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Self-field measurements of an HTS twisted stacked-tape cable conductor
Get PDFFor a twisted stacked-tape cable (TSTC) conductor composed of REBCO tapes, self-field measurements were conducted with Hall sensors. In the measurements, a 650 mm diameter single turn coil wound with the TSTC conductor, which was made with 48 REBCO tapes whose width was 6 mm, was utilized as a test sample. Based on the measurement results, the current distribution of the TSTC conductor was investigated with analytical models. The analytical results indicate the current distribution of the TSTC is uniform under the condition that the operating current is 10 kA and the sample temperature is approximately 30 K. On the other hand, the current distribution is not uniform at the excitation and the degauss of the TSTC conductor with the ramp rate of 50 A/s.journal articl
Development of 1-T Class Force-Balanced Helical Coils Using REBCO Tapes
Get PDFThe authors proposed the concept of the force-balanced helical coils (FBC) using high-temperature superconducting (HTS) tapes as a feasibility option for superconducting magnetic energy storage (SMES). Although the FBC can minimize the mechanical stresses induced by the electromagnetic forces, the FBC has three-dimensional complex shapes of helical winding. Therefore, when the tensile strain and the complex bending strain simultaneously apply to the HTS tapes, the critical current of the HTS coils may decrease irreversibly. The objective of this work is to clarify the critical current property of REBCO tapes depending on the applying complex mechanical strain due to the winding process, the winding configuration and the electromagnetic forces through the development of the HTS-FBC. As a first, design parameters of 1-T class FBC using REBCO tapes and coil winding trajectory were introduced, and the authors discussed the normalized critical current of the HTS-FBC for complex uniaxial strain distribution. The authors also reported a development of a helical winding machine whose motion was optimized to prevent from decreasing the critical current of the HTS tapes during winding process.journal articl
Development of HTS Current Leads for the ITER Project
Get PDFThe HTS current leads for the ITER project will be the largest ever operated, with unprecedented currents, up to 68 kA and voltages, up to 14 kV. According to the ITER agreement they will be provided in-kind by China. After an extensive development program at the Hefei Institute of Plasma Physics (ASIPP), the ITER current leads were designed and qualified. The following discusses the main highlights of this development, with particular emphasis on the description of the design of the different types of ITER current leads and their final qualification in dedicated cold tests in nominal conditions.journal articl
Gyrokinetic simulations for turbulent transport of multi-ion-species plasmas in helical systems
Get PDF0000-0002-2459-2392The turbulent transport of magnetic confinement plasmas including multi-ion-particle-species in helical systems such as the Large Helical Device (LHD) [Takeiri et al., Nucl. Fusion 57, 102023 (2017)] and their plasma profile sensitivities are investigated by local flux-tube gyrokinetic simulations. In the multi-ion-species plasmas, while the heat transport of each particle species has slightly different sensitivity towards the plasma temperature gradients and the density gradients, there exist quite different dependencies in the particle transport on the radial gradient profiles of the plasma temperatures and densities between each particle species. Furthermore, in the LHD plasma with the carbon impurity hole structure [Ida et al., Plasma Phys. 16, 056111 (2009)], the turbulent particle transport flux of the impurity carbon ion remains radially inward-directed robustly within the wide ranges of radial gradient profiles of the plasma temperatures and densities.journal articl
3D effects of neon injection positions on the toroidally symmetric/asymmetric heat flux distribution on EAST
Get PDF0000-0002-6114-1996The heat flux deposition on the divertor targets with neon impurity injection on EAST has been investigated using the three-dimensional (3D) edge transport code EMC3-EIRENE. The impact of different poloidal neon injection positions on heat flux deposition has been studied. It was found that neon impurities injected at the in- and out-board divertors (i.e. strike points) lead to toroidally asymmetric distributions of heat load on the in- and out-board targets, respectively. However, neon gas puffing upstream shows a toroidally symmetric distribution of heat load. The 3D effects of the neon radiation on the heat load have been investigated with the help of a field line tracing technique, which indicates that neon impurities injected near the strike point can radiate more power and result in a lower heat load compared with upstream neon injection. In order to further verify the asymmetric distribution of heat load, two impurity injection locations away from the strike points at the divertor are investigated, which show the symmetric distribution of heat load as with the upstream neon injection.journal articl
Influence of Neutron Irradiation on the Large Helical Device Thomson Scattering System
Get PDF0000-0002-7023-1539Since 2017, deuterium plasma experiments (DD experiments) have been performed in large helical device (LHD), where neutrons with a specific energy of 2.45 MeV are generated through deuterium thermonuclear fusion reactions, and the influence on the devices located near the LHD are concerned. For the LHD Thomson scattering system, a view window, a light collection mirror, and optical fibers have been installed near the LHD. Degradation by neutron irradiation may cause serious problems in the results from the Thomson scattering diagnostic. We discuss the calibration of the three components and the neutron influences on the LHD Thomson scattering diagnostics.journal articl
Design of Neutron Spectrum-Shaping Assembly Around the Pneumatic Tube-End in the LHD Torus Hall for the Medical Research Application
Get PDF0000-0003-0920-2154The designs of neutron spectrum-shaping assembly (NSSA) composed with various shielding materials with natural isotopic abundance were evaluated to construct the neutron field dominated with thermal neutron or epi-thermal neutron for the application of neutron filed in the torus hall of LHD toward the BNCT research. According to the neutron transport calculation by MCNP6, the fast neutron moderation efficiency was higher in polyethylene (PE) compared to lithium fluoride (LiF) and magnesium fluoride (MF), although LiF showed relatively large epi-thermal and thermal neutron absorption. This comparison showed that the thermal neutron field can be effectively achieved with using PE. For constructing the NSSA which can provide the neutron field dominated with epi-thermal neutron, several NSSA designs were evaluated with respect to fast neutron flux, epi-thermal neutron flux, and gamma-ray dose. The combination of MF, lead (Pb) and cadmium (Cd) can provide the good epi-thermal neutron field with the mitigations of fast neutron flux and gamma-ray dose, which is also suitable for BNCT research in the torus hall of LHD.journal articl
Investigation of remaining tritium in the LHD vacuum vessel after the first deuterium experimental campaign
Get PDF0000-0003-0161-0938Remaining tritium in the vacuum vessel after the first deuterium plasma experimental campaign conducted over four months was investigated in the large helical device (LHD) for the first time in stellarator/heliotron devices by using the tritium imaging plate technique. In-vessel components such as divertor tiles and first wall panels, and long-term material probes retrieved from the vacuum vessel were analyzed. The in-vessel component in which tritium remained most densely is the baffle part of divertor tiles made of graphite retrieved from the inboard-side divertor. Asymmetric tritium retention is observed on divertor tiles located at magnetically symmetric positions, and can be attributed to the toroidal field direction dependence of the asymmetric loss of energetic tritons generated by deuterium–deuterium nuclear fusion reactions. On the first wall, tritium remained in a deposited layer, which mainly consists of carbon.journal articl
Performance of the newly installed vertical neutron cameras for low neutron yield discharges in the Large Helical Device
Get PDF0000-0002-0160-0468Two new vertical neutron cameras characterized by high detection efficiency were developed on the Large Helical Device in order to observe poloidal structures of helically trapped beam ions created by the perpendicularly injected positive-ion based neutral beam (P-NB) and are newly operated since 2018. In this work, the neutron fields at the vertical neutron cameras are investigated using the Monte Carlo N-particle transport code to evaluate the performance of its collimators. The results indicate that neutrons are attenuated by the heavy concrete and are well collimated through the collimator to detectors. Neutron spectra at the detector position show over 99% of uncollided 2.45 MeV neutrons. Time evolution of neutron emission profiles during the short pulse of P-NB injection is measured by the vertical neutron cameras. Peaks on the neutron emission profiles corresponding to the helically trapped beam ion are successfully obtained, as designed. The decrease in line integrated neutron flux at the peak positions after the P-NB stops is consistent with the behavior of the total neutron emission rate measured by the neutron flux monitor.journal articl
Observation of neutron emission anisotropy by neutron activation measurement in beam-injected LHD deuterium plasmas
Get PDF0000-0002-0010-6310Neutron emission anisotropy caused by neutral beam injection was observed by the neutron
activation measurement in deuterium plasmas confined in the Large Helical Device. The
shot-integrated fast neutron flux was measured by the irradiation of activation foils at two
irradiation ends located at different ports. The ratio of the flux at the outside horizontal port to
that at the lower port was used as an index of neutron emission anisotropy. The dependence of
the ratio on the direction of the neutral beam injection was confirmed by comparing cases of
tangential, perpendicular and both tangential and perpendicular neutral beam injections.
Neutron emission anisotropy was numerically evaluated assuming these three cases of neutral
beam injection. The analysis of neutron emission anisotropy comprises the evaluation of the
velocity distribution function of energetic deuterons following guiding-centre orbits, calculation
of the double-differential emission spectrum of neutrons produced by the D(d, n)3He reaction
and neutron transport calculation. The obtained numerical results are qualitatively consistent in
the dependence of neutron emission anisotropy on the neutral-beam-injection direction with the
observed experimental data.journal articl