Plasma and Fusion Research
Online ISSN : 1880-6821
ISSN-L : 1880-6821
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Regular Articles
  • Ryosuke SAKAI, Takaaki FUJITA, Atsushi OKAMOTO
    Type: Regular Articles
    2019 Volume 14 Pages 1405040
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    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 (Pe−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 (Pcoil) 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 Pcoil 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.

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  • Atsushi OKAMOTO, Ryosuke OCHIAI, Katsuya SATOU, Hiroki HACHIKUBO, Mina ...
    2019 Volume 14 Pages 2401005
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    A high ion saturation current (Iis) phase, which is characterized by larger increase/decrease of Iis 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 Iis phase. The temporal evolution of ion saturation current observed in the experiment is well explained by the estimated plasma production rate and particle influx.

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  • Yushi KUBOTA, Mafumi HIRATA, Seowon JANG, Makoto ICHIMURA, Ryuya IKEZO ...
    2019 Volume 14 Pages 2401012
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    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.

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  • Kojiro SEKIGUCHI, Takahiro URANO, Shuya IWATA, Gaku SAKAI, Ryo MATSUMO ...
    2019 Volume 14 Pages 2401018
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    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.

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  • Kiyong LEE
    2019 Volume 14 Pages 2401019
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    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.

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  • Atsuto TANAKA, Makoto ICHIMURA, Mafumi HIRATA, Ryuya IKEZOE, Shuhei SU ...
    Type: Regular Articles
    2019 Volume 14 Pages 2401028
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    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.

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  • Ryo MATSUMOTO, Shuya IWATA, Takahiro URANO, Kojiro SEKIGUCHI, Gaku SAK ...
    Type: Regular Articles
    2019 Volume 14 Pages 2401035
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    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.

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  • Masayuki YOSHIKAWA, Tomoya MOURI, Junko KOHAGURA, Yoriko SHIMA, Tomoya ...
    2019 Volume 14 Pages 2402002
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    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.

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  • Ryuya IKEZOE, Yushi KUBOTA, Makoto ICHIMURA, Mafumi HIRATA, Shuhei SUM ...
    2019 Volume 14 Pages 2402003
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    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.

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  • Elena I. SOLDATKINA, Peter A. BAGRYANSKY, Alexey D. BEKLEMISHEV, Ed ...
    2019 Volume 14 Pages 2402006
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    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.

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  • Ryo SEKINE, Ryuya IKEZOE, Seowon JANG, Mafumi HIRATA, Makoto ICHIMURA, ...
    2019 Volume 14 Pages 2402011
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    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.

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  • Md. Shahinul ISLAM, Yousuke NAKASHIMA, Akiyoshi HATAYAMA, Hiroto MATS ...
    2019 Volume 14 Pages 2402016
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    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 (Te) 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.

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  • Anna A. INZHEVATKINA, Aleksander V. BURDAKOV, Ivan A. IVANOV, Vladi ...
    2019 Volume 14 Pages 2402020
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    The measurements of the plasma velocity in the SMOLA helical mirror by observation of the Doppler shift of the Hα spectral lines emission were done by high spatial resolution spectrometer. A set of experiments was carried out with the different configuration and amplitude of the magnetic field. Potential is driven by plasma gun potentials. The radial distribution of the Doppler shift of the Hα line is used to calculate the velocity of neutral hydrogen, which gives the estimate of the plasma rotation velocity ω ≈ 106 s−1. The indicated velocity corresponds to the presence of the radial electric field E ∼ 70 V/cm. The dependence of the plasma rotation velocity on the radial profile of the electrostatic potential is discussed.

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  • Anton V. SUDNIKOV, Aleksey D. BEKLEMISHEV, Vladimir V. POSTUPAEV, I ...
    2019 Volume 14 Pages 2402023
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    Experimental evidence of the plasma flow suppression by the helical magnetic mirror is presented. Reported experiments were done during the first plasma campaign in the SMOLA helical mirror device at self-consistent floating potentials of all in-vessel electrodes and at minimal magnetic fields suitable for confinement regime. The experimental results are consistent with two main theory predictions for the helical mirror confinement: a reduction of the axial plasma flow and the inward particle pinch. The helical mirror technology can dramatically improve fusion reactor prospects of open magnetic configurations.

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  • Vladimir I. DAVYDENKO, Petr P. DEICHULI, Alexander A. IVANOV, Serge ...
    Type: Regular Articles
    2019 Volume 14 Pages 2402024
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    In the Budker Institute, the CAT (Compact Axisymmtric Toroid) experiment is being prepared for obtaining a plasmoid with high diamagnetism in axially symmetric magnetic field. Reverse of magnetic field in the plasmoid is also possible in this experiment. The experiment is based on injection of powerful focused neutral beams with extremely large neutral power density in the plasma. Two neutral beam injectors with the energy of hydrogen atoms of 15 keV will be used in the experiment. The neutral beam power of each injector is 2 MW, pulse duration is 5 ms. In the ion source of the injector, plasma emitter is produced by plasma jets from four arc plasma generators. Proton beam with current up to 170 A is formed by multi-slit three-electrode ion-optical system with ballistic focusing. Measured angular divergence of the formed beam along the slits is 10 mrad, divergence in the direction across the slits is 35 mrad. The injector is equipped with a neutralizer, bending magnet, residual ion dump, calorimeter, high speed pumping system with titanium arc evaporation.

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  • Egor I. PINZHENIN, Aleksandr D. KHILCHENKO, Peter V. ZUBAREV, Andre ...
    Type: Regular Articles
    2019 Volume 14 Pages 2402025
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    Neutron/gamma ray spectrometer based on a single-crystal stilbene scintillator with the photomultiplier tube 9266B was developed and tested. Signal acquisition and real-time processing is enabled by the fast ADC with the wide-band preamplifier and the Field-Programmable Gate Array (FPGA) core. The method of n/γ event separation based on frequency gradient analysis was implemented. The paper shows the efficiency of n/γ separation delivered by the spectrometer. The energy scale calibration of gamma channel was carried out by radionuclide gamma sources. The neutron channel energy calibration was done using accelerator-based neutron sources with deuterium-deuterium and deuterium-tritium fusion reactions. Real time registration of neutron spectra and gamma spectra in different channels of spectrometer was shown when acquiring amixed neutron and gamma flux. The paper illustrates the possibility of simultaneous registrations of 2.45 MeV and 14 MeV neutrons. The energy resolution of neutron spectrometer was measured. The neutron count rate up to 2105 s−1 was demonstrated.

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  • Peter A. BAGRYANSKY, Egor D. GOSPODCHIKOV, Alexander A. IVANOV, And ...
    Type: Regular Articles
    2019 Volume 14 Pages 2402030
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    Paper presents a brief overview of the studies carried out in 2016-2018 at the Gas Dynamic Trap device at the Budker Institute. These studies were focused on the experimental substantiation of a new version of the Gas Dynamic Multi-mirror Trap project, which is aimed at developing the key technologies needed to implement a number of thermonuclear applications of linear magnetic traps. The paper reviews the work aimed at stable plasma confinement under auxiliary ECR heating. We showed that a value of on-axis electron temperature up to 450 eV at plasma density 1.2 × 1019 m−3 can be supported steadily. Studies on processes in expanders, which determine the axial thermal conductivity of the plasma, showed that the profile of the electric potential in the expander corresponds to a theory that gives favorable predictions regarding the thermal insulation properties of the expander. It was shown that the density of neutral gas in the expander in the range up to 1020 m−3 does not have a significant effect on energy confinement in the trap, despite an estimate of the critical density of 1018 m−3.

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  • Seowon JANG, Makoto ICHIMURA, Mafumi HIRATA, Ryuya IKEZOE, Mizuki SAKA ...
    Type: Regular Articles
    2019 Volume 14 Pages 2402032
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    In the GAMMA 10/PDX tandem mirror, studies on divertor physics have been performed in the west end region by utilizing end-loss plasmas flowing from the confinement region. Since the plasma density in the end region is quite low (∼1016 m−3), an increase of the end-loss ion flux is required. The increase of the end-loss ion flux has been obtained by increasing the density in the confinement region on previous experiments. When an additional ICRF heating using the antennas in the anchor cells has been performed, a significant increase of the ion flux has been observed with the increase of the potential in the central cell although the change of line densities in the confinement region is little. The effect of the potential on the ion flux has been examined on the GAMMA 10/PDX using about 10,000 discharges. The ion flux increases almost linearly with the potential and the density increase. By comparing with a simple calculation, the increase of the ion flux is explained by the expansion of loss cone boundary of ions and the decrease of the transport time of the end-loss ions from the confinement region to the end region.

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  • Koki IZUMI, Ryuya IKEZOE, Makoto ICHIMURA, Mafumi HIRATA, Mizuki SAKAM ...
    2019 Volume 14 Pages 2402033
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    Effective ICRF heating creates a high ion-temperature plasma with strong ion-temperature anisotropy in the GAMMA 10/PDX central cell, where several Alfvén-ion-cyclotron (AIC) waves are spontaneously excited. It is clearly measured with a microwave reflectometer installed in the central cell that waves with the difference frequencies of the AIC waves are excited in a core region. In addition, it has been observed with an end-loss high-energy ion detector that high-energy ions of over 6 keV are axially transported along the magnetic field lines with the same frequencies as the difference frequencies of the AIC waves. In this study, in order to understand the related wave-particle interaction, another end-loss high-energy ion detector using a micro-channel plate has been developed. By changing the ion retarding grid voltage, which the new detector equips, it is found that an energy dependence exists in the loss mechanism; some frequencies that the axial transport includes disappear for high-energy ions of over 6 keV while they are significant for low-energy ions. In addition, by changing the radial position of the new detector, a radial localization of the axial transport to a core region, which is consistent with the profile of the difference frequencies waves, is indicated.

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  • Ryutaro MINAMI, Tsuyoshi KARIYA, Tsuyoshi IMAI, Tomoharu NUMAKURA, Mak ...
    2019 Volume 14 Pages 2402034
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    Electron cyclotron heating (ECH) power modulation experiments have been conducted for GAMMA 10/PDX to generate and control the high heat flux and to develop an edge localized mode (ELM)-like intermittent heat load pattern for divertor simulation studies. Flux and energy spectra of end-loss electrons are measured using a multi-grid energy analyzer (loss electron diagnostics, LED). ECH-induced potential formation at plug regions (P-ECH) produces high-energy electron flows along the magnetic lines of force. The power scaling of electron flux in GAMMA 10/PDX indicates that higher ECH power generates higher electron flux. In this study,a new mirror antenna is developed to generate higher heat flux and concentrate the heating power on the axis. The energy density and heat flux obtained using previous systems are 0.06 MJ/m2 and 11.4 MW/m2, respectively,and those obtained using the new mirror systems are 0.09 MJ/m2 and 30 MW/m2, respectively. These values are still considerably lower than those of ITER ELM (mitigated ELMs in ITER is ∼0.5 MJ/m2 for t = 0.5 ms).

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  • Hirohiko TANAKA, Mizuki SAKAMOTO, Naomichi EZUMI, Akihiro TERAKADO, Ku ...
    Type: Regular Articles
    2019 Volume 14 Pages 2402036
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    High-speed camera measurement was performed for analyses of detached plasma fluctuation in the GAMMA 10/PDX tandem mirror device. Significant spectral peaks at frequencies of 1.5 and 3 kHz were observed to have several local maxima along the vertical, near the entrance of the V-shaped target. Wavelet analysis indicated that 1.5- and 3-kHz fluctuations became non-simultaneously strong. Their phase relationships demonstrated inversion-symmetric and symmetric features with respect to the midplane. Such spectral patterns were interpreted as the line-integral of odd- and even-mode structures. It is suspected that the vertical edge part was due to radially elongated structures with an azimuthal phase shift.

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  • Igor A. KOTELNIKOV, Ivan S. CHERNOSHTANOV, Vadim V. PRIKHODKO
    2019 Volume 14 Pages 2403001
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    Stability of the flute-like electrostatic Drift-Cyclotron Loss-Cone and Double-Humped modes in a mirror trap is critically revisited. The isotopic effect is taken into account as well as the anisotropy of warm ions used to stabilise these modes.

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  • Mikhail S. KHRISTO, Alexey D. BEKLEMISHEV
    2019 Volume 14 Pages 2403007
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    The high pressure limit of equilibrium in linear traps corresponds to the diamagnetic reduction of the confining field and the corresponding increase in the volume of flux tubes. In the gas-dynamic regime the axial losses from a flux tube are proportional to its cross-section in the mirror throat. Thus, the axial confinement time, which is proportional to the ratio of the flux-tube volume to its cross-section in the mirror throat, can grow significantly in the high-pressure limit. In this paper the numerical model of the axially symmetric equilibrium based on the coupled Grad-Shafranov and transport equations is presented. The results are in good agreement with the earlier analytical model [A.D. Beklemishev et al., Fusion Sci. Technol. 63(1T), 46 (2013)].

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  • Satoshi TOGO, Tomonori TAKIZUKA, Mizuki SAKAMOTO, Naomichi EZUMI, Yuic ...
    2019 Volume 14 Pages 2403010
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    A new closure model for the parallel conductive heat flux of the perpendicular component of ion energy (qi,⊥) is proposed which considers the effect of the spontaneous parallel gradient of the perpendicular ion temperature in inhomogeneous magnetic fields. Profiles of plasma parameters and the particle confinement efficiency are compared between the new qi,⊥ model and a conventional one in a simple mirror system. It is found that the conservation of the magnetic moment is reproduced with the new qi,⊥ model. Comparisons of ion power flux profiles show that the new qi,⊥ model changes the direction of qi,⊥ keeping the spontaneous parallel gradient of the perpendicular ion temperature. Almost linear relations between the particle confinement time and the ion-ion Coulomb collision time are also obtained with both qi,⊥ models.

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  • Md. Maidul ISLAM, Shinji KOBAYASHI, Nobuhiro NISHINO, Md. Shahinul I ...
    Type: Regular Articles
    2019 Volume 14 Pages 2403017
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    The gas fueling by supersonic molecular beam injection (SMBI) has been carried out in the world largest tandem mirror device GAMMA 10 and higher plasma density has been achieved compared with conventional gas-puffing. Three-dimensional Monte-Carlo code DEGAS is applied to GAMMA 10 and the spatial distribution of neutral particle density during SMBI is investigated. σdiv is introduced as divergence angle index of the initial particle to simulate the molecular beam injected by SMBI. It is defined to be unity in the case of cosine distribution of the angular profile of launched particles. It is found that the particles are suppressed and localized in the injection point according to the reduction of divergence angle index, σdiv and well explained the GAMMA 10 SMBI experimental results at divergence angle index, σdiv = 0.33. In this paper the simulation is carried out in the different profiles of electron temperature in order to check the sensitivity of the background plasma parameter. The simulation results indicate that the penetration depth depended on the background plasma parameter, electron temperature.

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  • Takahiro URANO, Toshiki TAKAHASHI, Akiyoshi HOSOZAWA, Tomohiko ASAI, S ...
    2019 Volume 14 Pages 2403022
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    Wave excitation and propagation by applying a low frequency wave to a high-beta plasma are simulated by a 3-dimensional hybrid model, where ions are treated as particles while electrons are regarded as fluids. It is found that excitation of the toroidal magnetic field occurs outside the separatrix and the wave attenuated significantly near the separatrix. Although the attenuation due to an ion cyclotron resonance is conceivable, no temperature rise in the resonance region is observed. The attenuation condition is given here on the basis of a linear theory,and it shows a good agreement with hybrid simulation results in terms of the attenuation position.

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  • Toshiki TAKAHASHI, Takahiro URANO
    Type: Regular Articles
    2019 Volume 14 Pages 2403037
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    In this paper, the relation between a magnetic flux decay and a spontaneous spin-up phenomenon of high-beta FRC plasma is outlined based on the research results so far. We propose a hypothesis that an anomalous resistivity produces a difference in the time change rate of the angular momentum of ions and electrons, resulting in the rotation of ions.

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  • Hiromasa TAKENO, Kazuya ICHIMURA, Satoshi NAKAMOTO, Yousuke NAKASHIMA, ...
    2019 Volume 14 Pages 2405013
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    Present plasma direct energy conversion (DEC) system has been developed since proposal of ARTEMIS. The system for D-3He reactor is composed of cusp-type DEC (CuspDEC) for particle discrimination, traveling wave DEC (TWDEC) for recovery of high energy protons, and secondary electron DEC (SEDEC) for recovery of extremely accelerated protons. Studies on each device are in the third stage, where higher capability of each device will be derived. Various proposals and examinations were reported and the present paper treats the researches comprehensively and shows explanation and discussion for some researches: separation of high density plasma and ion-ion separation in CuspDEC, studies on modulation in TWDEC, and improvement of electron collection in SEDEC.

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  • Hiromasa TAKENO, Hiroki SATO, Kazuhiro SHIBATA, Kazuya ICHIMURA, Yousu ...
    2019 Volume 14 Pages 2405014
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    As for traveling wave direct energy converter (TWDEC), which was expected to be used for energy recovery of fast protons in D-3He fusion, a new modulation scheme was proposed for better bunching. An analytical formula was derived for complete bunching as an ideal waveform, and use of dual-frequency was proposed for practical application. In the scheme, independent two modulation electrodes were used and applied voltages were obtained by Fourier components of the fundamental and the second harmonic frequencies of the ideal waveform with taking running time between electrodes into account. The effect was confirmed by numerical orbit calculation, and improvement of bunching was found even for the ion beam with energy spread. The effect was indirectly confirmed experimentally by comparing variation of the third harmonic signal with an equivalent value in the orbit calculation. The optimum amplitude of the second harmonic frequency was discussed by comparing the composed waveform with the ideal one.

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  • Kazuhiro SHIBATA, Hiroki SATO, Hiromasa TAKENO, Kazuya ICHIMURA, Satos ...
    Type: Regular Articles
    2019 Volume 14 Pages 2405027
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    Traveling wave direct energy converter (TWDEC) was proposed as an efficient energy recovery device for D-3He fusion power generation. It is designed to convert the kinetic energy of 14.7 MeV protons produced by fusion reaction and is based on the inverse process of a linear accelerator. It consists of a modulator and a decelerator. In modulation process, dual-frequency modulation was proposed to improve bunching. Following to the proposal, deceleration experiment was performed, where the conditions of conventional and proposed methods were in a sequence. The result included other effects such as time variation of modulation effect, thus the effect of dual-frequency modulation to deceleration has not been clarified yet. In this work, the deceleration experiment was performed with conventional and proposed methods independently. In addition, time variation of deceleration effect was observed to exclude the time variation of the modulation effect. As a result, the effect of dual-frequency modulation to deceleration process was observed clearly. Higher efficiency was obtained with dual-frequency modulation.

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  • Kazuya ICHIMURA, Sotaro YAMASHITA, Yousuke NAKASHIMA, Masakatsu FUKUMO ...
    Type: Regular Articles
    2019 Volume 14 Pages 2405029
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    The sensitivity of the ASDEX type ionization gauge (AIG) in the mixture of argon and hydrogen gas, which is a candidate of radiator gas in the radiative divertor, is studied. In a small vacuum chamber, the sensitivity of the AIG is calibrated against capacitance-manometers, which have constant sensitivity for all gas species. Increase of the output signal AIG was observed in the mixture of 25% Ar and 75% H2, although the actual sensitivity of the gauge against gas pressure is degraded. In the gas pressure larger than 0.8 Pa, the degradation of the sensitivity will be the main concern of the measurements. The results indicated that the molecular ions produced by the collision between the metastable argon atom and hydrogen molecule is the main cause of the change of the sensitivity. The change of sensitivity is analyzed by varying the collision energy of the electrons and the ionization cross-section of the ArH molecular ion is evaluated.

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  • Timur D. AKHMETOV, Vladimir I. DAVYDENKO, Alexandr A. IVANOV, Grigo ...
    2019 Volume 14 Pages 2406004
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    Operation of a plasma source with a hot disk cathode and a cylindrical hollow anode in axial magnetic field is sensitive to the cathode-to-anode diameter ratio. When the cathode edge maps along magnetic field lines to the inner anode surface, the discharge voltage is relatively low, and the plasma stream with moderate density occupies the entire cross-section of the anode bore. By contrast, when the cathode projection is fully inside the anode bore with the radial cathode-to-anode gap ∼ 1 cm, the discharge voltage jumps to much higher values exceeding 250 V. The plasma density profile becomes Gaussian-like with the width matching the cathode radius according to magnetic flux surfaces. The plasma density in the high-voltage cross-field discharge reaches 1013 cm−3, and the discharge parameters almost do not change with magnetic field up to 1.5 kG in the anode area. This plasma source is suitable for the use in linear devices for plasma-material interaction studies.

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  • Kazuo OGURA, Kei SEKINE, Yuta ANNAKA, Min Thu SAN
    2019 Volume 14 Pages 2406008
    Published: January 29, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    We experimentally studied spoof plasmons developed on a metal cylinder with rectangular corrugations. Cavity resonance method using vector network analyzer is employed to examine electromagnetic properties of the spoof plasmon. The dispersion characteristics are obtained using resonance frequencies and can be recognized as two regions: bounded and hybrid surface-wave regions. The bounded surface wave is formed near the upper cutoff frequency, while the hybrid surface wave similar to a Sommerfeld wave is formed away from the upper cutoff frequency. In addition to the dispersion characteristics, the reflectance of spoof plasmon at the corrugation end is examined, based on quality factors of resonant modes.

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  • Gaku SAKAI, Takahiro URANO, Shuya IWATA, Kojiro SEKIGUCHI, Ryo MATSUMO ...
    2019 Volume 14 Pages 2406009
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    This study particularly focuses on the dissipation processes of trapped ion beams such as deceleration and diffusion, which are caused by Coulomb binary collisions. It demonstrated that collisions in ions or low-temperature electrons have major influences on ion beams. Beam convergence was improved by applying a magnetic field. To assess the medical applicability of our neutron source, a combined Monte-Carlo simulation with Diffusion-Reaction model was employed to evaluate the available neutron yield for the Boron Neutron Capture Therapy (BNCT) neutron source under the beam diffusion conditions. The paper found that the proposed electrostatic trap of deuterium beam ions could provide sufficient neutron generation for the therapy.

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  • Yuta ANNAKA, Kazuo OGURA, Kosuke OZAWA, Makoto NAKASONE, Yuki SATO
    2019 Volume 14 Pages 2406015
    Published: January 24, 2019
    Released: February 22, 2019
    JOURNALS FREE ACCESS

    In this paper, non-axisymmetric radiation from a W-band surface wave oscillator (SWO) is observed. The SWO is based on a cylindrical corrugated waveguide with a periodic structure on its inner wall. This SWO is driven by electron beams with energy of less than 100 keV and a current on the order of 100 A. The waveguide has transverse magnetic (TM) and transverse electric (TE) modes as its axisymmetric normal modes. Nonaxisymmetric modes also appear as a hybrid of TM and TE modes and form surface waves near the periodic structure. The frequencies of the non-axisymmetric modes increase as the azimuthal mode number m increases. By injecting an annular electron beam into the SWO, many non-axisymmetric modes with m up to 30 are excited and intense radiation is generated at frequenies up to 140 GHz.

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  • Shuya IWATA, Ryo MATSUMOTO, Kojiro SEKIGUCHI, Takahiro URANO, Gaku SAK ...
    Type: Regular Articles
    2019 Volume 14 Pages 2406026
    Published: February 12, 2019
    Released: April 16, 2019
    JOURNALS FREE ACCESS

    The ion trajectory in a hollow cathode discharge plasma to which a magnetic field combined a solenoid and a Helmholtz coil is applied is analyzed, and the ion energy distribution at the cathode or the end of the device is examined. It was shown that the ratio of particles lost at the end of the device and those lost during collision with the cathode can be changed by varying the length of the cylindrical cathode.

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