March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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Physics ProcessesMissing from our Current

Simulation Tools

Tom Roberts

Muons, Inc.

This is the current list −Please help us to complete it.

Classes of Processes

• Single-particle processes• Collective effects in vacuum• Collective effects in matter• Polarized muon processes• Normalization and Computation of Emittance• RF breakdown• Neutrino processes• Details

Some of these are implemented in other tools;we need to consider adding to our toolbox

and/or enhancing the tools we use.March 2, 2011 TJR Physics Processes Missing from

our Current Simulation Tools2

Single-Particle Processes

• Accurate multiple-scattering model– Several are available in ICOOL– G4beamline has all Geant4 processes available

• Geant4 9.4 changes this (again)

• Energy-loss straggling model (incl. length dependence)– Vavilov model vs. Striganov model

• Material dependence of energy loss and straggling– ICOOL and G4beamline disagree for LiH

• Correlation of energy loss with multiple scattering angle• Effect of magnetic field on multiple scattering• Energy loss in matter for high-energy muons

(> ~200GeV)

March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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Collective Effects in Vacuum

• Space charge– Basic computation in ICOOL– Two computations in G4beamline

• Wake fields• Beam loading• Beam-beam interactions

– G4beamline space charge implementations apply

• Electron cloud effects• Decay of macro-particles• Interactions of macro-particles

March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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Collective Effects in Matter (1)

• Space charge screening by material• Bunch effect on the density term of the single-particle formula for

energy loss (plasma density)• Bunch-induced polarization of material causing intensity-dependent

increase in energy loss– Can induce an instability

• Plasma effects from ionized electrons and ions• Dense beam boring a “hole” in the absorber, with the front of the

bunch ionizing ~100%, so the back end of the bunch has reduced ionization loss

• Absorber bubble formation, melting, or other thermal damage• Beam particles “ganging up” on atomic nuclei – a hydrogen nucleus

is NOT heavy compared to 1,000 muons.• Energy loss and multiple scattering from ionized and excited atoms

(prepared by earlier beam particles).

March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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Collective Effects in Matter (2)

• Beam particles screening each other, for both multiple scattering and energy loss.

• Effect of plasma on atomic response, for both multiple scattering and energy loss.

• Effect of matter on wake fields and beam loss, including EM radiation from bunches transiting windows (resonates in RF cavity…).

• For all of the above:– Consider dependency on material properties– Consider time dependence

• Head vs. tail of a single bunch

• Effects involving successive bunches in a train

– Are LH2 and RF-cavity windows important?

March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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Polarized Muon Processes

• Geant4 has no muon-polarized processes, we need ot implement them

• Effect of ionization cooling on polarization.– For applications other than a muon collider or neutrino factory– Might it be interesting in a collider to trade a factor of ~100

reduction in luminosity for partially polarized beams? – Would it be possible?

March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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Normalization and Computation of Emittance

• Uncertainties remain about the accuracy of the pion production models used.– MARS, Fluka, MCNPX, Geant4, all differ in various ways– Direct experiments are scarce, but there are relevant ones

• Cavitation and other distortions of the mercury jet production target

• Proper calculation of the EM vector potential in the emittance computation.

March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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RF Breakdown

• While not directly part of the particle simulations, modeling RF breakdown is an important aspect of the overall simulation of a muon collider.– Vacuum

– High-pressure H2

– Surface effects and processing

• This is so important that experiments are required.– Will affect technology used, so must be done early

March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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Neutrino Processes

• Surface radiation assessment will require accurate simulations of neutrino interactions– Need to significantly increase neutrino interaction cross-sections

to make simulations feasible

• Also needed for studying backgrounds in the MC detector.

March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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Details

• Our current simulations are at best approximations to what would actually be built

• Many details must be assessed and included if necessary, such as:

– 3-D effects in RF cavity field models• Realistic, non-pillbox cavities• Couplers• HOM absorbers

– Engineering assessments• Thermal loads from the beam• Thermal loads from muon decay• Radiation levels• Surely others…

– Ability to model a large and complex detector for background studies– Surely more…

March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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Summary

• There are a number of complicated and subtle physics processes not included in our current simulation tools.

• We must expand the list to be as complete as possible.• Ultimately we will need a set of publications or MuCool

notes, estimating the importance of each one.• We need to implement those that can significantly affect

our modeling of facilities.• There are many other simulation tools available, and we

need to assess whether to acquire and use additional tools, or to enhance the ones we already use.

• There are of course myriads of engineering details, required for accurate simulations of a specific design.

March 2, 2011 TJR Physics Processes Missing from our Current Simulation Tools

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