Transcript Document

VORPAL for Simulating
RF Breakdown
Kevin Paul
[email protected]
VORPAL is a massively-parallel, fully electromagnetic particlein-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
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
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:
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Kinetic Plasma Model
Field & Impact Ionization
Field & Secondary Emission
Hybrid Particle-Fluid Modeling
Electrostatic & Electromagnetic
Fermilab MuCool RF Workshop III – 7 July 2009
• Uses:
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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:
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Consulting
Purchase
SBIR/STTR Collaboration
Web interface (In development!)
Electrostatic
Particle-in-Cell Simulation:
One Simulation Time Step
Initialization Steps...
Fields defined
and initialized
on a grid
Particle positions
& velocities
initialized
Particles
accelerated
by the fields
Particles
moved based on
new velocity
{Ei, Bi}
{xα, vα}
{v'α}
{x'α}
One
Time
Step

2   
0
E  

Fermilab MuCool RF Workshop III – 7 July 2009
New fields
computed from
charges
Charge
“deposited”
on the grid
{E’i}
{ρi}
Electromagnetic
Particle-in-Cell Simulation:
One Simulation Time Step
Initialization Steps...
Fields defined
and initialized
on a grid
Particle positions
& velocities
initialized
Particles
accelerated
by the fields
Particles
moved based on
new velocity
{Ei, Bi}
{xα, vα}
{v'α}
{x'α}
One
Time
Step
dE
1
1
  J  2 B
dt
0
c
dB
   E
dt

Fermilab MuCool RF Workshop III – 7 July 2009
New fields
computed from
old fields
Currents
“deposited”
on the grid
{E'i, B'i}
{Ji}
Electromagnetic
Particle-in-Cell Simulation:
One Simulation Time Step
New particles
added (lost
removed)
Particles
accelerated
by the fields
Particles
moved based on
new velocity
{xα, vα}
{v'α}
{x'α}
One Time Step
Collisions and
interactions
computed
Fermilab MuCool RF Workshop III – 7 July 2009
New fields
computed from
old fields
Currents
“deposited”
on the grid
{E'i, B'i}
{Ji}
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)
Particles
accelerated
by the fields
Particles
moved based on
new velocity
{xα, vα}
{v'α}
{x'α}
One Time Step
Collisions and
interactions
computed
Fermilab MuCool RF Workshop III – 7 July 2009
New fields
computed from
old fields
Currents
“deposited”
on the grid
{E'i, B'i}
{Ji}
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
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
VORPAL/TxPhysics Development:
What will VORPAL be able to do?
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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