Global full-wave simulation on electromagnetic wave propagation in toroidal plasma with an external magnetic field imaging a tokamak configuration is performed in two dimensions. The temporal behavior of an electromagnetic wave launched into plasma from a wave-guiding region is obtained.

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A neutral beam injection (NBI) system employed in magnetic fusion devices is overviewed with respect to both its technological aspects and plasma heating characteristics. Since a negative-ion-based NBI system is essential for plasma heating in the fusion reactor, technical problems to be solved and physical subjects to be clarified are discussed related to the negative-NBI. The acceleration of intense negative ion beams of over 1 MeV and continuous operation of the negative ion source for over 1 year are necessary, as for the technical issues. As for the physical issues, achievment of a high ion temperature is required in high energy NBI heating with which the plasma electrons are mainly heated, as well as that of an efficient current drive in high-density plasmas.

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In ITER, neutral beam (NB) heating and current drive (H&CD) system fires energetic particle beams of 1 MeV, 33 MW (16.5 MW/NB injector) into the fusion plasma. The design allows late installation of the third NB injector for upgrade in current drive experiment toward steady state operation. The ITER NB system has been designed to fulfill the requirements of the plasma physics, considering advanced scenario achieved with off-axis CD by NB. A design overview of the ITER NB H&CD system is described. The paper also reports the recent R&D status of ion source and accelerator, as key components of the NB system, toward ITER construction. The NB H&CD performance required in future tokamak reactors is discussed together with the necessary R&D issues.

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Fast neutral beam injection (NBI) is one of the most reliable heating methods in helical systems as well as in tokamaks. Recent studies regarding the Large Helical Device have also shown that NBI has the potentials of plasma initiation by itself and control of the magnetic structure by using the induced current. From these experimental results, it is considered that NBI can be an attractive multipurpose utility of helical reactors, that is, plasma production, heating and control. A key technical issue in adopting in NBI for nuclear fusion reactors involves negative-ion-beam technology, and recent experience in operating negative-ion based NBI shows its feasibility.

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Motional Stark effect (MSE) polarimetry is described as a diagnostic system utilizing neutral beam injection. MSE systems measure magnetic field profiles and (radial) electric field profiles in plasmas. When the electric field is much smaller than the motional Stark electric field (v_b × B),an MSE system can measure the magnetic field profile, that is, the safety factor profile q(r). The design of the MSE system for the ITER (International Thermonuclear Experimental Reactor) is briefly described.

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Relativistic laser-plasma interaction is one of the more active topics in recent plasma physics. In this paper, the laser-plasma interactions in underdense plasmas are explained briefly, and the related experimental results and numerical simulations are introduced. Several characteristic phenomena, including relativistic self-focusing, nonlinear laser wake field, nonlinear parametric scattering and so on, are analyzed using a quasi-static approximation model. However, this model does not provide sufficient understanding of complex interactions including the kinetic effect. Numerical simulation is an important and effective method for further analyzing relativistic particle dynamics.

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We start reviewing the relativistic effects when ultra-intense lasers are irradiated on low-density plasmas orsolids. The strong current accompanied by laser propagation generates strong quasi-static magnetic fields, consequently confining the laser beam to form ”super-channel”. We review next the physical mechanism of production of relativistic high-energy electrons by focusing mainly on three different physical processes. Then, we proceed to explain the Weibel instability accompanied by magnetic field, when extremely high current over 100 MA by such high-energy electrons penetrates into over-dense region. The instability gets into non-linear phase in a short time to break up the beam into many filaments and these beams tend to coalescence. The coalescence proceeds to form self-organized filaments in which the high-energy electrons are collimated in the core and the return current with thin sheath surrounding the core. One such filament can carry only the Alfven limit current. Consequent critical issue on the fast ignition is also summarized.

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Significant advances in microwave and millimeter wave technology have enabled the development of a new generation of imaging diagnostics in this frequency region. Millimeter wave imaging radar is expected to be one of the most promising diagnostic methods for this purpose. It consists of a frequency-modulated continuous wave or pulsed wave as a probe beam and quasi-optical focusing optics followed by a planar-type detector array. We have started to develop a diagnostic system for the achievement of imaging radar. Representative experimental results obtained with related diagnostic systems are presented.

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Resistive wall modes (RWM) associated with ideal magnetohydrodynamic current-driven (β_N < 0.2) and pressure-driven (β_N > 2.4) kink modes with low toroidal mode number n (n = 1) have been identified in JT-60U. The pressure-driven RWM occurs at the plasma toroidal rotation of about 1% the Alfvén speed without clear continuous slowing down of the plasma toroidal rotation. Occurrence of n = 1 RWMs result in thermal quench accompanied by higher n (n ≥ 2) modes. In the case of current-driven (˜ zero β) RWMs, a thermal quench occurs only at the peripheral region just after the RWM. In contrast, a thermal quench occurs in the whole plasma region following a drastic increase in the growth rate of the RWM from the order of τ_w^-1 (τ_w is the resistive diffusion time of the wall) to larger than 10² τ_w^-1in the case of pressure-driven (high β) RWMs.

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The compatibility of reduced activation ferritic steel (F82H), which is a leading candidate material for the demo reactor (e.g. SSTR), with plasma has been investigated in the JFT-2M tokamak with 3 steps in an AMTEX (Advanced Material Tokamak EXperiment). In the first step, the reduction of fast ion losses was well demonstrated with the ferritic steel outside the vacuum vessel. In the second step, the ferritic steel was installed inside the vacuum vessel in order to perform a preliminary investigation of the effect of the ferro-magnetism on plasma stability and control, and impurity release. For this purpose, ferritic steels of 7 mm thickness were installed to form 2 sets of toroidally uniform belts, which cover 20% of the vacuum vessel. No deteriorative effects were observed regarding mode locking, plasma control, and impurity desorption. The initial boron coating was applied in order to modify the surface of the ferritic steel. The impurity is remarkably reduced and high normalized-beta plasma was obtained. Thus encouraging results were obtained for the third step, where whole vacuum vessel wall will be covered with ferritic steel.

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Irradiation tests on many diagnostic components have been carried out as a part of the R&D program of the ITER Engineering Design Activities (EDA). Five kinds of ITER round robin fibers were irradiated in JMTR and⁶⁰Co γ-rays. Induced transmission loss of those fibers are much smaller than that of pure SiO₂ core fiber. Especially, KU-H2G from Russian Federation and F-doped fibers from Japan have rather good radiation hardness even in the visible range. Those fibers might be available in the diagnostic port of ITER. The transmissivity of KU-1 quartz, which is a candidate of the window material for UV and visible spectroscopy in ITER, was measured under the irradiation of 14 MeV neutrons and γ-rays in the UV range (200 - 400 nm). Significant transmission loss was observed in the wavelength range of 200-300 nm. The Mica substrate bolometer was irradiated in JMTR during three irradiation cycles. Total neutron fluence was about 1×10²⁴ n/m² which was equivalent to 0.1 dpa. Significant increase in the meander resistance was observed, which was causedby the nuclear transmutation of gold into mercury. The use of gold meanders might be problematic in ITER.

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