Compact plasma based beam dump Guoxing Xia Kieran

Compact plasma based beam dump Guoxing Xia, Kieran Hanahoe, Oznur Mete, Tom Pacey University of Manchester and the Cockcroft Institute 28/02/2021 CALIFES Workshop 2016 -CERN 1

Outline • • • Conventional beam dump Plasma beam dump Simulation of plasma beam dump Experiment test at CALIFES Conclusion 28/02/2021 CALIFES Workshop 2016 -CERN 2

Conventional beam dump ILC TDR 28/02/2021 CALIFES Workshop 2016 -CERN 3

Plasma beam dump-a comparison Conventional beam dumps use high density materials – metal, water etc. They require high power density cooling, can produce radionuclides and (for water) explosive gasses through decomposition. Stopping a beam with a low density material could have advantages. Noble gas beam dump Plasma beam dump A. Leuschner, LC-ABD dump meetings, Sept. 2005 H. C. Wu, T. Tajima et al. PR-STAB 13, 101303 (2010) � High � Very long length, but low power density. � Reduced radionuclide production. � No hydrogen/oxygen gas production. 28/02/2021 decelerating gradients with low density dump medium. � Effectiveness depends on bunch parameters. � Possibility for electrical energy recovery. � Cannot decelerate bunch head. CALIFES Workshop 2016 -CERN 4

Passive plasma beam dump 28/02/2021 CALIFES Workshop 2016 -CERN 5

Passive plasma beam dump 28/02/2021 CALIFES Workshop 2016 -CERN 6

Passive plasma beam dump 28/02/2021 CALIFES Workshop 2016 -CERN 7

Passive plasma beam dump 28/02/2021 CALIFES Workshop 2016 -CERN 8

Passive plasma beam dump 28/02/2021 CALIFES Workshop 2016 -CERN 9

Passive plasma beam dump 28/02/2021 CALIFES Workshop 2016 -CERN 10

Plasma beam dump Longitudinal phase space of plasma decelerated bunch Decelerating gradient saturates after some distance as a portion of the bunch is re-accelerated. The low energy particles need to be removed. Wu et al. proposed using a series of foils after the saturation length. Trajectory of decelerated particles Re-accelerated portion of bunch H. C. Wu, T. Tajima et al. PR-STAB 13, 101303 (2010) 28/02/2021 CALIFES Workshop 2016 -CERN 11

Modified plasma density An alternative to absorbing the low energy particles is to move them into a defocusing region of the wakefield by reducing the plasma wavelength. When the density increases, the decelerated portion of the bunch passes into a defocusing region. Stepped profile gives instant shift in wavelength while gradient shifts wavelength gradually. 28/02/2021 CALIFES Workshop 2016 -CERN 12

Simulation of plasma beam dump Simulations carried out for an ultrashort bunch: 7. 5 µm rms bunch length, 100 p. C, 250 Me. V. Initial decelerating gradient 4. 5 GV/m (peak), 1. 5 Ge. V/m (average). Left: Energy loss for different plasma profiles Right: Initial and final energy spectra for gradient plasma. Longitudinal phase space for uniform (L) and stepped (R) plasma. 28/02/2021 CALIFES Workshop 2016 -CERN 13

Experimental test at CALIFES After compression Courtesy of Jürgen Pfingstner 28/02/2021 CALIFES Workshop 2016 -CERN 14

CALIFES simulation 2 D PIC simulations of CALIFES beam using uniform plasma, assuming rms radius of 50 µm. Plasma density 2× 1020 m– 3. Longitudinal electric field and onaxis line out for hollow plasma Longitudinal phase space at z=20 cm for uniform plasma. Peak accelerating/decelerating field: Uniform plasma: 1 GV/m 28/02/2021 CALIFES Workshop 2016 -CERN 15

Conclusion • Plasma based beam dump is much compact than conventional beam dump and produce less radiation hazards • The plasma density step up/gradually increase could be used to damp the whole beam more effectively • Plasma based beam dump can be tested at CALIFES, with decelerating gradient ~1 GV/m for uncompressed bunch. Much higher decelerating field can be expected if short bunch is used • This plasma dump will enables the compactness of the overall scale for future machines 28/02/2021 CALIFES Workshop 2016 -CERN 16

Thanks for your attention! 28/02/2021 CALIFES Workshop 2016 -CERN 17