be gated to selectively blow-up individual trains of bunches. The speed of transverse blow-up can be precisely controlled. This opens the possibility to perform safely and efficiently aperture measurements and loss maps with high intensity bunch trains well above stored beam energies that are considered to be safe. In particular, lengthy procedures for measurements at top energy, otherwise requiring multiple fills of individual bunches, can be avoided. In this paper, the method is presented and results from beam measurements are discussed and compared with alternative blow-up methods.

WEPPR069	Measurements and Simulations of Transverse Coupled-Bunch Instability Rise Times in the LHC	3087
	N. Mounet, R. Alemany-Fernandez, W. Höfle, D. Jacquet, V. Kain, E. Métral, L. Ponce, S. Redaelli, G. Rumolo, R. Suykerbuyk, D. Valuch CERN, Geneva, Switzerland
	In the current configuration of the LHC, multibunch instabilities due to the beam-coupling impedance would be in principle a critical limitation if they were not damped by the transverse feedback. For the future operation of the machine, in particular at higher bunch intensities and/or higher number of bunches, one needs to make sure the coupled-bunch instability rise times are still manageable by the feedback system. Therefore, in May 2011 experiments were performed to measure those rise times and compare them with the results obtained from the LHC impedance model and the HEADTAIL wake fields simulation code. At injection energy, agreement turns out to be very good, while a larger discrepancy appears at top energy.