Transcript Document
Laser Magnetized Plasma Interactions for the Creation of Solid Density Warm (~200 eV) Matter M.S. Bakeman@, R. Presura, Y. Sentoku, A. Kemp, C. Plechaty, D. Martinez, T.E. Cowan Nevada Terrawatt Facility, University of Nevada Reno, Reno NV. 89506 @ I. ABSTRACT [email protected] V. ENERGY COUPLING BETWEEN SPECIES Ultra-intense lasers are the principal tools currently used in the production of short lived high energy density plasmas. The formation of solid density plasmas with temperatures of a few hundred eV by laser irradiation is hampered by the rapid diffusion of hot electrons throughout the target volume. The use of an ultra-high magnetic field to contain radial diffusion while isochorically heating a dense target for a picosecond with a laser, presents the possibility of creating a fundamentally new plasma regime in the laboratory to study HED physics, including ionization processes and opacities relevant to fusion and astrophysics. Moreover, the comprehensive understanding of hot electron transport in a dense plasma in the presence of strong external magnetic fields could open the prospect of Magnetized Fast Ignition to better couple PW laser energy into a magnetized compressed fuel core. VI. ELECTRON-ION COUPLING The three specie’s (cold electrons, hot electrons, and ions) temperature equilibration is calculated using a Spitzer-Eidmann hybrid collision frequency model. The hot electrons are found to couple with the cold electrons which then couple with the ions. The hot electrons are found to not heat the ions significantly. II. HOT ELECTRON CONFINEMENT In the absence of a magnetic field the hot electrons are confined inside the target by the electrostatic sheath fields excited at the target surface, but the electrons are not confined radially, and therefore they diffuse away from the focal region. In the presence of a magnetic field the hot electrons are confined inside the target not only by the electrostatic sheath fields excited at the target surface, but also by the axial magnetic field which acts by reducing the mean free path of the electrons. This slows down the radial diffusion long enough for the electrons to couple with the ions and heat the target. III. MAGNETIC FIELD GENERATION Our magnetic field is produced using the 1MA Zebra pulsed power generator. The current is passed through either a single/double turn helix, or a single/multi wire horse shoe coil. VII. ATOMIC NUMBER AND ION HEATING Due to the balance between the increased cold electron to hot electron coupling for high Z materials, and the increased energy loss for high Z materials due to bremsstrahlung, there exists an optimum range of materials suitable for picosecond ion heating. Note that this model does not include incomplete ionization or diffusion, and is optically thin. IV. MAGNETIC FIELD MEASUREMENTS Magnetic field measurements are made using a 532 nm laser and a Faraday probe. A magnetic field will create an anisotropy in the glass and change the indices of refraction for right and left circularly polarized light.. The polarization of laser light incident on the Faraday probe is compared to the polarization of the light exiting the Faraday probe in order to determine the magnitude of the magnetic field inside the probe. If the cold electrons are anomalously heated by the Weibel instability to a temperature proportional to 1/Z (1keV/Z in this model) the optimum range for picosecond ion heating is in the low Z range.