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Investigation into Quench Detection for a Multi-Stacked Pancake Coil Wound with Nb3Sn CIC Conductors
Get PDF0000-0002-1989-867XFor a multi-stacked (MS) pancake coil wound with Nb3Sn CIC conductors, quench detection methods using voltage measurements were investigated. In this study, we utilized two methods: the balanced voltage between two coil windings and the balanced voltage between one coil winding and a disk-shaped pickup coil. During the energization of the MS pancake coil, voltage measurements of the coil were conducted to compare the measurement results of the two quench detection methods. The measurement results indicate that the quench detection based on the balanced voltage between two coil windings is more reliable than the other. In the measurements, spike voltages were observed when there was a rapid change of a coil current. Magnetization of the MS pancake coil is considered one cause of the spikes. When determining criteria of quench detection, spike voltages should be taken into account to prevent malfunction of a quench detection system.journal articl
Neutron-Induced Signal on the Single Crystal CVD Diamond-Based Neutral Particle Analyzer
Get PDF0000-0003-0755-2433A diamond-based neutral particle analyzer (DNPA) array composed of single-crystal chemical vapor deposition (sCVD) diamond detectors was installed on the Large Helical Device (LHD) for measuring the helically trapped energetic particles. In high neutron flux experiments, the unwanted neutron-induced pulse counting rate should be estimated using the neutron diagnostics because a diamond detector is sensitive to neutrons as well as energetic neutral particles. In order to evaluate the quantitative neutron-induced pulse counting rate on the DNPA, the response functions of the sCVD diamond detector for mono-energetic neutrons were obtained using accelerator-based D–D and D–7Li neutron sources in Fast Neutron Laboratory (FNL). As a result of the neutron flux estimation by the Monte Carlo N-Particle code at the NPA position in the LHD and the response function obtained in the FNL experiment, the counting rate of the neutron-induced signal was predicted to be 1.1 kcps for the source neutron emission rate of Sn = 1 × 1015 n/s. In the LHD experiment, the neutron-induced signals were observed by closing the gate valve during the plasma discharges. It is found that the counting rates of the neutron-induced signals proportional to Sn reached 1.1 kcps at Sn = 1 × 1015 n/s. As a result of the quantitative estimation of the neutron-induced signals on the DNPA using other neutron measurements, it has become possible to accurately measure energetic neutral particles in the high neutron flux experiment.journal articl
Neutral particle drag on parallel flow shear driven instability
Get PDF0000-0001-6835-1569The neutral drag effect on the parallel velocity gradient driven instability (PVG) in the presence of density inhomogeneity is theoretically investigated. The dispersion relation of PVG mode with the effect of the density gradient and neutral particle drag is derived, and its solution is analytically obtained. The neutral particle drag gives rise to the phase shift between parallel flow and electrostatic potential fluctuations and modifies the parallel compression. As a result, the stability of the PVG mode changes. It is found that the neutral particle drag does not only reduce but also enhances the instability. Specifically, near the marginal condition, the neutral particle effect suppresses the density gradient effect, and the parameter region where the PVG mode is linearly unstable significantly expands.journal articl
Studies of the fast ion confinement in the Large Helical Device by using neutron measurement and integrated codes
Get PDF0000-0003-3293-488XThe neutral beam (NB) fast ion confinement in the Large Helical Device (LHD) is studied for several full field (????????∼2.75 T) magnetic configurations by a combination of neutron measurement and simulations. To investigate the NB fast ion confinement, we have performed a series of short-pulse NB injection experiments. The experiment results are analysed by the integrated code TASK3D-a. From this investigation, the effective particle diffusion coefficients of the tangential and perpendicular NBs are approximately ????eff∼0.1 m2 s−1 and ????eff∼1 m2 s−1 in the standard configuration. It is clarified that the NB fast ion confinement improves when the plasmas are shifted inward. Moreover, it is also found that the simulation, which considers the deuteron dilution effect due to the presence of impurity ions, can describe a neutron emission rate consistent with the measurement.journal articl
Edgewise-strain-free helical winding using high-temperature superconducting tape conductor
Get PDFOptimization of the helically-winding structure required for the helical fusion reactor utilizing the high temperature
superconductor (HTS) tape is studied by numerical calculation. When the HTS tapes are wound to be
the helical structure without the torsion, a significant edgewise strain appears. This might lead to the degradation
of the performance of the HTS tape. Therefore, the edgewise strain must be minimized. It is found that the edgewise strain can be suppressed by the proper determination of the torsion by the optimization utilizing the Fourier decomposition of the distribution of the edgewise strain. The HTS tapes with edgewise strain are intrinsically deformed due to the torsion to reduce the edgewise strain so to be an “edgewise-strain-free” helical shape.journal articl
Energetic particle transport and loss induced by helically-trapped energetic-ion-driven resistive interchange modes in the Large Helical Device
Get PDF0000-0003-4555-1837In this work, energetic-ion confinement and loss due to energetic-ion driven magnetohydrodynamic modes are studied using comprehensive neutron diagnostics and orbit-following numerical simulations for the Large Helical Device (LHD). The neutron flux monitor is employed in order to obtain global confinement of energetic ions and two installed vertical neutron cameras (VNCs) viewing different poloidal cross-sections are utilized in order to measure the radial profile of energetic ions. A strong helically-trapped energetic-ion-driven resistive interchange mode (EIC) excited in relatively low-density plasma terminated high-temperature state in LHD. Changes in the neutron emission profile due to the EIC excitation are clearly visualized by the VNCs. The reduction in the neutron signal for the helical ripple valley increases with EIC amplitude, which reaches approximately 50%. In addition to the EIC experiment, orbit-following simulations using the DELTA5D code with EIC fluctuations were performed to assess the energetic-ion transport and loss. Two-dimensional temporal evolution results show that the neutron emissivity at the helical ripple decreases significantly due to the EIC. The rapid reduction in neutron emissivity shows that the helically-trapped beam ions immediately escape from the plasma. The reduction in the VNC signals for the helical ripple valley and the total neutron emission rate increase with increasing EIC amplitude, as observed in the experiment. Calculated line-integrated neutron emission results show that the profile measured by VNC1 has one peak, whereas the profile measured by VNC2 has two peaks, as observed in the experiment. Although the neutron emission profile for VNC2 has a relatively wide peak compared with the experimental results, the significant decrease in neutron signal corresponding to the helical ripple valley was successfully reproduced.journal articl
Development of a compact ICRF antenna for high-power and long-pulse plasma heating in the KSTAR
Get PDF0000-0001-8972-6534For the high-power and long-pulse ion cyclotron range of frequencies (ICRF) heating of the KSTAR plasma, we developed the compact ICRF antenna (CIA). The target injection power of CIA is 2 MW for 300 s. In order to continue injecting the power into plasma even if drastic instantaneous changes occur in the plasma condition, such as ELM events, we adopted the internal conjugate-T method for the load resilience. Between antenna heads and the junction point, impedance transformers were inserted to satisfy the condition of conjugate-T in a limited space keeping the electric field on the transformer low enough. To reduce the risk of water leakage into the vacuum chamber, only the backsides of antenna heads are water-cooled in the in-vessel region.journal articl
Benchmark of a new multi-ion-species collision operator for δf Monte Carlo neoclassical simulation
Get PDF0000-0002-9387-9987A numerical method to implement a linearized Coulomb collision operator in the two-weight Monte Carlo method for multi-ion-species neoclassical transport simulation is developed. The conservation properties and the self-adjoint property of the operator in the collisions between two particle species with different temperatures are verified. The linearized operator in a Monte Carlo code is benchmarked with other two kinetic simulations, a continuum gyrokinetic code with the same linearized collision operator and a full-f PIC code with Nanbu collision operator. The benchmark simulations of the equilibration process of plasma flow and temperature fluctuation among several particle species show very good agreement between Monte Carlo code and the other two codes. An error in the H-theorem in the two-weight Monte Carlo method is found, which is caused by the weight spreading phenomenon inherent in the two-weight method. It is demonstrated that the weight averaging method serves to restoring the H-theorem without causing side effect.journal articl
Reduced models of turbulent transport in helical plasmas including effects of zonal flows and trapped electrons
Get PDF0000-0002-0712-8811Using transport models, the impacts of trapped electrons on zonal flows and turbulence in helical field configurations are studied. The effect of the trapped electrons on the characteristic quantities of the linear response for zonal flows is investigated for two different field configurations in the Large Helical Device. The turbulent potential fluctuation, zonal flow potential fluctuation and ion energy transport are quickly predicted by the reduced models for which the linear and nonlinear simulation results are used to determine dimensionless parameters related to turbulent saturation levels and typical zonal flow wavenumbers. The effects of zonal flows on the turbulent transport for the case of the kinetic electron response are much smaller than or comparable to those in an adiabatic electron condition for the two different field configurations. It is clarified that the effect of zonal flows on the turbulent transport due to the trapped electrons changes, depending on the field configurations.journal articl
Monitoring and Recovery of Tritium in a Fusion Test Facility
Get PDFIn a large fusion test facility, when a deuterium-plasma experiment is conducted a small amount of tritium is produced by the d(d, p)t reaction. From the viewpoints of radiation management and public acceptance, the tritium monitoring and recovery systems were developed and installed for the fusion test device. As for the tritium monitoring equipment, an expiratory test system of tritium was utilized for the internal dose assessment of workers. Active tritium samplers were operated continuously to monitor the amount of tritium released from the stack. As for the tritium recovery equipment, an exhaust detritiation system (EDS) for the plasma experiment has been developed and installed at the downstream of the vacuum pumping system in the fusion test device. All of the exhausted tritium from the vacuum vessel was treated by the EDS during the deuterium-plasma experimental campaign. Then, the tritium recovery rate achieved was more than 95%.journal articl