Professors J. Hanson and G. Hartwell
Plasma equilibrium reconstruction relies on many pin-point magnetic field measurements (~ 100) during the plasma discharge and rather detailed analysis. A widely used analysis code to perform these reconstructions is the VMEC MHD equilibrium code, developed for the 2-D magnetic field configuration of the tokamak device. One complication to the magnetic field measurements within the plasma is compensating for induced currents, eddy curents, in the metal vacuum vessel and magnet coil frame support. The equilibrium reconstruction is further complicated when dealing with 3-D magnetic topologies associated with stellerators and torusatrons. To adapt the standard VMEC code to the coil frame and vacuum vessel of the Auburn University Compact Toroidal Hybrid (CTH) device (Fig. 1), PPPL engineer Ali Zolfaghari used the SPARC analysis code to provide closed coil current loop representation of the eddy currents in a 1/5 cyclic symmetry model of CTH(Fig. 2). Further analysis was completed by a SULI (Science Undergraduate Laboratory Internship) intern, Andrew Michaels, over the summer. The student intern developed and tested a code, JFIL, to convert the current density data from the MAXWELL code for the finite element mesh into individual current filaments, representing the eddy currents, suitable for direct use in VMEC MHD reconstruction of CTH discharges. The results of the entire project were presented at TOFE conference in Nashville in August 2012 and a paper was published in Fusion Science and Technology. Coil files were delivered to Auburn University researchers for further evaluation and implementation in CTH plasma equilibrium analysis.
A few years ago the PPPL engineers assisted in the engineering design and specification of the CTH torus components under the OSUR program.
Figure 1: CTH Machine and OH Coils
Figure 2: Eddy Currents in coil frame & vacuum vessel calculated by the SPARK code.