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VORPAL for Simulating RF BreakdownPowerPoint Presentation

VORPAL for Simulating RF Breakdown

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RF Breakdown

Kevin Paul

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

- 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

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

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

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

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

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

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

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

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

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

Example: Impact Ionization, Elastic Scattering & Excitation

Fermilab MuCool RF Workshop III – 7 July 2009

Example: Impact Ionization, Elastic Scattering & Excitation

Fermilab MuCool RF Workshop III – 7 July 2009

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