Anomalous observations using the fast ignition for laser driven fusion energy are interpreted and experimental and theoretical results are reported which are in contrast to the very numerous effects usually observed at petawatt-picosecond laser interaction with plasmas. These anomalous mechanisms result in rather thin blocks (pistons) of these nonlinear (ponderomotive) force driven highly directed plasmas of modest temperatures. The blocks consist in space charge neutral plasmas with ion current densities above 1010A∕cm2. For the needs of applications in laser driven fusion energy, much thicker blocks are required. This may be reached by a spherical configuration where a conical propagation may lead to thick blocks for interaction with targets. First results are reported in view of applications for the proton fast igniter and other laser-fusion energy schemes.
This work reports on investigations of parameters
of ion streams emitted from a plasma produced with a picosecond
laser at the power densities ≥1016 W/cm2.
Not many papers dealing with such investigations have been
published up to now, in spite of the fact that the application
of precise corpuscular diagnostics enables better learning
of the physical properties of such a plasma. As a result
of the investigations carried out, the average and maximum
energies of Cu ions were 30 keV and 150 keV, respectively.
The maximum charge of Cu ions was 13+. The dependencies
of parameters of ions emitted from the plasma on the laser-pulse
energy as well as on the location of the focus of the laser
beam with respect to the target's surface were also
found out. The results obtained from the ion measurements
in relation to the results of measurements of X ray are
discussed.
Basic properties of generation of high-current ion beams using the
skin-layer ponderomotive acceleration (S-LPA) mechanism, induced by a
short laser pulse interacting with a solid target are studied. Simplified
scaling laws for the ion energies, the ion current densities, the ion beam
intensities, and the efficiency of ions' production are derived for
the cases of subrelativistic and relativistic laser-plasma interactions.
The results of the time-of-flight measurements performed for both
backward-accelerated ion beams from a massive target and
forward-accelerated beams from a thin foil target irradiated by 1-ps laser
pulse of intensity up to ∼ 1017 W/cm2 are
presented. The ion current densities and the ion beam intensities at the
source obtained from these measurements are compared to the ones achieved
in recent short-pulse experiments using the target normal sheath
acceleration (TNSA) mechanism at relativistic (>1019
W/cm2) laser intensities. The possibility of application of
high-current ion beams produced by S-LPA at relativistic intensities for
fast ignition of fusion target is considered. Using the derived scaling
laws for the ion beam parameters, the achievement conditions for ignition
of compressed DT fuel with ion beams driven by ps laser pulses of total
energy ≤ 100 kJ is shown.
Acceleration of dense matter to high velocities is of high importance for high energy density physics, inertial confinement fusion, or space research. The acceleration schemes employed so far are capable of accelerating dense microprojectiles to velocities approaching 1000 km/s; however, the energetic efficiency of acceleration is low. Here, we propose and demonstrate a highly efficient scheme of acceleration of dense matter in which a projectile placed in a cavity is irradiated by a laser beam introduced into the cavity through a hole and then accelerated in a guiding channel by the pressure of a hot plasma produced in the cavity by the laser beam or by the photon pressure of the ultra-intense laser radiation trapped in the cavity. We show that the acceleration efficiency in this scheme can be much higher than that achieved so far and that sub-relativisitic projectile velocities are feasible in the radiation pressure regime. V
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