/**
*
*
* <h2>Back-propagates the Defining State of the Probe Object</h2>
*
* <p>This method uses the same basic algorithm as in <code>EnvelopeTracker#advanceState()</code>,
* only the probe object is back-propagated. The method utilizes all the space charge mechanisms
* of the base class <code>EnvelopeTracker</code>.
*
* @param ifcElem interface to the beam element
* @param ifcProbe interface to the probe
* @param dblLen length of element subsection to retract
* @throws ModelException bad element transfer matrix/corrupt probe state
* @author Christopher K. Allen
* @since Feb 9, 2009
* @see xal.model.alg.EnvelopeTracker#advanceState(xal.model.IProbe, xal.model.IElement, double)
*/
protected void retractState(IProbe ifcProbe, IElement ifcElem, double dblLen)
throws ModelException {
// Identify probe
EnvelopeProbe probe = (EnvelopeProbe) ifcProbe;
// Get initial conditions of probe
// R3 vecPhs0 = probe.getBetatronPhase();
// Twiss[] twiss0 = probe.getCovariance().computeTwiss();
PhaseMatrix matResp0 = probe.getResponseMatrix();
PhaseMatrix matTau0 = probe.getCovariance();
// Remove the emittance growth
if (this.getEmittanceGrowth()) matTau0 = this.removeEmittanceGrowth(probe, ifcElem, matTau0);
// Compute the transfer matrix
// def PhaseMatrix matPhi = compTransferMatrix(dblLen, probe, ifcElem);
PhaseMatrix matPhi = compTransferMatrix(dblLen, probe, ifcElem);
// Advance the probe states
PhaseMatrix matResp1 = matPhi.times(matResp0);
PhaseMatrix matTau1 = matTau0.conjugateTrans(matPhi);
// Save the new state variables in the probe
probe.setResponseMatrix(matResp1);
probe.setCurrentResponseMatrix(matPhi);
probe.setCovariance(new CovarianceMatrix(matTau1));
// probe.advanceTwiss(matPhi, ifcElem.energyGain(probe, dblLen) );
// phase update:
// Twiss [] twiss1 = probe.getCovariance().computeTwiss();
// R3 vecPhs1 = vecPhs0.plus( matPhi.compPhaseAdvance(twiss0, twiss1) );
// probe.setBetatronPhase(vecPhs1);
/** sako treatment of ChargeExchangeFoil */
treatChargeExchange(probe, ifcElem);
}
/**
*
*
* <h2>Compute Transfer Matrix Including Space Charge</h2>
*
* <p>Computes the back-propagating transfer matrix over the incremental distance <code>dblLen
* </code> for the beamline modeling element <code>ifcElem</code>, and for the given <code>probe
* </code>. We include space charge and emittance growth effects if specified.
*
* <p><strong>NOTE</strong>: (CKA) <br>
* · If space charge is included, the space charge matrix is computed for length <code>
* dblLen</code>, but at a half-step location behind the current probe position. This method is
* the same technique used by Trace3D. The space charge matrix is then pre- and post- multiplied
* by the element transfer matrix for a half-step before and after the mid-step position,
* respectively. <br>
* · I do not know if this (leap-frog) technique buys us much more accuracy then full
* stepping.
*
* @param dblLen incremental path length
* @param probe beam probe under simulation
* @param ifcElem beamline element propagating probe
* @return transfer matrix for given element
* @throws ModelException bubbles up from IElement#transferMap()
* @see EnvelopeTracker#compScheffMatrix(double, EnvelopeProbe, PhaseMatrix)
* @see EnvelopeTracker#transferEmitGrowth(EnvelopeProbe, IElement, PhaseMatrix)
* @see EnvelopeTracker#modTransferMatrixForDisplError(double, double, double, PhaseMatrix)
*/
private PhaseMatrix compTransferMatrix(double dblLen, EnvelopeProbe probe, IElement ifcElem)
throws ModelException {
// Returned value
PhaseMatrix matPhi; // transfer matrix including all effects
// Check for exceptional circumstance and modify transfer matrix accordingly
if (ifcElem instanceof IdealRfGap) {
IdealRfGap elemRfGap = (IdealRfGap) ifcElem;
double dW = elemRfGap.energyGain(probe, dblLen);
double W = probe.getKineticEnergy();
probe.setKineticEnergy(W - dW);
PhaseMatrix matPhiI = elemRfGap.transferMap(probe, dblLen).getFirstOrder();
if (this.getEmittanceGrowth()) {
double dphi = this.effPhaseSpread(probe, elemRfGap);
matPhiI = super.modTransferMatrixForEmitGrowth(dphi, matPhiI);
}
matPhi = matPhiI.inverse();
probe.setKineticEnergy(W);
return matPhi;
}
if (dblLen == 0.0) {
matPhi = ifcElem.transferMap(probe, dblLen).getFirstOrder();
return matPhi;
}
// Check for easy case of no space charge
if (!this.getUseSpacecharge()) {
matPhi = ifcElem.transferMap(probe, dblLen).getFirstOrder();
// we must treat space charge
} else {
// Store the current probe state (for rollback)
EnvelopeProbeState state0 = probe.cloneCurrentProbeState();
// ProbeState state0 = probe.createProbeState();
// Get half-step back-propagation matrix at current probe location
// NOTE: invert by computing for negative propagation length
PhaseMap mapElem0 = ifcElem.transferMap(probe, -dblLen / 2.0);
PhaseMatrix matPhi0 = mapElem0.getFirstOrder();
// Get the RMS envelopes at probe location
CovarianceMatrix covTau0 = probe.getCovariance(); // covariance matrix at entrance
// Move probe back a half step for position-dependent transfer maps
double pos = probe.getPosition() - dblLen / 2.0;
PhaseMatrix matTau1 = covTau0.conjugateTrans(matPhi0);
CovarianceMatrix covTau1 = new CovarianceMatrix(matTau1);
probe.setPosition(pos);
probe.setCovariance(covTau1);
// space charge transfer matrix
// NOTE: invert by computing for negative propagation length
PhaseMatrix matPhiSc = this.compScheffMatrix(-dblLen, probe, ifcElem);
// Compute half-step transfer matrix at new probe location
PhaseMap mapElem1 = ifcElem.transferMap(probe, -dblLen / 2.0);
PhaseMatrix matPhi1 = mapElem1.getFirstOrder();
// Restore original probe state
probe.applyState(state0);
// Compute the full transfer matrix for the distance dblLen
matPhi = matPhi1.times(matPhiSc.times(matPhi0));
}
if (ifcElem instanceof IdealMagQuad) {
// sako put alignment error in sigma matrix
// NOTE the use of negative displacements for back-propagation
IdealMagQuad elemQuad = (IdealMagQuad) ifcElem;
double delx = -elemQuad.getAlignX();
double dely = -elemQuad.getAlignY();
double delz = -elemQuad.getAlignZ();
matPhi = this.modTransferMatrixForDisplError(delx, dely, delz, matPhi);
}
return matPhi;
}