Beam-Jet Interaction Update
Ben FreemireNorthern Illinois University
IOTA Instrumentation MeetingApril 5, 2018
April 5, 2018 B. Freemire - IOTA Instrumentation 2
Simulation Parameters● Transverse beam distribution Gaussian, σx,y = 3.5 mm
● 500 macroparticles injected per time step● 1 macroparticle proton = 900 real proton● 1 macroparticle ion/electron = 81 ions/electrons● x (-3.5,3.5) cm, y (-3.0,5.0) cm, z (-3.5,3.5) cm
– 70x80x350 simulation grid– 1 mm x, 1 mm y, 0.2 mm z grid spacing
● 9 ps time step● 1.8306 μs simulated (203,400 time steps)● Electrodes all annuli 2.5 cm ID, 3.0 cm OD, 0.5 cm lenth
– Base at y = -2.5 cm, 500 V
– E1 at y = 2.5 cm, -500 V
– E2 at y = 3.5 cm, -1000 V
– E3 at y = 4.5 cm, -1500 V
April 5, 2018 B. Freemire - IOTA Instrumentation 3
Potential Contours
[m] [m]
[m]
[m]
April 5, 2018 B. Freemire - IOTA Instrumentation 4
Ionization Parameters● Nitrogen gas density 4.0e11 cm-3 ● Ionization cross section 7.19e-17 cm2 ● 150 thin columns of nitrogen gas 7 cm x 0.2
mm x 0.2 mm arranged in step pattern– From (-1.5,-1.5) cm in y and z to (1.5,1.5) cm in y
and z
April 5, 2018 B. Freemire - IOTA Instrumentation 5
Ion Animation
Beam
April 5, 2018 B. Freemire - IOTA Instrumentation 6
Geometry / Comments● Beam imparting longitudinal momentum to ions
– Currently, momenta are equal, but ion momentum can be specified in Warp
– Results in non-Gaussian distribution of ions in z plane (see next slides)
● If the gas jet is rotated 45 degrees with respect to the beam, y profile of beam is z profile of jet– Jet thickness introduces some smearing
PRAB 20, 062801 (2017)
April 5, 2018 B. Freemire - IOTA Instrumentation 7
Profile Comparison● Every proton
present at 1.757 μs (last file before beam ends)
● Bin size = simulation grid size
● Every ion to have ever been within 2.39 < y < 2.50 cm
● Integration window chosen so as to not miss ions (based on ions’ y velocity)
April 5, 2018 B. Freemire - IOTA Instrumentation 8
Ion Profile● Ion distribution more closely matches beam (σ = 0.35 cm) closer
to sheet● Still somewhat distorted vertical distribution
April 5, 2018 B. Freemire - IOTA Instrumentation 9
Ion Profile● Ion distribution more closely matches beam (σ = 0.35 cm) closer
to sheet● Still somewhat distorted vertical distribution
April 5, 2018 B. Freemire - IOTA Instrumentation 10
Remarks● Realistic beam distribution implemented
– Can be improved by adding transverse momentum
● “Tilted” gas sheet implemented● Daughter products energies not realistic
– Relatively easy fix possible
– Will affect measured vertical profile
● Electrodes affecting ion transverse distributions– Worse match further from beam
– Scan of electrode strengths may shed some light on magnitude of effect
● Space charge of beam is significant; some estimation of effect on ions should be made● By end of simulation (i.e. beam revolution period, 1.83 μs), only half of all ions created
reach 2.5 cm above beam center– Pile up in detector from consecutive turns likely
● Longer simulation needed
– How do we mitigate this?
● Simulation diagnostics may be possible to improve by introducing virtual detector at fixed y– I’ve contacted Jean-Luc Vay, awaiting response
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