SciDAC Accelerator Simulation project:FNAL Booster modeling, status and plans

Robert D. Ryne, P. Spentzouris

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What are we trying to accomplish?

• Predict Booster losses1. @ injection (few ms time scale) –transverse space

charge (?)2. Longitudinal space charge effects causing distortion of

rf potential well and losses when machine ramps 3. Resistive wall instability effects4. Study effects due to field errors

Ability for realistic simulation of Booster from injection to extraction

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What is the relevant physics?

• Space charge of long bunches in rings

• Nonlinear beam dynamics in quads, bends,…

• Injection painting

• Impedance effects

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Modeling issues

• Systematic treatment of nonlinear dynamics

• Space charge implementation Number of kicks Number of macro-particles (multi-turn injection) Long bunches: 2.5D? 3D? Multiple reference particle treatment?

• Initial particle distribution, matching {how “realistic” is the simulation}

• Diagnostics of simulation results controlled experiment ?

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Simulation tool issues

• 3D parallel space charge routines First use those in IMPACT (parallel linac code) Eventually should be able to plug in a choice of solvers from

elsewhere that are appropriate for systems with long bunches

• Interface space-charge code to beam dynamics codes suitable for circular machine modeling Implement split-operator techniques Parallelize particle dynamics (presume 3D solvers are parallel)

Approach should work for other single-particle optics codes that can calculate maps for circular machines

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IMPACT uses a method that is extremely efficient for the problem at hand

• Philosophy: Do not take tiny steps to push millions of macroparticles Do take tiny steps to compute transfer maps; then push w/ maps

• rapidly varying s-dependence of external fields decoupled from slowly varying space charge

Split-Operator Methods

M=Mext M=Msc

H=Hext+Hsc

M(t)= Mext(t/2) Msc(t) Mext(t/2) + O(t3)

MagneticOptics

Multi-ParticleSimulation

H=Hext H=Hsc

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Current Status

• MaryLie 3.0 (maps to 3rd order) modified to use split-operator method and IMPACT 3D space charge routines Serial version now implemented (will need ~1 month to parallelize in High

Performance Fortran) “auto-slicing of elements” allows space-charge kicks as often as desired Current implementation has 3D space charge with (1) open boundary conditions

in all 3 dimensions or (2) open transversely and periodic longitudinally Code has been modified to allow for accelerating beam Added RF cavity model based on on-axis field from Superfish

• Once parallel, could use the simulation with simple description of Booster lattice (no correctors) to study single bunch propagation at injection, before capture

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Overall Plan

• Full parallelization of the space-charge code (in MPI), additional boundary conditions (~6 months)

• Further code development to allow more realistic modeling of the machine and simulation of capture and acceleration phase

• Ability to interface the code to other beam dynamics packages

New hire in CD Simulation Group and interaction with BD theory group are essential for timely completion of these tasks

• Need to coordinate with Booster group on design of studies which will help validate the simulation