IPAC2013 - List of Authors (Höfle, W.)

Paper

Title

Page

Investigations of the LHC Emittance Blow-Up during the 2012 Proton Run

1394

M. Kuhn
Uni HH, Hamburg, Germany
G. Arduini, P. Baudrenghien, J. Emery, A. Guerrero, W. Höfle, V. Kain, M. Lamont, T. Mastoridis, F. Roncarolo, M. Sapinski, M. Schaumann, R.J. Steinhagen, G. Trad, D. Valuch
CERN, Geneva, Switzerland

About 30 % of the potential luminosity performance is lost through the different phases of the LHC cycle, mainly due to transverse emittance blow-up. Measuring the emittance growth is a difficult task with high intensity beams and changing energies. Improvements of the LHC transverse profile instrumentation helped to study various effects. A breakdown of the growth through the different phases of the LHC cycle is given as well as a comparison with the data from the LHC experiments for transverse beam size. In 2012 a number of possible sources and remedies have been studied. Among these are intra beam scattering, 50 Hz noise and the effect of the transverse damper gain. The results of the investigations are summarized in this paper. Requirements for transverse profile instrumentation for post LHC long shutdown operation to finally tackle the emittance growth are given as well.

TUPME034

Experimental Studies for Future LHC Beams in the SPS

1652

H. Bartosik, T. Argyropoulos, T. Bohl, S. Cettour-Cave, J.F. Esteban Müller, W. Höfle, G. Iadarola, Y. Papaphilippou, G. Rumolo, B. Salvant, F. Schmidt, E.N. Shaposhnikova, H. Timko
CERN, Geneva, Switzerland
A.Y. Molodozhentsev
KEK, Ibaraki, Japan

The High Luminosity LHC (HL-LHC) project requires significantly higher beam intensity than presently accessible in the LHC injector chain. The aim of the LHC injectors upgrade project (LIU) is to prepare the CERN accelerators for the future needs of the LHC. Therefore a series of machine studies with high brightness beams were performed, assessing the present performance reach and identifying remaining limitations. Of particular concern are beam loading and longitudinal instabilities at high energy, space charge for beams with 50ns bunch spacing and electron cloud effects for beams with 25ns bunch spacing. This paper provides a summary of the performed studies, that have been possible thanks to the implementation of the SPS low gamma-transition optics.

WEPEA053

Progress with the Upgrade of the SPS for the HL-LHC Era

2624

B. Goddard, T. Argyropoulos, W. Bartmann, H. Bartosik, T. Bohl, F. Caspers, K. Cornelis, H. Damerau, L.N. Drøsdal, L. Ducimetière, J.F. Esteban Müller, R. Garoby, M. Gourber-Pace, W. Höfle, G. Iadarola, L.K. Jensen, V. Kain, R. Losito, M. Meddahi, A. Mereghetti, V. Mertens, Ö. Mete, E. Montesinos, Y. Papaphilippou, G. Rumolo, B. Salvant, E.N. Shaposhnikova, M. Taborelli, H. Timko, F.M. Velotti
CERN, Geneva, Switzerland
E. Gianfelice-Wendt
Fermilab, Batavia, USA

The demanding beam performance requirements of the HL-LHC project translate into a set of requirements and upgrade paths for the LHC injector complex. In this paper the performance requirements for the SPS and the known limitations are reviewed in the light of the 2012 operational experience. The various SPS upgrades in progress and still under consideration are described, in addition to the machine studies and simulations performed in 2012. The expected machine performance reach is estimated on the basis of the present knowledge, and the remaining decisions that still need to be made concerning upgrade options are detailed.

WEPME042

Modelling and Studies for a Wideband Feedback System for Mitigation of Transverse Single Bunch Instabilities

3019

K.S.B. Li, W. Höfle, G. Rumolo
CERN, Geneva, Switzerland
J.M. Cesaratto, J.E. Dusatko, J.D. Fox, M.T.F. Pivi, K.M. Pollock, C.H. Rivetta, O. Turgut
SLAC, Menlo Park, California, USA

As part of the LHC injector upgrade a wideband feedback system is under study for mitigation of coherent single bunch instabilities. This type of system may provide a generic way of shifting the instability threshold to regions that are currently inaccessible, thus, boosting the brightness of future beams. To study the effectiveness of such systems, a numerical model has been developed that constitutes a realistic feedback system including real transfer functions for pickup and kicker, realistic N-tap FIR and IIR filters as well as noise and saturation effects. Simulations of SPS cases have been performed with HeadTail to evaluate the feedback effectiveness in the presence of electron clouds and TMCI. Some results are presented addressing bandwidth limitations, noise issues and amplifier power requirements.

WEPME043

Performance of the LHC Transverse Damper with Bunch Trains

3022

W. Höfle, F. Dubouchet, G. Kotzian, D. Valuch
CERN, Geneva, Switzerland

In 2012 the LHC has operated for Physics with bunch trains at 50 ns spacing. Tests have been performed with the nominal design bunch spacing of 25 ns. The transverse damper has been an essential element to provide beam stability for the multi-bunch beam with up to 1380 bunches used at 50 ns spacing. We report on the experience gained with 50 ns spacing and the improvements in the signal processing tested for the future 25 ns operation. The increase in bandwidth required for 25 ns spacing constituted a particular challenge. The response of the system was carefully measured and the results used to digitally pre-distort the drive signal to compensate for a drop in gain of the power system for higher frequencies. The bunch-by-bunch data collected from the feedback signal path provided valuable information during the 2012 Physics run that can be further explored for beam diagnostics purposes and instability analysis in the future. Performance estimates are given for the 7 TeV run planned for 2015, at 25 ns bunch spacing.

WEPME044

Generation of Controlled Losses in Milisecond Timescale with Transverse Damper in LHC

3025

M. Sapinski, T. Baer, V. Chetvertkova, B. Dehning, W. Höfle, A. Priebe, R. Schmidt, D. Valuch
CERN, Geneva, Switzerland

A controlled way of generating of beam losses is required in order to investigate the quench limits of the superconducting magnets in the LHC. This is especially difficult to achieve for losses with millisecond duration. A series of experiments using the transverse damper system has proven that such a fast loss can be obtained even in the case of rigid 4 TeV beams. This paper describes the optimisation of beam parameters and transverse damper waveform required to mimic fast loss scenarios and reports on extensive tracking simulations undertaken to fully understand the time and spatial structure of these losses. The application of this method to the final quench tests is also presented.

WEPME059

A 4 GS/sec Instability Feedback Processing System for Intra-bunch Instabilities

3067

J.E. Dusatko, J.M. Cesaratto, J.D. Fox, J.J. Olsen, K.M. Pollock, C.H. Rivetta, O. Turgut
SLAC, Menlo Park, California, USA
W. Höfle
CERN, Geneva, Switzerland

Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 and the US LHC Accelerator Research program ( LARP)
We present the architecture and implementation overview of a proof-of-principle digital signal processing system developed to study control of Electron-Cloud and Transverse Mode Coupling Instabilities (TMCI) in the CERN SPS. This system is motivated by intensity increases planned as part of the High Luminosity LHC upgrade. It is based on a reconfigurable processing architecture which samples intra-bunch motion and applies correction signals at a 4GSa/s rate, allowing multiple samples across a single 2ns SPS bunch. This initial demonstration system is a rapidly developed prototype consisting of both commercial and custom-designed hardware that implements feedback control on a single bunch. It contains a high speed ADC and DAC, capable of sampling at up to 4GSa/s, with a 16-tap FIR control filter for each bunch sample slice. Other system features include a timing subsystem to synchronize the sampling to the injection and the bunch 1 markers, the capability of generating arbitrary time domain signals to drive the bunch and diagnostic functions including a snapshot memory for ADC data. This paper describes the design, construction and operational experience of this system.

WEPME060

First Results and Analysis of the Performance of a 4 GS/s Intra-bunch Vertical Feedback System at the SPS

3070

J.M. Cesaratto, J.E. Dusatko, J.D. Fox, J.J. Olsen, K.M. Pollock, C.H. Rivetta, O. Turgut
SLAC, Menlo Park, California, USA
H. Bartosik, W. Höfle, G. Kotzian, U. Wehrle
CERN, Geneva, Switzerland

Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 and the US LHC Accelerator Research program ( LARP)
We present experimental measurements taken from SPS machine development studies with an intra-bunch feedback channel. These studies use a digital signal processing system to implement general-purpose control algorithms on multiple samples across a single SPS bunch ( for ease of synchronization with the SPS RF frequency a sampling frequency of 3.2 GS/sec. is implemented). These initial studies concentrate on single-bunch motion, and study the vertical betatron motion as the feedback control is varied. The studies are focused on validating simulation models of the beam dynamics with feedback. Time and frequency domain results include excitation and damping of intra-bunch motion with positive and negative feedback. We present an overview of the challenges of intra-bunch feedback, and highlight methods to time-align the pickup and kicker signals within the closed-loop feedback channel.

WEPME061

A Wideband Slotted Kicker Design for SPS Transverse Intra-bunch Feedback

3073

J.M. Cesaratto, J.D. Fox, C.H. Rivetta
SLAC, Menlo Park, California, USA
D. Alesini, A. Drago, A. Gallo, F. Marcellini, M. Zobov
INFN/LNF, Frascati (Roma), Italy
S. De Santis
LBNL, Berkeley, California, USA
W. Höfle
CERN, Geneva, Switzerland

Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP) and by the EU FP7 HiLumi LHC - Grant Agreement 284404.
Control and mitigation of transverse beam instabilities caused by electron cloud and TMCI will be essential for the SPS to meet the beam intensity demands for the HL-LHC upgrade. A wideband intra-bunch feedback method is in development, based on a 4 GS/s data acquisition and processing, and with a back end frequency structure extending to 1 GHz. A slotted type kicker, similar to those used for stochastic cooling, has been considered as the terminal element of the feedback chain. It offers the most promising deflecting structure characteristics to meet the system requirements in terms of bandwidth, shunt impedance, and beam coupling impedance. Different types of slotted structures have been explored and simulated, including a ridged waveguide and coaxial type waveguide. In this paper we present our findings and the conceptual design of a vertical SPS wideband kicker consistent with the stay clear, vacuum, frequency band coverage, and peak shunt impedance requirements.

THPEA045

Beam Induced Quenches of LHC Magnets

3243

M. Sapinski, T. Baer, M. Bednarek, G. Bellodi, C. Bracco, R. Bruce, B. Dehning, W. Höfle, A. Lechner, E. Nebot Del Busto, A. Priebe, S. Redaelli, B. Salvachua, R. Schmidt, D. Valuch, A.P. Verweij, J. Wenninger, D. Wollmann, M. Zerlauth
CERN, Geneva, Switzerland

In the years 2009-2013 LHC was operating with the beam energy of 3.5 and 4 TeV instead of the nominal 7 TeV, with the corresponding currents in the superconducting magnets also half nominal. To date only a small number of beam-induced quenches have occurred, with most being due to specially designed quench tests. During normal collider operation with stored beam there has not been a single beam induced quench. This excellent result is mainly explained by the fact that the cleaning of the beam halo worked very well and, in case of beam losses, the beam was dumped before any significant energy was deposited in the magnets. However, conditions are expected to become much tougher after the long LHC shutdown, when the magnets will be working at near nominal currents in the presence of high energy and intensity beams. This paper summarizes the experience to date with beam-induced quenches. It describes the techniques used to generate controlled quench conditions which were used to study the limitations. Results are discussed along with their implication for LHC operation after the first Long Shutdown.

THPWO080

Operational Performance of the LHC Proton Beams with the SPS Low Transition Energy Optics

3945

Y. Papaphilippou, G. Arduini, T. Argyropoulos, W. Bartmann, H. Bartosik, T. Bohl, C. Bracco, S. Cettour-Cave, K. Cornelis, L.N. Drøsdal, J.F. Esteban Müller, B. Goddard, A. Guerrero, W. Höfle, V. Kain, G. Rumolo, B. Salvant, E.N. Shaposhnikova, H. Timko, D. Valuch, G. Vanbavinckhove, J. Wenninger
CERN, Geneva, Switzerland
E. Gianfelice-Wendt
Fermilab, Batavia, USA

An optics in the SPS with lower integer tunes (20 versus 26) was proposed and introduced in machine studies since 2010, as a measure for increasing transverse and longitudinal instability thresholds, especially at low energy, for the LHC proton beams. After two years of machine studies and careful optimisation, the new “Q20” optics became operational in September 2012 and steadily delivered beam to the LHC until the end of the run. This paper reviews the operational performance of the Q20 optics with respect to transverse and longitudinal beam characteristics in the SPS, enabling high brightness beams injected into the LHC. Aspects of longitudinal beam stability, transmission, high-energy orbit control and beam transfer are discussed.

FRXCA01

Progress in Transverse Feedbacks and Related Diagnostics for Hadron Machines

3990

W. Höfle
CERN, Geneva, Switzerland

Today Hadron Accelerators with high intensity and high brightness beams increasingly rely on transverse feedback systems for the control of instabilities and the preservation of the transverse emittance. With particular emphasis, but not limited, to the CERN Hadron Accelerator Chain the progress made in recent years and the performances achieved are reviewed. Hadron colliders such as the LHC represent a particular challenge as they ask for low noise electronic systems in these feedbacks for acceptable emittance growth. Achievements of the LHC transverse feedback system used for damping injection oscillations and to provide stability throughout the cycle are summarized. This includes its use for abort gap and injection cleaning as well as transverse blow-up for diagnostics purposes. Beyond systems already in operation, advances in technology and modern digital signal processing with increasingly higher digitization rates have made systems conceivable to cure intra-bunch motion. With its capabilities to both acquire beam oscillations and to actively excite motion, transverse feedback systems have a large variety of applications for beam diagnostics purposes.

Slides FRXCA01 [4.985 MB]

Paper	Title	Page
TUPFI026	Investigations of the LHC Emittance Blow-Up during the 2012 Proton Run	1394
	M. Kuhn Uni HH, Hamburg, Germany G. Arduini, P. Baudrenghien, J. Emery, A. Guerrero, W. Höfle, V. Kain, M. Lamont, T. Mastoridis, F. Roncarolo, M. Sapinski, M. Schaumann, R.J. Steinhagen, G. Trad, D. Valuch CERN, Geneva, Switzerland
	About 30 % of the potential luminosity performance is lost through the different phases of the LHC cycle, mainly due to transverse emittance blow-up. Measuring the emittance growth is a difficult task with high intensity beams and changing energies. Improvements of the LHC transverse profile instrumentation helped to study various effects. A breakdown of the growth through the different phases of the LHC cycle is given as well as a comparison with the data from the LHC experiments for transverse beam size. In 2012 a number of possible sources and remedies have been studied. Among these are intra beam scattering, 50 Hz noise and the effect of the transverse damper gain. The results of the investigations are summarized in this paper. Requirements for transverse profile instrumentation for post LHC long shutdown operation to finally tackle the emittance growth are given as well.

TUPME034	Experimental Studies for Future LHC Beams in the SPS	1652
	H. Bartosik, T. Argyropoulos, T. Bohl, S. Cettour-Cave, J.F. Esteban Müller, W. Höfle, G. Iadarola, Y. Papaphilippou, G. Rumolo, B. Salvant, F. Schmidt, E.N. Shaposhnikova, H. Timko CERN, Geneva, Switzerland A.Y. Molodozhentsev KEK, Ibaraki, Japan
	The High Luminosity LHC (HL-LHC) project requires significantly higher beam intensity than presently accessible in the LHC injector chain. The aim of the LHC injectors upgrade project (LIU) is to prepare the CERN accelerators for the future needs of the LHC. Therefore a series of machine studies with high brightness beams were performed, assessing the present performance reach and identifying remaining limitations. Of particular concern are beam loading and longitudinal instabilities at high energy, space charge for beams with 50ns bunch spacing and electron cloud effects for beams with 25ns bunch spacing. This paper provides a summary of the performed studies, that have been possible thanks to the implementation of the SPS low gamma-transition optics.

WEPEA053	Progress with the Upgrade of the SPS for the HL-LHC Era	2624
	B. Goddard, T. Argyropoulos, W. Bartmann, H. Bartosik, T. Bohl, F. Caspers, K. Cornelis, H. Damerau, L.N. Drøsdal, L. Ducimetière, J.F. Esteban Müller, R. Garoby, M. Gourber-Pace, W. Höfle, G. Iadarola, L.K. Jensen, V. Kain, R. Losito, M. Meddahi, A. Mereghetti, V. Mertens, Ö. Mete, E. Montesinos, Y. Papaphilippou, G. Rumolo, B. Salvant, E.N. Shaposhnikova, M. Taborelli, H. Timko, F.M. Velotti CERN, Geneva, Switzerland E. Gianfelice-Wendt Fermilab, Batavia, USA
	The demanding beam performance requirements of the HL-LHC project translate into a set of requirements and upgrade paths for the LHC injector complex. In this paper the performance requirements for the SPS and the known limitations are reviewed in the light of the 2012 operational experience. The various SPS upgrades in progress and still under consideration are described, in addition to the machine studies and simulations performed in 2012. The expected machine performance reach is estimated on the basis of the present knowledge, and the remaining decisions that still need to be made concerning upgrade options are detailed.

WEPME042	Modelling and Studies for a Wideband Feedback System for Mitigation of Transverse Single Bunch Instabilities	3019
	K.S.B. Li, W. Höfle, G. Rumolo CERN, Geneva, Switzerland J.M. Cesaratto, J.E. Dusatko, J.D. Fox, M.T.F. Pivi, K.M. Pollock, C.H. Rivetta, O. Turgut SLAC, Menlo Park, California, USA
	As part of the LHC injector upgrade a wideband feedback system is under study for mitigation of coherent single bunch instabilities. This type of system may provide a generic way of shifting the instability threshold to regions that are currently inaccessible, thus, boosting the brightness of future beams. To study the effectiveness of such systems, a numerical model has been developed that constitutes a realistic feedback system including real transfer functions for pickup and kicker, realistic N-tap FIR and IIR filters as well as noise and saturation effects. Simulations of SPS cases have been performed with HeadTail to evaluate the feedback effectiveness in the presence of electron clouds and TMCI. Some results are presented addressing bandwidth limitations, noise issues and amplifier power requirements.

WEPME043	Performance of the LHC Transverse Damper with Bunch Trains	3022
	W. Höfle, F. Dubouchet, G. Kotzian, D. Valuch CERN, Geneva, Switzerland
	In 2012 the LHC has operated for Physics with bunch trains at 50 ns spacing. Tests have been performed with the nominal design bunch spacing of 25 ns. The transverse damper has been an essential element to provide beam stability for the multi-bunch beam with up to 1380 bunches used at 50 ns spacing. We report on the experience gained with 50 ns spacing and the improvements in the signal processing tested for the future 25 ns operation. The increase in bandwidth required for 25 ns spacing constituted a particular challenge. The response of the system was carefully measured and the results used to digitally pre-distort the drive signal to compensate for a drop in gain of the power system for higher frequencies. The bunch-by-bunch data collected from the feedback signal path provided valuable information during the 2012 Physics run that can be further explored for beam diagnostics purposes and instability analysis in the future. Performance estimates are given for the 7 TeV run planned for 2015, at 25 ns bunch spacing.

WEPME044	Generation of Controlled Losses in Milisecond Timescale with Transverse Damper in LHC	3025
	M. Sapinski, T. Baer, V. Chetvertkova, B. Dehning, W. Höfle, A. Priebe, R. Schmidt, D. Valuch CERN, Geneva, Switzerland
	A controlled way of generating of beam losses is required in order to investigate the quench limits of the superconducting magnets in the LHC. This is especially difficult to achieve for losses with millisecond duration. A series of experiments using the transverse damper system has proven that such a fast loss can be obtained even in the case of rigid 4 TeV beams. This paper describes the optimisation of beam parameters and transverse damper waveform required to mimic fast loss scenarios and reports on extensive tracking simulations undertaken to fully understand the time and spatial structure of these losses. The application of this method to the final quench tests is also presented.

WEPME059	A 4 GS/sec Instability Feedback Processing System for Intra-bunch Instabilities	3067
	J.E. Dusatko, J.M. Cesaratto, J.D. Fox, J.J. Olsen, K.M. Pollock, C.H. Rivetta, O. Turgut SLAC, Menlo Park, California, USA W. Höfle CERN, Geneva, Switzerland
	Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 and the US LHC Accelerator Research program ( LARP) We present the architecture and implementation overview of a proof-of-principle digital signal processing system developed to study control of Electron-Cloud and Transverse Mode Coupling Instabilities (TMCI) in the CERN SPS. This system is motivated by intensity increases planned as part of the High Luminosity LHC upgrade. It is based on a reconfigurable processing architecture which samples intra-bunch motion and applies correction signals at a 4GSa/s rate, allowing multiple samples across a single 2ns SPS bunch. This initial demonstration system is a rapidly developed prototype consisting of both commercial and custom-designed hardware that implements feedback control on a single bunch. It contains a high speed ADC and DAC, capable of sampling at up to 4GSa/s, with a 16-tap FIR control filter for each bunch sample slice. Other system features include a timing subsystem to synchronize the sampling to the injection and the bunch 1 markers, the capability of generating arbitrary time domain signals to drive the bunch and diagnostic functions including a snapshot memory for ADC data. This paper describes the design, construction and operational experience of this system.

WEPME060	First Results and Analysis of the Performance of a 4 GS/s Intra-bunch Vertical Feedback System at the SPS	3070
	J.M. Cesaratto, J.E. Dusatko, J.D. Fox, J.J. Olsen, K.M. Pollock, C.H. Rivetta, O. Turgut SLAC, Menlo Park, California, USA H. Bartosik, W. Höfle, G. Kotzian, U. Wehrle CERN, Geneva, Switzerland
	Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 and the US LHC Accelerator Research program ( LARP) We present experimental measurements taken from SPS machine development studies with an intra-bunch feedback channel. These studies use a digital signal processing system to implement general-purpose control algorithms on multiple samples across a single SPS bunch ( for ease of synchronization with the SPS RF frequency a sampling frequency of 3.2 GS/sec. is implemented). These initial studies concentrate on single-bunch motion, and study the vertical betatron motion as the feedback control is varied. The studies are focused on validating simulation models of the beam dynamics with feedback. Time and frequency domain results include excitation and damping of intra-bunch motion with positive and negative feedback. We present an overview of the challenges of intra-bunch feedback, and highlight methods to time-align the pickup and kicker signals within the closed-loop feedback channel.

WEPME061	A Wideband Slotted Kicker Design for SPS Transverse Intra-bunch Feedback	3073
	J.M. Cesaratto, J.D. Fox, C.H. Rivetta SLAC, Menlo Park, California, USA D. Alesini, A. Drago, A. Gallo, F. Marcellini, M. Zobov INFN/LNF, Frascati (Roma), Italy S. De Santis LBNL, Berkeley, California, USA W. Höfle CERN, Geneva, Switzerland
	Funding: Work supported by the U.S. Department of Energy under contract DE-AC02-76SF00515 and the US LHC Accelerator Research Program (LARP) and by the EU FP7 HiLumi LHC - Grant Agreement 284404. Control and mitigation of transverse beam instabilities caused by electron cloud and TMCI will be essential for the SPS to meet the beam intensity demands for the HL-LHC upgrade. A wideband intra-bunch feedback method is in development, based on a 4 GS/s data acquisition and processing, and with a back end frequency structure extending to 1 GHz. A slotted type kicker, similar to those used for stochastic cooling, has been considered as the terminal element of the feedback chain. It offers the most promising deflecting structure characteristics to meet the system requirements in terms of bandwidth, shunt impedance, and beam coupling impedance. Different types of slotted structures have been explored and simulated, including a ridged waveguide and coaxial type waveguide. In this paper we present our findings and the conceptual design of a vertical SPS wideband kicker consistent with the stay clear, vacuum, frequency band coverage, and peak shunt impedance requirements.

THPEA045	Beam Induced Quenches of LHC Magnets	3243
	M. Sapinski, T. Baer, M. Bednarek, G. Bellodi, C. Bracco, R. Bruce, B. Dehning, W. Höfle, A. Lechner, E. Nebot Del Busto, A. Priebe, S. Redaelli, B. Salvachua, R. Schmidt, D. Valuch, A.P. Verweij, J. Wenninger, D. Wollmann, M. Zerlauth CERN, Geneva, Switzerland
	In the years 2009-2013 LHC was operating with the beam energy of 3.5 and 4 TeV instead of the nominal 7 TeV, with the corresponding currents in the superconducting magnets also half nominal. To date only a small number of beam-induced quenches have occurred, with most being due to specially designed quench tests. During normal collider operation with stored beam there has not been a single beam induced quench. This excellent result is mainly explained by the fact that the cleaning of the beam halo worked very well and, in case of beam losses, the beam was dumped before any significant energy was deposited in the magnets. However, conditions are expected to become much tougher after the long LHC shutdown, when the magnets will be working at near nominal currents in the presence of high energy and intensity beams. This paper summarizes the experience to date with beam-induced quenches. It describes the techniques used to generate controlled quench conditions which were used to study the limitations. Results are discussed along with their implication for LHC operation after the first Long Shutdown.

THPWO080	Operational Performance of the LHC Proton Beams with the SPS Low Transition Energy Optics	3945
	Y. Papaphilippou, G. Arduini, T. Argyropoulos, W. Bartmann, H. Bartosik, T. Bohl, C. Bracco, S. Cettour-Cave, K. Cornelis, L.N. Drøsdal, J.F. Esteban Müller, B. Goddard, A. Guerrero, W. Höfle, V. Kain, G. Rumolo, B. Salvant, E.N. Shaposhnikova, H. Timko, D. Valuch, G. Vanbavinckhove, J. Wenninger CERN, Geneva, Switzerland E. Gianfelice-Wendt Fermilab, Batavia, USA
	An optics in the SPS with lower integer tunes (20 versus 26) was proposed and introduced in machine studies since 2010, as a measure for increasing transverse and longitudinal instability thresholds, especially at low energy, for the LHC proton beams. After two years of machine studies and careful optimisation, the new “Q20” optics became operational in September 2012 and steadily delivered beam to the LHC until the end of the run. This paper reviews the operational performance of the Q20 optics with respect to transverse and longitudinal beam characteristics in the SPS, enabling high brightness beams injected into the LHC. Aspects of longitudinal beam stability, transmission, high-energy orbit control and beam transfer are discussed.

FRXCA01	Progress in Transverse Feedbacks and Related Diagnostics for Hadron Machines	3990
	W. Höfle CERN, Geneva, Switzerland
	Today Hadron Accelerators with high intensity and high brightness beams increasingly rely on transverse feedback systems for the control of instabilities and the preservation of the transverse emittance. With particular emphasis, but not limited, to the CERN Hadron Accelerator Chain the progress made in recent years and the performances achieved are reviewed. Hadron colliders such as the LHC represent a particular challenge as they ask for low noise electronic systems in these feedbacks for acceptable emittance growth. Achievements of the LHC transverse feedback system used for damping injection oscillations and to provide stability throughout the cycle are summarized. This includes its use for abort gap and injection cleaning as well as transverse blow-up for diagnostics purposes. Beyond systems already in operation, advances in technology and modern digital signal processing with increasingly higher digitization rates have made systems conceivable to cure intra-bunch motion. With its capabilities to both acquire beam oscillations and to actively excite motion, transverse feedback systems have a large variety of applications for beam diagnostics purposes.
	Slides FRXCA01 [4.985 MB]