Development and integration of models for the whole tokamak plasma have progressed on the basis of experimental analyses and first principle simulations. Integrated models of core, edge-pedestal and scrape-off-layer (SOL)-divertor clarified complex and autonomous features of reactor relevant plasmas. The integrated core plasma model including an anomalous transport of alpha particles by Alfven eigenmodes is developed in the core transport code TOPICS-IB and indicates the degradation of fusion performance. The integrated rotation model is developed in the advanced transport code TASK/TX and clarifies the mechanism of alpha particle-driven toroidal flow. A transport model of high-Z impurities is developed and predicts large inward pinch in a plasma rotating in the direction counter to the plasma current. TOPICS-IB is extended to include the edge-pedestal model by integrating with the stability code, simple SOL-divertor and pellet models, and clarifies the mechanism of pellet triggered ELM. The integrated SOL-divertor code SONIC is further integrated with TOPICS-IB and enables to study and design operation scenarios compatible with both the high confinement in the core and the low heat load on divertor plates.

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We develop a new Monte Carlo simulation method to calculate steady-state solutions of fluid equations for edge plasmas. To confirm the computational principle of the new method, benchmark tests including nonlinear problems in one dimensional (i.e., radial) coordinate space are attempted in the first trial; the code based on the method is called DIPS-1D. We confirm that DIPS-1D is useful for solving a Dirichlet problem and that the solution given by the present method provides sufficient numerical accuracy.

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The effect of equilibrium pressure diffusion parallel to the magnetic field on the interaction between a resistive interchange mode and a static magnetic island is studied by means of a nonlinear numerical simulation based on the reduced magnetohydrodynamics equations. Previous work for the case without the parallel diffusion of the equilibrium pressure [K. Saito et al., Phys. Plasmas 17, 062504 (2010)] showed that two solutions exist for a given error magnetic field: one indicates the increase of the island width in the nonlinear evolution of the interchange mode and the other indicates the decrease of the width. For the case with parallel diffusion of the equilibrium pressure, our present study shows that only the solution indicating the increase of the width exists; we discuss the causes for this.

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The linear growth rates of flute instability are investigated in the GAMMA10 A-divertor magnetic geometry. It is found that the minimum-B in the remaining anchor cell can stabilize the flute mode even in the GAMMA10 A-divertor which contains an axisymmetric divertor mirror cell, although the flute modes are not stabilized in case of weak magnetic well.

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Ion temperature gradient (ITG) driven turbulence is investigated by means of gyrokinetic simulations which include both kinetic ions and electrons in slab geometry with uniform equilibrium magnetic field. The study confirms that numerical results satisfy the entropy balance equation including both ions and electrons. The entropy variable is transferred from ions to electrons through the perturbation of electrostatic potential, and the transferred fluctuation is diffused by the electron collision dissipation. In the ITG turbulence with kinetic electrons ion heat diffusion is larger than that with adiabatic electrons. The former is close to the latter when the ion mass is comparable to or larger than the hydrogen one. The difference between the transport coefficients does not originate from the suppression of turbulence by zonal flow, but stems from the difference between their spectra. The lowest wavenumber mode dominates the coefficient in the adiabatic electron case, while the transport is caused not only by the the lowest mode but by higher wavenumbers in the kinetic electron cases.

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Results of one-dimensional time dependent analysis of a detachment front in a PDD plasma are reported. Effects of the cross-field particle and energy trasport in a divertor region on a partially detached plasma are particularly discussed. It was found that such transport effects in the divertor region can prevent the detachment fronts from moving upstream, and that the position of the detachment front in a steady state is thermally unstable against the neutral density in the divertor region.

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First results from nonlinear simulations of energetic particle modes and the resulting transport of energetic ions using realistic tokamak geometry are presented and compared with results obtained with a shifted-circle model equilibrium and otherwise equivalent parameters. The modes excited in both cases have similar frequencies and mode structures and cause a similar amount of energetic ion transport during the first few hundred Alfvén times of the nonlinear evolution. The similarity in transport is interesting since it stands in contrast to the reduced linear growth rate and saturation level in the non-circular case: for the parameters chosen, both are reduced by a factor of 2 compared to the circular case. These results motivate further studies, including a verification of our results with other codes, a clarification of the mechanisms underlying the linear stabilization, and a detailed analysis of the mode activity and particle redistribution during the nonlinear evolution.

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Ion temperature gradient driven drift wave instability and turbulence are investigated based on a gyrofluid slab model in the presence of a pressure gradient corrugation (PPC). It is shown that the PPC cannot only stabilize or destabilize the ITG mode through local flattening or steepening of the radial pressure gradient, but most importantly also play a stabilizing role due to the global effect of the wave-type corrugation. The latter effect dominates in the highly corrugated cases and is identified to result from a nonlocal mode coupling in radial wave-number space, which scatters the spectra from unstable modes to high dissipation region. While the local stabilization/destabilization is stronger than the global stabilization in the cases with less corrugation, the global stabilization effect dominates the highly corrugated cases. Interestingly, it is found that the global stabilization of the PPC causes ion heat intermittency, which closely connects to the zonal flow dynamics.

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Turbulent transport in the edge region of tokamak plasmas is simulated using a reduced set of magnetohydrodynamic equations. Repetitive and intermittent transport bursts driven by resistive ballooning turbulence with external heating are observed. The effect of a resonant magnetic perturbation (RMP) on turbulent heat transport is examined, where the electromagnetic response of the plasma to the RMP is solved consistently. The penetration of the RMP excites a magnetic island chain and damps the poloidal flow near the magnetic islands. The transport bursts are found to be replaced by more moderate and continuous transport. The change in the transport pattern is associated with the effect of the RMP on nonlinear coupling of fluctuations.

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The effects of anisotropic pressure on MHD equilibrium are investigated, particularly focused on the position of the magnetic axis. MHD equilibria are numerically calculated under anisotropic pressure conditions using an extension of the VMEC code which is widely applied to obtain three dimensional MHD equilibria. This code is called ANIMEC. A bi-Maxwellian model was invoked in this code in order to treat anisotropic pressure driven by energetic particles without any inconsistency. To investigate the properties of the plasma with p_∥ > p_⊥, numerical computations under various conditions are performed with a LHD magnetic configuration using the ANIMEC code. Comparisons of the plasma behavior between an analytical model that considers p_∥ and p_⊥ to be constant on each flux surface and ANIMEC numerical results will be discussed.

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The GNET code is used to study α particle confinement with energy diffusion and pitch angle scattering in helical plasmas based on the Monte Carlo technique. The dependency of the accuracy of the distribution function on the number of test particles is studied. It is found that, as the number of test particles is increased, the shape of the velocity space distribution becomes smooth and the scattering of the energy loss fraction becomes small and converges to 5.06%.

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The electron cyclotron current drive (ECCD) is studied in Heliotron J and LHD plasmas using GNET code in order to study the ECCD physics in helical configurations. The magnetic configuration dependence of ECCD is investigated in the Heliotron J plasma. It is found that the current direction is reversed in high bumpiness configuration compared with the other configurations. The ECCD in LHD is also investigated by changing electron cyclotron heating points fixing the configuration. It is found that the direction of the current reverses when we change the heating point from the ripple top to the ripple bottom.

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The operation with Internal Transport Barrier (ITB) is expected as a high performance operation. ITB is utilized to improve core plasma confinement in the reversed magnetic shear. It is considered that the changes of core plasma profile by the ITB cause changes of impurity transport. In a large fusion reactor, high-Z materials will be used as plasma facing components because high loads of heat and particles concentrate there. However, high-Z impurities from these components cause large radiation loss and dilute the fuel even if the amount of impurities is small. Therefore, in this study, firstly, the ITB formation which includes the effects of the magnetic shear and perturbed profiles by the pellet injection was simulated using the Toroidal Transport Analysis Linkage code TOTAL. Secondly, we analyzed transport of the tungsten impurities using an impurity model in TOTAL code, and compared the impurity profile in the case with ITB to the one without ITB in the tokamak reactor. The impurities decreased in the ITB formation region when ITB was formed, and the outward flux of total impurity density was observed there. It can be expected that outward flux of impurities is generated by the temperature and the density gradients.

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The radial diffusion of energetic ions is studied in the presence of high-m magnetic perturbation using DCOM code. Diffusion coefficients, D, are evaluated varying ion energy and strength of magnetic perturbation. The diffusion coefficient dependency of the magnetic perturbation strength is determined to be influenced by the ion energy. In addition, the ion energy dependence of D shows that D ∝ E^1/2 in lower energy (∼10 keV) and D ∝ E^3/2 in higher energy (>10 keV) states.

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A possible method for protecting beam ports and laser sources from alpha particles which are produced by a nuclear fusion in the fast ignition laser fusion power plant (KOYO-Fast) is proposed. Two simple dipolar magnetic fields generated by two coils installed at the tip of the beam port and at the side of the beam port are used for protecting the alpha particles coming into the inside of the beam port and colliding to the tip surface of the beam port. To calculate the behavior of alpha particles in the magnetic field, we use a 3D hybrid numerical simulation code. As a result, the intensity of 0.9 T of the magnetic flux density at the tip of the beam port is large enough for achieving the 10% reduction of the collision energy of the alpha particles to the tip surface of the beam port compared with the case without protection. Furthermore, the intensity of 1.35 T of the magnetic flux density at the center of the coil installed at the side of the beam port can guide the alpha particles coming into the inside of the beam port to the outside liquid wall perfectly.

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Collisionless shock wave generation in counter-streaming plasmas for several target materials (Al, C, Cu, and Pb) is investigated using a high-power laser system. Counter-streaming plasmas are produced by irradiating an inner surface of a double-plane target. For Al, C, and Pb, a shock wave is observed in self-emission measurements similar to the previous experiment using a CH target [Y. Kuramitsu et al., J. Phys.: Conf. Series. 24, 042008 (2010)], and the width of the transition region is much shorter than the ion-ion collision mean-free-paths. The mean-free-paths tend to be longer for heavier materials, because the ionization degrees Z are not so different among these materials.

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A typical FIREX target is assembled with a 500 µm diameter PS shell, a glass fill tube and a gold cone guide. Each part is glued together by an epoxy resin. To date, several assembled targets have been cooled down to cryogenic environment. However, they could not survive a cool down process and appeared to rupture around the glued boundary between the PS shell and cone guide. To reveal a crucial factor of the target destruction, its thermal stress after cool down was calculated using the ANSYS code. A two dimensional axisymmetric calculation model is composed of the PS shell and cone guide glued by an epoxy resin which is covered on by an epoxy fillet. A cool down process from 293 K to 10 K was simulated. The calculation showed that the rupture of the shell would start from the PS shell and gold cone guide boundary and the target validity depended on how the epoxy fillet could reinforce the PS shell.

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In the near future, the intensity of the ultra-short pulse laser will reach to 10²² W/cm² owe to the advancements of the laser technologies. The motion of the electron becomes relativism. If the electron is laid in such strong field, the effect of the “radiation reaction” is not negligible for electron motion. In general, if this motion is describe as the Lorentz-Abraham-Dirac equation, there is a “run-away” solution. A lot of researchers have tried to transform this equation for avoiding run-away. As one solution of this problem, we succeeded in the discovery of a new equation that takes the place of the Lorentz-Abraham-Dirac equation. I'll show the validity of this equation by using the simulation in this paper.

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Relativistic particle motion in a non-uniform linearly polarized high intensity laser field is analyzed by using the noncanonical Lie perturbation method, which is based on the perturbation theory of the phase space Lagrangian. By introducing the smallness parameter ε as the ratio between the excursion length l and the scale length of the laser field amplitude L, the relativistic ponderomotive force and particle motion are derived up to the second order with respect to ε, which correspond to the nonlocal extension of the conventional ponderomotive force. Specifically, the particle is found to exhibit a betatron-like oscillation with long period characterized by the curvature of the laser field amplitude.

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Tritium release in nuclear fusion power plants must be recovered as efficiently as possible in air cleanup system (ACS). In conventional ACS, the tritium gas is oxidized by catalysts, and then tritiated water vapor is collected by adsorbents, whereas which has a problem related to large ventilation force required to overcome high pressure drop in catalyst and adsorbent beds. Honeycomb-type catalyst and adsorbent offer a useful advantage in terms of their low-pressure drop, and honeycomb-type adsorbent using sepiolite-binder is feasible ability for application of ACS. In this study, we examined adsorption characteristics of water vapor on the building material, zeolitic materials using sepiolite-binder, for honeycomb-type adsorbent by changing temperature and concentration of water vapor, in comparison with those for conventional pebble-type adsorbent, and the experimental data were evaluated using Langmuir and Freundlich isotherm models. Each type of adsorbent includes mainly zeolite-4A. Adsorption capacity of zeolitic materials for both adsorbents gradually decreased with decreasing partial pressure of water or increasing temperature, and experimental data are found to fit Langmuir than Freundlich. The maximum adsorption capacity of water vapor on zeolitic material for honeycomb-type adsorbent, which was calculated by Langmuir isotherm model, is comparable to that for pebble-type adsorbent, and heat of water adsorption on zeolitic material for honeycomb-type adsorbent was higher than that for pebble-type adsorbent. These results indicate that honeycomb-type adsorbent using sepiolite-binder is applicable to ACS.

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In this study, local redeposition characteristics of hydrocarbon molecules from the ethane family are investigated using Monte Carlo simulation. Information about redeposition characteristics is required to estimate tritium retention via redeposition with chemically eroded hydrocarbon molecules. For the condition of multiple reflections at divertor surface and a plasma density of 1.0× 10¹⁹ m⁻³, the local redeposition characteristics for injection of ethane family (C₂H₂, C₂H₄, C₂H₆) have been investigated for plasma temperatures ranging from 1 to 100 eV. The number of redeposited hydrocarbon molecules increases with plasma temperature because of the increase in impinging particle energy. The increase in sheath potential results in the increase in particle energy. For plasma temperatures lower than 5 eV, there is a sudden increase in the number of redeposited particles with plasma temperature because of the increase in the number of impinging molecular ions. Sheath field acceleration is the main mechanism that causes the ions to move to the divertor plate, and the exponential increase in the number of redeposited particles results from the increase in hydrocarbon break-up products in the sheath potential region.

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We have proposed the application of a honeycomb-type adsorbent and catalyst for an advanced tritium removal system. Honeycomb-type materials exhibit a much lower pressure drop than pellet-type materials. In this study, the water vapor adsorption properties of various types of honeycomb adsorbents were evaluated using the breakthrough method at a constant flow rate of 307 cm³/min under various temperature and water vapor partial pressure conditions. The results revealed that the adsorption capacity of water vapor on the honeycomb-type zeolite increased with the water vapor partial pressure and the zeolite content of the honeycomb adsorbents. Furthermore, the honeycomb-type zeolite was found to have a higher adsorption rate than the pellet-type zeolite, and the temperature required for regeneration of the honeycomb-type zeolite was at least 450 K. From the viewpoint of practical use, the honeycomb-type adsorbent that contained 50% zeolite with 200 cells per square inch was considered to have superior adsorption properties and a lower pressure drop among a series of honeycomb-type adsorbents.

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A scheme for reducing the tritium fraction in DT fusion reactors is investigated by means of enhancing the fusion reactivity using high-power ICRF heating in heliotron reactors. We assume a situation that the density fraction of tritons is less than 10%, and the minority tritons are accelerated by ICRF waves. We then analyze the increase of fusion reactivity by assuming an effective temperature of high-energy tritons and examine the possibility of realizing a fusion reactor with this concept. The required ICRF power and the generated fusion power are also estimated.

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As an advanced option for SlimCS blanket, conceptual design study of water-cooled lithium lead (WCLL) blanket was performed. In SlimCS, the net tritium breeding ratio (TBR) supplied from WCLL blanket was not enough because the thickness of blanket in SlimCS was limited to about 0.5 m so as to allocate the conducting shell position near the plasma for high beta access and vertical stability of plasma. Therefore, the beryllium (Be) pebble bed was adopted as additional multiplier to reach a required TBR (≥ 1.05). Considering the operating temperature of blanket materials, a double pipe structure was adopted. The nuclear and thermal analysis were carried out by a nuclear-thermal-coupled code, ANIHEAT and DOHEAT so that blanket materials were appropriately arranged to satisfy the acceptable operation temperatures. The temperatures of materials were kept in appropriate range for the neutron wall load P_n = 5 MW/m². It was found that the local TBR of WCLL with Be blanket was comparable with that of solid breeder blanket.

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Negative binding energies between interstitial C (octahedral) and H (tetrahedral) in a bulk crystal of W (bcc) were obtained with the first-principle calculations, which indicate repulsive interaction in the interstitial C-H pair. The electron cloud associated to the each interstitial atom was analyzed with Bader's method. This analysis gives negative fractional charges of −0.35 and −0.37 for the interstitial C and H, respectively, supporting the repulsive interaction between them. Interstitial diffusion of C was studied including influences of ambient H atoms in the mean field approximation and the ergodic assumption. The calculated diffusion coefficients are significantly increased by the repulsive interaction with the H atoms.

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Hysteresis loss in poloidal coils of the Large Helical Device (LHD) has been measured during single-pulse operation. The superconductors of the coils are Nb-Ti cable-in-conduit conductors (CICC) cooled by forced-flow supercritical helium. The loss was measured by monitoring the enthalpy increase of the helium coolant between the inlet and outlet. Although the hysteresis loss was extracted by extrapolating several data sets from pulse excitations with different sweep rates, the extrapolated loss was much larger than the estimation using the magnetic hysteresis of the conductor. The anomalous increase in the loss is likely due to inter-strand coupling loss with long time constants from the order of 10 to 1000 s. The calculations show that the additional coupling loss behaves like a hysteresis loss.

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According to the achievements in the Large Helical Device (LHD) experiments, a design of a DEMO reactor with a LHD-type heliotron system is foreseeable. On the other hand, a DEMO is the next step reactor and high reliability and feasibility are demanded in its design. In this study, a robust design window, i.e., the design window that is not sensitive to a change in uncertain physics parameters, was surveyed through parametric scans using a system design code. It was found that a difference in main design parameters (major radius, magnetic field strength, fusion output) gives only a small change in a dependence of physics requirements on the physics conditions. Therefore, it is important to find the design window with a lower requirement on the confinement improvement to assure the design robustness. In this respect, a reduction in the minimum inboard blanket space, one of the key parameters in a LHD-type heliotron reactor design, can effectively expand the design window and contributes to the design robustness. An acceptance of higher neutron wall load and an achievement of further high confinement improvement are also expected to make both a DEMO and a commercial reactor to be more feasible and economically attractive.

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Alpha-particle slowing-down behaviors at low-temperature, high-density operation points in force-free helical reactors (FFHRs) are examined on the basis of a Fokker-Planck (FP) simulation that simultaneously consider the balance among generation, slowing down, and loss from the plasma in parallel with the density dependence of the Alfvén speed. An accurate treatment of the boundary velocity region between thermal and non-thermal components is shown to be important in evaluating the alpha particle population that can induce instability. In a typical high-density, low-temperature operation point in an FFHR, this population is reduced.

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In this work, effects of low levels of stress during aging at 823 and 973 K for 100 h on mechanical properties and microstructures were investigated for JLF-1 and CLAM steels. The results showed that hardness decreased and tensile strength increased after aging at 823 K for 100 h with stresses from 9 to 100 MPa for the both steels. The improvement of tensile properties was due to increase in number density of precipitates, especially with small size. On the contrary, hardness, tensile and creep strength decreased after aging at 973 K for 100 h, suggesting softening. The degradation of these properties was accelerated by applying stresses of 30 and 50 MPa during the aging. Decrease in number density of precipitates, partial recovery of martensitic structures and coarsening of lath width, were responsible for the degradation of mechanical properties at 973 K for 100 h and under applied stress.

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The blanket structure of the SlimCS has been studied under coolant condition of Pressurized Water Reactor (PWR) to improve the compatibility with F82 H. The neutronic and thermal calculation are performed for the simplified blanket structure, which Li₄SiO₄ pebbles or Li₂O pebbles for tritium breeding and Be₁₂Ti pebbles for neutron multiplication are mixed and these pebbles are filled in the blanket. As a result, the TBR of blanket by PWR water condition is higher than those of sub-critical water condition because the tritium breeding area in the blanket is extended by decreasing thickness of coolant tube in comparison with sub-critical water condition. The blanket with PWR water condition can attain target of the net TBR (≥ 1.05) and satisfy condition of conducting shell for MHD stability.

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A platform for an integrated design code has been developed in which the detailed analysis codes for many components of a nuclear fusion reactor are compiled and incorporated into the system analysis code. Here we have introduced the lasma equilibrium code into the integrated design code in order to optimize the poloidal coil system. This makes it possible to evaluate the capability of the flux supply for ramping up the plasma current and the controllability of an elongated plasma owing to vertical stability. We calculated the margin for vertical stability for various positions of a passive conductor.

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Neutron monitoring is quite important because neutron yield generated by fusion reactions corresponds to the fusion output. In design of the neutron monitor, Monte Carlo simulations play an important role to make corrections on various parameters, such as neutron energy spectrum and spatial distribution when determining the calibration constant. We consider the calibration procedures using a Cf point source toroidally rotating in the vacuum vessel, and evaluate uncertainties of the calibration constant for the neutron detector placed on the center axis.

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The development of functional layers such as a tritium permeation barrier and an anti-corrosion layer is the essential technology for the development of a molten salt type self cooled fusion blanket. In the present study, the characteristics of a nitriding treatment on a reduced activation ferritic steel, JLF-1 (Fe-9Cr-2W-0.1C) as the functional layer were investigated. The steel surface was nitrided by an ion nitriding treatment or a radical nitriding treatment. The nitridation characteristic of the steel surface was made clear based on the thermodynamic stability. The thermal diffusivity, the hydrogen permeability and the chemical stability in the molten salt Flinak were investigated. The results indicated that the nitriding treatment can improve the compatibility in the Flinak without the decrease of the thermal diffusivity, though there was little improvement as the hydrogen permeation barrier.

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V-4Cr-4Ti is a leading candidate material for self-cooled liquid Li blanket in a fusion reactor. The interaction between Li and the alloy is of concern, because the mechanical properties of the alloy may be influenced by the mass transfer between liquid Li and the alloy. The present study focuses on the mechanical properties of V-4Cr-4Ti alloy after exposure in static Li at 650 °C for 248 hrs. Results show that the V-4Cr-4Ti alloys are strengthened by the Li exposure. The strengthening for the alloys varies with thermomechanical treatments before exposure. The behavior seems to be corresponding to the formation of precipitates due to trapping of C and N by Ti from the liquid Li.

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An economical and environment-friendly fusion reactor system is needed for the realization of attractive power plants. Comparative system studies have been done for magnetic fusion energy (MFE) reactors, and been extended to include inertial fusion energy (IFE) reactors by Physics Engineering Cost (PEC) system code. In this study, we have evaluated both tokamak reactor (TR) and IFE reactor (IR). We clarify new scaling formulas for cost of electricity (COE) and CO₂ emission rate with respect to key design parameters. By the scaling formulas, it is clarified that the plant availability and operation year dependences are especially dominant for COE. On the other hand, the parameter dependences of CO₂ emission rate is rather weak than that of COE. This is because CO₂ emission percentage from manufacturing the fusion island is lower than COE percentage from that. Furthermore, the parameters dependences for IR are rather weak than those for TR. Because the CO₂ emission rate from manufacturing the laser system to be exchanged is very large in comparison with CO₂ emission rate from TR blanket exchanges.

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A new concept to achieve current drive with magnetic axis shift, which is caused by vertical magnetic field coil current change in LHD-type magnetic configuration, is proposed. It is confirmed numerically that an LHD-type helical fusion reactor can be ignited by high-current Joule heating. MHD stability of the plasma current in a helical system is analyzed theoretically. Large plasma current that flows in the opposite direction of the helical coil current is MHD stable. Currents with a hollow current profile are more stable than those with a flat-top profile. The central peak current profile will be redistributed to the hollow current profile. A new concept involving the current-driven and current-less hybrid operational scenario of an LHD-type helical reactor is discussed.

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Because QUEST tokamak has a divertor configuration with a higher κ and a negative n-index, a precise power supply with a rapid response is needed to control the vertical position of the plasma. A matrix converter is a direct power conversion device that uses an array of controlled bidirectional switches as the main power elements for creating a variable-output current system. This paper presents a novel three-phase to two-phase topological matrix converter as a proposed power supply that stabilizes the plasma vertical position and achieves unity input power factor. An indirect control strategy in which the matrix converter is split into a virtual rectifier stage and a virtual inverter stage is adopted. In the virtual rectifier stage, the instantaneous active power and reactive power are decoupled on the basis of system equations derived from the DQ transformation; hence, unity power factor is achieved. Space vector pulse width modulation is adopted to determine the switching time of each switch in the virtual rectifier; the output voltage of the virtual rectifier is adjusted by the virtual inverter stage to obtain the desired load current. Theoretical analyses and simulation results are provided to verify its feasibility.

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Stability and force equilibrium of toroidal helical coil with circular cross section were investigated. In this paper, we derived and calculated equations for equilibrium of toroidal helical coil based on an axisymmetric surface current model. The helical coil, which is modulated in such a way that a magnetic surface coincides with the coil surface, can reduce overturning force generated by electromagnetic forces. We analyzed the stability of the toroidally modulated helical coil and confirmed that this modulated configuration is held in equilibrium while it is unstable. This condition means the minimum inductance condition. Moreover, we formulated the relationships between electromagnetic forces and stresses acting on toroidal helical coil with circular cross section, and we compared the stress distributions calculated by the equations with those from finite element method (FEM) analysis.

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Magnetic field lines in ideal magnetohydrodynamics (MHD) are frozen into the fluid. Three-dimensional (3-D) visualization of the frozen-in magnetic field lines are useful for MHD dynamo study since it extracts stretching, twisting, and folding components of the flow. A 3-D, interactive, and immersive visualization method for the frozen-in field lines based on the virtual reality (VR) technology is proposed. A VR system with the head and hand tracking functions provides an ideal environment for the frozen-in line visualization since the seeding of the initial 3-D curve and stereoscopic observation of its motion are naturally realized in the VR space.

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We succeeded in integrating the visualization of both simulation results and experimental device data in virtual-reality (VR) space using CAVE system. Simulation results are shown using Virtual LHD software, which can show magnetic field line, particle trajectory, and isosurface of plasma pressure of the Large Helical Device (LHD) based on data from the magnetohydrodynamics equilibrium simulation. A three-dimensional mouse, or wand, determines the initial position and pitch angle of a drift particle or the starting point of a magnetic field line, interactively in the VR space. The trajectory of a particle and the stream-line of magnetic field are calculated using the Runge-Kutta-Huta integration method on the basis of the results obtained after pointing the initial condition. The LHD vessel is objectively visualized based on CAD-data. By using these results and data, the simulated LHD plasma can be interactively drawn in the objective description of the LHD experimental vessel. Through this integrated visualization, it is possible to grasp the three-dimensional relationship of the positions between the device and plasma in the VR space, opening a new path in contribution to future research.

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The anti-bacterial property of hydrogen-ion and oxygen-ion treated polytetrafluoroethylene (PTFE) materials is determined using contact angle measurements, scanning electron microscopy (SEM), and Escherichia coli (E. coli) adhesion tests. PTFE samples are irradiated using a gas discharge ion source (GDIS). Ion energies are varied by changing the plasma discharge current (I_d). Results show that both the hydrogen and oxygen plasma treatments modify the PTFE surface in morphology. Both treatments exhibited changes in the wettability of the samples at different I_d, Hydrogen treatment shows that lower I_d improved material hydrophobicity and higher I_d resulted in enhanced hydrophilicity, while oxygen treatment shows that as the I_d increases, PTFE becomes more hydrophilic. The hydrogen and the oxygen treated PTFE exhibited a reduced E. coli attachment on the samples. Oxygen treatment exhibited a lower E. coli adhesion as compared to using hydrogen.

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The dual planar magnetron (DPM) configuration features a mirror reactive magnetron sputtering system unlike that of a single planar unbalanced magnetron set-up. Optical emission signatures of a mixed species of oxygen and argon plasmas show a decrease in intensity peaks when only a single plane is biased. This manifests an oxide layer formation on the target for the single planar case thereby lowering the sputtering yield of the titanium target. No changes in emission intensity peaks are observed when the dual planes are biased. This is favorable for increasing the yield of sputtered titanium beneficial for raising the deposition rate of TiO₂ thin film. The DPM process exhibits the anatase and rutile phases of the synthesized TiO₂ films. The films are characterized by XRD, FE-SEM, reflectance and FTIR spectroscopy. Photo-reactive properties of the materials are also presented.

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Because the LHD project has been operating with the cooperation of many institutes in Japan, the remote participation facilities play an important role. Therefore, NIFS has been introducing these facilities to its remote participants. Because the authors regard Web services as essential tools for the current Internet communication, Web services for remote participation have been developed. However, because these services are dispersed among several servers in NIFS, users cannot find the required services easily. Therefore, the authors developed a portal Web server to list the existing and new Web services for the LHD experiment. The server provides services such as summary graph, plasma movie of the last plasma discharge, daily experiment logs, and daily experimental schedules. One of the most important information from these services is the summary graph. Usually, the plasma discharges of the LHD experiment are executed every three minutes. Between the discharges, the summary graph of the last plasma discharge is displayed on the front screen in the control room soon after the discharge is complete. The graph is useful in evaluating the last discharge, which is important information for determining the subsequent experiment schedule. Therefore, it is required to display the summary graph, which plots more than 10 data diagnostics, as soon as possible. On the other hand, the data-appearance time varies from one diagnostic to another. To display the graph faster, the new system retrieves the data asynchronously; several data retrieval processes work simultaneously, and the system plots the data all at once.

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To directly observe an arcjet inside the plasma discharge section, we developed an arcjet plasma device having a converging and diverging slit nozzle. Spectroscopic observations in the directions parallel and perpendicular to the plasma expansion axis were made to examine the characteristics of the arcjet plasma inside the nozzle. Intense continuum spectra due to bremsstrahlung were observed at visible and infrared wavelengths, from which the two-dimensional spatial distribution of the electron temperature was obtained. In addition, the electron density was determined by using the Stark broadening spectrum; the result indicated that high-density plasma was generated in the nozzle.

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When we design and construct a large-scale device, it is very important to confirm the interference among its parts. We might need to confirm not only the interference among the parts that are designed at the start but also the interference with some parts that are added after construction. However, sometimes even on using 3D CAD, we cannot detect the interference or the collision among parts, particularly when these parts form a complex 3D shape. On the other hand, virtual reality devices have been used in various fields such as design support systems; however, real-time collision detection among complex parts has been difficult to achieve. We constructed a system that can detect collision and interference in real time in a virtual reality system. This engine can detect interference between polygons. This enables to calculate more accurately than voxel-based detection engine. Moreover, we propose a dynamic interference vector for removing interference. This vector is defined as a local minimum vector which removes the interference from the same edge where the contact starts. This method enables to prevent an object moves discontinuously, when the interference is removed. Finally, we introduced an example of using this system for assembling parts.

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Penumbral imaging is a powerful technique for imaging with penetrating radiation such as neutrons and hard x rays. The reconstructed image can be obtained by the deconvolution of the detected image. Usually a Wiener filter is used for the reconstruction. The limitation of the Wiener filter is that it will introduce a significant distortion when the detected image contains noise. On the other hand, heuristic methods can obtain clear reconstructed image from noisy penumbral images. However, it significantly takes computation time. We proposed a new reconstruction method in the penumbral imaging to obtain clear reconstructed image by combining the multiple Wiener filters and the method can reduce computation time. The effectiveness of the proposed method has been demonstrated by computer simulation and real laser plasma experiment.

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The IR imaging video bolometer is an imaging bolometer which provides the intensity and distribution of plasma radiation. The sensitivity of the IR imaging bolometer is dependent on the properties of the bolometer foil. An evaluation of the thermal characteristics of various materials and thicknesses of the bolometer foil provides information on the sensitivity which is useful to choose the best foil material. We irradiated foils of various materials and thicknesses with a He-Ne laser (wavelength 633 nm), and measured the change in temperature distribution with an IR camera. As for foil materials, W, Ta, Au and Pt were employed. The foils were blackened either on both sides or on one side by graphite. For the same material foil, the temperature rise in the single-side blackened foil was always greater than the double-side blackened foil. For the double blacken foil, Ta had the largest temperature rise among foils with the same thickness. Pt had the shortest time constant for the temperature rise/decayamong foils except Au. In consideration of the attenuation thickness versus photon energy of each material, the Pt foil was the most suitable for the bolometer among the evaluated materials.

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This paper describes a method for the automated estimation of three-dimensional pose (position and orientation) of objects by autonomous robots, using multiple identification (ID) devices. Our goal is to estimate the object pose for assembly or maintenance tasks in a real nuclear fusion reactor system, with autonomous robots cooperating in a virtual assembly system. The method estimates the three-dimensional pose for autonomous robots. This paper discusses a method of motion generation for ID acquisition using the sensory data acquired by the measurement system attached to the robots and from the environment. Experimental results show the feasibility of the proposed method.

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The objective of the current MHD acceleration study is to thoroughly explain the compact experimental demo of MHD accelerator and to clarify some significant plasma variables both within and at the exit of the newly introduced mullite ceramic compact channel. The significant challenge of the current study is to use the 0.4-tesla neodymium magnetic as an MHD source, while the model rocket engine (C6-0, ESTES) is introduced and employed as a gas (plasma) source. The results of present demonstrations reveal that the highest gas velocity was calculated at 117.2 m/s using the gas pressure measurement through the pitot tube. The TOF method using two photo diodes showed the slowest speed of 50 m/s.

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A fast successive soft-X ray (SXR) imaging system where SXR camera and high-speed camera for the study of time evolution of magnetic islands has been constructed. A preliminary experimental result in which we observed tangential SXR images from quasi-periodic quasi-single helicity (QSH) state in low-aspect-ratio (low-A) reversed field pinch (RFP) is presented. We successfully obtained time evolution of SXR images from tangential port. By comparison obtained images with simulated images, we may conclude that the evolution of experimental SXR image suggests the rotating QSH RFP configuration. The filamentous configuration tends to be observed in QSH state rather than in multi-helicity (MH) state.

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