The goal of this theory is to study the conversion of a fraction of a laser beam to its phase-mismatch second and third harmonics. This conversion takes place by focusing an intense laser beam into a transversely magnetized plasma, as a nonlinear medium. The influence of the polarization field is considered, however, the plasma density is below the critical density. It has already been revealed that for dense plasma, the second and third harmonics efficiencies decreased with density increasing in the presence of a sufficiently strong magnetic field. This result is in contrast to the under dense and weakly magnetized plasma, which the harmonics efficiencies increased with density increasing. It is shown that the harmonics radiation cut-off, when the magnetic field increases up until the saturation strength Bsat. In addition, the results indicated that the average phase-mismatch third harmonic conversion efficiency is a little smaller than the phase-match case reported for non-magnetized plasma.

The design and constructional aspects of a novel pulse power generator for use in dense plasma research presently under construction are presented. The generator consists of two Marx capacitor banks, each of 0.25 μF, 480 kV, and 28.8 kJ. Each Marx generator drives a water transmission line, in which the live electrode is the central conductor. The transmission lines consist of a constant impedance section followed by a multielectrode gas linegap followed by an exponential taper to the load section. The novel feature is the use of an auxiliary exponential line coupled at the load. This line controls both the voltage and the effective impedance at the load section. In addition, by leaving this line circuit open, energy not coupled to the plasma in the initial high-impedance phase may be reflected back and deposited into the discharge, increasing the peak current by 50%. Circuit simulations using a real-time-varying load impedance show that the current pulse rises in an approximately linear way to a maximum of 1.2 MA at 250 ns. The current falls to zero in the following 250 ns. The current waveform may be flattened simply by disconnecting the auxiliary line, giving a rectangular pulse of 350 ns with a maximum value of 950 kA. The overall impedance of the entire system may be adjusted by varying the separation between the conductors. The equivalent source impedance at the load is 0.8 Ω. This low value is by virtue of the auxiliary line, which limits the voltage at the load section and reduces the insulator constraints. We present simulations of the generator under real load conditions. The model also is checked against analytical solutions of exponential line behavior and against other published models of pulse power generators.

The paper gives a review of investigations on generation of soft X-rays and EUV using a gas puff target irradiated with high-power laser pulses performed during last few years. In the studies a newly developed double-stream gas puff target approach was used. The gas puff targets were irradiated with various lasers, including Nd:glass, Kr:F, Nd:YAG, and iodine lasers. The aim of the studies was to develop efficient and debris-free laser plasma X-ray and EUV sources for applications in microscopy, lithography, micro- and nanotechnology.

In the present research work, the authors have investigated the self-focusing and defocusing of Hermite-cosh-Gaussian laser (HChG) beam in an inhomogeneous rippled density plasmas. By taking the relativistic non-linearity into account, an equation for envelope is set up and solved using Wentzel–Kramers–Brillouin and the paraxial ray approximation. An ordinary non-linear differential equation governing the beam width parameter as a function of propagation distance is set up for different mode structures of the beam. Further, a numerical study of this differential equation is carried for suitable set of plasma and laser parameters. The beam undergoes periodic self-focusing/defocusing due to relativistic non-linearity. We also report the comparison between self-focusing/defocusing of HChG beam in the absence and presence of density ripple. Presence of ripple does not only leads to substantial increase in self-focusing length, but also results in oscillatory character with decreasing f. In a relativistic case, strong oscillatory self-focusing and defocusing is observed. Further, self-focusing is enhanced with increased value of decentered parameter.

Interactions of cone targets with different shapes with laser pulses are studied numerically. Two important parameters which characterize the laser-cone interaction in 2006 are introduced, which are cone angle and ratio of laser spot and cone tip. By changing these two parameters, energy coupling from laser to electrons is controlled. Some fraction of high energy electrons generated at side wall and cone tip are not freely propagating out from the target, but confined around the cone tip due to the disturbed electric field.

This paper reports on a novel approach for producing high energy femtosecond pulses without external amplification. The so-called chirped-pulse oscillator (CPO) concept is based on an extended-cavity oscillator, operating at small net positive intracavity group delay dispersion (GDD), over a broad spectral range by the use of chirped multilayer mirrors. The resultant chirped picosecond pulses are compressed by a dispersive delay line external to the laser cavity. Utilizing this technique, sub-30 fs pulses with an energy exceeding 200 nJ at a repetition rate of 11 MHz were produced. The demonstrated peak power in excess of 5 MW is the highest ever achieved from a cw-pumped laser and is expected to be scaleable to tens of megawatts by increasing the pump power and/or decreasing the repetition rate. The demonstrated source allows micromachining of any materials under relaxed focusing conditions.

The experimental results of the investigations on the influence of external magnetic and electric fields on the characteristics of a tungsten ion stream emitted from a plasma produced by the Nd:glass laser (1 J, 1 ns) performed at IPPLM, Warsaw are presented. A negatively biased target up to −15 kV and a magnetic field up to 0.45 T were used in the experiment. A set of ion collectors and an electrostatic cylindrical ion energy analyzer located at small angles with respect to the laser beam axis and at large distances from the target were applied for ion measurements. The effect of an external magnetic field is essential to plasma expansion, but the effect of the retarding potential of the target is very weak in our experimental conditions. The aim of the studies was to prove the possibility of the optimization of ion beam parameters from laser-produced plasma for the particular application as a laser ion source coupled with the electron cyclotron resonance ion source for particle accelerators.

This paper presents a scheme for second harmonic generation (SHG) of q-Gaussian laser beam in plasma channel created by ignitor heater technique. The ignitor beam creates plasma by tunnel ionization of air. The heater beam heats the plasma electrons and establishes a parabolic density profile. The third beam (q-Gaussian beam) is guided in this plasma channel under the combined effects of density nonuniformity of the plasma channel and relativistic mass nonlinearity of the plasma electrons. The propagation of q-Gaussian laser beam through the plasma channel excites an electron plasma wave at pump frequency that interacts with the incident laser beam to produce its second harmonics. The formulation is based on finding the numerical solution of the nonlinear Schrodinger wave equation for the fields of the incident laser beams with the help of moment theory approach. Particular emphasis is put on dynamical variations of the spot size of the laser beams and conversion efficiency of the second harmonics with distance of propagation.

The longitudinal resistive microwave instability in storage rings has been identified in previous workshops as a key problem in heavy ion fusion. Here we show by means of computer simulation that the predictions from the linearized theory of instability are over-pessimistic in the case of non-relativistic ions. This is due to an early nonlinear saturation of the instability caused by the formation of a thin stabilizing tail of the momentum distribution, which provides enough Landau damping to suppress further growth. The main condition for this non-destructive self-stabilization lies in the slow resistive growth rate, as compared with the large coherent frequency shift induced by space charge. The important conclusion from this is a significant extension of the stable storage ring filling time to values that are comfortable from a design point of view. For the HIBALL reactor driver accelerator a safe storage time of 5 to 10 msec is expected, instead of only 1 msec according to the linearized theory e-folding times.

Strongly shocked cylindrically convergent implosions were conducted on the OMEGA laser. The directly driven targets consist of a low-density foam core and an embedded aluminum shell covered by an epoxy ablator. The outer surface of the aluminum shell has imposed single-mode perturbations with wave numbers k = 0.25, 0.7, 1.05, and 2.5 (rad/μm) and initial amplitudes η0 /λ = 0.04, 0.11, 0.33, and 0.4. In our convergent geometry, perturbation growth without evidence of saturation, for η/λ as large as 4.5 is observed for k < 1. For k > 1 growth rate scaling with wavenumber breaks down and transition to turbulence is suggested.

The test on an X-pinch device powered by a pulsed power generator (PPG-I) was carried out step by step. In the first step, a brass rod of 6 mm in diameter was used as a load to replace the X-pinch load. The results of the first step shows that all the current, about 200 kA in amplitude, output from PPG-I flows through the load and no breakdown or flashover in vacuum of the load section happens. The waveform of the current from PPG-I measured with a wall resistor coincides exactly with that of the load current measured with a Rogowski coil, which indicates that the calibrations of the wall resistor and Rogowski coil are correct. In the second step, an X-pinch load made of two molybdenum wires of 40 µm in diameter was used. It was found that the distance between the cathode and anode affects considerably the operation of the device. While breakdown in vacuum happens for the distance equal to 30 mm, it works very well for the distance equal to 16 mm. The reason for this phenomenon was given.

Nuclear fusion in ultra-dense deuterium D(-1) was reported previously to be induced by 0.2 J pulses with 5 ns pulse length, ejecting particles with energies in the MeV range. The ns-resolved signal from D(-1) to two in-line collectors at up to 1 m distance can be observed directly on an oscilloscope, showing particles with energies in the range 1–20 MeV u−1. They are probably mainly protons and deuterons in the form of neutral ultra-dense hydrogen H(-1) fragments. Electrons and photons give only small contributions to the fast signal. The observed signal at several mA peak current corresponds to 1 × 1013 particles released per laser shot and to an energy release >4 J assuming isotropic formation and average particle energy of 3 MeV. This corresponds to an energy gain of 30 in the process. A movable slit close to the laser target gives lateral resolution of the signal generation, showing almost only fast particles from the point of laser impact and penetrating photons from the plasma outside the laser impact point. The observation of multi-MeV particles indicates nuclear fusion, either as a source or as a result.

In this work, the generation of a super-short avalanche electron beam (SAEB) in SF6 in an inhomogeneous electric field is studied on two generators with pulse rise times of 0.5 and 2 ns, respectively. The SAEB parameters in SF6 are compared with those obtained in other gases (air, nitrogen, argon, and krypton). It is shown that the SAEB amplitude in SF6 at pressures ranging from 0.05 to 0.2 MPa is commensurable with that in krypton and is much lower than that in air and nitrogen. It is also found that in SF6, SF6 mixture with 2.5% of nitrogen, and other gases, a diffuse discharge is ignited not only at negative polarity but also at positive polarity of the electrode with small curvature radius. Furthermore, the velocity of the ionization wave front in SF6 in an inhomogeneous electric field is studied. Experimental results show that the velocity of the ionization wave front in SF6 is lower than that in air and nitrogen as well as such velocity decreases when the pressure increases from 0.05 to 0.3 MPa in all gases.

We propose the use of Focused Ion Beam/Scanning Electron Microscope (FIB/SEM) devices for the analysis of ablation results. Ablated samples have been obtained by irradiating an Al planar target with an optically smoothed iodine laser working at 0.44 μm. The interpretation of FIB images shows the high potentiality of the technique.

Validation of the direct-drive approach to inertial confinement fusion requires the development of a 351-nm wavelength, 30-kJ, 50-TW laser system with flexible pulse shaping and irradiation uniformity approaching 1%. An upgrade of the existing OMEGA direct-drive facility at Rochester is planned to meet these objectives. In this article, we review the design rationale and specifications of the OMEGA Upgrade laser with particular emphasis on techniques planned to achieve the required degree of beam smoothing, temporal pulse shape, and beam-to-beam power balance.

The conventional implosion scheme for high gain and high density compression depends upon the piston action of an accelerated heavy pusher. However, the contact surface between the pusher and the fuel layer is very unstable in the stagnation phase. In this paper, the laser pulse tailoring and the scaling laws for pellet gain, fuel ρR, etc. are discussed under the condition of very weak piston action of the pusher. The scaling laws indicate that the fuel will be ignited by 100 kJ, 0·35 μm wavelength laser irradiation.

The method of relativistic plasma control (RPC) for generation of single (sub-) attosecond pulses based on high harmonic generation at plasma surface is presented. Use is made of the concept of apparent reflection point (ARP), introduced for the sake of analytical treatment of the plasma dynamics. We show theoretically and numerically that managing the laser polarisation the ARP dynamics can be efficiently controlled and a single ultra-short pulse can be extracted out of the short pulse train generated by a multi-cycle driver. For the sake of future applications the structure of the pulse is studied analytically and numerically by particle-in-cell simulations.

Fast electrons are effectively generated from solid targets of cone-geometry by irradiating intense laser pulses, which is applied to fast ignition scheme. For realizing optimal core heating by those electrons, understanding the characteristics of electrons emitted from cone targets is crucial. In this paper, in order to understand the generation and transport processes of hot electrons inside the cone target, two-dimensional (2D) particle-in-cell (PIC) simulations were carried out. It is shown that hot electrons form current layers which are guided by self-generated surface magnetic field, which results in effective energy transfer from laser pulse to hot electrons. When the hot electrons propagate through the steep density gradient at the cone tip, electrostatic field is induced via Weibel instability. As a result, hot electrons are confined inside and emitted gradually from the target, as an electron beam of long duration. Energy spectrum and temporal profile of hot electrons are also evaluated at the rear side of the target, where the profile of rear side plasma is taken from the fluid code and the result is sent to Fokker-Planck code.

The very clean nuclear fusion reaction of hydrogen and boron-11 by inertial confinement arrives at conditions for power stations by volume ignition only at compressions to 100,000 times the solid state. The earlier (numerically) observed anomaly of decreasing gain at increasing density (retrograde behavior) is analyzed and the reason clarified: the strong stopping power mechanism, based on Gabor's collective model, is reaching its limit of too small Debye lengths at the extremely high densities because of the optimum temperature in the range of 30 keV due to the reabsorption of the bremsstrahlung. The relativistic correction of the bremsstrahlung for the always much higher temperatures after volume ignition is included from Maxon's model.

We present some experimental results on X-ray spectra obtained from plasmas produced using a compact Nd:YAG laser system. The beam was focused on different targets (Cu, Al, Ge,…) and both high resolution and low resolution X-ray spectra were recorded.