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https://github.com/bendudson/nibbler

Simple drift-kinetic particle following code in toroidal geometry (cylindrical coordinates). Reads EFIT 'g' files for the equilibrium, and can add perturbations from external field coils
https://github.com/bendudson/nibbler

Last synced: 5 months ago
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Simple drift-kinetic particle following code in toroidal geometry (cylindrical coordinates). Reads EFIT 'g' files for the equilibrium, and can add perturbations from external field coils

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Outline

=======



A 3D drift-kinetic particle tracking code in cylindrical coordinates

(R,Z,phi). Evolves the position and parallel velocity of particles

in a tokamak with RMP coils. Takes into account curvature and Grad-B

drifts, and the mirror force for trapping. Doesn't include electric

fields or any sort of coupling between particles.



Axisymmetric equilibrium field from EFIT, currently from a G-EQDSK

file (as in A&G output).



Calculates the field due to RMP coils from coil geometry settings.



License

=======



Copyright 2010 B.D.Dudson (University of York)



Nibbler is free software: you can redistribute it and/or modify

it under the terms of the GNU Lesser General Public License as published by

the Free Software Foundation, either version 3 of the License, or

(at your option) any later version.



Nibbler is distributed in the hope that it will be useful,

but WITHOUT ANY WARRANTY; without even the implied warranty of

MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

GNU Lesser General Public License for more details.



You should have received a copy of the GNU Lesser General Public License

along with Nibbler. If not, see .



A copy of the LGPL license is in COPYING.LESSER. Since this is based

on (and refers to) the GPL, this is included in COPYING.



Useage

======



To just see an example (trapped) orbit, just run



IDL> nibbler



and with RMP field on



IDL> nibbler, /rmp



Equilibrium / RMP settings

--------------------------



Since reading in and processing equilibria can take a while,

this bit can be done once and then re-used



/odd    Add this keyword to use odd RMP coil configuration

        Default is even configuration



Need to add options for reading shots from IDAM



o Once generated, the data is saved in "equil.idl"



Particle settings

-----------------



/rmp            Include RMP coils. Default is no



current=current Current in the RMP coils in Amp-turns. Defaults to 4 kAt



psin=psin       Normalised psi of starting point. All particles

                start at outboard midplane, field-lines at inboard midplane. 

                Default is 0.9



Nparticles=Nparticles    Number of particles to simulate

                         Spreads them out evenly in toroidal angle

                         Default is only 1 particle



/electron       Evolve electrons. Default is Deuterium ions



/field          Follow field-lines



temp = temp     Temperature in eV. This determines total kinetic energy

                using E = 3/2 kT

                Default is 200eV



kpar=kpar       Specifies the particle pitch angle

                Fraction of energy in parallel velocity Vpar^2 / V^2

                Sign determines Vpar relative to B field.

                Default is 0.3



output=output   Set name of output file for saving results

                Normally just stops at the end



runfor=runfor   Simulation time to run for in seconds.

                Default is 1ms



dtmul=dtmul     Timestep in gyro-orbit time (~1e-7s). Default is 1



Example

-------



nibbler, /rmp, output="kpar_p98_0.8.idl", n=100, psin=0.98, kpar=0.8



Loads an existing equilibrium, includes RMP coils (default 4kA), 

saves result to "kpar_p98_0.8.idl". Evolves 100 particles starting

at the outboard midplane at normalised psi 0.98 with Vpar^2 = 0.8 V^2

(a passing particle in this case)



Issues

======



o Suspect there is a minus sign in the poloidal field: in MAST

  poloidal field usually goes clockwise in R-Z plane. Here get opposite.



o No handling for cases where particle leaves domain. Should detect

  where hits targets



o IDL code is REALLY slow. Could keep most of the initialisation code in IDL

  to get equilibrium, calculate DCTs etc. but re-write the particle orbit

  evolution in C/Fortran.