IPAC2019 - Classification: MC5: Beam Dynamics and EM Fields / D12 Electron Cloud and Trapped Ion Effects

Paper	Title	Page
WEPTS050	Multi-Species Electron-Ion Simulations and their Application to the LHC	3228
	L. Mether, G. Iadarola, K.L. Poland, G. Rumolo, G. Skripka CERN, Meyrin, Switzerland
	During operation in 2017 and 2018, the LHC suffered from recurrent beam aborts associated with beam losses in one of its arc cells in correlation with quickly developing transverse coherent oscillations. The events are thought to have been caused by a localised high gas density resulting from the phase transition of a macro-particle that has entered the beam. In order to model the observed coherent effects through the interaction of the beam with the induced pressure bump, novel modelling capabilities have been implemented that allow for the simulation of multiple clouds of different particle species and their interaction with the beam. In this contribution the simulation model and its application are described.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS050
About •	paper received ※ 13 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019
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WEPTS051	Comparison of Electron Cloud Build-Up Simulations Against Heat Load Measurements for the LHC Arcs With Different Beam Configurations	3232
	G. Skripka, G. Iadarola, L. Mether, G. Rumolo, E.G.T. Wulff CERN, Meyrin, Switzerland P. Dijkstal PSI, Villigen PSI, Switzerland
	Electron cloud effects are among the main performance limitations for the operation of the Large Hadron Collider (LHC) with 25 ns bunch spacing. A large number of electrons impacting on the beam screens of the cold magnets induces significant heat load, reaching values close to the full cooling capacity available from the cryogenic system. Interestingly, it is observed that parts of the machine that are by design identical show very different heat loads. We used numerical simulations to investigate the possibility that these differences are induced by different surface properties, in particular maximum Secondary Electron Yield (SEY) for the different cryomagnets. Using the PyECLOUD code, the electron cloud build-up was simulated assuming different values of SEY in the LHC cold magnets. Comparing the measured heat loads to the simulation results for the 25 ns beams at 450 GeV we have identified the SEY values that match the observations in these conditions. These SEY values were found to be in good agreement with the heat loads measured with different beam configurations (changing the bunch pattern, the bunch intensity and the beam energy).
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS051
About •	paper received ※ 13 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPTS052	Electron Cloud Build-Up Simulations in the Two-Beam Common Chamber of the HL-LHC TDIS With Nonuniform Surface Properties	3236
	G. Skripka, C. Bracco, G. Iadarola, A. Perillo-Marcone CERN, Meyrin, Switzerland
	The segmented injection protection absorber (TDIS) foreseen for the High-Luminosity Large Hadron Collider (HL-LHC) project is designed to protect the machine in case of injection kicker malfunctioning. Since the current LHC injection protection absorber has suffered from vacuum issues possibly induced by electron multipacting, numerical studies were done to estimate the electron flux expected on the internal surfaces of the TDIS. This device will consist of three pairs of movable absorbing blocks above and below one beam and a beam screen surrounding the second circulating beam. The build-up of electron cloud in the TDIS was simulated accounting for the presence of two counter-rotating beams, for the configuration of the jaws and for the different materials used for the different surfaces in the device. The simulation studies have also investigated the possibility of coating the most critical surfaces with amorphous carbon in order to mitigate the multipacting.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS052
About •	paper received ※ 13 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Multi-Species Electron-Ion Simulations and their Application to the LHC

3228

L. Mether, G. Iadarola, K.L. Poland, G. Rumolo, G. Skripka
CERN, Meyrin, Switzerland

During operation in 2017 and 2018, the LHC suffered from recurrent beam aborts associated with beam losses in one of its arc cells in correlation with quickly developing transverse coherent oscillations. The events are thought to have been caused by a localised high gas density resulting from the phase transition of a macro-particle that has entered the beam. In order to model the observed coherent effects through the interaction of the beam with the induced pressure bump, novel modelling capabilities have been implemented that allow for the simulation of multiple clouds of different particle species and their interaction with the beam. In this contribution the simulation model and its application are described.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS050

About •

paper received ※ 13 May 2019 paper accepted ※ 21 May 2019 issue date ※ 21 June 2019

Export •

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

WEPTS051

Comparison of Electron Cloud Build-Up Simulations Against Heat Load Measurements for the LHC Arcs With Different Beam Configurations

3232

G. Skripka, G. Iadarola, L. Mether, G. Rumolo, E.G.T. Wulff
CERN, Meyrin, Switzerland
P. Dijkstal
PSI, Villigen PSI, Switzerland

Electron cloud effects are among the main performance limitations for the operation of the Large Hadron Collider (LHC) with 25 ns bunch spacing. A large number of electrons impacting on the beam screens of the cold magnets induces significant heat load, reaching values close to the full cooling capacity available from the cryogenic system. Interestingly, it is observed that parts of the machine that are by design identical show very different heat loads. We used numerical simulations to investigate the possibility that these differences are induced by different surface properties, in particular maximum Secondary Electron Yield (SEY) for the different cryomagnets. Using the PyECLOUD code, the electron cloud build-up was simulated assuming different values of SEY in the LHC cold magnets. Comparing the measured heat loads to the simulation results for the 25 ns beams at 450 GeV we have identified the SEY values that match the observations in these conditions. These SEY values were found to be in good agreement with the heat loads measured with different beam configurations (changing the bunch pattern, the bunch intensity and the beam energy).

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS051

About •

paper received ※ 13 May 2019 paper accepted ※ 22 May 2019 issue date ※ 21 June 2019

Export •

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

WEPTS052

Electron Cloud Build-Up Simulations in the Two-Beam Common Chamber of the HL-LHC TDIS With Nonuniform Surface Properties

3236

G. Skripka, C. Bracco, G. Iadarola, A. Perillo-Marcone
CERN, Meyrin, Switzerland

The segmented injection protection absorber (TDIS) foreseen for the High-Luminosity Large Hadron Collider (HL-LHC) project is designed to protect the machine in case of injection kicker malfunctioning. Since the current LHC injection protection absorber has suffered from vacuum issues possibly induced by electron multipacting, numerical studies were done to estimate the electron flux expected on the internal surfaces of the TDIS. This device will consist of three pairs of movable absorbing blocks above and below one beam and a beam screen surrounding the second circulating beam. The build-up of electron cloud in the TDIS was simulated accounting for the presence of two counter-rotating beams, for the configuration of the jaws and for the different materials used for the different surfaces in the device. The simulation studies have also investigated the possibility of coating the most critical surfaces with amorphous carbon in order to mitigate the multipacting.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2019-WEPTS052

About •

paper received ※ 13 May 2019 paper accepted ※ 20 May 2019 issue date ※ 21 June 2019

Export •

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