Speckle Reduction in Projection Systems

A speckle pattern is a quasi-random interference pattern which typically emerges when lasers are used as illumination sources in projection applications and which severely degrades the image quality. Since in most projection applications high speckle disturbance is not tolerable, speckle reduction is a major issue. This work gives an introduction into the theoretical description of speckle and investigates different practical methods for speckle reduction in laser projection systems

A coarse mesh transport method with novel source treatment

Treatment planning algorithms for use in the radiotherapeutic treatment of cancer have progressively evolved since the earliest attempts to develop automated dose calculation software in the mid-1950s. Modern algorithms use advanced techniques such as convolution superposition or grid-based Boltzmann solvers to perform external beam radiotherapy calculations. A new method of dose calculation was developed at the Georgia Institute of Technology based on transport theory called COMET-PE. The method combines stochastic pre-computation with a deterministic solver to achieve high accuracy and precision. For the COMET-PE method to be implemented clinically it needs a practical source model that closely mimics the physical characteristics of a typical radiation beam from a linear particle accelerator. The COMET-PE method should also be validated against a known benchmark. A novel linear accelerator source model is presented that models the geometry, angular distribution, spectrum, energy, and electron contamination of a 6 MV photon beam from a Varian c-series clinac. Of note is the use of a hemispherical harmonic expansion with the functional expansion tally method to model photonic fluence. The source was implemented in the COMET-PE radiation transport code and calculations performed with various field sizes and phantoms. The results are benchmarked against Monte Carlo reference solutions and compared with calculations performed with two popular commercially available treatment planning algorithms. The results indicate that the proposed source model when coupled with the COMET-PE method is capable of dosimetric calculations that in many cases more closely match Monte Carlo solutions than the commercially available options.Ph.D

New Type of sub-THz Oscillator and Amplifier Systems Based on Helical-Type Gyro-TWTs

This work presents the development of a new sub-THz source for the generation of trains of coherent high-power ultra-short pulses at 263 GHz via passive mode-locking of two coupled helical gyro-TWTs. For the first time, it is shown that the operation of such passive mode-locked helical gyro-TWTs in the hard excitation regime is of particular importance to reach the optimal coherency of the generated pulses. This could be of particular interest for some new time-domain DNP-NMR methods

GPGPU application in fusion science

GPGPUs have firmly earned their reputation in HPC (High Performance Computing) as hardware for massively parallel computation. However their application in fusion science is quite marginal and not considered a mainstream approach to numerical problems. Computation advances have increased immensely over the last decade and continue to accelerate. GPGPU boards were always an alternative and exotic approach to problem solving and scientific programming, which was cultivated only by enthusiasts and specialized programmers. Today it is about 10 years, since the first fully programmable GPUs appeared on the market. And due to exponential growth in processing power over the years GPGPUs are not the alternative choice any more, but they became the main choice for big problem solving. Originally developed for and dominating in fields such as image and media processing, image rendering, video encoding/decoding, image scaling, stereo vision and pattern recognition GPGPUs are also becoming mainstream computation platforms in scientific fields such as signal processing, physics, finance and biology. This PhD contains solutions and approaches to two relevant problems for fusion and plasma science using GPGPU processing. First problem belongs to the realms of plasma and accelerator physics. I will present number of plasma simulations built on a PIC (Particle In Cell) method such as plasma sheath simulation, electron beam simulation, negative ion beam simulation and space charge compensation simulation. Second problem belongs to the realms of tomography and real-time control. I will present number of simulated tomographic plasma reconstructions of Fourier-Bessel type and their analysis all in real-time oriented approach, i.e. GPGPU based implementations are integrated into MARTe environment. MARTe is a framework for real-time application developed at JET (Joint European Torus) and used in several european fusion labs. These two sets of problems represent a complete spectrum of GPGPU operation capabilities. PIC based problems are large complex simulations operated as batch processes, which do not have a time constraint and operate on huge amounts of memory. While tomographic plasma reconstructions are online (realtime) processes, which have a strict latency/time constraints suggested by the time scales of real-time control and operate on relatively small amounts of memory. Such a variety of problems covers a very broad range of disciplines and fields of science: such as plasma physics, NBI (Neutral Beam Injector) physics, tokamak physics, parallel computing, iterative/direct matrix solvers, PIC method, tomography and so on. PhD thesis also includes an extended performance analysis of Nvidia GPU cards considering the applicability to the real-time control and real-time performance. In order to approach the aforementioned problems I as a PhD candidate had to gain knowledge in those relevant fields and build a vast range of practical skills such as: parallel/sequential CPU programming, GPU programming, MARTe programming, MatLab programming, IDL programming and Python programming

New Type of sub-THz Oscillator and Amplifier Systems Based on Helical-Type Gyro-TWTs

This work presents the development and systematic investigation of a new sub-THz source for the generation of trains of coherent high-power ultra-short pulses at 263 GHz via passive mode-locking of two coupled helical gyrotron traveling wave tubes (helical gyro-TWT). The frequency of 263 GHz is an established figure for continuous wave (CW) DNP-NMR application and, therefore, the investigated source will allow the development of novel spectroscopy methods such as time-domain DNP-NMR for which powerful sub-THz pulses with highest coherency are required. For the first time, it is shown that the operation of the passive mode-locked helical gyro-TWTs in the hard excitation regime is of particular importance to reach the optimal coherency of the generated pulses. To enable the operation in the hard excitation regime, a new extended passive mode-locked oscillator is proposed. The extended passive mode-locked oscillator will furthermore enable the generation of specific pulse sequences in addition to the generation of pulses with constant repetition frequency. This could be of particular interest for some time-domain DNP-NMR methods where well-defined pulse sequences are required

New Type of sub-THz Oscillator and Amplifier Systems Based on Helical-Type Gyro-TWTs

This work presents the development of a new sub-THz source for the generation of trains of coherent high-power ultra-short pulses at 263 GHz via passive mode-locking of two coupled helical gyro-TWTs. For the first time, it is shown that the operation of such passive mode-locked helical gyro-TWTs in the hard excitation regime is of particular importance to reach the optimal coherency of the generated pulses. This could be of particular interest for some new time-domain DNP-NMR methods

Fiscal Year 1995

The mission of the Engineering Research, Development, and Technology Program at Lawrence Livermore National Laboratory (LLNL) is to develop the knowledge base, process technologies, specialized equipment, tools and facilities to support current and future LLNL programs. Engineering`s efforts are guided by a strategy that results in dual benefit: first, in support of Department of Energy missions, such as national security through nuclear deterrence; and second, in enhancing the nation`s economic competitiveness through their collaboration with US industry in pursuit of the most cost-effective engineering solutions to LLNL programs. To accomplish this mission, the Engineering Research, Development, and Technology Program has two important goals: (1) identify key technologies relevant to LLNL programs where they can establish unique competencies, and (2) conduct high-quality research and development to enhance their capabilities and establish themselves as the world leaders in these technologies. To focus Engineering`s efforts, technology thrust areas are identified and technical leaders are selected for each area. The thrust areas are comprised of integrated engineering activities, staffed by personnel from the nine electronics and mechanical engineering divisions, and from other LLNL organizations. This annual report, organized by thrust area, describes Engineering`s activities for fiscal year 1995. The report provides timely summaries of objectives methods, and key results from eight thrust areas: computational electronics and electromagnetics; computational mechanics; microtechnology; manufacturing technology; materials science and engineering; power conversion technologies; nondestructive evaluation; and information engineering