TJ-II:Magnetic coordinates: Difference between revisions
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In order to make comparisons between diagnostics, it is useful to convert these real-space co-ordinates to flux co-ordinates. This co-ordinate transform depends on the particular magnetic configuration used in a given experiment. Two tools are available to do so ([http://www-fusion.ciemat.es/cgi-bin/dir/dirnew.cgi?manuals/geometry_TJII/ See the on-line documentation] - only internal laboratory access): | In order to make comparisons between diagnostics, it is useful to convert these real-space co-ordinates to flux co-ordinates. This co-ordinate transform depends on the particular magnetic configuration used in a given experiment. Two tools are available to do so ([http://www-fusion.ciemat.es/cgi-bin/dir/dirnew.cgi?manuals/geometry_TJII/ See the on-line documentation] - only internal laboratory access): | ||
First, vacuum equilibrium calculations from VMEC. These are then used to obtain magnetic flux co-ordinates ''(ψ, θ, φ)''. A set of routines is available to perform the corresponding co-ordinate transforms.<ref>[[File:TJ2 Library V2.pdf| TJ-II Library Manual, Informe Técnico del CIEMAT Nº 963]]</ref> The drawback of the VMEC calculations is (a) that magnetic islands are ignored, and (b) that only a limited number of configurations is available. | First, vacuum equilibrium calculations from [[VMEC]]. These are then used to obtain magnetic flux co-ordinates ''(ψ, θ, φ)''. A set of routines is available to perform the corresponding co-ordinate transforms.<ref>[[File:TJ2 Library V2.pdf| TJ-II Library Manual, Informe Técnico del CIEMAT Nº 963]]</ref> The drawback of the VMEC calculations is (a) that magnetic islands are ignored, and (b) that only a limited number of configurations is available. | ||
Second, magnetic field line calculations using the Biot-Savart Law. The approximate magnetic flux is recovered from an interpolation procedure. A set of routines is available to perform the corresponding co-ordinate transforms. More information can be found in files [http://www-fusion.ciemat.es/cgi-bin/dir/dirnew.cgi?manuals/geometry_TJII/ g3d_readme.doc and g3d_gridfile.doc]. Since the latter procedure is more flexible and generally applicable than the VMEC-based calculations, the latter is preferred. | Second, magnetic field line calculations using the Biot-Savart Law. The approximate magnetic flux is recovered from an interpolation procedure. A set of routines is available to perform the corresponding co-ordinate transforms. More information can be found in files [http://www-fusion.ciemat.es/cgi-bin/dir/dirnew.cgi?manuals/geometry_TJII/ g3d_readme.doc and g3d_gridfile.doc]. Since the latter procedure is more flexible and generally applicable than the VMEC-based calculations, the latter is preferred. | ||
Revision as of 09:14, 23 July 2009
The diagnostics perform measurements in real space. The location of points is given in one of these co-ordinate systems (units according to the S.I. system, m and rad):
- Cartesian (X, Y, Z) with its origin at the point of gravity of the TJ-II device, the X-axis pointing due East, the Y-axis due North, and the Z-axis up.
- Cylindrical (R, φ, Z), where R2 = X2 + Y2 and tan φ = Y/X.
In order to make comparisons between diagnostics, it is useful to convert these real-space co-ordinates to flux co-ordinates. This co-ordinate transform depends on the particular magnetic configuration used in a given experiment. Two tools are available to do so (See the on-line documentation - only internal laboratory access):
First, vacuum equilibrium calculations from VMEC. These are then used to obtain magnetic flux co-ordinates (ψ, θ, φ). A set of routines is available to perform the corresponding co-ordinate transforms.[1] The drawback of the VMEC calculations is (a) that magnetic islands are ignored, and (b) that only a limited number of configurations is available.
Second, magnetic field line calculations using the Biot-Savart Law. The approximate magnetic flux is recovered from an interpolation procedure. A set of routines is available to perform the corresponding co-ordinate transforms. More information can be found in files g3d_readme.doc and g3d_gridfile.doc. Since the latter procedure is more flexible and generally applicable than the VMEC-based calculations, the latter is preferred.
It should be noted that these co-ordinate transforms are approximate and not error-free. The errors in the vacuum field calculation are due to three sources:
- The error in the placement of the coils.
- The error in the value of the currents flowing through the coils.
- The error due to the fact that the model uses a finite amount of filaments to model the current in the coils (which has a continuous distribution).
Additional errors are due to finite-pressure effects (estimated to be quite small in TJ-II) and net plasma currents.