CERN Program Library Long Writeup W5013 - CERNLIB ...

Geant 3.16 GEANT User’s Guide TRAK500
Origin : R.Brun, M.Hansroul Submitted: 01.10.81
Revision : Revised: 16.12.93
Documentation :
Tracking routines in magnetic field
CALL GUSWIM
(CHARGE,STEP,VECT,VOUT*)
CHARGE
STEP
VECT
VOUT
(REAL) particle charge in e unit;
(REAL) step size in cm;
(REAL) array of 7 with the initial coordinates, direction cosines and momentum (x, y, z, p x /p,
p y /p, p z /p, p);
(REAL) array of 7 with the final coordinates, direction cosines and momentum after the step.
This is the steering routine for calculating the deviation of a charged particle in magnetic field. It is called
by the GEANT tracking routines: GTELEC, GTHADR, GTMUON and GTHION. Even if this routine follows the
naming conventions of the user routines, the version provided in the GEANT library is quite adequate for
most situation, and users should have a very good reason to modify it.
It calls GRKUTA, GHELIX, GHELX3 according to the value 1, 2 or 3 of IFIELD in common /GCTMED/. IFIELD
correspond to the argument to the GSTMED routine (see [CONS200]). IFIELD = -1 is reserved for user
decision in case GUSWIM is modified by the user.
CALL GHELX3
(FIELD,STEP,VECT,VOUT*)
FIELD
STEP
VECT
VOUT
(REAL) field value in kilo-Gauss multiplied by the charge of the particle in e units;
(REAL) step size in cm;
(REAL) array of 7, same as for GUSWIM;
(REAL) array of 7, same as for GUSWIM;
Transport the particle by a length STEP in a magnetic field. The field is assumed to be uniform and parallel
to the z axis. The value of the field is the FIELDM argument to the GSTMED routine (see [CONS200]). The
particle is transported along an helix. The call to this routine is selected by GUSWIM when IFIELD=3 in the
call to GSTMED.
CALL GHELIX
(CHARGE,STEP,VECT,VOUT*)
CHARGE
STEP
VECT
VOUT
(REAL) particle charge in e units;
(REAL) step size in cm;
(REAL) array of 7, same as for GUSWIM;
(REAL) array of 7, same as for GUSWIM;
Transport the particle by a length STEP in a magnetic field. The magnetic field is calculated in the middle of
the step (along a straight line) and it is supposed to be constant along the step and the particle is transported
along an helix. The call to this routine is selected by GUSWIM when IFIELD=2 in the call to GSTMED. This
routine is intended for magnetic fields with a small gradient. The value of the field is obtained from the
routine GUFLD which must be coded by the user.
350 TRAK500 – 1