Scientific Significance

Visualization is an extremely vital component of the SciDAC effort at SLAC in facilitating the design of next generation accelerators, and in advancing the understanding of the complex processes that arise in their operation in new parameter regimes. For example, the important factors that limit the performance of accelerating structures at designed field gradients are dark current generation, RF breakdown and multipactoring. These are complex phenomena that involve particle dynamics in complicated 3D geometries and intricate interactions between particles and the structure surface. The latter process include both field-emitted as well as secondary particles, and produce plasma and X rays. To capture all these effects in a full scale simulation on an actual structure under realistic operating conditions presents a monumental challenge in data management, storage, manipulation (I/O) and most importantly, visualization. The end-to-end modeling will produce terabytes of unstructured, time-varying data consisting of multiple field and particle species that have to be visualized individually and simultaneously on both local and global scales. The development of effective visualization tools to meet this challenge is of the highest priority because they are crucial to the discovery and understanding of the physics involved. Progress in high-gradient structure development has been stymied by the lack of theory in explaining high power RF effects and SLAC's SciDAC team is committed to advance this important area of accelerator science through large-scale simulations

Advanced visualization is also essential for our collaborators at the Lawrence Berkeley National Laboratory to gain insight and understanding of phenomena that are simulated in large, complex computer models involving beams and plasmas. For example, large scale beam dynamics simulations are used to understand the physics of intense beams including the important phenomena of halo formation. The large dynamic range of beam density involved (roughly 6 orders of mangnitude) represents a challenge to scientific visualization, and has led to the development of new algorithms, such as hybrid algorithms, then enable the core and the low density halo to be visualized simultaneously with an efficiency that allows for interactive data analysis. Visualization techniques have also made it possible to study the origin of halo particles by tagging particles and representing their trajectories as streamlines in animations. In another example, the simulation of gas jets used in advanced accelerator applications, visualization is needed to view the (adaptive) grids that make up the gas nozzle, and to understand how the shape of the nozzle affects the gas flow. As a third example, the design of laser/plasma-based accelerators, visualization, including isosurface techniques, is needed to study and optimize the structure of the accelerating fields that must be tailored to effectively and efficiently accelerate the particles.