In the paper, nonlinear structure of electromagnetic field, electron temperature, and electron density in interaction with relativistic laser and collisional underdense rippled plasma are investigated. The results are shown that due to the combination influence of relativistic effect, ohmic heating and plasma density ripple, electromagnetic field profile presents obvious asynchronism, which the peak of electric field run ahead of the peak of magnetic field. Furthermore, the electromagnetic field profiles show obvious non-sinusoidal, and the profile of electron temperature and density become highly peaked. Especially, compared with the previous work, due to the added influence of plasma density ripple, electromagnetic field, electron temperature and electron density present obvious oscillation along plasma length rather than stabilization amplitude, and their peak are out of sync.

The effects of the polarized incident laser pulse on the electrons of the plasma surface and on the reflected pulse in the relativistic laser-plasma interaction is investigated. Based on the relativistic oscillating mirror and totally reflecting oscillating mirror (TROM) regimes, the interaction of the intense polarized laser pulses with over-dense plasma is considered. Based on the effect of ponderomotive force on the characteristic of generated electron nano-bunches, considerable increasing in the localization and charges of nano-bunches are realized. It is found that the circularly polarized laser pulse have Ne/Ncr of 1500 which is almost two and seven times more than the amounts for P-polarized and S-polarized, respectively.

Collisional effects on the current-filamentation instability (CFI), accounting for the space charge effect (SCE), are investigated kinetically for a relativistic beam propagating in dense plasmas. It is shown that collisions can completely suppress the SCE in low temperature dense plasma, leading to enhancement of the CFI. This kind of decoupling mechanism is quite different from the well-known resistive mechanism [Molvig (1975). Phys. Rev. Lett. 35, 1504]. In particular, we find the present decoupling mechanism can well explain the recent numerical simulation results [Karmakar et al. (2008). Phys. Rev. Lett. doi: 101, 255001]. In the parameter regime related to the laser-solid interaction and fast ignition scenario (FIS), the CFI growth rate with SCE included is enhanced in the low plasma density region through the decoupling mechanism. In the high plasma density region, it is enhanced mainly through the resistive mechanism.

Fast ignition of inertial fusion targets driven by quasi-monoenergetic ion beams is investigated by means of numerical simulations. Light and intermediate ions such as lithium, carbon, aluminum and vanadium have been considered. Simulations show that the minimum ignition energies of an ideal configuration of compressed Deuterium-Tritium are almost independent on the ion atomic number. However, they are obtained for increasing ion energies, which scale, approximately, as Z2, where Z is the ion atomic number. Assuming that the ion beam can be focused into 10 µm spots, a new irradiation scheme is proposed to reduce the ignition energies. The combination of intermediate Z ions, such as 5.5 GeV vanadium, and the new irradiation scheme allows a reduction of the number of ions required for ignition by, roughly, three orders of magnitude when compared with the standard proton fast ignition scheme.

The electromagnetic simulation of the monolithic radial transmission lines for future Z-pinch was performed. Focusing on the difference in the maximum transmitted power efficiency between the electromagnetic simulation and the circuit simulation, the monolithic radial transmission lines with different impedance profile (exponential, Gaussian, hyperbolic) were compared. The power efficiency for the exponential line is higher than that for the Gaussian lines and the hyperbolic line, which is similar to that from the circuit simulation. However, all the power efficiencies obtained with the electromagnetic simulation are about 15% lower than those obtained with the circuit simulation, indicating the existence of considerable non-TEM modes and a non-ignorable error in the circuit simulation based on the quasi-TEM mode approximation. In consideration of several monolithic radial transmission lines being stacked together and the flat electrodes required by the stacked lines, the hyperbolic line was compared with the exponential line with several wide radial slots cut on the flat electrodes. While the hyperbolic line has a little bit lower transmitted power efficiency than that of the exponential line, it is much easier in fabrication. For this reason, the hyperbolic line was recommended as the best choice.

This paper describes the spatial and temporal investigation of laser ablated plasma plume of cerium oxide target using Langmuir probe. Cerium oxide target was ablated using a KrF (λ ~ 248 nm) gas laser. Experimental studies confirmed that oxygen partial pressure of 2 × 10−2 mbar is sufficient enough to get good quality films of cerium oxide. At this pressure, plume was diagnosed for their spatial and temporal behavior. Spatial distribution was investigated at a distance of 15 mm, 30 mm, and up to a maximum distance of 45 mm from the target, whereas temporal behavior has been recorded in the range of 0 to 50 µS with an interval of 0.5 µS. The average electron densities are found to be maximum at 30 mm from the target position and the plasma current of the laser ablated ceria is found to be maximum at 22 µS.

A novel coaxial relativistic transit-time oscillator with low guiding magnetic field is proposed and investigated to generate high power microwave at Ku-band. With the coaxial structure and a quasi body wave adopted as the operating mode, the device has a larger space-charge limiting current, higher power handling capacity, and lower guiding magnetic field. Moreover, for further improving the output power, a coaxial TM02 mode resonant reflector is well designed. Main structure parameters of the device are optimized by particle in cell simulations. A typical simulation result is that, with a 358 keV, 7.25 kA beam guided by a magnetic field of about 0.7 T, an 810 MW microwave pulse at 14.25 GHz is generated, yielding a conversion efficiency of about 31%. The primary experiments are also carried out. At a low guiding magnetic field of 0.7 T, a microwave pulse with power of 400 MW, pulse duration of 30 ns, frequency of 14.3 GHz close to the simulation one, and efficiency of 15.4% is generated.

It is shown that in the focus of ultra-short pulses of duration t, the equivalent relation s = ct, where c is the speed of light and s the spatial extent of the pulse of the collimated pulse, does not hold. While the duration of one pulse is constant and independent of the measurement point, the spatial extension of the ultra-short pulse can be spatially shorter a factor more than 10 compared to the one obtained from the usual relation. The result is explained in correspondence with the extension of the Rayleigh range. Few femtosecond long gamma bursts can thus be generated in Thomson backscattering experiments performed in the lambda cube regime.

The interaction of a relativistic short laser pulse with thin foil is studied using 3D PIC simulations in the context of optimized high-energy proton generation for nuclear medicine and pharmacy. As an example, we analyze the Tc-99m yield from the Mo-100(p,2n)Tc-99m reaction with the International Coherent Amplification Network (ICAN) concept defined by a 10 J pulse energy and 10 kHz repetition rate. Based on 3D PIC simulation it has been demonstrated that normally incident 100 fs laser pulse with maximum intensity of 5 × 1021 W/cm2 is able to generate 1011 protons with energy upto 45 MeV from thin semi-transparent CH2 target. Such laser-produced proton beam after 6 hours bombardment of the thick metallic Mo-100 target gives around 300 Gbq activities of Tc-99m isotope. This gives reason to believe that laser technology for producing technetium is possible with ICAN concept to replace the traditional scheme through the fission of weapons-grade uranium.

In order to use two paralleled X-pinches as X-ray sources for the time-resolved backlighting of wire-array Z-pinch plasma, it is necessary to make these two X-pinches emit X-rays at different but roughly preset time instants. The timing of the X-ray burst from an X-pinch independence of the current, and the wire mass of the X-pinch was investigated. The currents flowing through two paralleled X-pinches were measured and it was found that the total current is almost equally divided between these two X-pinches no matter how different the wires for these two X-pinches are. The reason for the equal current division between two paralleled X-pinches was given based on the inductance calculation of the X-pinch circuit.

High-voltage pulse modulator has broad applications in industry. In order to pursue the qualities of compactness, solidification, and long life time, a high-voltage pulse modulator based on a helical Blumlein pulse forming line (HBPFL),a Marx generator and a self-coupling saturable pulse transformer (SPT) with fully cylindrical coaxial conductors is put forward and investigated in this paper. A new method that the fully cylindrical SPT simultaneously works as the charging pulse transformer and magnetic switch of the HBPFL is put forward and demonstrated. Traditional spark gap is substituted by the SPT to enable the features of solidification, compactness, and long life time of the modulator. Experimental results showed that the SPT had good response characteristics to short sinusoidal pulse and 100 ns-range square pulses. The fully cylindrical SPT driven by the 50–70 kV Marx generator can suppress the saturated inductance of the secondary windings to a level less than 500 nH, due to the strong reversed mutual induction between cylindrical windings after the core saturated. It also demonstrated that the pulse modulator was able to deliver a high-voltage pulse to a 160 Ω load, with amplitude of 148 kV, pulse duration of 130 ns, and pulse rise time ranging from 60 to 105 ns.

Laser ablation of graphite materials in the presence of an external magnetic field is studied with the use of the newly developed HEIGHTS-PIC particle-in-cell code and compared with both theoretical and experimental results. Carbon plumes behavior controlled by a strong magnetic field is of interest to evaluate the plume shielding effects to protect the original exposed target from further damage and erosion. Since intense power deposition on plasma facing components is expected during Tokamaks loss of plasma confinement events such as disruptions, vertical displacements event, runaway electrons, or during normal operating conditions such as edge-localized modes, it is critical to better understand the evolving target plasma behavior for more accurate prediction of the potential damage created by these high-energetic dumps which may not be easily mitigated without loss of structural and functional performance of the plasma facing components. Numerical experiments have been performed to provide benchmarking conditions for the HEIGHTS-PIC simulation package originally designed to evaluate the erosion of the Tokamak surfaces, splashing of the melted/ablated-vaporized material, and transport into the bulk plasma with consequent plasma contamination. Evolving target plasma temperature and density are calculated and compared with measured reported values available into literature for similar conditions and show good agreement with the HEIGHTS-PIC package predictions.

For the purpose of material studies for future nuclear fusion reactors, the IFMIF deuteron beams present a simultaneous combination of unprecedentedly high intensity (2 × 125 mA CW), power (2 × 5 MW) and space charge. Special considerations and new concepts have been developed in order to overcome these challenges. The global strategy for beam dynamics design of the 40 MeV IFMIF accelerators is presented, stressing on the control of micro-losses, and the possibility of online fine tuning. Start-to-end simulations without and with errors are presented for the prototype accelerator. Considerations about conflicts between halo and emittance minimization are then discussed in this very high space charge context.

In this work we reported low and high repetition frequency femtosecond laser-induced modifications of tungsten-based thin film. The tungsten-titanium (WTi) thin film, thickness of 190 nm, was deposited by sputtering on single crystal Si (100) wafer. Irradiations were performed in air by linearly polarized and focused femtosecond laser beams with following parameters: (1) pulse duration 160 fs, wavelength 800 nm, laser repetition frequency (LRF) 75 MHz — high LRF, and (2) duration 40 fs, wavelength 800 nm, LRF of 1 kHz — low LRF. The results of femtosecond lasers processing of the WTi thin film revealed laser induced periodical surface structures (LIPSS) in the case of low LRF regime. LIPSSs were formed with different periodicity and different orientation to the laser polarization at the surface: micro-scale LIPSSs with orientation perpendicular to the laser polarization and nano-scale LIPSSs parallel and perpendicular to the laser polarization. After processing of the WTi/Si system in high LRF regime ablation and nano-particles formation were registered.

This paper presents the results of a statistical and correlation analysis of the energy and energy density of an ion beam formed by a self-magnetically insulated diode with an explosive emission cathode. The experiments were carried out with the TEMP-4M accelerator operating in double-pulse mode: plasma formation occurs during the first pulse (negative polarity, 300–500 ns, 100–150 kV), and ion extraction and acceleration during the second pulse (positive polarity, 120 ns, 250–300 kV). Various arrangements of diodes have been investigated: strip focusing and planar diodes, a conical focusing diode and a spiral diode. The total ion beam energy was measured using both a calorimeter and an infrared camera and the beam energy density was measured by the thermal imaging and acoustic diagnostics. The correlation analysis showed that ion current density is only weakly dependent on the accelerating voltage and other output parameters of the accelerator, with the coefficient of determination <0.3. At the same time, in this paper, we have identified that the total energy of the beam and the energy density is strongly dependant on the accelerator output parameters, since the coefficient of determination >0.9. The mechanism governing stabilization of the beam energy density from shot to shot was discovered and attributed to formation of the neutral component in ion beam as being due to charge exchange between accelerated ions and neutral molecules from a neutral layer near the anode surface. Implementation using a self-magnetically insulated diode with an explosive-emission cathode, having an operational lifetime of up to 106 shots, has promising prospects for various technological applications.

The diode closure velocity has been investigated in pulsed high-power diodes operating with the mode of space-charge-limed bipolar flow. A combination of time-resolved electrical and optical diagnostics has been employed to study the basic phenomenon of the temporal and spatial evolutions of the diode plasmas. The results from the two diagnostics were compared. Since anode plasma rapidly expands, the diode closure speed vd increases in the end of the current pulse. The diode closure speed vd can be divided into three stages with a U-like whole shape. The obtained results can be used in various applications, for instance, the high-power microwave sources, electron-beam plasma heating, and material treating.

This paper presents an investigation of self-focusing of a q-Gaussian laser beam and its effect on harmonic generation in a preformed collisionless parabolic plasma channel. In the presence of a q-Gaussian laser beam, the carriers get redistributed from high field region to low field region on account of ponderomotive force as a result of which a transverse density gradient is produced in the channel which in turn generates plasma wave at pump frequency. Generated plasma wave interacts with the incident laser beam and generate higher harmonics of the incident laser beam. Moment theory has been used to derive differential equation for the spot size of laser beam propagating through the channel. The differential equation so obtained has been solved numerically. The effect of the intensity of laser beam, deviation of intensity distribution of laser beam along its wave front from Gaussian distribution, plasma density and depth of channel on beam width of laser beam and harmonic yield has been investigated. The effect of order of higher harmonic on harmonic yield has been also investigated.

This research reports the increased electron energy gain from laser wakefield acceleration in density-modulated plasma with an external magnetic field. Periodic plasma density- modulation can excite higher harmonics of different phase velocities of fundamental wakefield that can assist in improving the self-trapping of pre-accelerated electrons to accelerate them for higher energy. Furthermore, the applied magnetic field assisted self-injection can also contribute in electron energy enhancement during the acceleration. The physical mechanism is described with a theoretical formulation for this scheme. Results of two-dimensional particle-in-cell simulations are reported to understand the proposed idea.

The effect of laser-irradiance on the surface morphology and laser induced breakdown spectroscopy of zinc has been investigated by employing Nd:YAG laser (wavelength λ = 1064 nm, pulse duration t ~ 10 ns, and repetition rate = 10 Hz) under ambient environment of argon at a pressure of 20 Torr. For this purpose, zinc targets were exposed to various laser irradiances ranging from 13 GW/cm2 to 100 GW/cm2. Scanning electron microscope analysis has been performed to analyze the surface modification of irradiated zinc targets. Scanning electron microscope analysis revealed the formation of various kinds of structures such as ripples, cones, cavities, and wave like ridges at the center and peripheral regions of ablated zinc. In the central ablated region with increasing laser irradiance, the growth of distinct and well defined ripples is observed. Further increase in irradiance makes the appearance of these ripples diffusive and narrow. In order to correlate the plasma parameters with the surface modification, laser induced breakdown spectroscopy analysis has also been performed. The electron temperature and number density of zinc plasma have been evaluated at various laser irradiances. For both plasma parameters, an increasing trend up to a certain value of laser irradiance is observed which is due to enhanced energy deposition. Afterword a decreasing trend is achieved which is attributed to the shielding effect. With further increase in irradiance a saturation stage comes and almost no change in plasma parameters is observed. This saturation is explainable on the basis of the formation of a self-regulating regime near the target surface. A strong correlation between surface modification and plasma parameters is established.

Self-focusing of an intense circularly-polarized laser beam in a hot electron-positron-ion magneto-plasma is studied. Using a relativistic fluid model, nonlinear equation describing laser-plasma interaction in the quasi-neutral approximation is derived. Expanding nonlinear current density in terms of normalized vector potential and saving only the parabolic terms, we investigated the self-focusing phenomenon for right- and left-hand circularly polarized laser beams. The evolution of laser beam spot size with Gaussian profile is considered. Effects of the external magnetic field, fraction of electron-positron pairs, and also the kind of polarization on the self-focusing property are studied. It is shown that a mixture of electron-positron pairs to the ion-electron plasma modifies the behavior of plasma with respect to the external magnetic field.