LINAC2012 - List of Authors (Cheymol, B.)

Paper	Title	Page
TUPB041	Scattering of H⁻ Stripped Electrons from SEM Grids and Wire Scanners at the CERN LINAC4	567
	F. Roncarolo, E. Chevallay, M. Duraffourg, G.J. Focker, C. Heßler, U. Raich, VC. Vuitton, F. Zocca CERN, Geneva, Switzerland B. Cheymol ESS, Lund, Sweden
	At the CERN LINAC4, wire grids and scanners will be used to characterize the H⁻ beam transverse profile at different stages along the acceleration to 160 MeV. The wire signal will be determined by the balance between secondary emission and number of charges stopped in the wire, which will depend on the wire material and diameter, the possible choice of biasing (DC) the wires and the beam energy. The outermost electrons of H⁻ ions impinging on a wire are stripped in the first nanometers of material. A portion of such electrons are scattered away from the wire and can reach the neighboring wires. In addition, scattered electrons hitting the surrounding beam pipe generate secondary electrons that can also perturb the measurement. Monte Carlo simulations, analytical calculations and a laboratory experiment allowed quantifying the amount of scattering and the scattered particles distributions. The experiment was based on 70 keV electrons, well reproducing the case of 128 MeV H⁻ ions. For all the LINAC4 simulated cases the predicted effect on the beam size reconstruction results in a relative error of less than 5%.

THPB028	The ESS Low Energy Beam Transport Line Design	912
	L. Neri, L. Calabretta, A.C. Caruso, L. Celona, S. Gammino, A. Longhitano, D. Mascali INFN/LNS, Catania, Italy B. Cheymol, A. Ponton ESS, Lund, Sweden
	The linear accelerator of the European Spallation Source (ESS) will deliver proton beams of 50 mA and 2.5 GeV onto the 5 MW neutron production target. The Proton Source for ESS (PS-ESS) [1] is based on the experience of TRIPS and VIS developed at LNS Catania [2,3]. A two solenoid Low Energy Beam Transport (LEBT) is foreseen to match the beam into the first acceleration stage, the Radio-Frequency Quadrupole (RFQ) [4]. Beam production means also detailed characterization of produced beam, with this scope the LEBT houses many instrumentation devices and use different techniques that will be described in this work. The LEBT will be also equipped with an electrostatic chopper in order to remove the unwanted part of the beam pulse during the natural rise and fall times of the ion source. Beam dynamics calculations of the LEBT have been carried out considering also the Space Charge Compensation (SCC) produced by the interaction of the beam with the residual gas, and its effect on beam transport and chopping. Particular emphasis has been put on the evaluation of the beam transient behavior, due to the chopping process, at the entrance of the RFQ, results of the study are presented in this paper.

Paper

Title

Page

Scattering of H⁻ Stripped Electrons from SEM Grids and Wire Scanners at the CERN LINAC4

567

F. Roncarolo, E. Chevallay, M. Duraffourg, G.J. Focker, C. Heßler, U. Raich, VC. Vuitton, F. Zocca
CERN, Geneva, Switzerland
B. Cheymol
ESS, Lund, Sweden

At the CERN LINAC4, wire grids and scanners will be used to characterize the H⁻ beam transverse profile at different stages along the acceleration to 160 MeV. The wire signal will be determined by the balance between secondary emission and number of charges stopped in the wire, which will depend on the wire material and diameter, the possible choice of biasing (DC) the wires and the beam energy. The outermost electrons of H⁻ ions impinging on a wire are stripped in the first nanometers of material. A portion of such electrons are scattered away from the wire and can reach the neighboring wires. In addition, scattered electrons hitting the surrounding beam pipe generate secondary electrons that can also perturb the measurement. Monte Carlo simulations, analytical calculations and a laboratory experiment allowed quantifying the amount of scattering and the scattered particles distributions. The experiment was based on 70 keV electrons, well reproducing the case of 128 MeV H⁻ ions. For all the LINAC4 simulated cases the predicted effect on the beam size reconstruction results in a relative error of less than 5%.

THPB028

The ESS Low Energy Beam Transport Line Design

912

L. Neri, L. Calabretta, A.C. Caruso, L. Celona, S. Gammino, A. Longhitano, D. Mascali
INFN/LNS, Catania, Italy
B. Cheymol, A. Ponton
ESS, Lund, Sweden

The linear accelerator of the European Spallation Source (ESS) will deliver proton beams of 50 mA and 2.5 GeV onto the 5 MW neutron production target. The Proton Source for ESS (PS-ESS) [1] is based on the experience of TRIPS and VIS developed at LNS Catania [2,3]. A two solenoid Low Energy Beam Transport (LEBT) is foreseen to match the beam into the first acceleration stage, the Radio-Frequency Quadrupole (RFQ) [4]. Beam production means also detailed characterization of produced beam, with this scope the LEBT houses many instrumentation devices and use different techniques that will be described in this work. The LEBT will be also equipped with an electrostatic chopper in order to remove the unwanted part of the beam pulse during the natural rise and fall times of the ion source. Beam dynamics calculations of the LEBT have been carried out considering also the Space Charge Compensation (SCC) produced by the interaction of the beam with the residual gas, and its effect on beam transport and chopping. Particular emphasis has been put on the evaluation of the beam transient behavior, due to the chopping process, at the entrance of the RFQ, results of the study are presented in this paper.