The nonlinear evolution of dust acoustic wave in magnetized dusty plasma was shown to obey the Davey-Stewartson I equation, which admits the so called dromion solutions.

Fusion performance of reversed shear discharges with an L-mode edge has been significantly improved in a thermonuclear dominant regime with up to 2.8 MA of plasma current in the JT-60U tokamak. The core plasma energy is efficiently confined due to the existence of persistent internal transport barriers formed for both ions and electrons at a large minor radius of r͞a ϳ 0.7 near the boundary of the reversed shear region. In an assumed deuterium-tritium fuel, the peak fusion amplification factor defined for transient conditions involving the dW ͞dt term would be in excess of unity. [S0031-9007(97)04592-4] PACS numbers: 52.55.Fa, 52.55.PiThe reversed shear discharges are considered attractive for a steady state operation with a large bootstrap current fraction in tokamak reactors as proposed for SSTR [1] and ITER [2], since it would be possible to match the hollow current profile to a bootstrap current profile in a steady state. While the central magnetic shear in tokamak plasmas is naturally reversed during a sufficiently long discharge duration with a large bootstrap current fraction [3], the forced shear reversal operation by enhancing a skin current effect has become important for establishing a controlled approach to the steady state [4].In nuclear fusion research, critical conditions in which fusion power produced in plasmas is equal to loss power from the plasmas have been pursued as a crucial milestone ultimately towards the commercial use of thermonuclear fusion energy. In order to determine whether the reversed shear scenario is workable, it is crucially important to demonstrate the fusion-relevant performance, particularly in the thermonuclear fusion regime with the shear reversal operation. So far, however, most of the previous experiments addressing high fusion reactivity in tokamaks have been limited to a hot-ion regime with substantial beam-thermal reactions for deuterium plasmas in TFTR supershot [5], JET hot-ion H mode [6] and JT-60U high-b p H mode [7], and deuterium-tritium (D-T) plasmas in TFTR supershot [8]. Although fusion performance has been recently enhanced with strong profile and shaping control in deuterium reversed shear plasmas with an H-mode edge in DIII-D [9], the projected D-T fusion power is substantially below the loss power from the plasma. In the present paper, it is shown that fusion performance has been significantly improved in JT-60U for reversed shear discharges with an L-mode edge in a thermonuclear fusion regime, so that the transient fusion amplification factor defined as below would be in excess of unity.In JT-60U, the experimental campaign of the reversed shear discharges aiming at high fusion amplification factor ͑Q͒ has been intensively performed with D beams into D plasmas. The confinement properties for the reversed shear discharges created in JT-60U are characterized by (i) the significant reduction of heat and particle transport for electrons as well as ions around the internal transport barrier (ITB), (ii) a large extension of the enhanced confinement region up...

Soliton formation in plasma is addressed. Nonlinear acoustic waves in plasma where the combined effects of bounded spherical geometry and the transverse perturbation are dealt with, in two-temperature electron plasma are studied. Using the perturbation method, a spherical KadomtsevPetviashvili equation (SKP) that describes the ion acoustic waves is derived. The plasma is modeled by a kappa distribution function for both electrons components as found in Saturn's magnetosphere. It is found that parameters taken into account have significant effects on the properties of nonlinear waves. The model is applied to Saturn's magnetosphere, where two temperature superthermal electrons are present. Hence, ion acoustic waves are deduced for three regions, namely, the inner, the intermediate and the outer Saturn's magnetosphere. We point out, that this work has been motivated by recent observations of Saturn's magnetosphere.

In this work, the nonlinear evolution of dust acoustic wave in magnetized dust-ion plasma was investigated. The two component dusty plasma considered is valid as long as n e0 << Z d n d0 . We adopted reductive perturbation technique (RPT) to study the nonlinear evolution of these DAWs in two dimensions. It is shown that the governing equation for the two fluid systems is governed by the Davey-Stewartson I equation (DS) and may admit dromion solution . These solutions were illustrated for different cases (viz., Saturn's F ring, the tail of Halley's comet and laboratory). The amplitude and width of each dromion were also given.

Emphases in recent JT-60 experiments are placed on 1)lower-hybrid (LH) current drive characteristics with a multi-junction type launcher and 2 ) the confinement study with combination of neutral beam injection, LH current drive and pellet injection. The new multi-junction LH launcher provides a 2 . 7 x 1 0 1 9 m -3 and Ip=1-1.7 MA.Volt-sec saving of -2volt-sec was demonstrated by 2 sec long, 1.6MW LHCD during the plasma current ramp of 0.4MA/s.A broad radial distribution of high energy electron current and -30% reduction in sawtooth inversion radius were obtained by high N I I (-2.5) LH injection. In order to fully suppress the sawtooth activity, low NII (-1.3) injection was found to be more effective, in which up to 1.8 sec sawtooth-free phase was obtained by 2MW LHCD for lOMW NB heating of Ip=I.SMA discharge, Improved energy confinement has been obtained with hydrogen pellet injection. Energy confinement time was enhanced up to 40% relative to usual gas fuelled discharges. The discharge has a strongly peaked electron density profile with ne(O)/-5 and n e ( 0 ) -2 . 0 ~ 1020,-3,The improved discharges are characterized by a strongly peaked pressure profile within the q=l magnetic surface, and degrades when a large sawtooth recovers or the pressure gradient may reach a critical value. When large (3mm,4mm) and fast (2.2km/s) pellets were injected, 30% energy confinement improvement was obtained even during the NB heating of 14MW. Further investigations of IDC characteristics have been made.The oxygen impurity lines from the main plasma and the main radiative loss drop first. Then the plasma stored energy starts to rise. The particle recycling is reduced around the main plasma, and is localized in the neighborhood of the X-point with a time lag of -0.2 sec. Eventually the discharge shows a significant remote radiative cooling power at the divertor region. Most of the IDC characteristics is totally different from that of H-mode, although there are some similarities i.e., gas puff degrades the confinement, both have the same favorable BT direction.

Plasma expansion and soliton formation in laser created plasma are addressed. Nonlinear acoustic waves in plasma where the combined effect of trapped and non-thermal electrons are dealt with, in plasma expansion are studied. Using the perturbation method, a modified Korteweg–de Vries equation (mKdV) that describes how the ion acoustic waves (IAW) are derived. The plasma is modeled by a Cairns distribution function for non-thermal electrons combined with Gurevich distribution function for the trapped electrons. It is found that parameters taken into account have significant effects on the properties of nonlinear waves as well as on plasma expansion into vacuum. We point out, that this work has been motivated by space and laboratory plasma observations of plasmas containing energetic particles, combined with trapped particles. Furthermore, this study is of interest in the context of the investigation of mono-energetic ion beams from intense laser interactions with plasmas.

Recent lower hybrid current drive(LHCD), and heating(LHH) experiments on JT-60 are reported. The current drive product of KeRpI~p -12.5~10~~m-*MA was achieved at the LH power of -4.5MW, and the CD efficiency, the energy confinement, the global power balance and the heat load on divertor plates were investigated in high power LHCD plasmas. Nearly steady state H-mode discharges were found during LHCD with two different frequency injections. Sawtooth suppression in NB heated plasmas by LHCD have shown an improvement in confinement near the plasma center. Parametric instabilities in LH heating experiments were significantly reduced by increasing the plasma current, and the stored energy increased linearly with heating power of up to -9MW at iTe -7 ~1 0 ? ~m -~ and Ip = 2.75MA. Parametric instabilities near the plasma edge in the ion heating regime were also reduced in peaked density plasmas produced by pellet injection, and LH waves increased the central plasma pressure at n,(O) > 1.4 x 1020m-3.

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