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**
**  MACHINE GEOMETRY
**
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**
**  machine="toroidal" or machine="mirror"
**    Use of "mirror" makes available Gary Smith's B field option
**    (see below). Use of "toroidal" allows a variety of magnetic
**    field options (see below).
**    machine="mirror" is disabled for lrz .gt. 1
**    default: machine="toroidal"
**
**  psimodel determines the model used (or the method used) to determine
**    the magnetic field variation in the poloidal direction, that
**    is psi(z)=B(z)/B(0).
**  psimodel="axitorus" means standard 1/R variation for circular cross
**    sections is used. (Only slightly sensible for eqmod.ne."enabled";
**    even with eqmod.ne."enabled", I recommend psimodel="spline"BH000416)
**  psimodel="smith" means Gary Smith's model is used for mirror problems.
**  psimodel="spline" means that if through the use of some other model,
**    we have available on some arbitrary z (field line) grid an array
**    psi(z), then we utilize splines to determine psi(z) on the
**    computational z mesh. This option is generally used only when
**    the "eq"uilibrium module is enabled and an MHD "eqdsk" file is
**    available.  (Also works with eqmod.ne."enabled",machine="toroidal".)
**    default: psimodel="axitorus",
**             But psimodel reset to "spline" if eqmod.NE."disabled".
**
**  Set gsla and gslb if machine="mirror" and psimodel="smith"
**    gsla and gslb are field scale lengths such that:
**    psi(s)=[1+(s/gsla)^2
**              +gsb*(exp(-(s-gszb)^2/gslb^2)
**              +gsb*(exp(-(s+gszb)^2/gslb^2)]/N
**    Sets gsb and gszb so psi'(zmax)=0, psi(zmax)=rmirror
**    N is chosen so psi(0)=1 and psi'(0)=0 by construction
**    default: gsla=270. gslb=35.
**
**  ephicc is the throat potential jump in kV for machine="mirror"
**    This is used to determine the loss cone.
**    default:ephicc=0.
**
**  zmax(1) is the arclength along B from midplane to throat in 
**    machine="mirror"
**    YuP: Actually, zmax is found in eqfndpsi/eqorbit 
**         as zmax(lr_)=zmax_=es_(lorbit_) (last point of field line)
**  rmirror is the mirror ratio for machine="mirror"
**    rmirror=2.
**
**  radmin is the torus minor radius (cm) for machine="toroidal"
**    default: radmin=50.   Not required, for eqmod='enabled'.
**
**  rovera(1) (for rzset.ne."enabled") is the (normalized) minor radius
**     of the toroidal flux surface
**    (r/a=r/radmin) which also serves as the toroidal drift surface
**    in the zero banana width approximation for machine="toroidal"
**    For normal operation 1.e-8 < rovera < 1.
**    If rovera is positive and less that 1.e-8, it will be reset to 1.e-8.
**    Note the rovera input option is used only for cases where lrz=1, and
**    rzset.ne."enabled".
**  rovera(1) < 0 can be utilized only if eqmod="enabled"
**    In this case an input variable povdelp is utilized to determine
**    the flux surface of interest. povdelp is described in the "eq"
**    model input below.
**    default: rovera=.1
**
**  radmaj is the torus major radius (cm) for machine="toroidal",
**    for the case that eqmod="disabled" and psimodel="axitorus"  
**    default: radmaj=100.     Not required, for eqmod='enabled'.
**
**  btor is B(toroidal) (g) at the magnetic axis for machine="toroidal"
**    for the case that eqmod="disabled" and psimodel="axitorus"  
**    default: btor=1.e+4     Not required, for eqmod='enabled'.
**
**  bth is B(poloidal) (g) at the plasma edge for machine="toroidal"
**    for the case that eqmod="disabled" and psimodel="axitorus"  
**    The poloidal coordinate at which bth is defined is pi/2.
**    default: bth=1.e+3     Not required, for eqmod='enabled'.
**
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