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HOM Mitigation for FCC-ee

High electron and positron currents (1.5 A) are planned to be used in the Future Circular electron-positron Collider (FCC-ee) with a goal to archive high luminosity of order of 2.3 1036 cm-2s-2 at the Z-production collision at the beam energy of 45.6 GeV [1, 2]. Coherent effects at the high-current...

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Autor principal: Novokhatski, Alexander
Lenguaje:eng
Publicado: 2017
Materias:
Acceso en línea:http://cds.cern.ch/record/2816682
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author Novokhatski, Alexander
author_facet Novokhatski, Alexander
author_sort Novokhatski, Alexander
collection CERN
description High electron and positron currents (1.5 A) are planned to be used in the Future Circular electron-positron Collider (FCC-ee) with a goal to archive high luminosity of order of 2.3 1036 cm-2s-2 at the Z-production collision at the beam energy of 45.6 GeV [1, 2]. Coherent effects at the high-current machine impose certain limitations on the magnitude of the impedance of the machine. The potential well distortion due to inductive part of the impedance may give a large bunch lengthening. The microwave longitudinal and transverse instability set the total limit on the effective impedance. The multi bunch longitudinal and transverse mode-coupling can be more dangerous for the beam dynamics, but fortunately the feedback system can be used to damp these instabilities. An additional effect of the resonance part of the impedance is the HOM (Higher Order Modes) heating. It can happen not only in the RF cavities, but anywhere in the machine beam pipe where trapped mode or traveling waves absorb their power. Temperature raise due to HOM heating can be very high in the closed volumes without cooling. Very important the HOM heating is in the Interaction Region (IR), because it brings an additional background. The local heating in the IR can reach tens of kW of power. Some part of the electromagnetic waves, excited by the beam, with a frequency above the cutoff frequency will travel away from the IR and go down the beam pipe. The absorption of these waves can bring heating problems to other parts of the accelerator. A large energy loss of the beams in the interaction region can be a severe problem. The temperature of the IR chamber will go up and the vacuum will be spoiled. If the IR chamber has small gaps or hidden cavities (like in shielded bellows or valves), then electric sparks or arcing may cause additional vacuum spikes. Heating of nonevaporable getters (if they are will be used in the IR) may bring vacuum instability (the temperature can go above the recovery level). All of these things can make the backgrounds much higher. One can find a description of these effects in publications [3, 4]. Impedance study for FCC-ee can be found in reference [5].
id cern-2816682
institution Organización Europea para la Investigación Nuclear
language eng
publishDate 2017
record_format invenio
spelling cern-28166822022-07-27T08:25:41Zhttp://cds.cern.ch/record/2816682engNovokhatski, AlexanderHOM Mitigation for FCC-eeAccelerators and Storage RingsHigh electron and positron currents (1.5 A) are planned to be used in the Future Circular electron-positron Collider (FCC-ee) with a goal to archive high luminosity of order of 2.3 1036 cm-2s-2 at the Z-production collision at the beam energy of 45.6 GeV [1, 2]. Coherent effects at the high-current machine impose certain limitations on the magnitude of the impedance of the machine. The potential well distortion due to inductive part of the impedance may give a large bunch lengthening. The microwave longitudinal and transverse instability set the total limit on the effective impedance. The multi bunch longitudinal and transverse mode-coupling can be more dangerous for the beam dynamics, but fortunately the feedback system can be used to damp these instabilities. An additional effect of the resonance part of the impedance is the HOM (Higher Order Modes) heating. It can happen not only in the RF cavities, but anywhere in the machine beam pipe where trapped mode or traveling waves absorb their power. Temperature raise due to HOM heating can be very high in the closed volumes without cooling. Very important the HOM heating is in the Interaction Region (IR), because it brings an additional background. The local heating in the IR can reach tens of kW of power. Some part of the electromagnetic waves, excited by the beam, with a frequency above the cutoff frequency will travel away from the IR and go down the beam pipe. The absorption of these waves can bring heating problems to other parts of the accelerator. A large energy loss of the beams in the interaction region can be a severe problem. The temperature of the IR chamber will go up and the vacuum will be spoiled. If the IR chamber has small gaps or hidden cavities (like in shielded bellows or valves), then electric sparks or arcing may cause additional vacuum spikes. Heating of nonevaporable getters (if they are will be used in the IR) may bring vacuum instability (the temperature can go above the recovery level). All of these things can make the backgrounds much higher. One can find a description of these effects in publications [3, 4]. Impedance study for FCC-ee can be found in reference [5].oai:cds.cern.ch:28166822017
spellingShingle Accelerators and Storage Rings
Novokhatski, Alexander
HOM Mitigation for FCC-ee
title HOM Mitigation for FCC-ee
title_full HOM Mitigation for FCC-ee
title_fullStr HOM Mitigation for FCC-ee
title_full_unstemmed HOM Mitigation for FCC-ee
title_short HOM Mitigation for FCC-ee
title_sort hom mitigation for fcc-ee
topic Accelerators and Storage Rings
url http://cds.cern.ch/record/2816682
work_keys_str_mv AT novokhatskialexander hommitigationforfccee