IPAC2018 - List of Authors (Wollmann, D.)

Paper	Title	Page
MOPMF042	Crab Cavity Failures Combined with a Loss of the Beam-Beam Kick in the High Luminosity LHC	192
	B. Lindstrom, H. Burkhardt, V.K.B. Olsen, A. Santamaría García, K.N. Sjobak, M. Valette, D. Wollmann CERN, Geneva, Switzerland
	Crab cavities are an essential component of the High Luminosity LHC (HL-LHC) project. In case of a failure they can create large transverse kicks on the beam within tens of microseconds and, therefore, require a fast extraction of the circulating beam. In this paper, the effects of different crab cavity failures in combination with the missing beam-beam kick following the dump of only one LHC beam are presented and consequences for the interlocking strategy of crab cavities are discussed. Work supported by the High Luminosity LHC project.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF042
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MOPMF046	Simulation of Hydrodynamic Tunneling Caused by High Energy Proton Beam in Copper through Coupling of FLUKA and Autodyn	204
	Y.C. Nie, A. Bertarelli, F. Carra, C. Fichera, L.K. Mettler, R. Schmidt, D. Wollmann CERN, Geneva, Switzerland
	For machine protection of high-energy colliders, it is important to assess potential damages caused to accelerator components in case large number of bunches are lost at the same place. The numerical assessment requires an iterative execution of an energy-deposition code and a hydrodynamic code, since the hydrodynamic tunneling effect will likely play an important role in the beam-matter interactions. For proton accelerators at CERN and for the Future Circular Collider (FCC), case studies were performed, coupling FLUKA and BIG2. To compare different hydrocodes and not to rely only on BIG2, FLUKA and a commercial tool, Autodyn, have been used to perform these simulations. This paper reports a benchmarking study against a beam test performed at the HiRadMat (High-Radiation to Materials) facility using beams at 440 GeV from the Super Proton Synchrotron. Good agreement has been found between the simulation results and the test as well as previous simulations with FLUKA and BIG2, particularly in terms of penetration depth of the beam in copper. This makes the coupling of FLUKA and Autodyn an alternative solution to simulating the hydrodynamic tunneling. More case studies are planned for FCC and other high-beam-power accelerators.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF046
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MOPMF053	Observations, Analysis and Mitigation of Recurrent LHC Beam Dumps Caused by Fast Losses in Arc Half-Cell 16L2	228
	J.M. Jimenez, D. Amorim, S. A. Antipov, G. Arduini, A. Bertarelli, N. Biancacci, B. Bradu, E. Bravin, G. Bregliozzi, K. Brodzinski, R. Bruce, X. Buffat, L.R. Carver, P. Chiggiato, S.D. Claudet, P. Collier, R. Garcia Alia, M. Giovannozzi, L. K. Grob, E.B. Holzer, W. Höfle, G. Iadarola, G. Kotzian, A. Lechner, T.E. Levens, B. Lindstrom, T. Medvedeva, A. Milanese, D. Mirarchi, E. Métral, D. Perini, S. Redaelli, G. Rumolo, B. Salvant, R. Schmidt, M. Valette, D. Valuch, J. Wenninger, D. Wollmann, C. Yin Vallgren, C. Zamantzas, M. Zerlauth CERN, Geneva, Switzerland D. Amorim Université Grenoble Alpes, Grenoble, France A.A. Gorzawski University of Manchester, Manchester, United Kingdom L. Mether EPFL, Lausanne, Switzerland
	Recurrent beam dumps significantly perturbed the operation of the CERN LHC in the summer months of 2017, especially in August. These unexpected beam dumps were triggered by fast beam losses that built up in the cryogenic beam vacuum at the half-cell 16 left of LHC-IP2 and were detected either at that location but mainly in the collimation insertions. This contribution details the experimental observables (beam losses, coherent instabilities, heat load to cryogenic system, vacuum signals), the extent of the understanding of the beam loss and instability mechanisms and the mitigation steps and new settings that allowed recovering the luminosity performance of the LHC for the rest of the Run.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF053
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MOPMF060	Safe Disposal of the LHC Beam without Beam Dump - Method and Experimental Verification	253
	M. Valette, B. Lindstrom, A. Mereghetti, R. Schmidt, M. Solfaroli, J.A. Uythoven, D. Valuch, J. Wenninger, D. Wollmann, M. Zerlauth CERN, Geneva, Switzerland
	Funding: Research supported by the HL-LHC project. In the extremely unlikely event of a non-working beam dumping system in the LHC, the 360 MJ of stored beam energy can be dissipated in the collimation system as a last mitigation measure. In such a situation, it is important to reduce the stored beam energy both quickly and at the same time as smoothly as possible in order to limit the risk of trips of critical systems, to avoid quenches of superconducting magnets (which would lead to changes of the beam trajectory and damage to the accelerator) and ultimately damage to the collimators themselves. Detailed steps and parameters have been developed and validated during two dedicated experiments with beam in the LHC. This paper summarizes the key aspects in view of the preparation of such a procedure for operational use, which will allow for the safe disposal of the full LHC beam by the operation crews.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF060
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MOPMF063	Asynchronous Beam Dump Tests at LHC	265
	C. Wiesner, W. Bartmann, C. Bracco, E. Carlier, L. Ducimetière, M.I. Frankl, M.A. Fraser, B. Goddard, C. Heßler, T. Kramer, A. Lechner, N. Magnin, V. Senaj, D. Wollmann CERN, Geneva, Switzerland
	The detailed understanding of the beam-loss pattern in case of an asynchronous beam dump is essential for the safe operation of the future High Luminosity LHC (HL-LHC) with nearly twice the nominal LHC beam intensity, leading to correspondingly higher energy deposition on the protection elements. An asynchronous beam dump is provoked when the rise time of the extraction kickers is not synchronized to the 3 us long particle-free abort gap. Thus, particles that are not absorbed by dedicated protection elements can be lost on the machine aperture. Since asynchronous beam dumps are among the most critical failure cases of the LHC, experimental tests at low intensity are performed routinely. This paper reviews recent asynchronous beam dump tests performed in the LHC. It describes the test conditions, discusses the beam-loss behaviour and presents simulation and measurement results. In particular, it examines a test event from May 2016, which led to the quench of four superconducting magnets in the extraction region and which was studied by a dedicated beam experiment in December 2017.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF063
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MOPMF064	High-Energy LHC Design	269
	F. Zimmermann, D. Amorim, S. A. Antipov, S. Arsenyev, M. Benedikt, R. Bruce, M.P. Crouch, S.D. Fartoukh, M. Giovannozzi, B. Goddard, M. Hofer, R. Kersevan, V. Mertens, Y. Muttoni, J.A. Osborne, V. Parma, V. Raginel, S. Redaelli, T. Risselada, I. Ruehl, B. Salvant, D. Schoerling, E.N. Shaposhnikova, L.J. Tavian, E. Todesco, R. Tomás, D. Tommasini, F. Valchkova-Georgieva, V. Venturi, D. Wollmann CERN, Geneva, Switzerland J.L. Abelleira, E. Cruz Alaniz, P. Martinez Mirave, A. Seryi, L. van Riesen-Haupt JAI, Oxford, United Kingdom A. Apyan ANSL, Yerevan, Armenia J. Barranco García, L. Mether, T. Pieloni, L. Rivkin, C. Tambasco EPFL, Lausanne, Switzerland F. Burkart DESY, Hamburg, Germany Y. Cai, Y.M. Nosochkov SLAC, Menlo Park, California, USA G. Guillermo Cantón CINVESTAV, Mérida, Mexico K. Ohmi, K. Oide, D. Zhou KEK, Ibaraki, Japan
	In the frame of the FCC study we are designing a 27 TeV hadron collider in the LHC tunnel, called the High Energy LHC (HE-LHC).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-MOPMF064
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TUPAF028	Energy Deposition Studies and Analysis of the Quench Behavior in the Case of Asynchronous Dumps During 6.5 TeV LHC Proton Beam Operation	736
	M.I. Frankl, W. Bartmann, M. Bednarek, C. Bracco, A. Lechner, A.P. Verweij, C. Wiesner, D. Wollmann CERN, Geneva, Switzerland
	The CERN LHC beam dumping system comprises a series of septa and fast-pulsed kicker magnets for extracting the stored proton beams to the external beam dumps. Different absorbers in the extraction region protect superconducting magnets and other machine elements in case of abnormal beam aborts, where bunches are swept across the machine aperture. During Run 2 of the LHC, controlled beam loss experiments were carried out at 6.5 TeV probing the particle leakage from protection devices under realistic operation conditions. This paper presents particle shower simulations analyzing the energy deposition in superconducting coils and assessing if the observed magnet quenches are compatible with the presently known quench limits.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF028
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TUPAF040	Beam Loss Measurements for Recurring Fast Loss Events During 2017 LHC Operation Possibly Caused by Macroparticles	780
	A. Lechner, B. Auchmann, E. Bravin, A.A. Gorzawski, L. K. Grob, E.B. Holzer, B. Lindstrom, T. Medvedeva, D. Mirarchi, R. Schmidt, M. Valette, D. Wollmann CERN, Geneva, Switzerland
	The availability of the LHC machine was adversely affected in 2017 by tens of beam aborts provoked by frequent loss events in one standard arc cell (16L2). In most of the cases, the dumps were triggered by concurrently developing fast beam instabilities leading to particle losses in the betatron cleaning insertion. Many of the events started with a distinct sub-millisecond loss peak comparable to regular dust particle events, which have been observed along all the LHC since the start-up. In contrast to regular dust events, persistent losses developed in cell 16L2 after the initial peaks which can possibly be explained by a phase transition of macroparticles to the gas phase. In this paper, we summarize the observed loss characteristics such as spatial loss pattern and time profiles measured by Beam Loss Monitors (ionization chambers). Based on the measurements, we estimate the energy deposition in macroparticles and reconstruct proton loss rates as well as the gas densities after the phase transition. Differences between regular dust events and events in 16L2 are highlighted and the ability to induce magnet quenches is discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF040
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TUPAF049	Analysis of Loss Signatures of Unidentified Falling Objects in the LHC	814
	L. K. Grob, M. Dziadosz, E.B. Holzer, A. Lechner, B. Lindstrom, R. Schmidt, D. Wollmann, C. Zamantzas CERN, Geneva, Switzerland
	Particulates in the LHC beam pipes can interact with the proton beams and cause significant beam losses. The "UFOs" (unidentified falling objects) hypothesis describes a particle falling into the beam, creating particle showers, being ionized and repelled. Though the signals of the beam loss monitors support this, many aspects remain unknown. Neither the source of the dust nor the release mechanism from the beam pipe are understood. The same holds for the forces involved in the interaction and the observed UFO rate reduction over the years. These open questions are approached from different angles. Firstly, a new data analysis tool was established featuring advanced raw data selection and statistical analysis. Results of this analysis will be presented. Secondly, dust samples were extracted from LHC components and analyzed to gain insight into the size distribution and material composition of the contamination. The performed observations and analysis lead to a better modelling of the UFO events and helped to understand the physics involved. The validated UFO models will be crucial in view of the high luminosity upgrade of the LHC (HL-LHC) and the Future Circular Collider (FCC).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF049
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WEPMG006	Experimental Setup to Characterize the Radiation Hardness of Cryogenic Bypass Diodes for the HL-LHC Inner Triplet Circuits	2620
	A. Will, G. D'Angelo, R. Denz, M.F. Favre, D. Hagedorn, G. Kirby, T. Koettig, A. Monteuuis, F. Rodriguez-Mateos, A.P. Siemko, K. Stachon, M. Valette, A.P. Verweij, D. Wollmann CERN, Geneva, Switzerland A. Bernhard, A.-S. Müller KIT, Karlsruhe, Germany L. Kistrup KEA, Copenhagen, Denmark
	Funding: Work supported by the Wolfgang Gentner Programme of the German Federal Ministry of Education and Research For the high luminosity upgrade of the Large Hadron Collider (LHC), it is planned to replace the existing triplet quadrupole magnets with Nb₃Sn quadrupole magnets, which provide a comparable integrated field gradient with a significantly increased aperture. These magnets will be powered through a novel superconducting link based on MgB₂ cables. One option for the powering layout of this triplet circuit is the use of cryogenic bypass diodes, where the diodes are located inside an extension to the magnet cryostat and operated in superfluid helium. Hence, they are exposed to radiation. For this reason the radiation hardness of existing LHC type bypass diodes and more radiation tolerant prototype diodes needs to be tested up to the radiation doses expected at their planned position during their lifetime. A first irradiation test is planned in CERN's CHARM facility starting in spring 2018. Therefore, a cryo-cooler based cryostat to irradiate and test LHC type diodes in-situ has been designed and constructed. This paper will describe the properties of the sample diodes, the experimental roadmap and the setup installed in CHARM. Finally, the first measurement results will be discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMG006
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THYGBD2	Results of UFO Dynamics Studies with Beam in the LHC	2914
	B. Lindstrom, A. Apollonio, P. Bélanger, M. Dziadosz, A.A. Gorzawski, L. K. Grob, E.B. Holzer, A. Lechner, R. Schmidt, M. Valette, D. Valuch, D. Wollmann CERN, Geneva, Switzerland
	Micrometer sized particles entering the LHC beam (the so-called Unidentified Falling Objects or UFOs) are a known cause of localized beam losses since the beginning of high intensity beam operation, however the origin of these particles is not fully known. Their effect limits LHC availability by causing premature dumps due to excessive beam losses and occasionally even magnet quenches. This could become an important limitation for future accelerators such as the High Luminosity upgrade of the LHC (HL-LHC) and the Future Circular Collider (FCC). The dynamics of these UFOs was investigated in two dedicated experiments. In the first experiment, it was shown that the transverse movements of these particles can be studied by observing bunch-by-bunch losses from bunches with different horizontal and vertical emittances. In the second experiment, UFO-like events around the 16L2 interconnect in the LHC, which has seen intense UFO activity in 2017, were studied with the above method. This paper summarizes the results of both experiments.
	Slides THYGBD2 [1.357 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THYGBD2
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THPAF062	Impact of Superconducting Magnet Protection Equipment on the Circulating Beam in HL-LHC	3115
	M. Valette, L. Bortot, A.M. Fernandez Navarro, B. Lindstrom, M. Mentink, R. Schmidt, E. Stubberud, A.P. Verweij, D. Wollmann CERN, Geneva, Switzerland E. Ravaioli LBNL, Berkeley, California, USA
	Funding: Work supported by the HL-LHC project. The new superconducting quadrupole and dipole magnets for the High Luminosity LHC (HL-LHC) will rely on quench heaters or Coupling-Loss Induced Quench (CLIQ) units or a combination of both to protect the magnet coils in case of a quench. After the detection of a quench, the quench heater power supplies will discharge currents of several hundreds of amperes into the quench heater strips glued to the coils, and the CLIQ units will discharge an oscillating current in the order of 1~kA directly into the coils. These currents can have a significant effect on the circulating beam if the discharge occurs before the beam is dumped. In the HL-LHC inner triplet quadrupole magnets and 11 T dipole magnets, which will be installed in the collimation region dispersion suppressor, this effect will even be stronger due to the larger number of quench heaters and use of CLIQ units (triplet magnets only) as well as due to the greater value of beta function in comparison with the present LHC. In this paper, the expected effects of quench heater and CLIQ discharges on the circulating beam are summarized, and several mitigation methods are proposed and evaluated. Matthieu. Valette@cern.ch
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THPAF062
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FRXGBD1	Reliability and Availability of Particle Accelerators: Concepts, Lessons, Strategy	5014
	A. Apollonio, L. Ponce, O. Rey Orozko, R. Schmidt, A.P. Siemko, B. Todd, J.A. Uythoven, A.P. Verweij, D. Wollmann, M. Zerlauth CERN, Geneva, Switzerland
	This paper will present the results and latest status of an extensive effort to analyse and improve the reliability and availability of the LHC. After the introduction of basic concepts and definitions, the paper reviews the performance of the LHC in 2015-2017. A direct comparison of the luminosity production years 2016 and 2017 is presented, with a focus on the main differences in the observed failure modes. Based on the lessons learnt in this time window, expectations for the performance during future LHC runs are discussed. In particular, the thought process for the evaluation of the possible full energy exploitation of the LHC is described, considering relevant factors such as the expected availability loss and the risk associated to magnet training.
	Slides FRXGBD1 [7.090 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-FRXGBD1
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Paper

Title

Page

Crab Cavity Failures Combined with a Loss of the Beam-Beam Kick in the High Luminosity LHC

192

B. Lindstrom, H. Burkhardt, V.K.B. Olsen, A. Santamaría García, K.N. Sjobak, M. Valette, D. Wollmann
CERN, Geneva, Switzerland

Crab cavities are an essential component of the High Luminosity LHC (HL-LHC) project. In case of a failure they can create large transverse kicks on the beam within tens of microseconds and, therefore, require a fast extraction of the circulating beam. In this paper, the effects of different crab cavity failures in combination with the missing beam-beam kick following the dump of only one LHC beam are presented and consequences for the interlocking strategy of crab cavities are discussed.
Work supported by the High Luminosity LHC project.

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MOPMF046

Simulation of Hydrodynamic Tunneling Caused by High Energy Proton Beam in Copper through Coupling of FLUKA and Autodyn

204

Y.C. Nie, A. Bertarelli, F. Carra, C. Fichera, L.K. Mettler, R. Schmidt, D. Wollmann
CERN, Geneva, Switzerland

For machine protection of high-energy colliders, it is important to assess potential damages caused to accelerator components in case large number of bunches are lost at the same place. The numerical assessment requires an iterative execution of an energy-deposition code and a hydrodynamic code, since the hydrodynamic tunneling effect will likely play an important role in the beam-matter interactions. For proton accelerators at CERN and for the Future Circular Collider (FCC), case studies were performed, coupling FLUKA and BIG2. To compare different hydrocodes and not to rely only on BIG2, FLUKA and a commercial tool, Autodyn, have been used to perform these simulations. This paper reports a benchmarking study against a beam test performed at the HiRadMat (High-Radiation to Materials) facility using beams at 440 GeV from the Super Proton Synchrotron. Good agreement has been found between the simulation results and the test as well as previous simulations with FLUKA and BIG2, particularly in terms of penetration depth of the beam in copper. This makes the coupling of FLUKA and Autodyn an alternative solution to simulating the hydrodynamic tunneling. More case studies are planned for FCC and other high-beam-power accelerators.

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MOPMF053

Observations, Analysis and Mitigation of Recurrent LHC Beam Dumps Caused by Fast Losses in Arc Half-Cell 16L2

228

J.M. Jimenez, D. Amorim, S. A. Antipov, G. Arduini, A. Bertarelli, N. Biancacci, B. Bradu, E. Bravin, G. Bregliozzi, K. Brodzinski, R. Bruce, X. Buffat, L.R. Carver, P. Chiggiato, S.D. Claudet, P. Collier, R. Garcia Alia, M. Giovannozzi, L. K. Grob, E.B. Holzer, W. Höfle, G. Iadarola, G. Kotzian, A. Lechner, T.E. Levens, B. Lindstrom, T. Medvedeva, A. Milanese, D. Mirarchi, E. Métral, D. Perini, S. Redaelli, G. Rumolo, B. Salvant, R. Schmidt, M. Valette, D. Valuch, J. Wenninger, D. Wollmann, C. Yin Vallgren, C. Zamantzas, M. Zerlauth
CERN, Geneva, Switzerland
D. Amorim
Université Grenoble Alpes, Grenoble, France
A.A. Gorzawski
University of Manchester, Manchester, United Kingdom
L. Mether
EPFL, Lausanne, Switzerland

Recurrent beam dumps significantly perturbed the operation of the CERN LHC in the summer months of 2017, especially in August. These unexpected beam dumps were triggered by fast beam losses that built up in the cryogenic beam vacuum at the half-cell 16 left of LHC-IP2 and were detected either at that location but mainly in the collimation insertions. This contribution details the experimental observables (beam losses, coherent instabilities, heat load to cryogenic system, vacuum signals), the extent of the understanding of the beam loss and instability mechanisms and the mitigation steps and new settings that allowed recovering the luminosity performance of the LHC for the rest of the Run.

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MOPMF060

Safe Disposal of the LHC Beam without Beam Dump - Method and Experimental Verification

253

M. Valette, B. Lindstrom, A. Mereghetti, R. Schmidt, M. Solfaroli, J.A. Uythoven, D. Valuch, J. Wenninger, D. Wollmann, M. Zerlauth
CERN, Geneva, Switzerland

Funding: Research supported by the HL-LHC project.
In the extremely unlikely event of a non-working beam dumping system in the LHC, the 360 MJ of stored beam energy can be dissipated in the collimation system as a last mitigation measure. In such a situation, it is important to reduce the stored beam energy both quickly and at the same time as smoothly as possible in order to limit the risk of trips of critical systems, to avoid quenches of superconducting magnets (which would lead to changes of the beam trajectory and damage to the accelerator) and ultimately damage to the collimators themselves. Detailed steps and parameters have been developed and validated during two dedicated experiments with beam in the LHC. This paper summarizes the key aspects in view of the preparation of such a procedure for operational use, which will allow for the safe disposal of the full LHC beam by the operation crews.

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MOPMF063

Asynchronous Beam Dump Tests at LHC

265

C. Wiesner, W. Bartmann, C. Bracco, E. Carlier, L. Ducimetière, M.I. Frankl, M.A. Fraser, B. Goddard, C. Heßler, T. Kramer, A. Lechner, N. Magnin, V. Senaj, D. Wollmann
CERN, Geneva, Switzerland

The detailed understanding of the beam-loss pattern in case of an asynchronous beam dump is essential for the safe operation of the future High Luminosity LHC (HL-LHC) with nearly twice the nominal LHC beam intensity, leading to correspondingly higher energy deposition on the protection elements. An asynchronous beam dump is provoked when the rise time of the extraction kickers is not synchronized to the 3 us long particle-free abort gap. Thus, particles that are not absorbed by dedicated protection elements can be lost on the machine aperture. Since asynchronous beam dumps are among the most critical failure cases of the LHC, experimental tests at low intensity are performed routinely. This paper reviews recent asynchronous beam dump tests performed in the LHC. It describes the test conditions, discusses the beam-loss behaviour and presents simulation and measurement results. In particular, it examines a test event from May 2016, which led to the quench of four superconducting magnets in the extraction region and which was studied by a dedicated beam experiment in December 2017.

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MOPMF064

High-Energy LHC Design

269

F. Zimmermann, D. Amorim, S. A. Antipov, S. Arsenyev, M. Benedikt, R. Bruce, M.P. Crouch, S.D. Fartoukh, M. Giovannozzi, B. Goddard, M. Hofer, R. Kersevan, V. Mertens, Y. Muttoni, J.A. Osborne, V. Parma, V. Raginel, S. Redaelli, T. Risselada, I. Ruehl, B. Salvant, D. Schoerling, E.N. Shaposhnikova, L.J. Tavian, E. Todesco, R. Tomás, D. Tommasini, F. Valchkova-Georgieva, V. Venturi, D. Wollmann
CERN, Geneva, Switzerland
J.L. Abelleira, E. Cruz Alaniz, P. Martinez Mirave, A. Seryi, L. van Riesen-Haupt
JAI, Oxford, United Kingdom
A. Apyan
ANSL, Yerevan, Armenia
J. Barranco García, L. Mether, T. Pieloni, L. Rivkin, C. Tambasco
EPFL, Lausanne, Switzerland
F. Burkart
DESY, Hamburg, Germany
Y. Cai, Y.M. Nosochkov
SLAC, Menlo Park, California, USA
G. Guillermo Cantón
CINVESTAV, Mérida, Mexico
K. Ohmi, K. Oide, D. Zhou
KEK, Ibaraki, Japan

In the frame of the FCC study we are designing a 27 TeV hadron collider in the LHC tunnel, called the High Energy LHC (HE-LHC).

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TUPAF028

Energy Deposition Studies and Analysis of the Quench Behavior in the Case of Asynchronous Dumps During 6.5 TeV LHC Proton Beam Operation

736

M.I. Frankl, W. Bartmann, M. Bednarek, C. Bracco, A. Lechner, A.P. Verweij, C. Wiesner, D. Wollmann
CERN, Geneva, Switzerland

The CERN LHC beam dumping system comprises a series of septa and fast-pulsed kicker magnets for extracting the stored proton beams to the external beam dumps. Different absorbers in the extraction region protect superconducting magnets and other machine elements in case of abnormal beam aborts, where bunches are swept across the machine aperture. During Run 2 of the LHC, controlled beam loss experiments were carried out at 6.5 TeV probing the particle leakage from protection devices under realistic operation conditions. This paper presents particle shower simulations analyzing the energy deposition in superconducting coils and assessing if the observed magnet quenches are compatible with the presently known quench limits.

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TUPAF040

Beam Loss Measurements for Recurring Fast Loss Events During 2017 LHC Operation Possibly Caused by Macroparticles

780

A. Lechner, B. Auchmann, E. Bravin, A.A. Gorzawski, L. K. Grob, E.B. Holzer, B. Lindstrom, T. Medvedeva, D. Mirarchi, R. Schmidt, M. Valette, D. Wollmann
CERN, Geneva, Switzerland

The availability of the LHC machine was adversely affected in 2017 by tens of beam aborts provoked by frequent loss events in one standard arc cell (16L2). In most of the cases, the dumps were triggered by concurrently developing fast beam instabilities leading to particle losses in the betatron cleaning insertion. Many of the events started with a distinct sub-millisecond loss peak comparable to regular dust particle events, which have been observed along all the LHC since the start-up. In contrast to regular dust events, persistent losses developed in cell 16L2 after the initial peaks which can possibly be explained by a phase transition of macroparticles to the gas phase. In this paper, we summarize the observed loss characteristics such as spatial loss pattern and time profiles measured by Beam Loss Monitors (ionization chambers). Based on the measurements, we estimate the energy deposition in macroparticles and reconstruct proton loss rates as well as the gas densities after the phase transition. Differences between regular dust events and events in 16L2 are highlighted and the ability to induce magnet quenches is discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF040

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TUPAF049

Analysis of Loss Signatures of Unidentified Falling Objects in the LHC

814

L. K. Grob, M. Dziadosz, E.B. Holzer, A. Lechner, B. Lindstrom, R. Schmidt, D. Wollmann, C. Zamantzas
CERN, Geneva, Switzerland

Particulates in the LHC beam pipes can interact with the proton beams and cause significant beam losses. The "UFOs" (unidentified falling objects) hypothesis describes a particle falling into the beam, creating particle showers, being ionized and repelled. Though the signals of the beam loss monitors support this, many aspects remain unknown. Neither the source of the dust nor the release mechanism from the beam pipe are understood. The same holds for the forces involved in the interaction and the observed UFO rate reduction over the years. These open questions are approached from different angles. Firstly, a new data analysis tool was established featuring advanced raw data selection and statistical analysis. Results of this analysis will be presented. Secondly, dust samples were extracted from LHC components and analyzed to gain insight into the size distribution and material composition of the contamination. The performed observations and analysis lead to a better modelling of the UFO events and helped to understand the physics involved. The validated UFO models will be crucial in view of the high luminosity upgrade of the LHC (HL-LHC) and the Future Circular Collider (FCC).

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-TUPAF049

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WEPMG006

Experimental Setup to Characterize the Radiation Hardness of Cryogenic Bypass Diodes for the HL-LHC Inner Triplet Circuits

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A. Will, G. D'Angelo, R. Denz, M.F. Favre, D. Hagedorn, G. Kirby, T. Koettig, A. Monteuuis, F. Rodriguez-Mateos, A.P. Siemko, K. Stachon, M. Valette, A.P. Verweij, D. Wollmann
CERN, Geneva, Switzerland
A. Bernhard, A.-S. Müller
KIT, Karlsruhe, Germany
L. Kistrup
KEA, Copenhagen, Denmark

Funding: Work supported by the Wolfgang Gentner Programme of the German Federal Ministry of Education and Research
For the high luminosity upgrade of the Large Hadron Collider (LHC), it is planned to replace the existing triplet quadrupole magnets with Nb₃Sn quadrupole magnets, which provide a comparable integrated field gradient with a significantly increased aperture. These magnets will be powered through a novel superconducting link based on MgB₂ cables. One option for the powering layout of this triplet circuit is the use of cryogenic bypass diodes, where the diodes are located inside an extension to the magnet cryostat and operated in superfluid helium. Hence, they are exposed to radiation. For this reason the radiation hardness of existing LHC type bypass diodes and more radiation tolerant prototype diodes needs to be tested up to the radiation doses expected at their planned position during their lifetime. A first irradiation test is planned in CERN's CHARM facility starting in spring 2018. Therefore, a cryo-cooler based cryostat to irradiate and test LHC type diodes in-situ has been designed and constructed. This paper will describe the properties of the sample diodes, the experimental roadmap and the setup installed in CHARM. Finally, the first measurement results will be discussed.

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-WEPMG006

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THYGBD2

Results of UFO Dynamics Studies with Beam in the LHC

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B. Lindstrom, A. Apollonio, P. Bélanger, M. Dziadosz, A.A. Gorzawski, L. K. Grob, E.B. Holzer, A. Lechner, R. Schmidt, M. Valette, D. Valuch, D. Wollmann
CERN, Geneva, Switzerland

Micrometer sized particles entering the LHC beam (the so-called Unidentified Falling Objects or UFOs) are a known cause of localized beam losses since the beginning of high intensity beam operation, however the origin of these particles is not fully known. Their effect limits LHC availability by causing premature dumps due to excessive beam losses and occasionally even magnet quenches. This could become an important limitation for future accelerators such as the High Luminosity upgrade of the LHC (HL-LHC) and the Future Circular Collider (FCC). The dynamics of these UFOs was investigated in two dedicated experiments. In the first experiment, it was shown that the transverse movements of these particles can be studied by observing bunch-by-bunch losses from bunches with different horizontal and vertical emittances. In the second experiment, UFO-like events around the 16L2 interconnect in the LHC, which has seen intense UFO activity in 2017, were studied with the above method. This paper summarizes the results of both experiments.

Slides THYGBD2 [1.357 MB]

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reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2018-THYGBD2

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THPAF062

Impact of Superconducting Magnet Protection Equipment on the Circulating Beam in HL-LHC

3115

M. Valette, L. Bortot, A.M. Fernandez Navarro, B. Lindstrom, M. Mentink, R. Schmidt, E. Stubberud, A.P. Verweij, D. Wollmann
CERN, Geneva, Switzerland
E. Ravaioli
LBNL, Berkeley, California, USA

Funding: Work supported by the HL-LHC project.
The new superconducting quadrupole and dipole magnets for the High Luminosity LHC (HL-LHC) will rely on quench heaters or Coupling-Loss Induced Quench (CLIQ) units or a combination of both to protect the magnet coils in case of a quench. After the detection of a quench, the quench heater power supplies will discharge currents of several hundreds of amperes into the quench heater strips glued to the coils, and the CLIQ units will discharge an oscillating current in the order of 1~kA directly into the coils. These currents can have a significant effect on the circulating beam if the discharge occurs before the beam is dumped. In the HL-LHC inner triplet quadrupole magnets and 11 T dipole magnets, which will be installed in the collimation region dispersion suppressor, this effect will even be stronger due to the larger number of quench heaters and use of CLIQ units (triplet magnets only) as well as due to the greater value of beta function in comparison with the present LHC. In this paper, the expected effects of quench heater and CLIQ discharges on the circulating beam are summarized, and several mitigation methods are proposed and evaluated.
Matthieu. Valette@cern.ch

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FRXGBD1

Reliability and Availability of Particle Accelerators: Concepts, Lessons, Strategy

5014

A. Apollonio, L. Ponce, O. Rey Orozko, R. Schmidt, A.P. Siemko, B. Todd, J.A. Uythoven, A.P. Verweij, D. Wollmann, M. Zerlauth
CERN, Geneva, Switzerland

This paper will present the results and latest status of an extensive effort to analyse and improve the reliability and availability of the LHC. After the introduction of basic concepts and definitions, the paper reviews the performance of the LHC in 2015-2017. A direct comparison of the luminosity production years 2016 and 2017 is presented, with a focus on the main differences in the observed failure modes. Based on the lessons learnt in this time window, expectations for the performance during future LHC runs are discussed. In particular, the thought process for the evaluation of the possible full energy exploitation of the LHC is described, considering relevant factors such as the expected availability loss and the risk associated to magnet training.

Slides FRXGBD1 [7.090 MB]

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