H. Hora

Laser fusion with nonlinear force driven plasma blocks: Thresholds and dielectric effects

Anomalous interaction of picosecond laser pulses of terawatt to petawatt power is due to suppression of relativistic selffocusing if prepulses are cut-off by a contrast ratio higher than 10 8 , resulting in quasi-neutral directed plasma blocks with deuterium tritium ion current densities above 10 11 A/cm 2 . This is still not high enough for ignition of solid-state density deuterium tritium because the energy flux density E* has to be higher than the threshold of 4 � 10 8 J/cm 2 obtained within the theory of Chu (1972). A revision of this evaluation shows a reduction of this threshold by a factor 20 if the later discovered inhibition factors for thermal conduction because of double layer effects as well as the shorter stopping lengths of the alpha particles due to collective effects are taken into account. Under these relaxed conditions, the parameters of nonlinear force generated blocks of dielectrically increased thickness for deuterium tritium ignition with directed ions of energies near the 80 keV resonances are discussed.

Twenty times lower ignition threshold for laser driven fusion using collective effects and the inhibition factor

Hydrodynamic analysis for ignition of inertial fusion by Chu [Phys. Fluids 15, 413 (1972)] arrived at extremely high thresholds of a minimum energy flux density E* at 4×108J∕cm2 which could be provided, e.g., by spark ignition. In view of alternative schemes of fast ignition, a re-evaluation of the early analysis including later discovered collective stopping power and the inhibition factor results in a 20 times lowering of the threshold for E*.

Layers from initial Rayleigh density profiles by directed nonlinear force driven plasma blocks for alternative fast ignition

Measurement of extremely new phenomena during the interaction of laser Pulses with terawatt and higher power and picosecond; with plasmas arrived at drastically different anomalies in contrast to the usual observations if the laser pulses were very clean with a contrast ratio higher than 10(8). This was guaranteed by the Suppression of prepulses during less than dozens of ps before the arrival of the main pulse resulting in the suppression of relativistic self-focusing. This anomaly was confirmed in many experimental details, and explained and numerically reproduced as a nonlinear force acceleration of skin layers generating quasi-neutral plasma blocks with ion current densities above M, I A/cm(2). This may support the requirement to produce a fast ignition deuterium tritium fusion at densities not much higher than the solid state by a single shot PW-ps laser Pulse. With the aim to achieve separately studied ignition conditions, we are studying numerically how the necessary nonlinear force accelerated plasma blocks may reach the highest possible thickness by using optimized dielectric properties of the irradiated plasma. The use of double Rayleigh initial density profiles results in many wavelength thick low reflectivity directed plasma blocks of modest temperatures. Results of computations with the genuine two-fluid model are presented.

Analytical description of rippling effect and ion acceleration in plasma produced by a short laser pulse

In this paper we present the analytical description of two processes dealing with the skin-layer ponderomotive acceleration method of fast ion generation by a short laser pulse: ion density rippling in the underdense plasma region and generation of ion beams by trapped electromagnetic field in plasma. Some numerical examples of hydrodynamic simulation illustrating these processes are shown. The effect of using the laser pulse consisting of different frequency components on the ion density rippling and on phenomena connected with trapped electromagnetic field is analyzed.

Studies on laser-driven generation of fast high-density plasma blocks for fast ignition

Proton fast ignition (FI) of fusion targets [1] requires ps proton beams of PW power and of extremely high proton current densities (ji >10 12 A/cm 2 ) and proton beam intensities (Ii > 10 19 W/cm 2 ) [2, 3], which are not attainable at present even with the biggest conventional accelerators [4]. Potentially, such extreme proton beam parameters can be achieved using ballistic focusing of fast proton beams generated by the target normal sheath acceleration (TNSA) mechanism [5] driven by a short (≤ 1ps) laser pulse of relativistic intensity. Achieving required proton beam intensities with sufficiently high efficiency with this method can encounter, however, severe difficulties. One of the reasons is relatively low density of accelerated protons at the source (in a close vicinity of the rear target surface), which typically is ~ 10 19 cm -3 [6 – 9] or less (see further). As the relation between the ion beam intensity, Ii, the ion density, ni, and the ion (mean) energy, Ei, can be expressed by the equation (see e.g. [9]):

Ultrahigh acceleration of plasma by picosecond terawatt laser pulses for fast ignition of fusion

A fundamental different mechanism dominates laser interaction with picosecond-terawatt pulses in contrast to the thermalpressure processes with ns pulses. At ps-interaction, the thermal effects are mostly diminished and the nonlinear (ponderomotive) forces convert laser energy instantly with nearly 100% efficiency into the space charge neutral electron cloud, whose motion is determined by the inertia of the attached ion cloud. These facts were realized only by steps in the past and are expressed by the ultrahigh plasma acceleration, which is more than few thousand times higher than observed by any thermokinetic mechanism. The subsequent application for side-on ignition of uncompressed fusion fuel by the ultrahigh accelerated plasma blocks is studied for the first time by using the genuine two-fluid hydrodynamics. Details of the shock-like flame propagation can be evaluated for the transition to ignition conditions at velocities near 2000 km/s for solid deuterium-tritium.

Nonlinear force driven plasma blocks igniting solid density hydrogen boron: Laser fusion energy without radioactivity

Energy production by laser driven fusion energy is highly matured by spherical compression and ignition of deuteriumtritium (DT) fuel. An alternative scheme is the fast ignition where petawatt (PW)-picosecond (ps) laser pulses are used. A significant anomaly was measured and theoretically analyzed with very clean PW-ps laser pulses for avoiding relativistic self focusing. This permits a come-back of the side-on ignition scheme of uncompressed solid DT, which is in essential contrast to the spherical compression scheme. The conditions of side-on ignition thresholds needed exorbitantly high energy flux densities E*. These conditions are now in reach by using PW-ps laser pulses to verify side-on ignition for DT. Generalizing this to side-on igniting solid state density proton-Boron-11 (HB11) arrives at the surprising result that this is one order of magnitude more difficult than the DT fusion. This is in contrast to the well known impossibility of igniting HB11 by spherical laser compression and may offer fusion energy production with exclusion of neutron generation and nuclear radiation effects with a minimum of heat pollution in power stations and application for long mission space propulsion.

Resonance effect for strong increase of fusion gains at thermal compression for volume ignition of Hydrogen Boron-11

An anomalously strong increase of nuclear fusion gains for laser driven compression and thermal ignition of hydrogen-boron11 has been discovered from computations by using the latest results of Newins and Swain about details of a resonance maximum of the astrophysical S-function at 148 keV for the reaction cross-sections. Extensive computations based on volume ignition showed some usual improvements of the fusion gains. However, for a very narrow range of parameters, the increase of the gain was found to be higher by more than a factor 6. This is very unusual in all similar computations and is related to retrograde properties which were known for other parameter values. On top it is most important that the anomalous range is in the practically very interesting range for incorporation of laser pulse energies of few megajoules. The gains of up to 20 may be of interest for power generation in future by the high density fusion scheme.

Fiber ICAN laser with exawatt-picosecond pulses for fusion without nuclear radiation problems

One of the numerous applications of the ICAN laser using the advantage of fiber optics with chirped pulse amplification (CPA), is the scheme of side-on initiation of a nuclear fusion flame in solid density fuel with laser pulses of shorter than picosecond (ps) duration and power in the petawatt (PW) and higher range. The ICAN Fiber optics has special advantages with the potential that >900 PW spherical laser pulses may ignite the proton reaction with 11 B (HB11) without the problem of dangerous radioactive radiation. Though secondary reactions can be estimated very roughly, the feasibility of a power station with the necessary energy gains can be concluded.

Focusing and defocusing of the nonlinear paraxial equation at laser–plasma interaction

This paper presents a numerical and theoretical study of the generation and propagation of oscillation in the semiclassical limit T → 0 of the nonlinear paraxial equation at laser-plasma interaction. In a general setting of both dimension and nonlinearity, the essential differences between the focusing and defocusing cases is identified due to the nonlinearity, and dispersion effects involved in the propagation of solitons at laser plasma interaction. A sequence of codes has been developed in mathematics to explore the focusing and defocusing of the soliton formation and propagation.