Svion.for

      SUBROUTINE SVION(J,DSVDN,DSVDT,FLUXN)
      INCLUDE 'Soldiv.fi'
      PARAMETER (J3=56)
      DIMENSION GAM(J3)
C           CALCULATES T & N DERIVATIVES OF IONIZATION SOURCE

C           *******NEUTRAL ATOM MODEL**************
C     USE THOMAS SV @ 100eV
      IF(J.GT.1) GOTO 50
      SIGEL = 17.0E-19
      SIGVEL = 16.0E-14
      SIGCX = 4.0E-19
      SIGVCX = 3.7E-14
      SIGION = 4.2E-19
      SIGVION = 4.0E-14
      SIGVTOT = SIGVEL + SIGVCX + SIGVION
C     RECYLING FLUX= PLASMA ION LOSS X RECYCLE COEF RCOEF
      GAM(56) = (XNAV/TAUP)*AMINOR*RCOEF/2.
      FLUXN = GAM(56)
C     CURRENT ATTENUATION BY E2 FUNCTION
      Z = (SIGEL + SIGCX + SIGION)*XNC(56)*0.5*DELC
      IF(Z.GT.1.)  GOTO 5
      E1 = -LOG(Z)-.57721566+.999999193*Z-.24991055*(Z**2)+.05519968*
     2     (Z**3)-.00976004*(Z**4)+.00107857*(Z**5)
      GOTO 6
 5    E1 = (EXP(-Z)/Z)*(Z**2+2.334733*Z+.250621)/(Z**2+3.330657*Z+
     2    1.681534)
 6    E2 = (EXP(-Z) - Z*E1)/1.
      GAM(55) = GAM(56)*E2
      DO 10 I = 1,54
        J = 55 - I
        Z = (SIGEL + SIGCX + SIGION)*XNC(J)*DEL
        IF(Z.GT.1.)  GOTO 7
        E1 = -LOG(Z)-.57721566+.999999193*Z-.24991055*(Z**2)+.05519968*
     2       (Z**3)-.00976004*(Z**4)+.00107857*(Z**5)
        GOTO 8
 7      E1 = (EXP(-Z)/Z)*(Z**2+2.334733*Z+.250621)/(Z**2+3.330657*Z+
     2      1.681534)
 8      E2 = (EXP(-Z) - Z*E1)/1.
        GAM(J) = GAM(J+1)*E2
 10   CONTINUE
C     NEUTRAL DENSITY
      XNEUT(56) = (GAM(56)-GAM(55))/(SIGVTOT*XNC(56)*0.5*DELC)
      DO 20 I =2,55
        XNEUT(I) = (GAM(I)-GAM(I-1))/(SIGVTOT*XNC(I)*DELC)
 20   CONTINUE
      XNEUT(1) = 0.

C           DSDN
 50   DSVDN = XNEUT(J)*SIGVION

C           DSDT
      DSVDT = 0.

      RETURN
      END