afterb_li.inp

pic 模拟程序！面向对象

afterB_Li.inp
{

High-energy electron bunch enters a quiet plasma in cylindrical geometry --
Modeling the SLAC "afterburner" concept of Tom Katsouleas.

Tunneling ionization effects are ignored..
Collisional effects are ignored for both beam and plasma electrons.

This simulation models a beam-plasma wake-field accelerator:
a)  The background plasma is pre-ionized.  Ions are assumed stationary.
b)  Beam density exceeds electron plasma density, so the beam "blows out"
    plasma electrons near the symmetry axis.
c)  The electron beam is Gaussian in z and r.
d)  The electron beam is overfocussed by these fields and so executes
    betatron oscillations;  however, the focussing force varies axially.

Moving window:
a)  Once the electron beam has entered the grid and is close to the far
    edge of the simulation region, a moving window algorithm is invoked
    so that the beam can be modeled for long times.

Boundary conditions:
a)  The simulation region must be bounded by either conductors or
    insulators, in order to capture lost particles.
b)  Conductors were chosen, to avoid any charge build up.
c)  The choice of conducting boundary conditions means that electric
    fields parallel to the boundaries are forced to zero;  however,
    fields near the boundaries of the simulation must be small anyway
    to accurately model a semi-infinite plasma, so this is OK.
}

// Define variables that can be used throughout this input file.

Variables
{
// First, define some useful constants.
  pi = 3.14159
  speedOfLight = 2.998e+08
  unitCharge = 1.602e-19
  electronCharge = -1 * unitCharge
  electronMass = 9.1095e-31
  electronMassEV = electronMass * speedOfLight * speedOfLight / unitCharge
  ionCharge = unitCharge
  unitMassMKS = 1.6606e-27
  lithiumMassNum = 6.942
  lithiumMass = unitMassMKS * lithiumMassNum

// Next, define the parameters of the high-energy electron beam.
  beamEnergyEV = 50.0e+09
  beamTempEV = 0.0
  thermalBeamSpeedEV = 0.5 * beamTempEV
  totalNumBeam = 2.0e+10
  totalBeamCharge = totalNumBeam * electronCharge
  rmsBeamRadius = 20.e-06
  rmsBeamLength = 63.e-06
  rmsBeamTime = rmsBeamLength / speedOfLight
  radialCutoffFac = 3
  axialCutoffFac = 3
  totalBeamRadius = radialCutoffFac * rmsBeamRadius
  totalBeamLength = 2 * axialCutoffFac * rmsBeamLength
  beamAspectRatio = totalBeamLength / totalBeamRadius
  totalBeamArea = pi * totalBeamRadius * totalBeamRadius
  rmsBeamVolume = pi * rmsBeamRadius * rmsBeamRadius * rmsBeamLength
//	rmsBeamEmittanceNormPiMRad = 1.25e-04

// Define the number of grids in R and Z
  lengthOverRadiusAspectRatio = 3
  simRadiusOverBeamRadius = 8
  numRgridsAcrossBeam = 8
  numZgridsAcrossBeam = numRgridsAcrossBeam * beamAspectRatio
  numRgrids = numRgridsAcrossBeam * simRadiusOverBeamRadius
  numZgrids = numRgrids * lengthOverRadiusAspectRatio
  numCells = numRgrids * numZgrids

// Number of beam particles
  numBeamPtclsPerCell = 100
  numBeamCells = numRgridsAcrossBeam * numZgridsAcrossBeam
  numBeamPtcls = numBeamPtclsPerCell * numBeamCells
  beamNumRatio = totalNumBeam / numBeamPtcls

// Intermediate calculations for modeling Gaussian shape of the beam.
  invSigRsq = 1.0 / ( rmsBeamRadius * rmsBeamRadius )
  invSigZsq = 0.5 / ( rmsBeamLength * rmsBeamLength )
  invSigTsq = invSigZsq * speedOfLight * speedOfLight

// Calculate the size of the simulation region, grid spacings, time step.
// We are assuming the same grid size in both z and r	
  maxRadiusMKS = simRadiusOverBeamRadius * totalBeamRadius
  rGridSize = maxRadiusMKS / numRgrids
  zGridSize = rGridSize
  maxLengthMKS = numZgrids * zGridSize
  timeStep = 0.5 * rGridSize / speedOfLight

// This is the desired delay time before the moving window algorithm activates.
  movingWindowDelay = 0.97 * maxLengthMKS / speedOfLight

// Calculate peak currents for defining emission of the high-energy beam.
  peakCurrentDensity=totalBeamCharge*speedOfLight/rmsBeamVolume/sqrt(2.*pi)
  peakCurrent = peakCurrentDensity * totalBeamArea
  pulseLengthSec = totalBeamLength / speedOfLight
  oneHalfPulse = pulseLengthSec/2.
  oneEighthPulse = pulseLengthSec/8.
  threeEighthsPulse = 3.*oneEighthPulse
  sevenEighthsPulse = 7.*oneEighthPulse

// Define the plasma density, number of plasma electron macro-particles, etc.
  plasmaDensityMKS = 1.8e+22
  simulationVolume = pi * maxRadiusMKS * maxRadiusMKS * maxLengthMKS
  totalNumPlasma = plasmaDensityMKS * simulationVolume
  numPtclsPerCell = 8
  numPlasmaPtcls = numPtclsPerCell * numCells
  plasmaNumRatio = totalNumPlasma / numPlasmaPtcls
}

// This simulation has only one "region", which contains grid, all particles, etc.
Region
{

// Define the grid for this region.
Grid
{

// Define number of grids along Z-axis and physical coordinates.
  J = numZgrids
  x1s = 0.0
  x1f = maxLengthMKS
  n1 = 1.0

// Define number of grids along R-axis and physical coordinates.
  K = numRgrids
  x2s = 0.0
  x2f = maxRadiusMKS
  n2 = 1.0
}

// Specify "control" parameters for this region
Control
{
// Specify the time step.
  dt = timeStep

// Turn on the moving window algorithm.
  movingWindow = 1
  shiftDelayTime = movingWindowDelay

// Turn on damping for the high-frequency EM fields
  emdamping = 0.49

// Turn off the initial Poisson solve
  initPoissonSolve = 0

// Use bilinear current weighting
  CurrentWeighting=1
}

// Define the plasma ions.
Species
{
  name = lithium
  m = lithiumMass
  q = ionCharge
// advance the ions only once every 100 steps, because they
//   are essentially stationary
  subcycle = 100
// prevent out-of-control growth in # of ptcls
  particleLimit = 8.e+05
}

// Define the plasma electrons.
Species
{
  name = electrons
  m = electronMass
  q = electronCharge
// prevent out-of-control growth in # of ptcls
  particleLimit = 8.e+05
}

// Define the beam electrons.
Species
{
  name = beam_electrons
  m = electronMass
  q = electronCharge
//  collisionModel = 1
}


// Define the beam emitter, which introduces the high-energy beam into the
// simulation.
VarWeightBeamEmitter
{
  speciesName = beam_electrons
  I = peakCurrent

// Define the 2-D function F(x,t) that specifies beam emission profile.
  xtFlag = 3
  nIntervals = 32
  F=exp(-invSigRsq*x*x)*exp(-invSigTsq*(t-oneHalfPulse)*(t-oneHalfPulse))*step(pulseLengthSec-t)

// Macroparticles are emitted from the left boundary, close to the axis of symmetry.
  j1 = 0
  j2 = 0
  k1 = 0
  k2 = numRgridsAcrossBeam
  normal = 1
  np2c = beamNumRatio

// Emit particles, directed along the Z-axis,  with specified energy and temperature.
  units = EV
  v1drift = beamEnergyEV
}


// Specify a perfect conductor along the left boundary.  This serves as a particle
//   boundary condition (catches particles that leave the simulation) and as a
//   field boundary condition (E_r is forced to vanish).
Conductor
{
  j1 = 0
  j2 = 0
  k1 = 0
  k2 = numRgrids
  normal = 1
}

// Specify a perfect conductor along the radial boundary.  This serves as a
//   particle boundary condition (catches particles that leave the simulation)
//   and as a field boundary condition (E_z is forced to vanish).
Conductor
{
  j1 = 0
  j2 = numZgrids
  k1 = numRgrids
  k2 = numRgrids
  normal = -1
}

// Specify a perfect conductor along the right boundary.  This serves as a
//   particle boundary condition (catches particles that leave the simulation)
//   and as a field boundary condition (E_r is forced to vanish).
Conductor
{
  j1 = numZgrids
  j2 = numZgrids
  k1 = numRgrids
  k2 = 0
  normal = -1
}

// Define the cylindrical symmetry axis.
CylindricalAxis
{
  j1 = 0
  j2 = numZgrids
  k1 = 0
  k2 = 0
  normal = 1
}

// Load the plasma ions over the entire simulation region.
Load
{
  speciesName = lithium
  density = plasmaDensityMKS
  x1MinMKS = 0.5*maxLengthMKS
  x1MaxMKS = maxLengthMKS
  x2MinMKS = 0.0
  x2MaxMKS = maxRadiusMKS

// This specifies a static uniform background (no macro-particles).
  np2c = 0
}

// Load the plasma electrons over the entire simulation region, but
//   leave the last dz strip of cells empty, because this strip must
//   be handled separately to accomodate the moving window algorithm.
VarWeightLoad
{
  speciesName = electrons
  density = plasmaDensityMKS
  x1MinMKS = 0.5*maxLengthMKS
  x1MaxMKS = maxLengthMKS - zGridSize
  x2MinMKS = 0.0
  x2MaxMKS = maxRadiusMKS
  np2c = 2 * plasmaNumRatio
// Specify loading that is more uniform than random
  LoadMethodFlag = 1
}

// Load the plasma electrons into the last dz strip of cells, which was
//   omitted by the load instruction above.
VarWeightLoad
{
// Name this load group "shiftLoad" so that the moving window algorithm
//   knows to invoke it every time the simulation window is shifted.
  Name = shiftLoad
  speciesName = electrons
  density = plasmaDensityMKS

  x1MinMKS = maxLengthMKS - zGridSize
  x1MaxMKS = maxLengthMKS
  x2MinMKS = 0.0
  x2MaxMKS = maxRadiusMKS
  np2c = 2 * plasmaNumRatio

// Specify loading that is more uniform than random
	LoadMethodFlag = 1
}

}