Inertial Confinement Fusion

The Plasma and Ultrafast Physics Group (PUPG) at the Laboratory for Laser Energetics focuses on the physics of laser coupling to a direct-drive fusion capsule. This includes the physics of laser–plasma interactions and the transfer of energy from the absorbed laser to the imploding target.

Self-emission x-ray images taken to measure the mass ablation rate in direct-drive implosion experiments on the OMEGA laser [1].

Implosion Physics

The PUPG uses both OMEGA and the National Ignition Facility (NIF) to study direct-drive–implosion physics. Direct-drive inertial confinement fusion uses laser beams to implode a spherical shell. The laser energy is absorbed near the critical surface of the target, transferred through the conduction zone to the ablation region, and converted into the kinetic energy of the shell through the rocket effect [2, 3]. Near peak compression, a fraction of the kinetic energy of the imploding shell is converted to the internal energy of the fuel. When the ion temperature of the central region (hot spot) and the areal density of the compressed fuel are sufficiently large, a burn wave originating from the alpha particles produced by the fusion of deuterium (D) and tritium (T) will propagate through the confined fuel in the shell (ignition).

Laser–Plasma Interactions

A significant focus of the PUPG is to understand how laser light propagates through a plasma. The high-power beams used in ICF excite laser–plasma instabilities that must be understood and managed for a successful fusion demonstration [4]. Direct-drive ignition is most susceptible to multibeam laser–plasma instabilities because single-beam intensities are low (Is ~ 1014 W/cm2) and the electron temperature in the underdense plasma is high (Te ~ 3.5 keV). Cross-beam energy transfer (CBET) is driven by multiple laser beams and can significantly reduce the hydrodynamic efficiency in direct-drive experiments on OMEGA. Two-plasmon decay (TPD) can be driven by multiple laser beams [5] and is responsible for generating hot electrons that can degrade the implosion performance. See related publications and reports below for work performed in the group [6–8].

Schematic of the direct-drive density profile and potential laser–plasma interactions encountered by incident direct-drive beams. As a result of the relatively low single-beam intensities (Is), direct-drive experiments are most susceptible to the laser-beam instabilities that are driven by multiple laser beams (e.g., CBET and TPD).

Related Publications

(UR graduate students are underlined)

Related DOE Monthly Reports