Theory Weekly Highlights for June 2007

June 29, 2007

AutoONETWO has been added to the Session Leader's Checklist website. This web interface will allow users to easily update the parameters needed to run between-shot AutoONETWO. Users will also be able to create templates of preset parameters prior to operations and apply them quickly.

Dr. Junya Shiraishi arrived at GA to start his 1-year ORISE Postdoctoral Fellowship. He will be working on an extension of the MARG2D ideal MHD stability code for studying resistive wall mode stability.

June 22, 2007

Perturbations of axisymmetric tokamak equilibrium may lead to singular currents flowing along the magnetic field line on the mode singular surfaces that can modify the plasma response. Magnetic perturbations from these currents may be formulated in terms of singular current filaments or window-frame like current loops. Singular currents with a pure toroidal mode number on one singular surface are found to produce perturbed magnetic fields with larger amplitude on the inboard side of the torus (anti-ballooning behavior). Superposition of perturbed magnetic fields from currents on different singular surfaces produces the usual magnetic fields with larger amplitudes on the outboard side of the torus that manifests the observed ballooning effect. The formulation is being extended to include the non-resonant plasma response.

Dr. Emilia Solano of Asociacion EURATOM-CIEMAT para Fusion completed her 4-week visit to collaborate on EFIT equilibrium reconstruction and returned to JET. Professor Yueqiang Liu of Chalmers University of Technology in Sweden is visiting GA for a month to collaborate on the study of the stabilization of the resistive wall mode in a slowly rotating tokamak.

June 15, 2007

Gheni Abla and David Schissel attended the 6th IAEA Technical Meeting on Control, Data Acquisition, and Remote Participation for Fusion Research in Inuyama Japan last week and gave two oral presentations on “A Remote Control Room at DIII-D” and “A Vision for a Collaborative Control Room for ITER” respectively. Abla’s presentation described the remote control room build at DIII-D used to support involvement in numerous experimental activities worldwide, notably including the start of EAST operation last year. Schissel's paper presented a vision for a collaborative control room for ITER that will support worldwide experimental collaboration and operation. Despite the considerable experience of the fusion community in this area, significant work remains to be done. The paper presented by Schissel elaborated on the benefits in conducting joint research with other communities, like High-Energy Physics, who have similar requirements.

June 08, 2007

In an ideal stability study, it is found that a moderate ratio of edge to internal transport barrier height is beneficial to magnetohydrodynamics (MHD) stability and the stability is limited by global low-n modes (n is the toroidal mode number). Combining an internal transport barrier (ITB) with an H-mode edge transport barrier (ETB), i.e. producing a double transport barrier (DB) plasma, is a promising regime for advanced tokamak steady state operation with high beta. However, the large pressure gradient and the associated large bootstrap current at the transport barriers can drive MHD instabilities, which limit the beta. The stability study was carried out using model pressure and q profiles and plasma shape based on DIII-D experiments and the GATO ideal stability code. For moderate ITB width with weak ETB, the stability is limited by n = 1 global modes, whereas if the ETB is strong it is limited by moderate-n peeling-ballooning modes. Broadening ITB width can improve stability. For very broad ITB width DB plasmas, high normalized beta is obtained and the stability is limited by low-n (n > 1) modes.

June 01, 2007

Recent nonlinear simulations of the elongation κ and triangularity δ on ITG/TEM transport using the GYRO code show that increasing positive δ is destabilizing while decreasing δ is stabilizing. These results are in qualitative agreement with recent results from a series of L-mode experiments in the TCV tokamak, were the same trend is observed in the global energy confinement time. The GYRO simulations included kinetic electrons and were assumed to be electrostatic. As δ was varied, all other local quantities were held fixed (including κ) using the Miller equilibrium model. The dependence on δ is found to be greatest for moderately elongated plasmas. The effect on transport in the plasma edge region from the ITG/TEM destabilization with positive δ can counter improvements in MHD stability and both effects need consideration when studying the H-mode pedestal region.

These highlights are reports of research work in progress and are accordingly subject to change or modification