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By the effort to identify candidate signaling molecules important for the formation of robust circadian rhythms in the suprachiasmatic nucleus (SCN), the mammalian circadian center, here we characterize the role of α2δ proteins, synaptic molecules initially identified as an auxiliary subunit of the voltage dependent calcium channel, in circadian rhythm formation. In situ hybridization study demonstrated that type 3 α2δ gene (α2δ3) was strongly expressed in the SCN. Mice without this isoform (Cacna2d3⁻/⁻) did not maintain proper circadian locomotor activity rhythms under a constant light (LL) condition, whereas under a constant dark (DD) condition, these mice showed a similar period length and similar light-responsiveness as compared to wild type mice. Reflecting this behavioral phenotype, Cacna2d3⁻/⁻ mice showed a severely impaired Per1 expression rhythm in the SCN under LL, but not under DD. Cultured SCN slices from Per1-luc transgenic Cacna2d3⁻/⁻ mice revealed reduced synchrony of Per1-luc gene expression rhythms among SCN neurons. These findings suggest that α2δ3 is essential for synchronized cellular oscillations in the SCN and thereby contributes to enhancing the sustainability of circadian rhythms in behavior.

With respect to a particle fueling method in a spherical tokamak reactor with an advanced fuel, we investigate the availability of a merging process following the translation of a small torus plasma through which a plasma current flows in the same direction as the main plasma. A three-dimensional resistive MHD model is used to examine the particle fueling effect by reproducing the translation process and simultaneously performing an ion trajectory calculation. The simulation shows the merging process between the translated plasma and the main plasma and exhibits potential as a particle fueling method. The results of the study indicate that up to 30% of the ions in the secondary plasma are supplied to the main plasma.

Theoretical MHD analyses of the Large Helical Device (LHD) plasmas have progressed extensively. Recent results with respect to three-dimensional equilibrium, linear stability, and nonlinear dynamic...

Three-dimensional resistive MHD simulation was carried out in order to develop a method to fuel the plasma core by merging two Spherical Torus (ST) plasmas. A relatively small ST plasma was translated into the axial direction by external magnetic field control and made to collide with the larger ST. In this calculation, ballooning instability occurred in both plasmas during translation, while the magnetic surface was observed to collapse from the Poincare plot of the magnetic lines. It was observed that the magnetic lines in the core regions of the two STs were connected to each other and that the merging was completed.

An overview of conceptual design activities on the LHD-type helical reactor FFHR is presented, mainly focusing on optimization studies on the reactor size and the proposal of a long-life blanket. A major radius of around 15 m is the present candidate under the constraints of the energy confinement achieved in LHD, a maximum magnetic field around 13 T with a current density around 30 A/mm2 and a neutron wall loading around 1.5 MW/m2. R&D on super-conducting magnet systems of large scale, high field and high current-density are new challenging targets based on the LHD. The development of new design tools has been started aiming at establishing a virtual power plant (VPP) and a virtual reality system for 3D design assisting. Next design issues are mainly on engineering optimization of the first wall thickness, the detailed 3D blanket system, and unscheduled replacements of breeder blankets.

A new type of aid system for fusion reactor design, to which the virtual reality (VR) visualization and sonification techniques are applied, is developed. This system provides us with an intuitive interaction environment in the VR space between the observer and the designed objects constructed by the conventional 3D computer-aided design (CAD) system. We have applied the design aid tool to the heliotron-type fusion reactor design activity FFHR2m [A. Sagara, S. Imagawa, O. Mitarai, T. Dolan, T. Tanaka, Y. Kubota, et al., Improved structure and long -life blanket concepts for heliotron reactors, Nucl. Fusion 45 (2005) 258–263] on the virtual reality system CompleXcope [Y. Tamura, A. Kageyama, T. Sato, S. Fujiwara, H. Nakamura, Virtual reality system to visualize and auralize numerical imulation data, Comp. Phys. Comm. 142 (2001) 227–230] of the National Institute for Fusion Science, Japan, and have evaluated its performance. The tool includes the functions of transfer of the observer, translation and scaling of the objects, recording of the operations and the check of interference.

New design approaches are proposed for the LHD-type heliotron D–T demo-reactor FFHR2 to solve the key engineering issues of blanket space limitation and replacement difficulty. A major radius of over 14 m is selected to permit a blanket-shield thickness of about 1 m and to reduce the neutron wall loading and toroidal field, while achieving an acceptable cost of electricity. Two sets of optimization are successfully carried out. One is to reduce the magnetic hoop force on the helical coil support structures by adjustment of the helical winding coil pitch parameter and the poloidal coils design, which facilitates expansion of the maintenance ports. The other is a long-life blanket concept using carbon armour tiles that soften the neutron energy spectrum incident on the self-cooled flibe-reduced activation ferritic steel blanket. In this adaptation of the spectral-shifter and tritium breeder blanket (STB) concept a local tritium breeding ratio over 1.2 is feasible by optimized arrangement of the neutron multiplier Be in the carbon tiles, and the radiation shielding of the superconducting magnet coils is also significantly improved. Using constant cross sections of a helically winding shape, the 'screw coaster' concept is proposed to replace in-vessel components such as the STB armour tiles. The key R&D issues for developing the STB concept, such as radiation effects on carbon and enhanced heat transfer of Flibe, are elucidated.

A numerical modeling for the dynamics of an edge-localized mode(ELM) crash in the spherical toka- mak is proposed with a consecutive scenario which is initiated by the spontaneous growth of the ballooning mode instability by means of a three-dimensional nonlinear magnetohydrodynamic simulation. The simulation result shows a two-step relaxation process which is induced by the intermediate-n ballooning instability fol- lowed by the m/n=1/1 internal kink mode, where m and n represent the poloidal and toroidal mode numbers, re- spectively. By comparing with the experimental observations, we have found that the simulation result can re- produce several characteristic features of the so-called type-I ELM in an appropriate time scale:(1)relation to the ballooning instability, (2)intermediate-n precursors, (3)low-n structure on the crash, (4)formation and separation of the filament, and (5)considerable amount of loss of plasma. Furthermore, the model is verified by examining the effect of diamagnetic stabilization and comparing the nonlinear behavior with that of the peeling modes. The ion diamagnetic drift terms are found to stabilize some specific components linearly; nevertheless they are not so effective in the nonlinear dynamics such as the filament formation and the amount of loss. For the peeling mode case, no prominent filament structure is formed in contrast to the ballooning case.

The potential characteristics of spherical tokamak configurations with current hole are investigated from the point of view of magnetohydrodynamic (MHD) equilibrium and stability. The effect of the toroidal shear flows is also considered by using a modified Grad-Shafranov equation. Linear and nonlinear stability for low-n kink modes and intermediate-n ballooning mode is analyzed by means of numerical simulations.

In order to explore the high-beta attainability of a spherical tokamak, theoretical and simulation researches on the stability and relaxation phenomena problems were reviewed. By classifying various magnetohydrodynamic activities by the impact on the high beta stability, the problems to be solved were identified.

As the finalization of a hydrogen experiment towards the deuterium phase, the exploration of the best performance of hydrogen plasma was intensively performed in the large helical device. High ion and electron temperatures, Ti and Te, of more than 6 keV were simultaneously achieved by superimposing high-power electron cyclotron resonance heating onneutral beam injection (NBI) heated plasma. Although flattening of the ion temperature profile in the core region was observed during the discharges, one could avoid degradation by increasing the electron density. Another key parameter to present plasma performance is an averaged beta value $\left\langle \beta \right\rangle $ . The high $\left\langle \beta \right\rangle $ regime around 4% was extended to an order of magnitude lower than the earlier collisional regime. Impurity behaviour in hydrogen discharges with NBI heating was also classified with a wide range of edge plasma parameters. The existence of a no impurity accumulation regime, where the high performance plasma is maintained with high power heating >10 MW, was identified. Wide parameter scan experiments suggest that the toroidal rotation and the turbulence are the candidates for expelling impurities from the core region.

The features of the two-dimensional (2D) line-averaged electron-temperature (Te) distribution in low-aspect-ratio (low-A) reversed field pinch (RFP) plasmas are reported. We successfully obtain the time evolution of line-averaged Te images in a low-A RFP plasma with a soft X-ray (SXR) camera with two pin-holes for two-kinds of absorber foils in cojunction with a high-speed camera. Our obtained line-averaged Te is positively correlated with plasma current (Ip), and data are consistent with core and edge Te obtained by other methods. In multi helicity (MH) discharge, up-down symmetry is not changed as time goes by. On the other hand, tilting of the high temperature region is observed quasi-periodically in quasi-single helicity (QSH) discharge, with a steeper Te gradient appearing during the QSH state.

We have developed a two-dimensional (2D) electron temperature (T(e)) diagnostic system for thermal structure studies in a low-aspect-ratio reversed field pinch (RFP). The system consists of a soft x-ray (SXR) camera with two pin holes for two-kinds of absorber foils, combined with a high-speed camera. Two SXR images with almost the same viewing area are formed through different absorber foils on a single micro-channel plate (MCP). A 2D Te image can then be obtained by calculating the intensity ratio for each element of the images. We have succeeded in distinguishing T(e) image in quasi-single helicity (QSH) from that in multi-helicity (MH) RFP states, where the former is characterized by concentrated magnetic fluctuation spectrum and the latter, by broad spectrum of edge magnetic fluctuations.

Nonlinear magnetohydrodynamic (MHD) simulations are executed to investigate the dynamical behavior of the relaxation phenomenon observed in spherical tokamak (ST) plasma that is known as the Internal Reconnection Event (IRE). The simulation results successfully reproduce several key features of IRE, and the physical mechanisms are revealed. A sudden collapse of the pressure profile takes place as a result of a nonlinear time development of a pressure-driven instability. A magnetic reconnection induced between the internal and the external magnetic field is found to play a crucial role in determining the nature of the overall process, namely, the rapid expulsion of the plasma heat energy due to the pressure imbalance along the reconnected field lines, and the large distortion in the overall shape. The resultant deformations in overall shape of the plasma are in good agreement with the experimental observations.

We report here the simulation results of two colliding accelerated field-reversed configurations (FRCs). In our simulation code, we separately modeled the external magnetic field and that generated by plasma. By using a time-variable external magnetic field, we reproduced the translation of FRCs. Since the Hall effect is expected to play an important role in the magnetic reconnection research, we employed both the 2D resistive magnetohydrodynamic (MHD) model and the 2D resistive Hall-MHD model. We compare the simulation results and report on the changes in the properties of plasma.

To ensure the maintenance of tissues in mammals, cell loss must be balanced with cell production, the proliferative activity being different from tissue to tissue. In this article, the authors propose a new method for the quantification of the proliferative activity, defined as the S-phase fraction of actively cycling cells, by dual labeling with fluorescence and peroxidase immunohistochemistry using BrdU (marker of S-phase) and Ki67 antibodies (marker of G1-, S-, G2-, and M-phases) after a one-step antigen retrieval. In the generative cell zones of fundic and pyloric glandular stomachs, where the majority of cells were cycling, the authors measured a proliferative activity of 31%. In the epithelium of the forestomach and the skin, where cycling cells are intermingled with G0 and differentiated cells, proliferative activities were 21% and 13%, respectively. In the adrenal cortex, in which cycling cells were sparsely distributed, the proliferative activity reached 32%. During the regenerative process in the skin after a lesion, the proliferative activity increased in proximity to the wound. The present one-step dual-labeling method has revealed that the proliferative activity is different between tissues and depends on the physiological or pathological state.

A 66-year-old man without paticular complaints was referred to the department because of a colonic lesion revealed on a barium enema study for follow-up of a polyp of the colon. Barium enema showed a protruding lesion near the splenic flexure of the transverse colon. Colonoscopic examination confirmed the potbellied protruding lesion covered with a smooth, white, normal mucous membrane. A transverse colectomy was performed with a diagnosis of submucosal tumor of the transverse colon. The tumor was 2.0 × 1.8cm in size. Histopathologically it was non-Hodgkin lymphoma, B-cell type and follicular medium cell existed from the submucosal layer to surface of mucous membrane. It was in Stage IIA. The patient received several course of chemotherapy in another hospital after the operation, and has been followed on an ambulant basis. There have been no signs of recurrence.

Beam ion loss due to the charge exchange with deuterium atoms in the open field region of a field-reversed configuration (FRC) is investigated by tracing its orbit. The beam ion is tangentially injected as neutral beams (NBs) into the FRC. The ionization process is reproduced by the Monte-Carlo method. Almost all of the 15 keV beam ions injected toward the field null are found to be confined in the case with an external magnetic field of 0.2 T. It is found that about 90% of the NB injection power is transferred to the plasma when the neutral atom density in the open field region is lower than 1017 m-3.

Nonlinear three-dimensional magnetohydrodynamic(MHD) simulations were applied to a reversed-field pinch(RFP) plasma to reveal the physical mechanism of the formation of helical structures such as the so-called quasi-single helicity and single helical axis states. The simulations were executed using the MHD Infrastructure for Plasma Simulation (MIPS) code in a realistic experimental geometry of the REversed field pinch of Low-Aspect ratio eXperiment (RELAX) device with reconstructed initial equilibria calculated by the RELAXFit code. Long-term evolutions showed remarkable formation of n = 4 structures as a result of the dominant growth of resistive modes. The resultant relaxed helical state consists of a bean-shaped, hollow pressure profile in the poloidal cross section for both the cases of resonant and non-resonant triggering instabilities.

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.

We introduce new software for analysis of time-varying simulation data and new approach for contribution of simulation to experiment by virtual reality (VR) technology. In the new software, the objects of time-varying field are visualized in VR space and the particle trajectories in the time-varying electromagnetic field are also traced. In the new approach, both simulation results and experimental device data are simultaneously visualized in VR space. These developments enhance the study of the phenomena in plasma physics and fusion plasmas.

Dynamics of a relaxation phenomenon observed in Spherical Tokamak experiments, which is called Internal Reconnection Event (IRE), is studied by magnetohydrodynamic computer simulation. Coupling between the torus magnetic field and the external field induced by nonlinear growth of pressure driven instabilities, and resultant formation of tunnel-like plasma jet flow are found to play crucial roles in the mechanism of quick expulsion of the plasma heat energy into the external region.

Remarkable progress in the physical parameters of net-current free plasmas has been made in the Large Helical Device (LHD) since the last Fusion Energy Conference in Chengdu, 2006 (Motojima et al 2007 Nucl. Fusion 47 S668). The beta value reached 5% and a high-beta state beyond 4.5% from the diamagnetic measurement has been maintained for longer than 100 times the energy confinement time. The density and temperature regimes have also been extended. The central density has exceeded 1 × 1021 m−3 due to the formation of an internal diffusion barrier. The ion temperature has reached 5.2 keV at the density of 1.6 × 1019 m−3, which is associated with the suppression of ion heat conduction loss. Although these parameters have been obtained in separated discharges, each fusion-reactor relevant parameter has elucidated the potential of net-current free heliotron plasmas. Diversified studies in recent LHD experiments are reviewed in this paper.

Recent two major topics of Large Helical Device (LHD) towards fusion relevant conditions, high-density operation and high-ion-temperature operation, are reported. Super dense core plasma was obtained by the combination of repetitive hydrogen ice pellet injection and high power neutral beam injection (NBI) heating. A very peaked density profile with the highest central density of 1.1 × 1021 m-3 was produced showing that the particle transport was suppressed very well in the plasma core. The spatial density profile varies as the position of magnetic axis (Rax), and the steepest profile is obtained at Rax = 3.95 m. The highest central ion temperature of 5.6 keV was obtained in hydrogen plasma at electron density of 1.6 × 1019 m-3 by NBI, where a peaked ion-temperature profile with internal ion energy transport barrier was observed. The profile of electron temperature did not change much and was broad even when the ion temperature had a peaked profile. The central ion temperature is higher than the electron temperature, which is a new operation regime of LHD. High central ion temperature accompanied strong toroidal rotation and an extreme hollow profile of carbon ions (impurity hole). These steep temperature profiles were obtained so far at around Rax = 3.6 m. The compatibility between particle and energy confinement is a new issue of LHD to explore a new operation regime for attractive fusion reactor.

Nonlinear magneto-hydrodynamics (MHD) simulations are executed for a helical plasma with large pressure gradient to investigate the collapsing event that is induced by the MHD instabilities. The simulation results show that the ballooning-like instabilities with intermediate spatial scale induce both the disordering of the structures in the barrier region and the drop of the central pressure. It has been revealed that the core pressure fall is related to the disordering of the magnetic eld structure. The simulation results are compared qualitatively with the experimental observations of the collapse events in the super dense core state of the Large Helical Device (LHD). Compared with our previous simulation studies for the similar situations in the spherical tokamak (ST) plasma, the results for the helical cases show milder collapse than those in the ST case.

A new explanation regarding the toroidal spin-up of a field-reversed configuration (FRC) is provided. A physical picture showing that the poloidal flux can convert directly to kinetic angular momentum is described. Through the use of an ion orbit calculation in resistively decaying FRC plasma, toroidal rotation at both the separatrix and the field-null is found to occur.

One of the most practical objectives for the use of virtual reality (VR) systems in science is facilitating an intuitive understanding of complex physical phenomena. We developed a VR system, called Comple X cope, which can represent a 'real' three-dimensional visual and aural environment. However, communication with other researchers at a remote site (VR space) regarding simulation results is difficult, since this system is very large and is not portable. Therefore, it is important to construct a multilateral communication network system, in which researchers at any remote site are equally able to observe simulation results from any point and take initiative in controlling the display of the image in a virtual environment (VE), and in which the control is simultaneously transmitted to all of the remote sites. In the present paper, we describe a collaborative virtual environment and an example in which the simulation results are applied.

Reconnection is a transient process in essence, and causality is a key point in dealing with reconnection. The driven concept came from this viewpoint. Computer simulation is a powerful tool to understand the overall processes in a self-consistent manner. One example of global scale nonlinear processes observed in laboratory plasmas, where the driven magnetic reconnection plays important roles, is described.

It is well known that relaxation phenomena which take place in thermonuclear plasma have great influence on the confinement in not only that it is usually harmful to sustainment of configuration, but sometimes that the confinement is improved to much better state by relaxation. The Taylor's theory [J.B. Taylor, Rev. Mod. Phys. 58, 741(1986)] is one of the most successful and useful theory describing relaxation phenomena, in which the total magnetic energy is minimized under the constraint that the total magnetic helicity is conserved. However, it is not sufficient to be applied for real fusion plasma because it ignores the existence of plasma pressure. On the other hand, the achievable plasma beta value in experiments has been increasing in recent years. In particular, the spherical tokamak concept is attracting a great deal of attention because it has excellent properties in the confinement and the stability at high β, and the engineering economy. Therefore, a generalized theory on relaxation phenomena including the effect of plasma pressure is needed. In this thesis, we shall try to reveal the dynamics of pressure-driven relaxation phenomena observed in spherical tokamak plasma, which is so-called IRE (Internal Reconnection Event), by means of a numerical simulation. IRE is observed as a rapid fall in the soft X-ray signal and an increase in the net toroidal current, together with a drastic deformation in overall shape. However, the physical mechanism of IRE had not been clarified at all until this study was carried out. The simulation results are full of suggestion for both improving the confinement of spherical tokamak plasma and understanding the general nature of the pressure-driven relaxation phenomena. The simulation is based on a nonlinear three-dimensional magnetohydrodynamic equations. It is executed in a full toroidal spherical tokamak geometry including an open external magnetic field region, so that the dynamical behavior of an IRE, such as a large distortion in overall shape, can be properly treated. The spontaneous time development of tiny perturbations applied on an initial unstable equilibrium is pursued by a high-accuracy scheme. The simulation results successfully reproduce the key features of IRE in good agreement with experimental observations. The dominant linear eigenmodes for an initial condition including a q = 1 rational surface are found to be a combination of several low-n modes. Especially, the m = 2/n = 2 and the m = 1/n = 1 pressure-driven interchange modes grow simultaneously with almost the same large growth rate. As a result of the nonlinear development of such low-n modes, which induce an elliptically elongating and shifting convection flow in the poloidal cross section, a pressure bulge appears on the surface of the torus in a toroidally localized region, where the radial positive displacements of each mode are aligned to each other. The localized deformation generates a current sheet structure near the separatrix, which induces magnetic reconnection between the internal and external magnetic fields. The reconnected field line links the core region at high pressure and the peripheral region at low pressure, so that a large pressure gradient is formed along the reconnected field line. The confined plasma is rapidly expelled out of the torus due to the flows induced by the pressure gradient. The expelled plasma extends in the periphery, forming a characteristic helically twisted conical layers at the top and the bottom of the torus, which is in good agreement with experimental results observed by using a CCD camera. On the other hand, the plasma pressure at the center of the torus falls into about 40% of that at the initial state in a short time scale of several tens of Alfven transit time, which also agrees well with experiments. After releasing a part of heat energy out of the separatrix, the system is once stabilized with respect to ideal modes. However, another kind of an instability, which has a nature of a resistive mode, is excited. This instability includes an m = 2/n = 1 component dominantly, and can be destructive compared to the original ideal modes. Due to the growth of this insta- bility, the overall shape of the torus is largely distorted, which agrees with experimental observations, such as the tilting and the axis-asymmetric elongation of the torus. More detailed analyses of the simulation results show several interesting dynamics on pressure-driven relaxation phenomena, such as an almost parallel magnetic reconnec- tion, formation of a tunnel-like convective loss channel due to the magnetic reconnection between the internal and the external fields, and spontaneous phase alignment among multiple modes on weakly nonlinear development of pressure-driven instability.