Magnetized Laser-Plasma Interactions to Create Solid Density Warm Matter

Summary form only given. Collisional particle-in-cell simulations predict that solid density matter irradiated with a short pulse high intensity laser can be heated to keV temperatures by applying an external magnetic field. The role of the magnetic field is to restrict the radial diffusion of the hot electrons accelerated by the laser field. The confinement can be effective if the gvro-period is less than the collision time. This reduces the radial diffusion of the hot electrons long enough so that they can couple to the cold electrons which in turn couple to the ions. To test these predictions, an experiment is being developed that takes advantage of the coupled Tomcat/Leopard -Zebra facility. According to simulations performed for achievable values of the parameters, with a laser intensity higher than 10¹⁷ W/cm² and a magnetic field of the order of 1 MG material volumes of 10⁵ mum can be heated for several ps to temperatures of several hundred eV. These parameters make this technique extremely appealing for fusion and opacity studies with numerous applications that include modeling the radiation transport in the interiors of stars. In preparation for the integrated experiment, magnetic fields higher than 1 MG were produced in vacuum with the pulsed power generator Zebra (0.6 MA, 200 ns) using horseshoe shaped coils. In the configuration used, no plasma was created on the surface of a CM laser target placed inside the coil. To date, the best parameters measured for the Tomcat compressed laser pulse are: energy 4 J, duration 0.8 ps, and focal spot FWHM 30 mum (measured with the unamplified beam), resulting in an irradiance on target around 10¹⁸ W/cm². Higher irradiance will be soon available using the 100 TW laser Leopard, the pulse compression of which is currently under way. The jitter of Zebra was reduced to less than 15 ns rms assuring successful synchronization with the lasers. The goal of the experiment i- s to demonstrate enhanced heating of a solid target irradiated by an intense, short pulse laser in the presence of an external magnetic field. Several types of targets including homogeneous Si and CD targets, as well as layered targets CD-Si-CD will be used, and their heating compared. The electron temperature and ionization balance will be inferred from X-ray spectra. A von Hamos KAP crystal spectrograph was built and used to record single shot Al and Si spectra from laser irradiated targets. Neutron yield measurements with scintillator-photomultiplier detectors will be used to determine the deuteron temperature.