Mitsumori Tanimoto

Demonstration of quasi-monoenergetic electron-beam generation in laser-driven plasma acceleration

The generation of a quasi-monoenergetic electron beam in laser-driven plasma acceleration is reported. A monoenergetic electron beam with an energy of 7 MeV was emitted from a high-density plasma (electron density >1020cm−3) produced by a 2 TW 50 fs laser pulse. The divergence of the monoenergetic beam was ±1.2°. The first Stokes satellite peak of stimulated forward Raman scattering was observed in the spectrum of the light transmitted through the plasma. The plasma wave was excited in the region of which electron density was around 1.3×1020cm−3. The acceleration length was estimated to be 500μm from the length of the side-scattered light image. It is considered that the monoenergetic beam generation is due to the matching of the acceleration length to the dephasing length determined by the velocity difference between the accelerated electrons and the plasma wave.

Removal processes of nitric oxide along positive streamers observed by laser-induced fluorescence imaging spectroscopy

Abstract Removal processes of nitric oxide (NO) in pulsed corona discharges were observed by laser-induced fluorescence (LIF) imaging spectroscopy in a reactor filled with N 2 /NO mixtures. Distributions of NO along the streamers and effective energy costs of NO removal ( e rem ) obtained from the LIF images were compared with those predicted by a model taking account of the diffusion. For an initial NO concentration [NO] 0 of 1000 ppm e rem was 120±31 eV/molecule, while it was increased up to 620±160 eV/molecule for [NO] 0 of 30 ppm, due to a higher recombination loss of the reducing species of the nitrogen atoms.

Energy scaling of monoenergetic electron beams generated by the laser-driven plasma based accelerator

Monoenergetic electron beams were generated in the self-modulated laser wakefield acceleration regime using a 2–6TW, 50fs Ti:sapphire laser system. The monoenergetic electron beams of energies up to 15MeV and 30MeV, with a plasma density around 1.5×1020cm−3 and 3.5×1019cm−3, respectively, were observed. The monoenergetic energy was found to be inversely proportional to the plasma density. The monoenergetic electron beam was generated at only specific plasma densities for each experimental condition. The plasma density dependence of the electron energy spectrum, the forward scattered light spectrum, and the side scattered light image of the laser pulse was studied in detail. The conditions for monoenergetic electron beam generation are discussed based on the results of the plasma diagnostics.

Development of a high-power KrF laser system, ASHURA

The present status of the development of a high-power KrF laser system, Ashura, is described. The main amplifier has generated 710 J (95 ns) at the pumping density of 1·lMW/cm 3 with the wall plug efficiency of 2·0%. Maximum power of 9·0 GW (200 J/22 ns) per beam has been obtained from the beam lines of six-time pulse multiplexing. Power density of 1 × 10 14 W/cm 2 has been achieved on target with a 10 −6 pre-pulse.

The stability of multiply charged vanadium, niobium and tantalum clusters

Abstract We have studied the stability of multiply charged vanadium, niobium and tantalum clusters with charges up to z =4. Although the multiply charged clusters are less stable compared with the predictions of the symmetric liquid droplet models, the experimental results can be explained well by an asymmetric fission model assuming an emission of an atomic ion.

Efficient High Power-Density Operation Regime of KrF * -Laser Amplifiers for Fusion Driver

The kinetics in electron-beam-excited KrF*-medium is numerically analysed in order to study the dependence of the fundamental laser characteristics on gas constitution, specific pump power and cavity flux. There appears the prospect of the compact fusion driver operating at considerably higher laser intensity (~100 MW/cm2) and higher intrinsic efficiency (~20%) in Kr-rich media at the pump power density of 10 MW/cm3 than in conventional Ar-diluted mixtures.

A new efficient solution method for a system of linear equations: Partially Solving Method (PSM)

We present a new method of solving a system of linear equations, called Partially Solving Method (PSM). The PSM can essentially deal with only a subsystem at each processing stage without complete knowledge of the entire system. For dense systems, it reduces the necessary memory space effectively by a factor of four as compared with the conventional LU-decomposition method. For sparse systems, the method operates up to, twice as fast as Gaussian elimination method, and the efficiency in both space and time is further enhanced by a proper ordering of selections of the equations. It may be feasible to apply the PSM in a parallel processing environment, when the entire system is divided into subsystems.

Resistive Ion-Acceleration in a Plasma Focus

It is shown that there appears a strong resistive electric field in plasma focus discharges due to the effect of the self-magnetic-field insulation. This field, much more prevalent than an inductive one, can accelerate ions up to a directed energy of the order of MeV. A simple scaling is given for peak ion-energy and compared with recent experimental results.

Development of a 1-kJ KrF laser system for laser fusion research

A l-kj KrF laser system under development is described. The system has an oscillator, three electron-beam (e-beam) amplifiers, and a Raman pulse compression system. The second stage e-beam amplifier has generated 170 J at the overall efficiency of 1.9%. The final stage amplifier is designed to deliver a 1-kJ optical output in 100 ns.

Development of a Compact Time-of-Flight Mass Spectrometer with a Length of 1 m for Processing Plasma Diagnostics

It is desired that mass spectrometers should be compact and cost effective for use as diagnostic or monitoring tools. We examine the factors which restrict the optimum value of mass resolution attainable for time-of-flight mass spectrometers (TOF-MSs) of compact size. We have developed a 1 m long TOF-MS to diagnose plasma processes. As basic specifications, we obtained a wide mass range of over 20,000 u/e as well as a high mass resolution of up to 2,500. We succeeded in observing various kinds of positive and negative ionic polysilane molecules in addition to the neutrals in a demonstrative diagnosis of the typical silane plasmas relevant to the deposition of the hydrogenated amorphous-silicon thin-film solar cells. This diagnostic system may be a versatile and powerful tool to investigate the detailed reaction processes in various processing plasmas for thin-film deposition and surface treatment.