Theory Weekly Highlights for August 2006

August 25, 2006

A collaborative Wiki-based Web Site is being testing for Magnetic Fusion Research at General Atomics. A Wiki is a website that allows users to easily add, remove, or otherwise edit and change some available content. The ease of interaction and operation makes a Wiki an effective tool for collaborative authoring, which will be of substantial benefit to the international makeup of the DIII-D Research Team. Initial response to the new site is very positive and it is expected to become the official website in the near future.

The DIII-D jabber Instant Messaging (IM) server was made available to all collaborators after a review of the security implications. An IM service was implemented previously for the DIII-D site and selected collaborating institutions, and integrated with a number of tokomak operation and data analysis software applications. These included operations status, electronic logbook and the data analysis monitor. The service now provides a unified portal interface for team collaboration and remote participation in which scientists can exchange text and presence information as well as monitor experiments in real time.

August 18, 2006

The fast linear eigenmode code TGLF has been installed as an option in the gyro-kinetic stability analysis code GKS. TGLF is a new gyro-fluid system that yields accurate growth rates for drift-wave instabilities and includes nearly all of the same physics as GKS. The TGLF solver is fast enough to be able to perform between-discharge stability analyses in the DIII-D control room. A new feature of TGLF is the ability to compute growth rates for sub-dominant instabilities. The default settings for the GKS code include Miller shaped geometry, one impurity ion, electron-ion collisions and electromagnetic fluctuations. Analysis options for finding critical temperature gradient and maximum growth rate profiles and the mode spectrum at one location are all available for either the original GKS or the TGLF models.

August 11, 2006

Relativistic electrons are efficiently generated when multi-Terawatt lasers, focused to ultrahigh intensities above 1019 W/cm2, illuminate the surface of dense plasma targets. A new study finds that during typical pico-second pulse widths, significant amounts of Dreicer-produced runaway electrons can build up due to the high axial electric field driving a neutralizing return current. An important consequence is that there will then be a conversion of plasma current to runaway current, which is maximized at some optimum value of the beam-to-plasma density ratio nb/ne, depending on the plasma collisionality. At collisionalities representative of solid target experiments, complete conversion to runaway electrons takes place less than 1 psec when nb/ne ~ 0.018. At higher collisionalities, typical of the conditions in inertial confinement fusion fast ignition, up to 90% conversion takes place at nb/ne ~ 0.06. Significant lessening of target material heating by Joule dissipation of the plasma return current can also occur since part the beam energy loss can be transferred through the electric field directly to the runaway electrons.

August 04, 2006

A new approach to derive a self-consistent effect of turbulent short wave length high frequency waves on long wavelength long timescale growth of resistive modes has been initiated. Analytic methods are being employed in simple geometry, while computational formulations are planned for toroidal geometries. The approach is at an early stage but, if successful, promises to describe the local effects on the resistive MHD perturbations as well as the reverse effect of the resistive modes on the turbulent transport in their coupled state.

Chris Holland is the 2006 GA Rosenbluth Fusion Theory Award winner (see the 2006 Announcement ). Dr. Holland received his doctoral degree from the physics department of the University of California, San Diego. He is currently an assistant research scientist in the Center for Energy Research at UCSD (see for details).

Dr. Klaus Hallatschek (IPP Garching) won a prestigious 5-year European Young Investigator EURYI 2006 Award from the European Science Foundation to study zonal flows. This award is one of 25 from a European wide competition covering all fields of science and mathematics with only 3-4 awarded in physics (see ) Klaus is the 2005 Rosenbluth Fellow working with the GA Theory Group this year on gyrokinetic simulations of L/H edge physics.

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