We observed and directly measured the M1 transition between the two states of the fine structure splitting in the ground state of Ba⁷⁺ with a visible spectrometer coupled to a compact electron beam ion trap. To validate the measurement accuracy, we demonstrated a calibration method using Ar⁺ emissions from buffer gas. The wavenumber in vacuum was determined to be 23591.57 (15) cm⁻¹.

Methods for controlling accurately the diameter d_e of a pure electron plasma in a nested trap of the BX-U machine are described. By controlling the acceleration voltages and the number of electron guns activated, we can successfully change d_e over the range between 0.28 and 2.27 cm. Therefore, d_e can be made almost exactly the same as the diameter of a lithium ion plasma enabling the investigation of a two-fluid plasma state by using non-neutral plasmas.

In this study, a new single-shot method is developed for obtaining the parallel energy spectra of pure electron plasmas that rotate around the machine axis by the E × B drift. When the confinement voltage is raised to the ground level on a timescale that is comparable with the E × B rotation period, the electrons escape from the confinement region along the magnetic field lines over the potential barrier and onto a phosphor screen in the descending order of the energy of the electrons. This causes the phosphors to emit light at different points on the screen along the E × B rotation trajectory depending on the electron's energies. Further, the energy distribution can be derived from the luminosity distribution along this trajectory by appropriately converting these positions into their corresponding energy levels.

Axial neutral gas transport has been experimentally investigated in a partially ionized cylindrical plasma. The high-accuracy laser induced fluorescence spectroscopy is embraced to evaluate the absolute flow velocity of ions and neutral particles, and the axial flow velocity associated with the mass transport parallel to the magnetic field has been measured by changing the filling gas pressure. It has been found that the neutral gas flow is spatially non-uniform, and the axial flow reversal takes place under a certain circumstance. The experimental results indicate that non-uniformity of neutral gas flow field is generated as a consequence of the plasma-neutral coupling and the axial neutral transport plays an important role in the plasma structure formation.

A frequency comb sweep microwave reflectometer is developed in PANTA to realize multi-point electron density measurements with high temporal resolution. A radial profile of the electron density is successfully reconstructed from simultaneous 17-point measurements with 2-µs temporal resolution. This result demonstrates the reliability and feasibility of the system for electron density profile diagnostics.

A high dispersion and high time-resolution spectrometer equipped with two slits in output ports is developed to observe variation of Doppler broadening in the high-temperature bubbles [K. Terasaka, et. al., Phys. Plasmas 25, 052113 (2018)]. Reduction of Doppler broadening in a line spectrum of helium ion is experimentally observed when the bubbles emerge in the viewing chord of spectrometer. The results suggest possibilities of ion temperature reduction during the high-temperature bubbles.

We have developed a tomographic reconstruction method using a conditional Generative Adversarial Network to obtain local-intensity profiles from imaging-diagnostic data. To train the network we prepared pairs of local-emissivity and line-integrated images that simulate the experimental system. After validating the accuracy of the trained network, we used it to reconstruct a local image from a measured line-integrated image. We applied this procedure to the He II-emission imaging diagnostic for RT-1 magnetospheric plasmas, including the effects of stray light within the measured image to remove reflections from the chamber walls in the reconstruction. The local intensity profiles we obtain clearly elucidate the effect of ion-cyclotron-resonance heating. This method is a powerful tool for systems where it is difficult to solve the inversion problem due to the involved contributions of nonlocal optical effects or measurement restrictions.

Feasibility of an ion sensitive probe was evaluated in high electron density (> 5 × 10¹⁹ m⁻³) helium plasmas produced in the Magnum-PSI device. The ion sensitive probe showed that the ion temperature was ∼ 1 eV and almost equal to the electron temperature. Increasing the neutral pressure to efficiently lead to the electron-ion recombination processes, the electron currents were collected at the ion collector. A secondary electron emission in the guard electrode might have an effect on the ion current.

A study of the resonant magnetic perturbation (RMP) effect on transit beam ion behavior is performed using the total neutron emission rate (S_n) measurement of the deuterium plasma in the Large Helical Device. We conducted no RMP field, one-half RMP field, and full RMP field discharges and compared S_n that reflects the global beam ion confinement information. It is determined that owing to the RMP field, S_n decreased by approximately 15 - 30%. Numerical calculations based on the classical confinement of beam ions were performed to investigate the bulk plasma parameter effect on S_n. The calculated S_n shows that the degradation of S_n by RMP is mainly caused by the degradation of the electron temperature owing to island formation which results in a shorter slowing down time of beam ions.

Using a hybrid simulation code, we studied the application of low-frequency wave to a field-reversed configuration plasma. The wave application antenna was arranged to sandwich the separatrix, and the antenna current was varied sinusoidally with a maximum of 30 kA and a frequency of 80 kHz. The simulation revealed that when the ion pressure is regarded as a tensor, the parallel ion temperature estimated from the axial velocity distribution near the midplane exceeds the perpendicular temperature. That is, the plasma ions respond anisotropically to a low-frequency wave.

An ingenious model for large-scale electromagnetic (EM) plasma simulations is proposed. By introducing a dielectric tensor ε with enlarged permittivity elements ε_∗ » ε₀ to Poisson equation, ∇· (ε∇φ) = −ρ (ε₀ is the permittivity of free space, φ is electrostatic potential and ρ is charge density), the Debye length is artificially elongated and the large-scale system can be numerically treated even for including the self-consistent electron dynamics [T. Takizuka et al., Plasma Fusion Res.13, 1203088 (2018)]. In cylindrical coordinates (R, θ, Z) for three-dimensional tokamak simulations, a toroidal element ε_θθ is chosen much larger than poloidal elements ε_RR = ε_ZZ = ε_∗, and a toroidal mesh size Δ_θ can be set much larger than poloidal mesh sizes Δ_R,Z. Resultantly the total mesh number becomes reasonably small and computation cost can be reduced. EM responses are also simulated using a modified Darwin model for Ampere's law, ∇² A = −μ₀(J − ε∂∇φ/∂t)(A is magnetic vector potential, J is current density, and μ₀ is the permeability of free space), where light-speed EM waves are neglected. This modification is consistent with the charge-density continuity.

High field side (HFS) injection of eXtra-ordinary X-mode for electron Bernstein wave (EBW) conversion was conducted in the QUEST tokamak. Radio frequency (RF; 8.2 GHz) power was delivered from the low field side (LFS) to the high field side HFS through waveguides, and from the HFS placed 20 cm above the mid-plane of the vacuum vessel. The aim was to compare the RF launches from the LFS and HFS. The plasma brightness, measured by a fast camera, as well as the H_α signal captured along the mid-plane, was noticeably higher in the HFS launch than in the LFS launch. The HFS injection achieved a plasma current of approximately 130 A, versus 35 A in the LFS injection. The electron density n_e predicted from the position of the upper hybrid resonance agreed with the line-averaged n_e measured by an interferometer, confirming the effective conversion and subsequent damping of the EBW mode. The RF leakage of the HFS injection was less than one-sixth that of the LFS injection. These results indicate that HFS delivers better RF coupling and conversion efficiency to EBW than LFS injection. Such efficient plasma heating via EBW will significantly enhance the plasma production.

This study aims to develop a novel flat oxygen plasma source containing a magnetic filter. The aspect ratio of the diameter to the length of the source vessel was approximately four. A pair of small permanent magnets was inserted in a metal flange to generate the magnetic filter at the exit hole of the plasma source. Measured current-voltage characteristics indicated that a clear decrease in the electron temperature was successfully attained across the magnetic filter, which was adequate for producing negative oxygen ions via dissociative electron attachment.

A large diameter plasma window was developed for accelerator applications. In this study, a pressure separation using the plasma window was demonstrated, and the maximum diameter of the plasma window reached up to 20 mm. The prediction formula based on the viscous flow for confinement pressure cannot be applied in the case of large diameters due to low input power density to the plasma.

Axial and radial momentum fluxes near a lateral wall in a helicon plasma source are preliminarily investigated by installing a momentum vector measurement instrument, which has a detector plate mounted on a double-pendulum structure movable in both the axial and radial directions. The result demonstrates the presence of the axial momentum flux transferred to the radial wall, which seems to be delivered by the ions having the axial velocity and lost to the wall. Furthermore, a significantly greater radial momentum flux is lost to the radial wall, implying that the energy loss occurs at the radial wall. The presently shown technique would be useful for identifying the spatial profile of the momentum vector of the plasma.

Reconstruction of turbulence time series in a statistically stationary state is discussed by using a machine learning algorithm. We use data obtained by Langmuir probes in the Plasma Assembly for Nonlinear Turbulence Analysis (PANTA). It is shown that even if the distance between two probes is not adequate to resolve the turbulence, the nonlinear regression via the machine learning can give reconstruction better than those by the linear regression and the linear interpolation. Wave forms and frequency spectra show that drift waves are well reconstructed by the machine learning.

The practicability of a statistically induced thermal transport model (fit to the database) by exploiting transport analyses database accumulated by TASK3D-a (integrated transport analysis suite for LHD plasmas) is examined. The promising results, such as reproduction of measured ion temperature profiles and observed tendency, have been obtained through a systematic comparison against LHD plasmas. It encourages to further pursue a statistical approach for transport modelling of fusion plasmas.

A cost model for a tokamak fusion power plant (FPP) is improved to evaluate material cost and manufacture cost, separately. Then, the improved cost model is applied to a commercial tokamak FPP, and reduction of FPP construction cost is investigated considering learning effect on manufacture of the fusion island part and the advanced manufacture of toroidal field (TF) coils. Finally, a development scenario of a tokamak FPP is proposed to contribute substantially to global climate stabilization under the framework of the Paris Agreement.

Multi-channel scanning filter spectrometer with narrow band pass of 2 nm is installed in Large Helical Device (LHD) for Beam Emission Spectroscopy (BES) using hydrogen (H) and deuterium beam (D). The spectral shape of transmitted light (half width at half maximum, skewness and kurtosis) is measured using the monitor grating spectrometer coupled with the filter spectrometer. No distortion of the spectrum shape is observed in the wavelength scan range of 8 nm required for the Doppler shift of the BES emission from H-beam and D-beam.

The latest measurement of the absorbed dose rate in air was performed at the National Institute for Fusion Science (NIFS) site during the period for the first deuterium plasma experiment conducted in Large Helical Device (LHD). The arithmetic mean of the absorbed dose rates in air for 222 measurement points at the NIFS site was 43 nGy h⁻¹. Very little change was observed in the distribution maps of the absorbed dose rates in air before and after the deuterium experiment in the LHD. In addition, the absorbed dose rates in air around the buildings were distributed at similar high levels before and after the deuterium experiment. A radionuclide analysis of soil and broken stone was conducted using a high-purity Ge semiconductor detector. The absorbed dose rates in air at the NIFS site were mainly defined by the radiation from the ground and the building material around the measurement points. The effect of the deuterium experiment was so small that it was undetectable in this study.

It is important in divertor physics research to investigate thermal response process of beryllium deposited tungsten to high transient heat load such as ELMs. We investigated the heat load on aluminum-coated tungsten by comparing the measured back surface temperature and calculation results of the one-dimensional heat conduction equation. When the plasma power was low enough so that the evaporation did not occur sufficiently, the heat load on the aluminum-coated tungsten was higher than the virgin tungsten. It was caused by the reduction in the energy reflection coefficient due to the formation of aluminum layer. The results suggested that the beryllium deposited layer adversely affects the heat load on the divertor plate when the heat load was not high such as Grassy-ELM.

Numerical analyses using a gyro-fluid model have been performed to investigate the finite-Larmor-radius (FLR) effect on ion-temperature-gradient (ITG) instability in cylindrical plasmas. A spectrum code with Fourier-Bessel expansion has been developed for the analysis of global mode structures. The analytical expression of the η (ratio between the density and temperature gradient lengths) threshold value for linear ITG instability has been obtained from the local dispersion relation, whose dependency on the ion temperature comes from the FLR effect. Dependency of the threshold by the global analysis is reproduced by the local analysis with appropriate selection of the perpendicular wavenumber. Break of the Boltzmann relation by the FLR effect is not strong as to generate another unstable branch of the ITG mode.

It is demonstrated that the zonal flow is controlled by the parallel flow in the cylindrical plasmas. A three-dimensional turbulence simulation is performed, based on the reduced fluid model. The background parallel flow is applied by introducing the time independent parallel momentum source. Changing the magnitude of the momentum source, the behavior of the zonal flow is investigated. The drift wave turbulence is affected by the parallel flow, and it shows the spatial competition between turbulence modes. The spatial competition appears/disappears abruptly, depending on the intensity of the parallel momentum source. As a consequence of the transition between the turbulence state, the radial profile of the turbulence drastically changes, which leads to the change of the turbulence force to drive the zonal flow. In this way, the parallel flow indirectly affects the zonal flow through the deformation of the turbulence.

The stray light is a major problem in Thomson scattering (TS) measurements. The main cause of stray light is unnecessary divergence of the incident laser beam and an aperture is a standard component to reduce it. In order to improve the aperture configuration (including size, number and position in the laser injection tube), a peripheral beam profile monitor, consisting of a screen with a through hole for the laser beam and a CMOS camera, was developed. Instead of the actual laser injection tube a mock-up tube was used to measure the peripheral beam profiles under various aperture configurations. The configuration with four 15mm diameter apertures was chosen and installed on the TS system for the TST-2 spherical tokamak. The stray light was reduced to about 4% compared to the smaller diameter injection tube with no apertures. As a result, it became possible to make TS measurements in the electron density range above 1.0 × 10¹⁷ m⁻³.

Verification of carbon density profile measurements with charge exchange spectroscopy of CVI (Δn = 8 - 7, λ = 529.2 nm) using hydrogen and deuterium neutral beams is described. This is a key issue in the study of the comparison of the carbon density profile between hydrogen and deuterium plasma, because the hydrogen neutral beams are injected in the hydrogen plasma and the deuterium neutral beams are injected in the deuterium plasma. By applying the precise beam attenuation calculation using precise atomic data, identical carbon density profile is obtained for the plasma with hydrogen beam and deuterium beam. A Verification of the measurement is performed by comparison of carbon density profile measured with charge exchange spectroscopy and increment of electron density profile just after the carbon pellet injection.

We proposed a new method to evaluate particle flux in magnetized turbulent plasma. To extract fundamental fluctuation pattern, we used template method which is a kind of statistical conditional averaging technique. The method allows as not only to extract coherent patterns of density and potential fluctuations but also to evaluate time delay between them. We succeeded to calculate particle flux driven by fluctuation pattern and observed this pattern drives inward particle flux. Result obtained by the method is in good agreement with that obtained by a conventional method.

The comparison of conditional averaging using so-called threshold and template methods is made in their application on quasi-periodic burst of I-mode in ASDEX Upgrade (AUG) I-mode plasma. For obtaining conditionally averaged waveforms, three different manners to determine the ‘clocks', using raw signal, envelope of the signal and numerical filtering, are applied to each method. The comparison demonstrates the excellency of the template method to extract typical characteristics of target phenomena in its uniqueness to select the ensemble waveforms and its good convergence property.

A two-dimensional (2D) soft X-ray (SXR) imaging system for obtaining tangential views of plasma-produced SXR has been installed on the QUEST tokamak. The system comprises a chevron micro-channel plate (MCP) and a phosphor screen, which together serve as an SXR detector and image intensifier, along with a high-speed video camera for capturing and storing image data. The system can be used in imaging mode to obtain high spatial- and time-resolution images or in photon counting mode at an ultra-high framing rate of 100 kHz to obtain SXR energy spectra. Here, we propose a method of in situ energy calibration based on the transmission characteristics of a 25-µm Be filter. The proposed method was used to obtain SXR spectra in the energy range 1.5 - 3.5 keV with a core electron temperature in agreement with electron temperatures measured by the Thomson scattering method. Furthermore, oscillations based on the modification of plasma parameters and rapid increases in impurity radiation were detected in imaging mode. This dual-mode-compatible method for obtaining 2D SXR diagnostics is useful for the study of high temperature plasmas.

The present study is an analysis between radial emissivity profiles of the 650.024 nm transition of the O⁴⁺ ion obtained using two separate Photon Emissivity Coefficient (PEC) databases. Emissivity values of the 650.024 nm O⁴⁺ transition in visible-spectral region have been experimentally obtained for the Aditya tokamak. The radial number density distributions of different charge states of oxygen are estimated using a semi-implicit numerical method applied over the radial impurity transport equation. The 650.024 nm emissivity is calculated using the obtained impurity number density and with PECs from two separate databases namely the ADAS (Atomic Data and Analysis Structure) and the NIFS (National Institute for Fusion Science) database. Although impurity diffusivity profiles must not be dependent upon the choice of PEC databases; yet a requirement of separate impurity (oxygen) diffusivity profiles for the two PEC databases is observed, such that their corresponding calculated O⁴⁺ emissivities best depict the experimental emissivity data. A difference in the ionization and recombination rate coefficients provided in the ADAS and NIFS databases can lead to discrepancies in the impurity number densities calculated. The effects upon the impurity diffusivity while using ionization and recombination rate coefficients from two separate databases are further studied.

This paper evaluates the economy of a tokamak neutron source for transuranics transmutation using the Physics-Engineering-Cost system code. We compared two devices, one with normal conductive coil (NCC) and another with superconducting coil (SCC). The plasma performance was assumed to be moderate ones. The cost of neutron (CON) was used to measure the economy, taking into account the selling net electricity (P_e−net). We scanned the plasma aspect ratio (A) and thickness of inboard-side shield of an NCC device. It was revealed that ohmic loss in the magnetic coils (P_coil) is the dominant factor on determining the optimum aspect ratio for the economy of an NCC device. On the other hand, in an SCC device, the dependence of CON on the aspect ratio is relatively weak due to the absence of P_coil and smaller weight of the coils. Moreover, as the inboard-side shield of an NCC device became thicker, the economy of the device became worse. It was found that enough plant availability in SCC settings, which presupposes development of a remote-handling system, results in the relatively higher economic potential of SCC settings than of NCC settings.

The visible spectroscopy reference system (VSRS) diagnostic will be used to measure the continuum visible light emitted from the plasma in ITER. Because the field of view of the VSRS system is aligned to a hole on a blanket module with a retroreflector on the bottom, which will be shared with an interferometer measurement, it has a potential to be free from the stray light, which may disturb signals for optical diagnostics in ITER. In this study, performance of the stray light reduction in the VSRS is investigated using a ray tracing simulation. We investigated the influences of the reflection property of the retroreflector and first mirror for the signal and stray light intensity.

Release behaviors of tritium from molten FLiNaBe (LiF-NaF-BeF₂) have been examined in a series of low flux neutron irradiation experiments with an AmBe neutron source at the OKTAVIAN facility of Osaka University. Tritium released from FLiNaBe is swept by He and Ar gases, and recovered by water bubblers. The recovery rate of tritium released from 300 cm³ of FLiNaBe was 58.0 mBq/h in a steady state, and it was close to the tritium production rate of 58.0 mBq/h calculated by the MCNP6 code. The values of the overall mass transfer coefficients for tritium release from FLiNaBe were close to those for FLiNaK (LiF-NaF-KF) at 773 K. The influence of the diffusivity and the solubility of tritium on the overall mass transfer coefficients has been examined on molten FLiNaBe.

MHD effect of a liquid metal sheath jet, which is the jet stabilized by an inserted chain, has been experimentally investigated to examine its applicability to the divertor target of a fusion reactor. The deflection of the liquid metal jet together with the chain was observed when the electric current was applied to the jet under the presence of the magnetic field perpendicular to the jet flow direction. This means that the stabilization of the liquid meal jet by the chain is maintained when the jet is deformed by the magnetohydrodynamics (MHD) effect. However, the magnitude of the jet deflection agrees with the calculation result of the deflection of jet by the Lorentz force when the jet is regarded as a conductor. This indicates that mitigation of the Lorentz force and further investigation of the behavior of the liquid metal sheath jet under the exposure of divertor plasma is necessary to realize the divertor target using the liquid metal sheath jet.

Effect of the re-deposition layers formed on plasma-exposed stainless steel type 316L (SS316L) in QUEST on the retention and depth profile of tritium has been studied by both methods of tritium exposure experiments and numerical analyses of X-ray spectra observed by the β-ray-induced X-ray spectrometry (BIXS). Both samples of plasma-exposed and non-exposed SS316L were exposed to tritium gas under given temperature, time and pressure conditions. Surface of the former sample was covered with re-deposition layers after exposing to the plasma experiments. After tritium exposure, X-ray spectra induced by β-rays emitted from tritium atoms retained in the surface layers and/or dissolved into the bulk were measured using an ultra-low energy X-ray detector consisting of pure Ge semiconductor, and numerical analysis of the observed spectrum was conducted to estimate a tritium depth profile in the sample. As a result, it was found that the amount of tritium in surface layers of the plasma-exposed sample was about five times larger than that of the non-exposed sample, and the tritium depth profile for the plasma-exposed sample was about half depth in comparison with that for the non-exposed sample although the degassing temperature and tritium exposure conditions were the same for both samples. It was suggested, therefore, that the re-deposition layers played a role of diffusion barrier of tritium atoms formed on the sample surface.

The cartridge-type helical blanket system called the CARDISTRY-B has been proposed for the helical fusion reactor FFHR-d1. The CARDISTRY-B is aimed at easy construction and maintenance. However, there remain many issues in the design. For example, these include a large number of cartridges, no tangential ports, low compatibility with the helical divertor, and others. To solve these issues, an improved design of the cartridge-type blanket is proposed and named the CARDISTRY-B2. This is composed of the tritium breeding blanket (BB) filled with the flowing molten salt and the neutron shielding blanket (SB) filled with the tungsten-carbide. The number of the BB (or, SB) cartridges in the 1/10 section of the full torus are reduced from 32 to 17 (or, from 44 to 17). Tangential ports for the neutral beam injection heating are newly equipped together with the multi-purpose blanket cartridge. Compatibility with the helical divertor is also improved. The BB cartridges are fixed on the fixing units set on the top of the SB. No other part of the BB is touching the SB except the fixing ribs. The SB cartridges surround the superconducting magnet coils and work as the cryostat inside the vacuum vessel. This makes the large bellows for the large maintenance ports unnecessary. Details of the CARDISTRY-B2 designed for a small helical fusion reactor FFHR-b1 are described in this paper.

This paper describes an emergency fast discharge scheme of toroidal field (TF) coils of fusion demo reactors for reduction of induced voltage applied to turn insulations of conductors. TF coils are divided into serially connected segments that are electrically isolated from each other and only the coil segment having a failed coil is rapidly discharged. It was found from a circuit current analysis that this discharge scheme enables to reduce the insulation voltage with a factor of ~0.6 or less and which would contribute to ensure reliability of the turn insulations.

A high power sub-THz pulsed gyrotron with a frequency of 303 GHz has been developed for use as the power source of the collective Thomson scattering (CTS) diagnostics in the Large Helical Device (LHD) at the National Institute for Fusion Science. Based on careful design considerations, a whispering gallery mode TE_22,2 was adopted to avoid mode competition. More than 320 kW was attained with single-mode oscillation. The spectrum of the oscillation frequency is very narrow and stable during the entire pulse duration for pulse widths up to 100 µs. No parasitic mode is excited at the turn-on and turn-off phases nor during the steady state of the oscillation pulse. In addition to the adoption of the whispering gallery mode, a fast but finite rise time of the beam voltage is an important role for the realization of single-mode oscillation. Self-consistent calculations show that, for the finite voltage rise time corresponding to the present experiment, gradual evolution to the high power regime is attained from backward wave oscillation. This high power regime corresponds to the hard self-excitation region in the case of instantaneous voltage rise.

A high ion saturation current (I_is) phase, which is characterized by larger increase/decrease of I_is compared with the magnetic field variation, is observed in a converging field following an electron cyclotron resonance plasma source with a magnetic beach configuration. Plasma production rate and particle influx are considered in terms of orbits of collisionless electrons. While the ionization probability of one-pass electron is order of 0.1, the mirror trapped electron cause ionization within several or dozen bouncing. This is an essence of improved ionization rate resulting in the high I_is phase. The temporal evolution of ion saturation current observed in the experiment is well explained by the estimated plasma production rate and particle influx.

In the west end of GAMMA 10/PDX, the end-loss ion flux is utilized for divertor simulation experiments. It is important for controlling parameters of the end-loss ion flux to investigate the efficiency of ion cyclotron range of frequency (ICRF) heating in the west plug/barrier cell, which is next to the west end region. The ICRF heating experiments in the west plug/barrier cell have been performed. In this study, three-dimensional simulations of the ICRF wave propagation were carried out in the plug/barrier cell for the first time. Two types of antennas, a Double Half Turn (WB-DHT) and a Nagoya Type-III (WB-Type-III) antennas, are evaluated. As the results, it is clarified that the WB-Type-III antenna is more effective for the ion heating than the WB-DHT antenna when the frequency is near the ion cyclotron resonance frequency at the midplane of the plug/barrier cell. An additional experiment with the WB-Type-III antenna which is located near the midplane of the plug/barrier cell has been performed. The improvement of the power absorption has been observed. The WB-Type-III antenna located near the midplane is more effective for the ion heating. The experimental results are consistent with the simulation of the wave propagation analysis.

We investigate instabilities of electron beam particles confined in a cylindrical chamber using a 3-dimensional full particle simulation. The global structure of electron beam plasma changes within 1 µs, and deforms to those formed by the instabilities such and the sausage and kink instabilities. The azimuthal mode of the electron density on the midplane of beam plasma is analyzed and the amplitude of mode number of 1 or more increases at 0.2 µs. It was also found that the temporal change of the electron density on the geometric axis is caused by the plasma oscillation.

A possible intensified camera based Thomson scattering (TS) system for high temperature plasma measurement of over 100 eV is investigated. The TS system is not specific to a certain device, but can be applicable to any plasma source capable of producing high temperatures with densities of over 1 × 10¹⁹/m⁻³ range. A code has been developed to estimate the number of collectable scattered photons and its corresponding photoelectrons. The system uses an sCMOS intensified camera, which comes with many convenient features in terms of precise timing, digitization, and its compactness. Due to the broad wavelength range of the scattering spectrum, to increase detection of photons per pixel, the optical setup have to compromise of the most efficient element that uses volume phase holographic (VPH) grating and a wire grid polarizer. Off-the-shelf components have been chosen for the VPH spectrometer, intensified camera, and the 532 nm Nd:YAG laser that is available up to 5 J/pulse without custom request. Two separate magnification ratio 1:2 and 1:3 of the collection lens are considered for estimating the TS signal during a single laser shot.

We used the additional Ion Cyclotron Range of Frequency (ICRF) heating in the anchor cell for the high density plasma production. When the ICRF waves are excited with antennas installed in the anchor cell, it is observed that the plasma potential increases significantly and forms non-axisymmetric potential distribution in the periphery of the central cell. Experiments with different frequencies were carried out to understand the physical mechanism of this potential change due to the ICRF waves. It is confirmed that the ion heating does not play an important role to the potential increase. The floating potentials on some tips set outside of the plasma in the anchor cell remarkably decrease during the additional heating and non-axisymmetric distribution of the floating potential in the central cell depends on the antenna location in the anchor cell. It is suggested that the radial transport of electrons near the antennas in the non-axisymmetric anchor cells with the ICRF antennas is a possible candidate of the potential increase in the central cell.

The Lyapunov exponent analysis is carried out for ion motions in a non-adiabatic trap where the axial magnetic field from a solenoid is partially cancelled by that from a Helmholtz coil. In particular, relation between the Lyapunov exponents and the trapped rate of ions injected in the axial direction is numerically studied. It is found that there exist energy minimizing the particle trapped rate, and the Lyapunov exponent for the axial velocity is found to be minimized with that energy.

The effect of high ion temperature on the ion polytropic coefficient (γ) was experimentally investigated in the end region of the GAMMA 10/PDX tandem mirror. The ion temperature parallel to the magnetic field (T_i||) was varied using the ion cyclotron range of frequencies (ICRF) waves, which heat the plasma in the central cell, and by applying an additional gas puff in the central cell. Assuming the ion sound speed, γT_i|| was evaluated by a Langmuir probe, and T_i|| was evaluated in an ion energy analyzer. These parameters were combined to evaluate γ. The time evolutions of γT_i|| obtained from the probe and T_i|| obtained from the energy analyzer were similar. The plasma in the end region can be regarded as collisionless, but γ was lower with ICRF heating than without the heating. A high T_i|| component was identified in the heated case. As mentioned in a previous numerical study [B. Lin et al., Phys. Plasmas 23, 083508 (2016)], it is experimentally suggested that γ can be reduced by the high T_i|| component resulting from the ICRF heating.

Plasma parameters in the upstream and downstream regions in the divertor simulation experimental module (D-module) of the tandem mirror plasma device GAMMA 10/PDX were conducted using Langmuir probes. The detached plasma was produced using hydrogen puffing. In the upstream region, the electron temperature decreased from 30 to 7 eV, and the electron density increased. On the other hand, rollover of n_e at the V-shaped corner was observed in the downstream region. Increasing H_α/H_β at the corner of the V-shaped target was attributed to the molecular activated recombination processes. H_α/H_β in the downstream region was different from that in the upstream region. Therefore, the ionization front appeared in the upstream region of the D-module.

We developed an yttrium aluminum garnet (YAG)-Thomson scattering (TS) system for radial profile measurements of electron temperature and density in the GAMMA 10/PDX central cell. The optical collection system for TS light was constructed from three spherical mirrors and nine bundled optical fibers. The radial positions were intervals less than 5cm in the range of ±20 cm and were measured by moving the fixed fiber bundle position from shot to shot. We constructed a multi-pass TS system with laser amplification, which can increase the signal intensity and time resolution of the TS diagnostic system. In addition, we installed the end-TS system using the central-TS YAG laser in order to measure the electron temperature and density in a divertor simulation experimental module in the GAMMA 10/PDX end cell.

Beach heating using a slow Alfvén wave in ion cyclotron range of frequencies would be the first candidate for ion heating in a DEMO-relevant divertor testing linear plasma device if it is applicable to a high-density regime. To clarify its availability, the density dependence of a slow wave excitation is investigated using a full wave simulation with TASK/WF3D code in the GAMMA 10/PDX central cell configuration, where there is an extensive track record of a beach heating. A shielding effect is successfully demonstrated and well understood under a three-dimensional configuration in the limit of cold plasma approximation. As the density increases, excitable left-handed electric field, which contributes to ion cyclotron heating, degrades more and more from a core region, and resultantly the ion absorption region goes outwards with reducing its power. For core densities above 10²⁰ m⁻³, the wave field exists only at a very edge, and ion heating becomes negligible unless the wave frequency is much increased with a correspondent magnetic field enhancement.

Presented paper is the next step in the research of axial transport in Gas Dynamic Trap. Experiments dedicated to the neutral gas role in the expander of mirror device were carried out. Ion current density distribution measured at the end plate does not depend on neutral gas density in the expander. Experimental indications of neutral gas extrusion from the axis of the expander to its periphery were observed. Numerical model describing such extrusion by elastic collisions of neutrals with plasma ions is in agreement with experimental data.

Slow Alfvén wave with a frequency just below an ion cyclotron frequency can be destabilized by the anisotropy of ion temperature and called as Alfvén-Ion-Cyclotron (AIC) wave. In the GAMMA 10/PDX central cell, several AIC waves simultaneously appear in an unstable frequency range. In addition, low-frequency waves with the difference frequencies (DF) between the AIC waves are observed, and their characteristics have to be clarified to reveal their unknown contributions to the ion transport suggested in GAMMA 10/PDX. In this study, simultaneous two-point measurements in the azimuthal and axial directions were conducted by using a two-channel microwave reflectometer with multi horn antennas. The azimuthal mode number (m) of the DF waves was confirmed at inner plasma region for the first time, and was zero, which satisfies azimuthal mode matching with the m = −1 AIC waves. In addition, it was shown that the DF waves were radially localized in an inner region, which is different from rather broad profiles of the AIC waves.

This paper investigates the impact of Krypton (Kr) seeding on plasma parameters in the D-module of GAMMA 10/PDX experimentally based on the calorimeter, Langmuir probe and high-speed camera measurements. The heat flux distribution along the V-shaped target plate reduces with the increasing Kr injection. The time behavior of ion flux shows that it decreases with the increase of Kr seeding. The electron temperature (T_e) reduces significantly due to Kr seeding into the D-module. The electron density shows a so-called roll-over phenomenon during Kr seeding. The heat and ion fluxes reduce with the increasing Kr seeding into the D-module. Two-dimensional images captured by the high-speed camera also show that the emission intensity significantly reduces inside the V-shaped target at the higher Kr injection. These outcomes represent the impact of Kr seeding for generating the detached plasma.