two_photon.cpp

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/* This file is part of Cloudy and is copyright (C)1978-2022 by Gary J. Ferland and
 * others.  For conditions of distribution and use see copyright notice in license.txt */

#include "cddefines.h"
#include "ipoint.h"
#include "rfield.h"
#include "transition.h"
#include "two_photon.h"

void TwoPhotonSetup( vector<two_photon> &tnu_vec, const long &ipHi, const long &ipLo, const double &Aul, const TransitionProxy &tr, const long ipISO, const long nelem )
{
        DEBUG_ENTRY( "TwoPhotonSetup()" );

        tnu_vec.resize( tnu_vec.size() + 1 );
        two_photon &tnu = tnu_vec.back();

        tnu.ipHi = ipHi;
        tnu.ipLo = ipLo;
        tnu.AulTotal = Aul;
        tnu.Pop = &(*tr.Hi()).Pop();
        tnu.E2nu = tr.EnergyRyd();
        tnu.induc_dn_max = 0.;
        
        /* pointer to the Lya energy */
        tnu.ipTwoPhoE = ipoint(tnu.E2nu);
        while( rfield.anu(tnu.ipTwoPhoE) > tnu.E2nu )
        {
                --tnu.ipTwoPhoE;
        }
        tnu.ipSym2nu.resize( tnu.ipTwoPhoE );
        tnu.As2nu.resize( tnu.ipTwoPhoE );
        tnu.local_emis.resize( tnu.ipTwoPhoE );

        /* >>chng 02 aug 14, change upper limit to full Lya energy */
        for( long i=0; i < tnu.ipTwoPhoE; i++ )
        {
                /* energy is symmetric energy, the other side of half E2nu */
                double energy = tnu.E2nu - rfield.anu(i);
                /* this is needed since mirror image of cell next to two-nu energy
                * may be slightly negative */
                energy = MAX2( energy, rfield.anumax(0) );
                /* find index for this symmetric energy */
                tnu.ipSym2nu[i] = ipoint(energy);
                while( rfield.anu(tnu.ipSym2nu[i]) > tnu.E2nu ||
                        tnu.ipSym2nu[i] >= tnu.ipTwoPhoE)
                {
                        --tnu.ipSym2nu[i];
                }
                ASSERT( tnu.ipSym2nu[i] >= 0 );
        }

        double SumShapeFunction = 0., Renorm= 0.;

        /* ipTwoPhoE is the cell holding the 2nu energy itself, and we do not want
         * to include that in the following sum */
        ASSERT( rfield.anu(tnu.ipTwoPhoE-1)<=tnu.E2nu );
        for( long i=0; i < tnu.ipTwoPhoE; i++ )
        {
                double ShapeFunction;

                ShapeFunction = atmdat_2phot_shapefunction( rfield.anu(i)/tnu.E2nu, ipISO, nelem )*rfield.widflx(i)/tnu.E2nu;
                SumShapeFunction += ShapeFunction;

                /* >>refer      HI      2nu     Spitzer, L., & Greenstein, J., 1951, ApJ, 114, 407 */
                /* As2nu will add up to the A, so its units are s-1     */ 
                tnu.As2nu[i] = (realnum)( tnu.AulTotal * ShapeFunction );
        }

        /* The spline function in twophoton.c causes a bit of an error in the integral of the
         * shape function.  So we renormalize the integral to 1.        */
        Renorm = 1./SumShapeFunction;

        for( long i=0; i < tnu.ipTwoPhoE; i++ )
        {
                tnu.As2nu[i] *= (realnum)Renorm;
        }

        /* The result should be VERY close to 1.        */
        ASSERT( fabs( SumShapeFunction*Renorm - 1. ) < 0.00001 );

        return;
}

void CalcTwoPhotonRates( two_photon& tnu, bool lgDoInduced )
{
        DEBUG_ENTRY( "CalcTwoPhotonRates()" );
                        
        /* this could fail when pops very low and Pop2Ion is zero */
        ASSERT( tnu.ipTwoPhoE>0 && tnu.E2nu>0. );

        double sum = 0.;
        tnu.induc_up = 0.;
        tnu.induc_dn = 0.;
        /* two photon emission, ipTwoPhoE is 
        * continuum array index for Lya energy */
        ASSERT( rfield.anu(tnu.ipTwoPhoE-1) < 1.01*tnu.E2nu || rfield.anu(tnu.ipTwoPhoE-2)<tnu.E2nu );
        for( long nu=0; nu < tnu.ipTwoPhoE; nu++ )
        {
                // We do not assert rfield.anu(nu)<=tnu.E2nu because the maximum 
                // index could be set to point to the next highest bin.

                // As2nu[nu] is transition probability A per bin
                // So sum is the total transition probability
                sum += tnu.As2nu[nu];
                                        
                // only include this if induced processes turned on,
                // otherwise inconsistent with rate solver treatment.
                if( lgDoInduced )
                {
                        double rate_up = tnu.As2nu[nu] *
                                rfield.SummedOcc[nu] * rfield.SummedOcc[tnu.ipSym2nu[nu]-1];
                        tnu.induc_up += rate_up;
                        tnu.induc_dn += rate_up + tnu.As2nu[nu] *
                                (rfield.SummedOcc[nu] + rfield.SummedOcc[tnu.ipSym2nu[nu]-1]);
                }
        }

        /* a sanity check on the code, see Spitzer and Greenstein (1951), eqn 4.        */
        /* >>refer      HI      2nu     Spitzer, L., & Greenstein, J., 1951, ApJ, 114, 407 */
        ASSERT( fabs( 1.f - (realnum)sum/tnu.AulTotal ) < 0.01f );

        return;
}

void CalcTwoPhotonEmission( two_photon& tnu, bool lgDoInduced )
{
        DEBUG_ENTRY( "CalcTwoPhotonEmission()" );
                        
        /* this could fail when pops very low and Pop2Ion is zero */
        ASSERT( tnu.ipTwoPhoE>0 );

        /* two photon emission, ipTwoPhoE is 
         * continuum array index for Lya energy */
        for( long nu=0; nu < tnu.ipTwoPhoE; nu++ )
        {
                // Pop has dimension cm^-3.  The factor of 2 is for two photons per 
                // transition. Thus two_photon_emiss has dimension photons cm-3 s-1.
                tnu.local_emis[nu] = 2.f * (realnum)(*tnu.Pop) * tnu.As2nu[nu];
        }

        // only include this if induced processes turned on,
        // otherwise inconsistent with rate solver treatment.
        if( lgDoInduced )
        {
                for( long nu=0; nu < tnu.ipTwoPhoE; nu++ )
                {
                        // this is the total rate (in this energy bin)
                        tnu.local_emis[nu] *= (1.f + rfield.SummedOcc[nu]) *
                                (1.f+rfield.SummedOcc[tnu.ipSym2nu[nu]-1]);
                }
        }

        return;
}

/* option to print hydrogen and helium two-photon emission coefficients?        */
void PrtTwoPhotonEmissCoef( const two_photon& tnu, const double& densityProduct )
{
        DEBUG_ENTRY( "PrtTwoPhotonEmissCoef()" );
                                
        fprintf( ioQQQ, "\ny\tGammaNot(2q)\n");

        for( long yTimes20=1; yTimes20<=10; yTimes20++ )
        {
                double y = yTimes20/20.;

                fprintf( ioQQQ, "%.3e\t", (double)y );  

                long i = ipoint(y*tnu.E2nu);
                fprintf( ioQQQ, "%.3e\n", 
                        8./3.*HPLANCK*(*tnu.Pop)/densityProduct*y*tnu.As2nu[i]*tnu.E2nu/rfield.widflx(i) );
        }

        return;
}