IPAC2012 - List of Authors (Schmidt, R.)

Paper	Title	Page
MOPPC004	Experiments on the Margin of Beam Induced Quenches for LHC Superconducting Quadrupole Magnet in the LHC	124
	C. Bracco, W. Bartmann, M. Bednarek, B. Goddard, E.B. Holzer, A. Nordt, M. Sapinski, R. Schmidt, M. Solfaroli Camillocci, M. Zerlauth, E.N. del Busto CERN, Geneva, Switzerland
	Protection of LHC equipment relies on a complex system of collimators to capture injected or circulating beam in case of LHC injection kicker magnet failures. However, for specific failures of the injection kicker, the beam can graze the injection protection collimators and induce quenches of downstream superconducting magnets. This occurred twice during 2011 operation and can also not be excluded during further operation. Tests were performed during Machine Development periods of the LHC to assess the quench margin of the quadrupole located just downstream of the last injection protection collimator in point 8. In addition to the existing Quench Protection System, a special monitoring instrumentation was installed at this magnet to detect any resistance increase below the quench limit. The correlation between the magnet and Beam Loss Monitor signals was analysed for different beam intensities and magnet current. The results of the experiments are presented in this paper.

THPPD028	Studies on the LHC Superconducting Circuits and Routine Qualification of Their Functionalities	3563
	M. Pojer, G. D'Angelo, R. Mompo, R. Schmidt, M. Solfaroli Camillocci CERN, Geneva, Switzerland
	The Large Hadron Collider (LHC) is systematically undergoing periods of maintenance stop (either 4-5 days stops or longer Christmas breaks), after which some of the superconducting circuits (or the totality of them) have to be re-commissioned to check the correct functionality of all powering and protection systems. Detailed procedures have been developed during the past few years and they have been optimized to increase powering tests efficiency, thus reducing beam downtime. The approach to the routine qualification of the LHC powering systems is described in this paper. During 2011 technical stops, some particular studies on the superconducting circuits were performed, to assess the quality of the superconducting splices of individually powered magnets and to study the quench propagation in the main magnet bus-bars. The methodology of these tests and some results are also presented.

THPPD029	Machine Availability at the Large Hadron Collider	3566
	M. Pojer, R. Schmidt, M. Solfaroli Camillocci, S. Wagner CERN, Geneva, Switzerland
	One of the most important parameters for a particle accelerator is its uptime, the period of time when it is functioning and available for use. In its second year of operation, the Large Hadron Collider (LHC) has experienced very high machine availability, which is one of the ingredients of its brilliant performance. Some of the strategies followed to increase MTBF are described in the paper. The approach of periodic maintenance stops, often questioned, is also discussed. Some considerations on the ideal length of a physics fill are also drawn.

THPPD031	Measurement of the Residual Resistivity Ratio of the Bus Bars Copper Stabilizer of the 13 kA Circuits of the LHC	3572
	A. Apollonio, S.D. Claudet, M. Koratzinos, R. Schmidt, A.P. Siemko, M. Solfaroli Camillocci, J. Steckert, H. Thiesen, A.P. Verweij CERN, Geneva, Switzerland
	After the incident of September 2008, the operational beam energy of the LHC has been set to 3.5 TeV, since not all joints of the superconducting busbars between magnets have the required quality for 7 TeV operation. This choice is based on simulations to determine the safe current in the main dipole and quadrupole magnets, reproducing the thermal behavior of a quenched superconducting joint by taking into account all relevant factors that affect a possible thermal runaway. One important parameter of the simulation is the RRR (Residual Resistivity Ratio) of the copper stabilizer of the busbar connecting superconducting magnets. A dedicated campaign to measure this quantity for the main 13kA circuits of the LHC on all sectors was performed during the Christmas stop in December 2010 and January 2011. The measurement method as well as the data analysis and results are presented in this paper.

THPPP010	LHC Orbit Correction Reproducibility and Related Machine Protection	3746
	K. Fuchsberger, T. Baer, R. Schmidt, J. Wenninger CERN, Geneva, Switzerland
	The Large Hadron Collider (LHC) has an unprecedented nominal stored beam energy of up to 362 MJ per beam. In order to ensure an adequate machine protection by the collimation system, a high reproducibility of the beam position at collimators and special elements like the final focus quadrupoles is essential. This is realized by a combination of manual orbit corrections, feed forward and real time feedback. In order to protect the LHC against inconsistent orbit corrections, which could put the machine in a vulnerable state, a novel software-based interlock system for orbit corrector currents was developed. In this paper, the principle of the new interlock system is described and the reproducibility of the LHC orbit correction is discussed against the background of this system.

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.

THPPR040	First Operational Experience with the LHC Machine Protection System when Operating with Beam Energies Beyond the 100 MJ Range	4062
	M. Zerlauth, R.W. Assmann, B. Dehning, M. Ferro-Luzzi, B. Goddard, M. Lamont, R. Schmidt, A.P. Siemko, J.A. Uythoven, J. Wenninger CERN, Geneva, Switzerland
	The LHC made a remarkable progress in luminosity production during 2011 operation. This was made possible by a progressive increase of beam intensities by more than 5 orders of magnitude, reaching stored beam energies beyond 100MJ at the end of the year. The correct functioning of the machine protection systems was vital during initial operation and even more when approaching nominal beam parameters, where an uncontrolled loss of a small fraction of the beam is already sufficient to damage accelerator equipment or the large experimental detectors The machine protection system depends on the interplay of many different elements: beam dumping system, beam interlocks, beam instrumentation, equipment monitoring, collimators and absorbers, etc. The strategy applied during 2011 to allow for an efficient but yet safe increase of the beam intensities is presented along with the associated risks and drawbacks of a too aggressive approach. The experience gained with the key systems will be discussed along with possibilities to further enhance machine availability whilst maintaining the current level of safety.

Paper

Title

Page

Experiments on the Margin of Beam Induced Quenches for LHC Superconducting Quadrupole Magnet in the LHC

124

C. Bracco, W. Bartmann, M. Bednarek, B. Goddard, E.B. Holzer, A. Nordt, M. Sapinski, R. Schmidt, M. Solfaroli Camillocci, M. Zerlauth, E.N. del Busto
CERN, Geneva, Switzerland

Protection of LHC equipment relies on a complex system of collimators to capture injected or circulating beam in case of LHC injection kicker magnet failures. However, for specific failures of the injection kicker, the beam can graze the injection protection collimators and induce quenches of downstream superconducting magnets. This occurred twice during 2011 operation and can also not be excluded during further operation. Tests were performed during Machine Development periods of the LHC to assess the quench margin of the quadrupole located just downstream of the last injection protection collimator in point 8. In addition to the existing Quench Protection System, a special monitoring instrumentation was installed at this magnet to detect any resistance increase below the quench limit. The correlation between the magnet and Beam Loss Monitor signals was analysed for different beam intensities and magnet current. The results of the experiments are presented in this paper.

THPPD028

Studies on the LHC Superconducting Circuits and Routine Qualification of Their Functionalities

3563

M. Pojer, G. D'Angelo, R. Mompo, R. Schmidt, M. Solfaroli Camillocci
CERN, Geneva, Switzerland

The Large Hadron Collider (LHC) is systematically undergoing periods of maintenance stop (either 4-5 days stops or longer Christmas breaks), after which some of the superconducting circuits (or the totality of them) have to be re-commissioned to check the correct functionality of all powering and protection systems. Detailed procedures have been developed during the past few years and they have been optimized to increase powering tests efficiency, thus reducing beam downtime. The approach to the routine qualification of the LHC powering systems is described in this paper. During 2011 technical stops, some particular studies on the superconducting circuits were performed, to assess the quality of the superconducting splices of individually powered magnets and to study the quench propagation in the main magnet bus-bars. The methodology of these tests and some results are also presented.

THPPD029

Machine Availability at the Large Hadron Collider

3566

M. Pojer, R. Schmidt, M. Solfaroli Camillocci, S. Wagner
CERN, Geneva, Switzerland

One of the most important parameters for a particle accelerator is its uptime, the period of time when it is functioning and available for use. In its second year of operation, the Large Hadron Collider (LHC) has experienced very high machine availability, which is one of the ingredients of its brilliant performance. Some of the strategies followed to increase MTBF are described in the paper. The approach of periodic maintenance stops, often questioned, is also discussed. Some considerations on the ideal length of a physics fill are also drawn.

THPPD031

Measurement of the Residual Resistivity Ratio of the Bus Bars Copper Stabilizer of the 13 kA Circuits of the LHC

3572

A. Apollonio, S.D. Claudet, M. Koratzinos, R. Schmidt, A.P. Siemko, M. Solfaroli Camillocci, J. Steckert, H. Thiesen, A.P. Verweij
CERN, Geneva, Switzerland

After the incident of September 2008, the operational beam energy of the LHC has been set to 3.5 TeV, since not all joints of the superconducting busbars between magnets have the required quality for 7 TeV operation. This choice is based on simulations to determine the safe current in the main dipole and quadrupole magnets, reproducing the thermal behavior of a quenched superconducting joint by taking into account all relevant factors that affect a possible thermal runaway. One important parameter of the simulation is the RRR (Residual Resistivity Ratio) of the copper stabilizer of the busbar connecting superconducting magnets. A dedicated campaign to measure this quantity for the main 13kA circuits of the LHC on all sectors was performed during the Christmas stop in December 2010 and January 2011. The measurement method as well as the data analysis and results are presented in this paper.

THPPP010

LHC Orbit Correction Reproducibility and Related Machine Protection

3746

K. Fuchsberger, T. Baer, R. Schmidt, J. Wenninger
CERN, Geneva, Switzerland

The Large Hadron Collider (LHC) has an unprecedented nominal stored beam energy of up to 362 MJ per beam. In order to ensure an adequate machine protection by the collimation system, a high reproducibility of the beam position at collimators and special elements like the final focus quadrupoles is essential. This is realized by a combination of manual orbit corrections, feed forward and real time feedback. In order to protect the LHC against inconsistent orbit corrections, which could put the machine in a vulnerable state, a novel software-based interlock system for orbit corrector currents was developed. In this paper, the principle of the new interlock system is described and the reproducibility of the LHC orbit correction is discussed against the background of this system.

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.

THPPR040

First Operational Experience with the LHC Machine Protection System when Operating with Beam Energies Beyond the 100 MJ Range

4062

M. Zerlauth, R.W. Assmann, B. Dehning, M. Ferro-Luzzi, B. Goddard, M. Lamont, R. Schmidt, A.P. Siemko, J.A. Uythoven, J. Wenninger
CERN, Geneva, Switzerland

The LHC made a remarkable progress in luminosity production during 2011 operation. This was made possible by a progressive increase of beam intensities by more than 5 orders of magnitude, reaching stored beam energies beyond 100MJ at the end of the year. The correct functioning of the machine protection systems was vital during initial operation and even more when approaching nominal beam parameters, where an uncontrolled loss of a small fraction of the beam is already sufficient to damage accelerator equipment or the large experimental detectors The machine protection system depends on the interplay of many different elements: beam dumping system, beam interlocks, beam instrumentation, equipment monitoring, collimators and absorbers, etc. The strategy applied during 2011 to allow for an efficient but yet safe increase of the beam intensities is presented along with the associated risks and drawbacks of a too aggressive approach. The experience gained with the key systems will be discussed along with possibilities to further enhance machine availability whilst maintaining the current level of safety.