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An efficient and robust method was developed to introduce the triazole unit of Ensitrelvir, a COVID-19 therapeutic agent. One of the key steps is introducing the triazole unit in the triazinone with Cs2CO3 and KI in a heterogeneous system. Detailed reaction screening revealed that addition of LiCl allowed the reaction to proceed quantitatively in the presence of inexpensive Et3N, and the selectivity of the N-alkylation was greatly improved. The key to promoting the reaction is the mild formation of the lithium triazinolate accompanied by precipitation of Et3N·HCl (the only insoluble matter in this reaction). Dissolving all the substrates and reagents should contribute to further improvement of the process robustness.

We describe the development of the practical manufacturing of Ensitrelvir, which was discovered as a SARS-CoV-2 antiviral candidate. Scalable synthetic methods of indazole, 1,2,4-triazole and 1,3,5-triazinone structures were established, and convergent couplings of these fragments enabled the development of a concise and efficient scale-up process to Ensitrelvir. In this process, introducing a meta-cresolyl moiety successfully enhanced the stability of intermediates. Compared to the initial route in the medicinal synthetic stage, the overall yield of the longest linear sequence (six steps) was improved by approximately 7-fold. Furthermore, nine out of the twelve isolated intermediates were crystallized directly from each reaction mixture without any extractive work-up (direct isolation). This led to an efficient and environmentally friendly manufacturing process that minimizes waste of organic solvents, reagents, and processing time. This practical process for manufacturing Ensitrelvir should contribute to protection against COVID-19.

Toward a total synthesis of acremoxanthone A, we report a model study on the construction of the EFG ring system. The key steps include (1) an intermolecular 1,3-dipolar cycloaddition of an aryl nitrile oxide with a dienone, and (2) an SNAr reaction for construction of the F ring.

This is a full account of our synthetic endeavor on the total synthesis of bis-anthraquinone antibiotic BE-43472B, an unusual octacyclic aromatic polyketide with a bis-anthraquinone scaffold. Three key steps enabled a facile access to the anthraquinone unit corresponding to the ABCF rings; (1) cyclo-condensation or -addition of benzonitrile oxides with cyclic enone derivatives, (2) benzoin cyclization for the stereoselective ring fusion with an angular hydroxy group, and (3) pinacol rearrangement for stereoselective installation of the angular aryl group. Other keys for the success include, (4) diastereoselective methylation of a lactol derivative, and (5) late-stage installation of the C3 hydroxy group through stereoselective oxirane ring formation via halohydrin derivatives. Whereas oxidation of the double bond in the enone with an adjacent 1,3-diketone moiety failed, the projected oxidation was achieved with the alkene keeping the isoxazole moiety intact as a 1,3-diketone equivalent. In the racemic total synthesis, X-ray crystal structure analysis of the target was achieved, proving the three-dimensional architecture for the first time. The asymmetric total synthesis was also achieved by exploiting a cycloadduct of the nitrile oxide and the enantiomerically pure cyclohexenone, which was convertible to the common intermediate via dehydrogenation followed by alkoxycarbonylation.

Two different directions of scale-to-scale energy transfer that corresponds to forward and inverse energy cascades, respectively, were clarified in toroidal plasma turbulence by means of experimental analysis. In the present work we first report the evidence that the turbulence dominated by broad wavenumber spectrum was developed under the action of forward (direct) energy cascade in a reversed field pinch (RFP) plasma, while the generation of GAM zonal flow (ZF) was related with the energy concentrating into low frequency region from higher frequency region due to inverse energy cascade in a tokamak plasma. The two evidences are compared. The results indicate a modulation mechanism in turbulence which is relative to the generation or development of specific turbulent flows. This hints a correlation between energy transfer and the development of toroidal plasma turbulence.

The developability of thin circular cylindrical shells of infinite length leads to the postbuckling modes described by Yoshimura for shells under axial compression. Yamaki et al. calculated and measured experimentally the postbuckling modes of a cylindrical shell of finite length under axial compression. However, they did not calculate the buckling mode of the cylinder. To clarify the entire process of mode changes during buckling and postbuckling, an axial buckling mode is calculated and drawn for the cylinder whose corresponding postbuckling modes have been investigated by Yamaki et al. The axial postbuckling modes of finite length cylinders are shown to be deployable on flat surfaces due to the developability of cylindrical shells.

O VER the past 100 years, much research has been directed at circular cylindrical shell buckling. One area of particular interest is in clarifying the reasons for the discrepancy between theoretical and experimental buckling stress of thin isotropic circular cylindrical shells, especially under axial compression. Postbuckling behavior, initial imperfections, or boundary conditions have been used to explain the discrepancy, although the main causes are now considered to be the effects of initial imperfections and their relationship to postbuckling characteristics [1,2]. The effects of boundary conditions, on the other hand, were discussed by Hoff [3], who showed that axial buckling stress calculated for the special boundary conditions is one-half of the classical value. The employed boundary conditions, however, are considered to be unrealistic [4]. Yoshimura [5] attributed postbuckling characteristics under axial compression to the developability of the initial cylindrical surface; that is, the Gauss curvature equals zero. The postbuckling mode presented by Yoshimura is a developable polyhedral surface (Fig. 1a) that is different from the chessboard-type (rectangle-type) mode andwas named the “Yoshimura pattern” byHoff et al. [6]. Key references related to the present problem are found in texts by Yamaki [7] and Singer et al. [8]. In recent years, numerous studies have focused on buckling of composite or laminated cylindrical shells. For example, Riddick and Hyer [9] employed finite element analysis for segmented circular composite cylindrical models under axial compression, ultimately showing calculated postbuckling modes. Here, it is shown that the developability of cylindrical surfaces also leads to buckling mode patterns under torsional load (Fig. 2a) and external lateral pressure (Fig. 2b). Such developability leads to buckling and postbuckling characteristics that are quite different from flat-plate problems. In other words, the developability provides the mechanics of the cylindrical shell buckling process. It is concluded that 1) Buckling and postbuckling modes under axial compression should be the same. 2) The number of waves may change during the postbuckling process. Moreover, the axial buckling modes should be similar to the modes described by Yoshimura [5], being different from the socalled chessboard pattern that has been traditionally been used in previous studies.

Time differences between medalists at Olympic or World Cup alpine ski races are often less than 0.01 s. One factor that could affect these small differences is the line taken between the numerous gates passed through while speeding down the ski slope. The determination of the ‘quickest line’ is therefore critical to winning races. In this study the quickest lines are calculated by direct optimal control theory which converts an optimal control problem into a parameter optimization problem that is solved using a nonlinear programming method. Specifically, the problem is described in terms of an objective function in which state and control variables are implicitly involved. The objective function is the time between the starting point and finishing gate, while state variables are positions of the ski-skier systems on a ski slope, rotational angles of skis, velocities, and rotational velocity at a discrete time, i.e., a node. The control variable at each node is the skier-controlled edging angle between the ski sole and snow surface. Equations of motion of the ski-skier system on a ski slope are numerically satisfied at the midpoint between neighbouring nodes, and the original problem is converted into a nonlinear programming problem with equality and inequality constraints. The problem is solved by the sequential quadratic programming method in which numerical calculations are carried out using the MATLAB Optimization Toolbox. Numerical calculations are presented to determine the quickest lines of an uphill and a downhill ski turn with a starting point, first gate, and second gate (finish line) having been successfully carried out. The quickest line through four gates could not be calculated due to numerical difficulty. Instead, the descent line was respectively calculated for an uphill and downhill turn and simply added, giving a resultant time that represents an upper bound.

According to a simplified costing algorithm for a steady-state fusion reactor power plant, the relative attractiveness of advanced physics modes mainly depends on the stability and noninductive current drive of the equilibrium. The high-stability beta and the good alignment of the equilibrium current profile with a self-induced plasma current profile are compatible with the low-aspect-ratio neoclassical Reversed-Field-Pinch equilibrium solved self-consistently considering the self-induced plasma current. The high-stability beta is due to the hollow current profile making the magnetic shear increase and the force-free field dominant. The good alignment of the current profile significantly reduces the power required for noninductive current drive to generate the steady-state magnetic field configuration. As a result, the fusion power plant based on the neoclassical RFP equilibrium with low aspect ratio enables electricity to be generated at relatively low cost.

We report that the thermal wall load due to locked modes can be decreased by means of gas puffing in the reversed-field pinch (RFP) device, TPE-RX [Y. Yagi et al.: Fus. Eng. Design 45 (1999) 409]. Under standard RFP operation in TPE-RX, the phase- and wall-locked modes, i.e., spatially localized and stationary magnetic perturbations, respectively, appear after the current-rising phase. The locked modes cause a severe thermal wall load of the order of 100 MW/m2 on the first wall. It is estimated that the temperature on the plasma-facing wall at the mode-locking position sometimes exceeds the melting temperature of stainless steel. The thermal wall load increases with plasma current, Ip. We have succeeded in mitigating the high thermal wall load by gas puffing during discharges. It is shown that the maximum temperature increment of the vacuum vessel wall is halved when a gas-puffing rate of 200 Pa m3/s is applied at Ip=350 kA. The characteristics of the temperature increase of the vacuum vessel are presented, and they indicate the nature of the locked mode in RFP discharges in TPE-RX.

A confinement database of the reversed-field pinch (RFP) devices of the toroidal pinch experiment (TPE) series has been established. The TPE database contains global confinement properties under various experimental conditions for four different devices and seven different cases, which cover two decades of experiments. Characteristics of the TPE database have been extracted under consistent experimental conditions of conventional RFP discharges, and scaling laws of the poloidal beta, ?p and energy confinement time, ? E, are given against independent parameters that include the size of the plasma and the pinch parameter ?. Scaling laws of and are obtained for a set of scans, where a is the plasma minor radius, Ip the plasma current and N the column density. The scaling of ? E on a, Ip, and I/N is similar to that dominated by the transport under tearing instability. Another scaling shows that ? E is inversely proportional to the Joule input power. The scaling for the apparent effective charge shows a positive correlation both with Ip and I/N.

The locked mode (LM), which is locked both in phase and to the wall, is successfully controlled using a rotating toroidal field (RTF) in TPE-RX (large reversed-field pinch machine with R/a = 1.72 m/0.45 m and plasma current Ip up to 480 kA) at a low Ip (~200 kA) and high filling pressure (~0.8 mTorr). It is demonstrated that the onset of the LM can be delayed or even eliminated by applying the RTF. Only the Fourier component with m=0/n=1 of the magnetic fluctuation exhibits rotation with the RTF, but other modes do not exhibit systematic movement synchronizing with the m=0/n=1 mode rotation. The phase relation between the m=0/n=1 mode and the other modes becomes random, which probably prevents the phases of the other modes from locking and results in the elimination of the LM. It is found, however, after the LM has taken place, it cannot be controlled by the RTF and hence an early start and fast rotation of the RTF are required for control. It is not possible to control the LM at a high Ip (\gtrsim250 kA), since the LM takes place from the early stage of discharge. Compared with discharges without the LM, plasma performance is degraded by the LM. The performance can be recovered by eliminating the LM with the RTF. However, the RTF itself degrades the plasma performance when applied to LM-free discharges with a RTF value comparable to that necessary for controlling the LM.

The pulsed poloidal current drive (PPCD) [J. S. Sarff et al., Phys. Rev. Lett. 72, 3670 (1994)] experiment is conducted in a reversed-field pinch device, the toroidal pinch experiment RX (TPE-RX) after providing an auxiliary power supply system with increased energy in the main power supply system for the PPCD. The PPCD system thus provides double-pulsed operation with higher current in the toroidal coil than that in single-pulsed PPCD operation in TPE-RX [Y. Yagi et al., Plasma Phys. Controlled Fusion 44, 335 (2002)]. The central electron temperature, ion temperature, and electron density increase during PPCD, and there is, on average, a fivefold improvement in energy confinement, τE, relative to standard discharges. Double-pulsed PPCD yields better performance than that of single-pulsed PPCD operation where twofold improvement in τE was obtained. It is shown that the enhancement factor of τE in the double-pulsed PPCD experiment in TPE-RX is consistent with the trends, observed previously, versus magneti...

Pulsed poloidal current drive (PPCD) (Sarff J S et al 1994 Phys. Rev. Lett. 72 3670) is conducted in a reversed-field pinch (RFP) machine, TPE-RX. The PPCD yields a twofold improvement of poloidal beta and energy confinement time. A quiescent phase is observed in the magnetic fluctuations, δb, during the PPCD. The result is discussed in terms of the change of the equilibrium configuration along the F-Θ trajectory (F and Θ are the reversal and pinch parameters, respectively). Representative mode amplitude is numerically simulated. The result indicates that a transient nature of the PPCD, where τPPCD (characteristic time of the PPCD operation) <

Resistance forces from the surface of snow acting on an alpine ski–skier system make the turning motion of the system possible. When the system has high velocity, the snow impacting force is predominant, while at low velocity, the snow cutting force plays a more important role. Using compact snow, we measure the three-dimensional compact snow cutting forces, apply multiple regression analysis to determine the empirical equations of these forces, and then use the resultant equations to simulate the turning motion of skis.

Assuming continued stability, favorable energy confinement time scaling, and an effective current drive and maintenance methods, a feasible DT fusion reactor design is proposed for field-reversed configuration (FRC) which uses normal conductive copper magnetic field coils at room temperature. The reactor has 3 GW fusion power, 1.5 MW m−2 neutron wall loading at the first wall, and thermal loading less than 1 MW m−2 at diverter plates. Plasma has an almost straight cylindrical shape of 40 m in length and 8.6 m in diameter. FRC can obtain very high beta (over 0.7 in average) and the magnetic field strength of the reactor will be 1.215 T, which can be produced by normal conductive coils having 70 m in length, 17.6 m in diameter, and 1.5 m in thickness with 0.6 effective conductive area ratio. Its Ohmic power loss is ~74 MW, which is less than 10% of the expected electric power output. A scenario to reach ignition from the initial formation is considered. At first, two FRCs are formed at the both ends of the reactor by fast theta-pinch with a negative bias magnetic field 6 m in length and 0.5 m in diameter. The FRCs are accelerated up to 250 km s−1 by the gradient of magnetic field strength towards the center of the burning region, collide with each other, and form a single large FRC. Their kinetic energy is converted to thermal energy, and the merged FRC is 10 m in length and 1.8 m in diameter. This FRC plasma is brought to ignition by intensive neutral beam injection (NBI) heating and particle supply. Given 200 s heating duration, the maximum NBI power is ~250 MW before alpha particle heating becomes significant. After ignition, NBI heating is not required, but there is a possibility that some part of equilibrium current must be supplied by the NBI in the MeV region.

One of the hypotheses for the cause of the locked mode in reversed-field pinch (RFP) plasmas is examined using a large RFP machine, TPE-RX. A hypothetical model was proposed [Phys. Plasmas 6 (1999) 3824], which speculates that the halo current in the vacuum vessel might be the cause of the locked mode. We directly measured the toroidal distribution of the vessel current and correlated it with the position and the magnitude of the locked mode. The vessel current is found to flow into the contact point of the last closed flux surface where the locked mode exists. Magnitude of the vessel current is much smaller than the level expected to form the locked mode. From these observations, we conclude that this vessel current is a result of the local shift of the plasma column due to the locked mode, and may not be the cause of the locked mode.

The plasma rotation velocities in both toroidal and poloidal directions are measured by the Doppler shift of the impurity spectral line in a new large reversed-field pinch device, TPE-RX. It is found that the magnitude of the toroidal rotation velocities varies with the plasma current. The poloidal rotation velocities are almost zero in the plasma current region studied here. The radial electric field around the plasma edge region varies with the plasma current under some assumptions. This behavior is discussed in relation to both the finite Larmor radius effect and the magnetic field line stochasticity.

The effects of field errors at the poloidal gap of the thick shell on the plasma performance and the wall-locking are intensively studied. The coil system of TPE-RX (major/minor radii, R /a = 1.72/0.45 m) has several features for cancelling the field errors at the thick shell gap and for controlling the equilibrium position of the plasma column. It is confirmed that these field error cancellation schemes work well for the normal operating conditions in TPE-RX. It is shown quantitatively that the global performance of the revised-field pinch operation is affected if the shell gap field error exceeds about 5% of the poloidal magnetic field. As expected, the probability of the mode to lock at the shell gap increases as the field error increases.

Fast magnetic fluctuation (δB) levels are measured using a newly developed complex edge probe (CEP) in the edge region of TPE-RX reversed-field pinch plasma. The CEP is installed inside a vacuum vessel and is sensitive to fast δB. The δB levels measured using the CEP are compared with those measured using an extensive magnetic measurement system (MMS), which is located outside the vacuum vessel and has little sensitivity to fast δB. The δB levels before and after the appearance of the locked mode (LM) are compared in both the CEP and MMS signals. It was found that the rapid increase in the δB signal level obtained using the MMS just after the appearance of LM is mainly caused by the slowing of plasma rotation.

The particle confinement time of boron, tau B, is studied in the TPE-1RM20 reversed field pinch plasma by means of a laser ablation technique. The experimental conditions were as follows: pinch parameter, Theta , and plasma current, Ip, are scanned, and tau B obtained from a zero dimensional approximation is compared with the energy confinement time, tau E. The results show that tau B increases almost linearly with tau E, and the implication of this is discussed in terms of energy loss channels. The increase of tau B with Theta supports the recently obtained improved confinement at high Theta . Laser ablation results are compared with the particle confinement time of deuterium, tau p, from the Dalpha line spectrum measurement. It is shown that tau b approximately= tau p, which indicates a weak mass dependence in particle transport. Numerical simulation is also conducted and compared on a one dimensional basis with the experimentally obtained spatial distribution of the line emission intensity of the boron impurity injected by the laser ablation. The result shows reasonable agreement with experiment.

Results of self-organization of the magnetic field and associating plasma loss are reviewed in the reversed field pinch (RFP) experiments on TPE machines. It is shown that the RFP plasma has a strong tendency to relax to a certain magnetic configuration similar to the energy minimum state predicted by Taylor. Thus the RFP configuration is self-organized and self-sustained with appropriate control of experimental conditions. Interestingly, however, it is observed in some cases that the relaxation can take place without the conservation of total magnetic helicity. The mechanisms of the self-organization and associated loss are discussed in some detail. In the low pinch parameter region (< 1.6), the self-organization is continuous and the main loss mechanism seems to be the electron motion along the stochastic magnetic field line caused by the overlapping of multiple modes of the magnetic fluctuations being excited simultaneously. In the high pinch parameter region, self-organization is characterized by the pulse-like relaxation (intermittent in many cases), which seems to destroy the magnetic surface in a certain position of the torus and causes rapid loss of plasma energy. Attempts to improve RFP confinement by controlling the relaxation are described. One example is the improved high-theta mode in TPE-1RM20 and another is the pulsed poloidal current drive in MST.

Discharges with improved plasma confinement in a high pinch parameter region ( Theta ~2) have been discovered in the TPE-1RMSO reversed field pinch experiment. These discharges become possible with careful control of the waveforms of the plasma current and the toroidal magnetic field after intensive discharge cleaning and are called the `Improved High Theta Mode' (IHTM). In these discharges the increase of electron density is distinct when compared with low Theta cases (~1.55). The electron temperature increases slightly with Theta but the ion temperature remains almost constant. Consequently, the poloidal beta increases, from 8% at Theta ~1.55 to 18% at Theta ~2.0, and the energy confinement time increases from 0.2 to 0.4 ms. The fluctuation level of the magnetic field corresponding to the dynamo activities is reduced by about a factor of 3 in IHTM, which may explain this improvement. Possible causes of IHTM are discussed. It is found that the m=1 mode rotates continuously during IHTM, while it always stops rotating just before a large soft X-ray emission crash occurs

A series of the detailed experiments has been conducted in three laboratory plasma devices to measure the dynamo electric field along the equilibrium field line (the {alpha} effect) arising from the correlation between the fluctuating flow velocity and magnetic field. The fluctuating flow velocity is obtained from probe measurement of the fluctuating E x B drift and electron diamagnetic drift. The three major findings are (1) the {alpha} effect accounts for the dynamo current generation, even in the time dependence through a ``sawtooth`` cycle; (2) at low collisionality the dynamo is explained primarily by the widely studied pressureless Magnetohydrodynamic (MHD) model, i.e., the fluctuating velocity is dominated by the E x B drift; (3) at high collisionality, a new ``electron diamagnetic dynamo`` is observed, in which the fluctuating velocity is dominated by the diamagnetic drift. In addition, direct measurements of the helicity flux indicate that the dynamo activity transports magnetic helicity from one part of the plasma to another, but the total helicity is roughly conserved, verifying J.B. Taylor`s conjecture.

A new, two dimensional and fast diagnostic system has been developed for studying the dynamic structure of plasma turbulence; it will be used in the edge of the reversed-field pinch devices TPE-RX and RFX. The system consists of a gas-puffing nozzle, 32 optical channels measuring H-alpha emitted from the puffed gas (to study the optical emissivity of turbulent patterns and to analyze structures in two dimensions), and an array of Langmuir probes (to compare the turbulent pattern with the optical method and to measure the local plasma parameters). The signals can be acquired at 10 Msamples/s with 2 MHz band width. The design of the system, calibrations, and tests of the electronic circuitry and the optical sensors are presented. (C) 2004 American Institute of Physics.

In this article, the measurement system for the total radiation and electron temperature profiles to be installed in a reversed-field pinch machine, toroidal pinch experiment, RX [TPE-RX, R/a=1.72/0.45 m, Ip

Zero-dimensional power balance is analyzed, and an operation boundary is deduced in a `beam-assisted reversed-field pinch`; the latter utilizes partial poloidal current drive by neutral beams so that transport losses arising from magnetohydrodynamics (MHD)-dynamo, i.e., tearing mode instability are reduced. Changes of power flow and heat conductivity due to a beam driven current are treated by considering an MHD-dynamo-based power balance model that assumes linear dependence of magnetic fluctuation level on the externally driven current. It is shown that a ratio of a beam driven current to a dynamo current must not exceed nearly 40% regarding a beta-limit in the next generation of plasma experiments (minor radius/major radius = 0.6 m/1.8 m, plasma current = 1 MA, poloidal beta = 0. 1). At that point, the energy confinement time is predicted to increase by a multiple or so of that estimated from the MHD dynamo model without a current drive. 41 refs., 12 figs., 2 tabs.

We measured the variation of magnetic and electrostatic fluctuations observed during the transition between the quasi-single helicity (QSH) and multi helicity (MH) states in the edge region of the Toroidal Pinch Experiment-Reversed eXperiment reversed-field pinch plasma [Yagi et al., Fusion Eng. Des. 45, 421 (1999)]. The high-frequency magnetic fluctuations largely decrease at the start of the QSH state. During the QSH state, the toroidal and radial magnetic fluctuations slightly increase again between 12 and 18 kHz but the decrease in the poloidal magnetic fluctuation is maintained. The confinement of fast electrons may be improved in the period of the QSH state although the radial magnetic fluctuation increases between 12 and 18 kHz. It is suggested that the improved confinement of fast electrons may be obtained by the decrease in the fast radial magnetic fluctuation having the frequency higher than 20 kHz in the period of the QSH state. Contrarily, the transition from QSH to MH states occurs with the i...

Fluctuation-induced dynamo electric fields are measured over a wide range of electron collisionality in the edge of TPE-1RM20 reversed-field pinch (RFP). In the collisionless region the magnetohydrodynamic dynamo alone can sustain the parallel current, while in the collisional region a new dynamo mechanism resulting from the fluctuations in the electron diamagnetic drift becomes dominant. A comprehensive picture of the RFP dynamo emerges by combining with earlier results from MST and REPUTE RFPs.

We measured the variation of magnetic and electrostatic fluctuations observed during the gas puffing in the edge region of the toroidal pinch experiment–reversed experiment (TPE–RX) reversed-field pinch plasma. In the short period in which the electron density increased slowly just after the gas puffing, the confinement of fast electrons in the core region was maintained by the decrease in the fast radial magnetic fluctuation with the deepening of the reversal of the toroidal field. During the following period in which the electron density increased rapidly, the radial gradient of electron density decreased, and the loss of fast electrons from the core region increased owing to the increase in the toroidal and radial magnetic fluctuations in the high-frequency band, although the poloidal magnetic fluctuation decreased. Therefore, the confinement of fast electrons would be maintained by keeping the radial gradient of plasma thermal pressure with a moderate neutral particle supply of small quantity in a sho...

Confinement properties of a reversed field pinch (RFP), TPE-1RM20, are intensively presented. Plasma current, I{sub p}, dependencies of confinement properties are particularly shown in comparison with the forerunner machine, TPE-1RM15. The results without any active density controls are presented in this paper. It is shown that both machines have almost the same, relatively high, I/N values (

The emission spectrum of deuterium atoms (D α ) was measured at the surface of a movable molybdenum limiter in the reversed field pinch machine (RFP: TPE-1RM20). The intensity of the D α line increased with the insertion depth of the limiter. The observed line profile was fitted by a combination of two Gaussian functions with different temperatures. The temperatures derived from the fitted functions were approximately 5000 K and 50 000 K. The temperatures were independent of the insertion depth. No Doppler shifted shoulder, which would correspond to neutralized reflected ions at the limiter surface, was observed in the present experiment.

Edge plasma fluctuations are studied with inserted triple Langmuir probes and magnetic coils in the TPE‐1RM20 reversed‐field pinch [Y. Yagi et al., in Plasma Physics and Controlled Nuclear Fusion Research 1992 (International Atomic Energy Agency, Vienna, 1993), Vol. 2, p. 611]. Two‐point measurements show that density and potential fluctuations have relatively low mode numbers (m

Modelling the turning motion of snow skis is simulated via a single-ski representation followed by numerically solving the associated differential equations of motion. The forces applied to the ski are assumed to be gravity, the longitudinal friction occurring between the ski and snow, and a skidding force (snow resistance force) corresponding to a system centripetal force and making curvilinear motion possible. The skidding force is calculated via a water jet analogy. Our model quantitatively shows that a ski's side-cut, i.e. its midlength taper, remarkably effects the radius of curvature of a ski trail made when skiing down a ski slope.

A new protection system for capacitor banks in the case of a short-circuiting accident is described. A pulsed power system composed of many capacitor units and closing switches is well known for producing a controlled pulse current of high power as for the power source of a plasma experimental device, etc. According to the increase of capacity of a bank system, it becomes important to protect the whole bank system from a short-circuiting accident in a capacitor unit. Although some protective ideas have been proposed, these conventional ideas have not been sufficient to absorb the energy flowing into the failure unit from other normal units. Constructing the new 1-MJ capacitor bank for a plasma experimental device, a newly conceived protective device is designed. The new protection system can absorb the bank energy and suppress the short-circuiting current flowing into the failure capacitor units, and overcomes the defect in former protection systems. To confirm the utility of a new protection system, a test of a protection resistor imitating the actual bank circuit was made. The test result showed that absorbable energy for the unit ceramic resistor amounted to 1500 Joule/cc. The new system is adopted to the bank system of the TPE-1RM15 plasma experimental device.

This paper summarizes the main achievements of the RFX fusion science program in the period between the 2008 and 2010 IAEA Fusion Energy Conferences. RFX-mod is the largest reversed field pinch in the world, equipped with a system of 192 coils for active control of MHD stability. The discovery and understanding of helical states with electron internal transport barriers and core electron temperature >1.5 keV significantly advances the perspectives of the configuration. Optimized experiments with plasma current up to 1.8 MA have been realized, confirming positive scaling. The first evidence of edge transport barriers is presented. Progress has been made also in the control of first-wall properties and of density profiles, with initial first-wall lithization experiments. Micro-turbulence mechanisms such as ion temperature gradient and micro-tearing are discussed in the framework of understanding gradient-driven transport in low magnetic chaos helical regimes. Both tearing mode and resistive wall mode active control have been optimized and experimental data have been used to benchmark numerical codes. The RFX programme also provides important results for the fusion community and in particular for tokamaks and stellarators on feedback control of MHD stability and on three-dimensional physics. On the latter topic, the result of the application of stellarator codes to describe three-dimensional reversed field pinch physics will be presented. © 2011 IAEA, Vienna.

A high poloidal beta, βp, was achieved using pulsed poloidal current drive (PPCD) in a toroidal pinch experiment-RX (TPE-RX). The plasma electron density and temperature increased, hence improving βp from 5 to 30% during PPCD. βp is almost equal to the total beta in the reversed-field pinch (RFP). D-alpha emission from recycling deuterium by the plasma-wall interaction decreased during the PPCD. An improved particle confinement time was indicated by a ten fold increase in the ratio of the total number of particles to the D-alpha emission. Single pellet injection into the good particle confinement plasma, achieved by the PPCD, produced high density plasma with high beta values. The plasma electron density rapidly increased to triple that of standard plasma, and high density was maintained till the end of the PPCD period. The electron temperature was lower than that of PPCD without ice pellet injection, but βp remained almost the same because the plasma electron density was higher with pellet injection.

Recent results of the Reversed Field Pinch (RFP) research are reviewed. Characteristics and present problematic issues of RFP are summarized and a short introduction to the theoretical bases of RFP is presented. Recent experimental status of RFP is summarized, such as long ischarge duration (>80ms), high electron temperature (-1ke V), anomalous ion heating, scaling laws, etc. Several topics are described in some detail, such as the loop voltage anomaly, equilibrium control and error field, mechanism of MHD dynamo-action and kinetic dynamo theory (high energy electron flow).