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VORPAL for Simulating RF Breakdown. Kevin Paul [email protected]

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VORPAL for Simulating

RF Breakdown

Kevin Paul

[email protected]

VORPAL is a massively-parallel, fully electromagnetic particle-in-cell (PIC) code, originally developed for laser-plasma simulation. Since it's creation in 2004, VORPAL has expanded its capabilities to include electrostatics, cross-section-based particle-particle interactions, hybrid particle-fluid modeling, and a variety of numerical models for everything from field ionization, impact ionization, secondary electron emission, field emission, and particle-impact heating.

Fermilab MuCool RF Workshop III – 7 July 2009


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Tech-X Corporation Projects

  • Breakdown Phase II:

    • Seth Veitzer

    • July 2008 – July 2010

    • Developing VORPAL to do 3D simulations of RF breakdown

    • Built off of a Phase I project using OOPIC (2D/r-z)

  • eSHIELD Phase I:

    • Me

    • July 2009 – March 2010

    • More VORPAL development to test magnetic insulation

    • Will couple small-scale with large-scale simulations

Fermilab MuCool RF Workshop III – 7 July 2009


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VORPAL:

Versatile Plasma Simulation Code

  • Technical Features:

    • Object-oriented C++

    • 1D/2D/3D Massively Parallel Scaling to 10,000+ Processors

    • Compressed Binary Data Formatting (HDF5)

    • Mac OS X / Microsoft Windows / Linux

  • Multi-physics Capability:

    • Kinetic Plasma Model

    • Field & Impact Ionization

    • Field & Secondary Emission

    • Hybrid Particle-Fluid Modeling

    • Electrostatic & Electromagnetic

  • Uses:

    • Laser wake-field accelerators

    • Electron cooling

    • Photonic Band Gap Devices

    • RF Heating in Fusion Plasmas

    • Breakdown in Microwave Guides

    • Simulation of Ion Sources & Penning Sources

    • Modeling of Plasma Thrusters

  • Availability:

    • Consulting

    • Purchase

    • SBIR/STTR Collaboration

    • Web interface (In development!)

Fermilab MuCool RF Workshop III – 7 July 2009


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Electrostatic

Particle-in-Cell Simulation:One Simulation Time Step

Initialization Steps...

Fields defined

and initialized

on a grid

{Ei, Bi}

Particle positions

& velocities

initialized

{xα, vα}

Particles

accelerated

by the fields

{v'α}

Particles

moved based on

new velocity

{x'α}

One Time Step

New fields

computed from

charges

{E’i}

Charge

“deposited”

on the grid

{ρi}

Fermilab MuCool RF Workshop III – 7 July 2009


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Electromagnetic

Particle-in-Cell Simulation:One Simulation Time Step

Initialization Steps...

Fields defined

and initialized

on a grid

{Ei, Bi}

Particle positions

& velocities

initialized

{xα, vα}

Particles

accelerated

by the fields

{v'α}

Particles

moved based on

new velocity

{x'α}

One Time Step

New fields

computed from

old fields

{E'i, B'i}

Currents

“deposited”

on the grid

{Ji}

Fermilab MuCool RF Workshop III – 7 July 2009


Slide6 l.jpg

Electromagnetic

Particle-in-Cell Simulation:One Simulation Time Step

New particles

added (lost

removed)

{xα, vα}

Particles

accelerated

by the fields

{v'α}

Particles

moved based on

new velocity

{x'α}

One Time Step

Collisions and

interactions

computed

New fields

computed from

old fields

{E'i, B'i}

Currents

“deposited”

on the grid

{Ji}

Fermilab MuCool RF Workshop III – 7 July 2009


Slide7 l.jpg

Electromagnetic

Particle-in-Cell Simulation:One Simulation Time Step

This is where all the interesting physics for RF breakdown takes place!!!

New particles

added (lost

removed)

{xα, vα}

Particles

accelerated

by the fields

{v'α}

Particles

moved based on

new velocity

{x'α}

One Time Step

Collisions and

interactions

computed

New fields

computed from

old fields

{E'i, B'i}

Currents

“deposited”

on the grid

{Ji}

Fermilab MuCool RF Workshop III – 7 July 2009


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RF Breakdown Physics:

What must be modeled?

  • Field emission of electrons from conductor surfaces

  • Secondary emission of electrons from conductor surfaces

  • Sputtering

  • Neutral Desorption

  • Field-induced ionization (Tunneling ionization)

  • Impact ionization

  • X-ray production from electron impact on conductor surfaces

  • Surface heating due to particle impact

  • Surface deformation due to melting

  • Radiative cooling of ions

Fermilab MuCool RF Workshop III – 7 July 2009


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Physics Models in VORPAL/TxPhysics:

What can VORPAL do now?

  • Fowler-Nordheim model for field emission from “assumed asperity”

  • Jensen model for field, thermal, and photo-induced electron emission

  • Rothard model for ion-induced secondary electron emission (depends strongly on nuclear stopping power of material)

  • Furman-Pivi (LBNL) model for electron-induced secondary electron emission

  • Yamamura model for sputtering (nuclear stopping dependent threshold model)

  • Molvik model for neutral desorption (akin to Rothard model)

  • Tunneling ionization rates for various materials from Keldysh

  • Parameterized impact ionization, excitation, and recombination cross sections for electrons and ions

  • Diagnostics for recording energy deposited in absorbing boundaries

  • Coronal model for computing radiated power by ions in a plasma (a diagnostic, no radiation transport)

Fermilab MuCool RF Workshop III – 7 July 2009


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VORPAL/TxPhysics Development:

What will VORPAL be able to do?

  • X-ray emission model for various materials due to electron bombardment

  • Impurity radiation model for ion cooling

  • Simple radiation transport

  • Couple VORPAL simulations to molecular dynamics models for surface damage and deformation

  • Temperature and emission yield “diagnostic mapping” to more easily visualize the simulations

  • A web-based interface to VORPAL with the capability of providing computational resources to researchers anywhere

  • Surface damage and heating model due to bombardment

  • Multi-scale simulation capability, coupling “fine-grain” (surface asperity) simulations with “course-grain” (RF cavity) simulations

…all are about 1 year away!

Fermilab MuCool RF Workshop III – 7 July 2009


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Example: Impact Ionization, Elastic Scattering & Excitation

  • A beam of 40 eV electrons is incident on a “droplet” of Xenon and Argon gas.

  • Impact ionization, elastic scattering, and neutral gas excitation are all computed.

Fermilab MuCool RF Workshop III – 7 July 2009


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Example: Impact Ionization, Elastic Scattering & Excitation

Fermilab MuCool RF Workshop III – 7 July 2009


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Example: Impact Ionization, Elastic Scattering & Excitation

Fermilab MuCool RF Workshop III – 7 July 2009


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