Theory Weekly Highlights for May 2004

May 28, 2004

A new gyro-Landau fluid (GLF) system of moment equations that includes both trapped and passing particles, covering both electrons and ions has been completed. This unified model has been a long-sought goal. For each species, the new GLF system has twelve moments for passing and three for trapped particles, but in the absence of trapped particles, reduces to the six-moment Beer and Hammett equations. The system is solved as an eigenmode problem and can resolve subdominant instabilities not found by an initial value calculation; the eigenmode solution is no more expensive near threshold and is faster than existing initial value gyro-kinetic linear stability codes. The model has been tested for wavenumbers from the lowest trapped ion range to the highest electron temperature gradient mode. Benchmark scans over subsets of a large database of gyro-kinetic linear stability calculations find growth rate and frequency standard deviations typically about 10%. The new model has wide application as a data analysis tool and will be incorporated in a successor to the GLF23 transport model.

May 21, 2004

In an external initiative to test the scalability of the new vector architecture Cray X1 supercomputer, GYRO was run on a temporarily configured X1 with 504 Multi-Streaming Processors (MSPs). Using the full machine, a GYRO benchmark case was run showing very good scalability and a step time of 0.07s. The same case was tested on the IBM Power3 at NERSC using up to 2688 processors, with the best step time of 0.41s at 1792 processors. Thus, the Cray exceeded the peak IBM performance by a factor of 6 using 3.5 times fewer processors. This is very good news for Cray and clearly highlights the effectiveness of their new vector architecture for our compute-intensive simulation problems.

May 14, 2004

In new work on pellet fueling of tokamak plasmas, it was shown that injection through a guide tube that is bent through 90 degrees can still deliver the pellet largely intact, though strongly deformed into a long pencil-shape. Normally, the tubes used to guide pellets from the low field side to their injection point at the high-field point, as called for in the ITER design, must bend through a considerable angle to achieve the desired trajectories normal to the magnetic surface. It was found that an initial right-cylinder pellet of volumeπa3/4, deforms into an object of length (= a(R/a)2/5 and diameter r=a(a/R)1/5 upon executing a 90° guide tube bend. Here R denotes the radius of curvature. This result depends on the validity of the fluid model, which is generally well satisfied, and is independent of pellet velocity. For ITER parameters, (λ = 4.8 cm and r = 0.45 cm when a=1 cm and R= 50 cm. Future work will focus on the ablation of such pencil-thin pellets from the high field side.

May 07, 2004

Torkil Jensen died peacefully on May 1 2004 after a long battle with cancer, and ended a long, productive, and uniquely innovative career at General Atomics and DIII-D spanning almost 50 years. His humanity, his wonderfully playful sense of humor, and, of course, his famous Limericks, will be deeply missed. He contributed this highlight:

The Highlightwriter's Plight
Each Friday he turns on his lights
To search for spectacular sights
Of new innovations
And mental gestations
Each week he will aim for new heights

T. Jensen.
17|Theory Weekly Highlights for July 2017]]

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