Magnetic Reconnection and Energetic Particles

Observations of prominence-cavity systems
Davina Innes, Navdeep Panesar (PhD student), Don Schmit (Postdoc)

Prominences are cool, over dense structures seen suspended in the lower corona above the solar limb. They mainly reside in highly tangled magnetic fields. Coronal cavities, regions of relatively low density, and high temperature, are often seen surrounding the cooler prominence plasma. The cavity structures often contain closed loops which surround the prominence. When the stability of the system is disrupted, the prominence and surrounding cavity material is ejected into interplanetary space as a Coronal Mass Ejection (CME). The aim of our research is to identify conditions leading to instability, by taking full advantage of modern high resolution imaging (e.g. Solar Dynamics Observatory (SDO) and   STEREO) and spectroscopic (IRIS) observations of the Sun. The figure shows two views of a prominence-cavity system just after the prominence plasma was seen to rise up and start rotating, resembling a tornado. In this particular case the tornado-like activity was triggered by flares in the neighbouring active region (identified as AR).

Disk and limb views of a solar prominence on 25 September 2011 showing tornado-like activity: a) On the disk, prominences appear as long dark filament channels; b) The corresponding prominence structure seen on the limb.   (a) was taken by STEREO-A   at 195A when it was 103º ahead of Earth, and (b) by SDO at 171A. In (a) the dashed line is the position of the solar limb seen by SDO (Earth) and the long diagonal arrow is the projection of the position marked with a ‘+’ at the base of the prominence in the SDO image.

magnetic reconnection

Energetic Particles

In order to provide predictive capabilities for the transport of energetic particles (EP) in future fusion devices, its scaling with respect to crucial parameters of the EP distribution function and the plasma background conditions has to be well understood. Especially the non-linear saturation mechanisms o f global Alfvenic modes in the presence of the full background plasma dynamics   is a long term goal that is planned to be addressed in a systematic way within the IPP-PPPL centre.

The project builds on the unique capabilities of PPPL and IPP for modeling t he physics of energetic particle driven instabilities and validating the models quantitatively with the high quality data of ASDEX-Upgrade and NSTX.

The numerical models available within the collaboration are essentially complementary (linear kinetic MHD, linear gyrokinetic, hybrid non-linear, non-linear kinetic, gyrokinetic non-linear), however for benchmarking efforts overlapping regimes can be easily identified. In the view of an extrapolation to ITER and DEMO, special emphasis will be given to different plasma betas a nd to different energetic particle distribution functions.