Self-generated Electric Fields Research Articles

Particle acceleration in relativistic laser channels

Energy spectra of ions and fast electrons accelerated by a channeling laser pulse in near-critical plasma are studied using three-dimensional (3D) Particle-In-Cell simulations. The realistic 3D geometry of the simulations allows us to obtain not only the shape of the spectra, but also the absolute numbers of accelerated particles. It is shown that ions are accelerated by a collisionless radial expansion of the channel and have nonthermal energy spectra. The electron energy spectra instead are Boltzmann-like. The effective temperature Teff scales as I1/2. The form of electron spectra and Teff depends also on the length of the plasma channel. The major mechanism of electron acceleration in relativistic channels is identified. Electrons make transverse betatron oscillations in the self-generated static electric and magnetic fields. When the betatron frequency coincides with the laser frequency as witnessed by the relativistic electron, a resonance occurs, leading to an effective energy exchange between the laser and electron. This is the inverse free-electron laser mechanism. Electrons are accelerated at the betatron resonance when the laser power overcomes significantly the critical power for self-focusing.

On the role of neutral particles on edge turbulence and electric fields in the Advanced Toroidal Facility

Measurements of edge plasma turbulence properties have been carried out in the Advanced Toroidal Facility (ATF) [Fusion Technol. 10, 179 (1986)] during experiments in which hydrogen and neon gas puffing are used to vary the edge temperature in the range 5<Te<40 eV in a controlled way. In the temperature range where the rate coefficients for ionization processes are strongly temperature dependent (5<Te<15 eV) the electron temperature plays an important role in determining the level of edge turbulence and the value of the self-generated radial electric fields. These results provide evidence of edge turbulence and flows modified by the presence of neutral particles.

Inertial Confinement Fusion with Light Ion Beams

The Particle Beam Fusion Accelerator II (PBFA II) is presently under construction and is the only existing facility with the potential of igniting thermonuclear fuel in the laboratory. The accelerator will generate up to 5 megamperes of lithium ions at 30 million electron volts and will focus them onto an inertial confinement fusion (ICF) target after beam production and focusing have been optimized. Since its inception, the light ion approach to ICF has been considered the one that combines low cost, high risk, and high payoff. The beams are of such high density that their self-generated electric and magnetic fields were thought to prohibit high focal intensities. Recent advances in beam production and focusing demonstrate that these self-forces can be controlled to the degree required for ignition, break-even, and high gain experiments. ICF has been pursued primarily for its potential military applications. However, the high efficiency and cost-effectiveness of the light ion approach enhance its potential for commercial energy application as well.