102 research outputs found
Predictive analysis for triton burnup ratio in HL-2A and HL-2M plasmas
No full text0000-0003-4555-1837The expected triton burnup ratio was analyzed based on numerical simulation to study the feasibility of demonstrating energetic particle confinement through 1 MeV triton burnup experiments in HL-2A and HL-2M. Calculations were conducted using LORBIT, a collisionless Lorentz orbit code, and FBURN, a neutron emission calculation code based on the classical confinement of energetic particles. First, the orbit loss and radial distribution of the tritons were evaluated using the LORBIT code. The LORBIT code revealed that all tritons were lost within ∼10−6 s in HL-2A, whereas in HL-2M, most of the tritons were still confined at 10−3 s. The FBURN code calculated the deuterium–tritium neutron emission rate using the radial distribution of 1 MeV tritons. The predictive analysis found that nearly no deuterium–tritium neutrons remained in HL-2A at a plasma current of 160 kA. Also, in HL-2M, a significant triton burnup ratio could be obtained at the relatively high plasma currents of 1MA, 2MA, and 3MA. This analysis predicts that the triton burnup ratio exceeds 1% under relatively high plasma current conditions.journal articl
Extending the total neutron emission rate of steady-state deuterium large helical plasma guided by a data-driven approach
No full text0000-0003-4555-1837A trial for extending the total neutron emission rate (Sn) was performed in the Large Helical Device (LHD) deuterium plasma experiment using a gas puff in order to show the way to realize a steady-state fusion reactor. In the 22nd experimental campaign of the LHD, a high Sn discharge was performed by the experimental scenario guided by a data-driven approach. A regression analysis of Sn was conducted beforehand using the externally controllable parameters based on the database of the previous three campaigns. Then, the high Sn record was successfully updated to be 3.7 × 1015 n/s in a steady-state discharge during the 22nd campaign in line with the regression expression. This study demonstrates that such a data-driven approach is effective for the gradual extension of Sn beyond the employed database.journal articl
Extending the total neutron emission rate of steady-state deuterium large helical plasma guided by a data-driven approach
No full text0000-0003-4555-1837A trial for extending the total neutron emission rate (Sn) was performed in the Large Helical Device (LHD) deuterium plasma experiment using a gas puff in order to show the way to realize a steady-state fusion reactor. In the 22nd experimental campaign of the LHD, a high Sn discharge was performed by the experimental scenario guided by a data-driven approach. A regression analysis of Sn was conducted beforehand using the externally controllable parameters based on the database of the previous three campaigns. Then, the high Sn record was successfully updated to be 3.7 × 1015 n/s in a steady-state discharge during the 22nd campaign in line with the regression expression. This study demonstrates that such a data-driven approach is effective for the gradual extension of Sn beyond the employed database
Estimation of the Fast-Ion Anisotropy Effect on the Neutron Source Intensity Measurement and the Experimental Observation
No full text0000-0003-2254-3164In the large helical device (LHD) deuterium plasma experiment, the neutron emission rate and the shot-integrated neutron yield are measured with the neutron flux monitor (NFM) and the neutron activation system (NAS), respectively, where the neutron emission is assumed to be isotropic in the plasma. The differential cross section of the D(d,n) 3 He reaction has a large anisotropy for the forward direction of the incident deuteron direction. LHD has intensive tangential neutral beam injectors (NBIs), which may cause an anisotropic neutron emission in the plasma. The angular distribution of the neutron emission is calculated from the fast-ion distribution function evaluated by a code that solves Fokker-Plank equations for the 180-keV tangential NBI. The effect of the anisotropic neutron emission on the NFM and NAS measurements is estimated by a general-purpose Monte Carlo N-particle (MCNP) code calculations. Also, the effect is confirmed experimentally. The neutron emission rate measured with the NFM near the equatorial port is about 10% larger than that with the NFM at the top of the LHD center axis. The shot-integrated neutron yield measured with NAS is 25% larger than that with NFM at the top of the LHD center axis in the case of the tangential neutral beam injection, which is consistent with the MCNP calculation.journal articl
Hybrid simulation of NBI fast-ion losses due to the Alfvén eigenmode bursts in the Large Helical Device and the comparison with the fast-ion loss detector measurements
No full text0000-0002-5364-805XThe multiphase simulations are conducted with the kinetic-magnetohydrodynamics hybrid code MEGA to investigate the spatial and the velocity distributions of lost fast ions due to the Alfvén eigenmode (AE) bursts in the Large Helical Device plasmas. It is found that fast ions are lost along the divertor region with helical symmetry both before and during the AE burst except for the promptly lost particles. On the other hand, several peaks are present in the spatial distribution of lost fast ions along the divertor region. These peaks along the divertor region can be attributed to the deviation of the fast-ion orbits from the magnetic surfaces due to the grad-B and the curvature drifts. For comparison with the velocity distribution of lost fast ions measured by the fast-ion loss detector (FILD), the ‘numerical FILD’ which solves the Newton–Lorentz equation is constructed in the MEGA code. The velocity distribution of lost fast ions detected by the numerical FILD during AE burst is in good qualitative agreement with the experimental FILD measurements. During the AE burst, fast ions with high energy (100–180 keV) are detected by the numerical FILD, while co-going fast ions lost to the divertor region are the particles with energy lower than 50 keV.journal articl
Effects of gamma-ray irradiation on electronic and non-electronic equipment of Large Helical Device
No full text0000-0003-4555-1837In a deuterium operation on the Large Helical Device, the measurement and control equipment placed in the torus hall must survive under an environment of radiation. To study the effects of gamma-ray irradiation on the equipment, an irradiation experiment is performed at the Cobalt-60 irradiation facility of Nagoya University. Transient and permanent effects on a personal computer, media converters, programmable logic controllers, isolation amplifiers, a web camera, optical flow meters, and water sealing gaskets are experimentally surveyed. Transient noise appears on the web camera. Offset of the signal increases with an increase of the integrated dose on the programmable logic controller. The DeviceNet module on the programmable logic controller is broken at the integrated dose of 72 Gy, which is the expected range of the integrated dose of the torus hall. The other equipment can survive under the gamma-ray field in the torus hall.journal articl
The large helical device vertical neutron camera operating in the MHz counting rate range
No full text0000-0003-4555-1837In the currently performed neutral beam (NB) -heated deuterium plasma experiments, neutrons are mainly produced by a beam-plasma reaction. Therefore, time-resolved measurement of the neutron emission profile can enhance the understanding of the classical and/or anomalous transport of beam ions. To measure radial neutron emission profiles as a function of time, the vertical neutron camera (VNC) capable of operation with a counting rate in the MHz range was newly installed on the Large Helical Device (LHD). This is the world’s first neutron camera for stellarator/heliotron devices. The VNC consists of a multichannel collimator, eleven fast-neutron detectors, and the digital-signal-processing-based data acquisition system (DAQ). The multichannel collimator having little cross talk was made from hematite-doped heavy concrete, which has a high shielding performance against both neutrons and gamma-rays. A stilbene crystal coupled with a photomultiplier having high-gain-stability in the high-count rate regime was utilized as a fast-neutron scintillation detector because it has a high neutron-gamma discrimination capability at high count rates. The DAQ system equipped with a field programmable logic controller was developed to obtain the waveform acquired with a 1 GHz sampling rate and the shaping parameter of each pulse simultaneously at up to 106 cps (counts per second). Neutron emission profiles were successfully obtained in the first deuterium campaign of LHD in 2017. The neutron emission profile was measured in tangentially co-injected NB-heated plasma with different magnetic axes (Rax). The neutron counts became larger in the inward-shifted configuration, which was consistent with the total neutron rate measured by the neutron flux monitor. The radial peak position of the line-integrated neutron profile which changed according to Rax showed that the VNC worked successfully as designed. The VNC demonstrated the expected performance conducive to extending energetic-particle physics studies in LHD
Study of first orbit losses of 1 MeV tritons using the Lorentz orbit code in the LHD
No full text0000-0003-4555-1837Shot-integrated measurement of the triton burnup ratio has been performed in the Large Helical Device. It was reported that the triton burnup ratio, defined as total DT neutron yield divided by total DD neutron yield, increases significantly in inward shifted configurations. To understand the magnetic configuration dependence of the triton burnup ratio, the first orbit loss fraction of 1 MeV tritons is evaluated by means of the Lorentz orbit code for various magnetic configurations. The first orbit loss of 1 MeV tritons is seen at t of less than 10−5 s and loss points of the triton are concentrated on the side of the helical coil case where the magnetic field is relatively weak. The significant decrease of the first orbit loss fraction by 15% is obtained with the inward shift of the magnetic axis position from 3.90 to 3.55 m. It is found that the decrease of first orbit loss is due to the reduction of the first orbit loss of transition and helically trapped tritons.journal articl
Scintillating fiber detectors for time evolution measurement of the triton burnup on the Large Helical Device
No full textObservation of Enhanced Radial Transport of Energetic Ion due to Energetic Particle Mode Destabilized by Helically-trapped Energetic Ion in the Large Helical Device
No full text0000-0003-4555-1837A deuterium experiment was initiated to achieve higher-temperature and higher-density plasmas in March 2017 in the Large Helical Device (LHD). The central ion temperature notably increases compared with that in hydrogen experiments. However, an energetic particle mode called the helically-trapped energetic-ion-driven resistive interchange (EIC) mode is often excited by intensive perpendicular neutral beam injections on high ion-temperature discharges. The mode leads to significant decrease of the ion temperature or to limiting the sustainment of the high ion-temperature state. To understand the effect of EIC on the energetic ion confinement, the radial transport of energetic ions is studied by means of the neutron flux monitor and vertical neutron camera newly installed on the LHD. Decreases of the line-integrated neutron profile in core channels show that helically-trapped energetic ions are lost from the plasma.journal articl
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