ELCFIELD¶

Summary

Sets the tracking conditions for transport in electric fields and may also define a homogeneous electric field

For SDUM = RUNGKUTT¶

WHAT(1): largest fraction of a round angle that a particle is allowed to travel in one sub-step.
Default: : 0.026, corresponding to 10 degrees
WHAT(2): upper limit to the error of the boundary iteration (cm), the minimum accuracy accepted in determining a boundary intersection with Runge–Kutta–Gill tracking.
Default: : 0.05 cm
WHAT(3): tentative step length (cm) in zones of zero local field for Runge–Kutta–Gill tracking. See also MAGFLD.
Default: : 0.5 cm
WHAT(4), WHAT(5), WHAT(6): \(E_x\), \(E_y\), \(E_z\), the components of the electric field in MV/m.
Default: : \(E_x=E_y=E_z=0.0\); ELEFLD supplies the actual values.

For all other SDUM values¶

WHAT(1): = largest angle (in degrees) that a particle is allowed to travel in a single step
Default: : 20\(^{\circ}\)
WHAT(2): = error of the boundary iteration (minimum accuracy accepted in determining a boundary intersection)
Default: : 0.01 cm
WHAT(3): = minimum step if the step is forced to be smaller due to a too large angle. It is also the maximum step length in areas of zero field (see ELEFLD and MAGFLD).
Default: : 0.1 cm
WHAT(4): = E\(_{x}\) (x-component of the electric field, in MV/m)
WHAT(5): = E\(_{y}\) (y-component of the electric field, in MV/m)
WHAT(6): = E\(_{z}\) (z-component of the electric field, in MV/m)
Default: : \(E_x=E_y=E_z=0.0\); user-supplied subroutine ELEFLD provides the actual values .

Notes

If E\(_x\) = E\(_y\) = E\(_z\) = 0.0, the user-written subroutine ELEFLD is called at each step to get the direction cosines and the module (in MV/m) of the electric field as a function of region or of coordinates. A sample subroutine is provided with the FLUKA code; instructions on how to write user-supplied routines can be found in User routines.
Note that the argument list of subroutine ELCFLD is (X,Y,Z,T,ETX,ETY,ETZ,E,NREG,IDISC), where ETX, ETY, ETZ are the direction cosines of the electric field at point X,Y,Z and time T (not the components of the field! The field magnitude is given by E). For this reason, it is imperative that ELEFLD returns normalised values of ETX, ETY and ETZ such that the sum of their squares is = 1.0 in double precision.

Three zero values are not accepted: if the field is zero at the point in question, you must return for instance 0.0, 0.0, 1.0 and E = 0.0.

On the contrary, note that E\(_x\), E\(_y\), E\(_z\) in the ELCFIELD option, given by WHAT(4)…WHAT(6) as described above, are the field components and not the cosines.
Electric field tracking is performed only in regions defined as electric field regions by command ASSIGNMAt. It is strongly recommended to define as such only regions where an electric field effectively exists, due to the complexity of the tracking algorithm used in electric/magnetic fields.

To define a region as having an electric field and to return systematically E = 0.0 in that region via subroutine ELEFLD, is not allowed.
Tracking in electric fields is possible at present only in vacuum regions or rarefied gases. Arbitrary combinations of electric and magnetic fields are supported. Whenever an electric field is present the tracking is performed with a Runge-Kutta-Gill 4th order algorithm for the combined electric and magnetic (if any) fields. The same approach can be requested also for dis-homogeneous magnetic fields (in vacuum) even if no electric field is present, using SDUM=RUNGKUTT in the MGNFIELD card.
For gases, Runge–Kutta tracking, whether explicitly requested or automatically activated by an electric field, forces single scattering in the relevant regions, with a corresponding CPU-time penalty.