This award is made in response to a proposal submitted to and reviewed under the NSF/DoE Partnership in Basic Plasma Science and Engineering joint solicitation NSF 08-589. The award provides funds to support undergraduate participation in the overall research effort, which is being funded separately by the DoE under contract UCSD (Science report #09ER55038).
This research investigates strongly driven MHD systems and the influence of magnetic field topology on plasma evolution in pulsed-power driven plasmas. This will be examined using an advanced diagnostic method, namely proton probing, and involves both experimental and computational work. The experimental campaign to assess and optimize proton deflectometry will be done for various exploding wire configurations on the 1MA ZEBRA generator at the Nevada Terawatt Facility using the 50TW Leopard laser, with data interpretation by use of the 3D resistive MHD GORGON and 3D hybrid-PIC LSP codes. The experimental program involves intense field-matter interaction in the generation of the proton probe, as well as the generation of plasma subjected to MG scale magnetic fields. The computational aspect will apply two well documented plasma simulation codes, one 3D resistive MHD and one 3D Particle-in-Cell (PIC), in combination for the first time to provide accurate interpretation of the experimental results.
This research includes 2 graduate students, one at UCSD and one at NTF, who will be involved with both the experimental physics work and the MHD and PIC modeling of the system. Data resulting from the research program will be broadly disseminated by publication in scientific journals, and presentation at international and national conferences and workshops. Graduate and undergraduate students will present results.
The NSF support of undergraduate participation adds a broader educational impact through the early-year training of students by introducing them to scientific research as a possible career path.
Proton radiography has been widely used as a method of assessing the magnitude and structure of electromagnetic fields generated in laser-plasma interaction experiments. It has proven to be a valuable tool for verifying theory, validating code, and providing general insight into the dynamics of high-energy-density physics systems. Its implementation for laser experiments was a natural evolution, since multiple laser beams are often available within a single target chamber. For this reason, proton deflectometry has primarily been used in such facilities, where additional beams may be used to readily produce high energy protons for use as a diagnostic. Few z-pinch facilities are equipped with short-pulse high-intensity lasers capable of producing diagnostic protons. In the U.S., only two such facilities are in place, namely the Z-petawatt high intensity laser & Z-R at Sandia National Laboratories, and the Leopard laser & Zebra at the Nevada Terawatt Facility. The development of this technique is crucial to verifying theory and answering long-standing questions about electromagnetic field configurations in pulsed-power-produced plasma experiments. Such measurements have previously been very difficult to obtain and limited in quantity. Electrical probes have been used to this end, but are subject to mega-volt potentials, which often cause failure early in the experiment. There is also the question of charge-screening interference with such probes. Optical Faraday rotation has also been applied, but is limited to areas where the critical density of the plasma is low enough to allow propagation through the system. This project aimed to provide the first demonstrations of the application of proton deflectometry for the diagnosis of electromagnetic field configurations and current-carrying regions in Z-pinch plasma experiments. Over the course of this project several milestones were achieved. High-energy proton beam generation was demonstrated on the short-pulse high-intensity Leopard laser, 10 Joules in ~350 femtoseconds, the proton beam generation was shown to be reproducible. Next, protons were used to probe the electromagnetic field structure of short circuit loads in order to benchmark the two numerical codes, the resistive-magnetohydrodynamics (MHD) code, Gorgon, and the hybrid particle-in-cell code, LSP for the interpretation of results. Lastly, the proton deflectometry technique was used to map the magnetic field structure of a pulsed-power-driven plasma load with one million Amperes current. Good agreements between the modeling and experiments have been obtained. The demonstrated technique holds great promise to significantly improve the understanding of current flow and electromagnetic field topology in pulsed power driven high energy density plasmas. Proton probing with a high intensity laser was for the first time implemented in the presence of the harsh debris and x-ray producing z-pinch environment driven by a mega-ampere-scale pulsed-power machine. The intellectual merit of the program was that it investigated strongly driven MHD systems and the influence of magnetic field topology on plasma evolution in pulsed power driven plasmas. The experimental program involved intense field-matter interaction in the generation of the proton probe, as well as the generation of plasma subjected to 1 million Gauss scale magnetic fields. The computational aspect included two well-documented codes, in combination for the first time to provide accurate interpretation of the experimental results. The broader impact included the support of 2 graduate students, one at UCSD and one at NTF, who were exposed to both the experimental physics work, the MHD and PIC modeling of the system. A first generation college undergraduate student was employed to assist in experiments and data analysis throughout the project. Data resulting from the research program were broadly disseminated by publication in scientific journals, and presentation at the international and national conferences and workshops.
