HB2016 - Table of Session: TUA2 (Working Group A

Paper	Title	Page
TUAM2X01	Measurement and Interpretation of Transverse Beam Instabilities in the CERN Large Hadron Collider (LHC) and Extrapolations to HL-LHC	254
	E. Métral, G. Arduini, N. Biancacci, X. Buffat, L.R. Carver, G. Iadarola, K.S.B. Li, T. Pieloni, A. Romano, G. Rumolo, B. Salvant, M. Schenk, C. Tambasco CERN, Geneva, Switzerland J. Barranco EPFL, Lausanne, Switzerland
	Since the first transverse instability observed in 2010, many studies have been performed on both measurement and simulation sides and several lessons have been learned. In a machine like the LHC, not only all the mechanisms have to be understood separately, but the possible interplays between the different phenomena need to be analyzed in detail, including the beam-coupling impedance (with in particular all the necessary collimators to protect the machine but also new equipment such as crab cavities for HL-LHC), linear and nonlinear chromaticity, Landau octupoles (and other intrinsic nonlinearities), transverse damper, space charge, beam-beam (long-range and head-on), electron cloud, linear coupling strength, tune separation between the transverse planes, tune split between the two beams, transverse beam separation between the two beams, etc. This paper reviews all the transverse beam instabilities observed and simulated so far, the mitigation measures which have been put in place, the remaining questions and challenges and some recommendations for the future.
	Slides TUAM2X01 [36.385 MB]
DOI •	reference for this paper ※ DOI:10.18429/JACoW-HB2016-TUAM2X01
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TUAM3X01	Identification and Reduction of the CERN SPS Impedance	260
	E.N. Shaposhnikova, T. Argyropoulos, T. Bohl, A. Lasheen, J. Repond, H. Timko CERN, Geneva, Switzerland
	The first SPS impedance reduction programme has been completed in 2001, preparing the ring for its role as an injector of the LHC. This action has eliminated microwave instability on the SPS flat bottom and later nominal beam could be delivered to the LHC. The High Luminosity (HL-) LHC project is based on beam with twice higher intensity than the nominal one. One of the important SPS intensity limitations are longitudinal instabilities with minimum threshold reached on the 450 GeV flat top. In this paper the work which was carried on to identify the impedance sources driving these instabilities is described together with the next campaign of the SPS impedance reduction planned by the LHC Injector Upgrade (LIU) project. The present knowledge of the SPS transverse impedance is also presented.
	Slides TUAM3X01 [6.457 MB]
DOI •	reference for this paper ※ DOI:10.18429/JACoW-HB2016-TUAM3X01
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUAM4X01	Electron Cloud in the CERN Accelerator Complex	266
	G. Rumolo, H. Bartosik, E. Belli, G. Iadarola, K.S.B. Li, L. Mether, A. Romano CERN, Geneva, Switzerland M. Schenk EPFL, Lausanne, Switzerland
	Operation with closely spaced bunched beams causes the build up of an Electron Cloud (EC) in both the LHC and the two last synchrotrons of its injector chain (PS and SPS). Pressure rise and beam instabilities are observed at the PS during the last stage of preparation of the LHC beams. The SPS was affected by coherent and incoherent emittance growth along the LHC bunch train over many years, before scrubbing has finally suppressed the EC in a large fraction of the machine. When the LHC started regular operation with 50 ns beams in 2011, EC phenomena appeared in the arcs during the early phases, and in the interaction regions with two beams all along the run. Operation with 25 ns beams (late 2012 and 2015), which is nominal for LHC, has been hampered by EC induced high heat load in the cold arcs, bunch dependent emittance growth and degraded beam lifetime. Dedicated and parasitic machine scrubbing is presently the weapon used at the LHC to combat EC in this mode of operation. This talk summarises the EC experience in the CERN machines (PS, SPS, LHC) and highlight the dangers for future operation with more intense beams as well as the strategies to mitigate or suppress the effect.
	Slides TUAM4X01 [9.785 MB]
DOI •	reference for this paper ※ DOI:10.18429/JACoW-HB2016-TUAM4X01
Export •	reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Measurement and Interpretation of Transverse Beam Instabilities in the CERN Large Hadron Collider (LHC) and Extrapolations to HL-LHC

254

E. Métral, G. Arduini, N. Biancacci, X. Buffat, L.R. Carver, G. Iadarola, K.S.B. Li, T. Pieloni, A. Romano, G. Rumolo, B. Salvant, M. Schenk, C. Tambasco
CERN, Geneva, Switzerland
J. Barranco
EPFL, Lausanne, Switzerland

Since the first transverse instability observed in 2010, many studies have been performed on both measurement and simulation sides and several lessons have been learned. In a machine like the LHC, not only all the mechanisms have to be understood separately, but the possible interplays between the different phenomena need to be analyzed in detail, including the beam-coupling impedance (with in particular all the necessary collimators to protect the machine but also new equipment such as crab cavities for HL-LHC), linear and nonlinear chromaticity, Landau octupoles (and other intrinsic nonlinearities), transverse damper, space charge, beam-beam (long-range and head-on), electron cloud, linear coupling strength, tune separation between the transverse planes, tune split between the two beams, transverse beam separation between the two beams, etc. This paper reviews all the transverse beam instabilities observed and simulated so far, the mitigation measures which have been put in place, the remaining questions and challenges and some recommendations for the future.

Slides TUAM2X01 [36.385 MB]

DOI •

reference for this paper ※ DOI:10.18429/JACoW-HB2016-TUAM2X01

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUAM3X01

Identification and Reduction of the CERN SPS Impedance

260

E.N. Shaposhnikova, T. Argyropoulos, T. Bohl, A. Lasheen, J. Repond, H. Timko
CERN, Geneva, Switzerland

The first SPS impedance reduction programme has been completed in 2001, preparing the ring for its role as an injector of the LHC. This action has eliminated microwave instability on the SPS flat bottom and later nominal beam could be delivered to the LHC. The High Luminosity (HL-) LHC project is based on beam with twice higher intensity than the nominal one. One of the important SPS intensity limitations are longitudinal instabilities with minimum threshold reached on the 450 GeV flat top. In this paper the work which was carried on to identify the impedance sources driving these instabilities is described together with the next campaign of the SPS impedance reduction planned by the LHC Injector Upgrade (LIU) project. The present knowledge of the SPS transverse impedance is also presented.

Slides TUAM3X01 [6.457 MB]

DOI •

reference for this paper ※ DOI:10.18429/JACoW-HB2016-TUAM3X01

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUAM4X01

Electron Cloud in the CERN Accelerator Complex

266

G. Rumolo, H. Bartosik, E. Belli, G. Iadarola, K.S.B. Li, L. Mether, A. Romano
CERN, Geneva, Switzerland
M. Schenk
EPFL, Lausanne, Switzerland

Operation with closely spaced bunched beams causes the build up of an Electron Cloud (EC) in both the LHC and the two last synchrotrons of its injector chain (PS and SPS). Pressure rise and beam instabilities are observed at the PS during the last stage of preparation of the LHC beams. The SPS was affected by coherent and incoherent emittance growth along the LHC bunch train over many years, before scrubbing has finally suppressed the EC in a large fraction of the machine. When the LHC started regular operation with 50 ns beams in 2011, EC phenomena appeared in the arcs during the early phases, and in the interaction regions with two beams all along the run. Operation with 25 ns beams (late 2012 and 2015), which is nominal for LHC, has been hampered by EC induced high heat load in the cold arcs, bunch dependent emittance growth and degraded beam lifetime. Dedicated and parasitic machine scrubbing is presently the weapon used at the LHC to combat EC in this mode of operation. This talk summarises the EC experience in the CERN machines (PS, SPS, LHC) and highlight the dangers for future operation with more intense beams as well as the strategies to mitigate or suppress the effect.

Slides TUAM4X01 [9.785 MB]

DOI •

reference for this paper ※ DOI:10.18429/JACoW-HB2016-TUAM4X01

Export •

reference for this paper to ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)