NIFS-Repository (National Institute for Fusion Science)
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Analysis of NB Fast-Ion Loss Mechanisms in MHD Quiescent LHD Plasmas
Get PDF0000-0003-3293-488XNeutral beam (NB) fast-ion loss mechanisms in the large helical device (LHD) are investigated by the combination of the neutron measurement, the classical slowing-down simulation, and the neo-classical guiding center orbit following simulation. It is found that the neo-classical transport provides little contribution to the loss of tangentially injected NB fast-ions. For perpendicularly injected NB fast-ions, the neo-classical transport has more than 40% contribution to the NB fast ion loss. These results indicate that there are other loss mechanisms dominant in LHD plasmas. The charge exchange loss is one of the plausible candidates for the loss mechanism.journal articl
Characterization of the New Vertical Neutron Camera Designed for the Low Neutron Emission Rate Plasma in Large Helical Device
Get PDF0000-0002-0160-0468Characteristics of the new vertical neutron camera (VNC3) installed for the study of energetic-particle transport in the relatively low neutron emission rate (Sn) in Large Helical Device (LHD) deuterium plasma is investigated. Dependence of signal of VNC3 operating with the current mode on Sn shows that accurate neutron signal is obtained using VNC3 in low Sn range with 10 ms time bin where the error of neutron counts of first vertical neutron camera (VNC1) operating with the pulse counting mode is significantly large. Time-resolved measurements of neutron emission profiles in deuterium beam heated low Sn plasmas are performed. Although the line-integrated neutron obtained by VNC3 is wider due to its larger inner diameter of the collimator compared to VNC1, the neutron profile measured by VNC3 is almost matched with the neutron profile measured by VNC1. The time-resolved neutron profile measurement in low Sn discharge with relatively short time period becomes possible using VNC3.journal articl
Neutron yield calculation of thin and thick d-D targets by using PHITS with frag data table
Get PDF0000-0003-2254-3164The D(d, n)3He reaction is one of the common monoenergetic neutron sources. We compile the Frag Data table of D(d, n)3He reaction from the literature as an external cross-section data for PHITS. We confirm the validity of the Frag Data table by the calculation of the total and angular neutron yield calculations for an ideal deuterium thin target. Finally, PHITS with the Frag Data table is applied to the angular neutron yield and spectrum calculations of the gas target and the deuterium-loaded titanium target of the Tohoku University Fast Neutron Laboratory.journal articl
Development of a weighted sum estimate of the total radiated power from large helical device plasma
Get PDF0000-0001-7005-0562Diagnosing the amount of radiated power is an important research goal for fusion devices. This research aims at better understanding and diagnosing the radiated power from the Large Helical Device (LHD). The current radiated power estimate in the LHD is based on one wide-angle resistive bolometer. Because the estimate stems from one bolometer location toroidally and has a wide-angle poloidal view, this estimate does not take into account toroidal and poloidal radiation asymmetries that are observed in the LHD in discharges with gas puffing. This research develops a method based on the EMC3-Eirene model to calculate the set of coefficients for a weighted-sum method of estimating the radiated power. This study calculates these coefficients by using a least-squares method to solve for a coefficient set, using a variety of simulated cases generated by the EMC3-Eirene model, combined with corresponding geometric radiated power density considerations. If this set of coefficients is multiplied by the detector signal of each bolometer and summed up, this gives a total radiated power estimate. This new estimate takes into account toroidal and poloidal asymmetries by using the bolometer channels viewing different toroidal and poloidal locations, thereby reducing the estimation error and providing information about toroidal asymmetries.journal articl
A study of beam ion and deuterium–deuterium fusion-born triton transports due to energetic particle-driven magnetohydrodynamic instability in the large helical device deuterium plasmas
Get PDF0000-0003-4555-1837Understanding energetic particle transport due to magnetohydrodynamic instabilities excited by energetic particles is essential to apprehend alpha particle confinement in a fusion burning plasma. In the large helical device (LHD), beam ion and deuterium–deuterium fusion-born triton transport due to resistive interchange mode destabilized by helically-trapped energetic ions (EIC) are studied employing comprehensive neutron diagnostics, such as the neutron flux monitor and a newly developed scintillating fiber detector characterized by high detection efficiency. Beam ion transport due to EIC is studied in deuterium plasmas with full deuterium or hydrogen/deuterium beam injections. The total neutron emission rate (Sn) measurement indicates that EIC induces about a 6% loss of passing transit beam ions and a 60% loss of helically-trapped ions. The loss rate of helically-trapped ions, which drive EIC, is larger than the loss rate of passing transit beam ions. Furthermore, the drop of Sn increasing linearly with the EIC amplitude shows that barely confined beam ions existing near the confinement-loss boundary are lost due to EIC. In full deuterium conditions, a study of deuterium–deuterium fusion-born triton transport due to EIC is performed by time-resolved measurement of total secondary deuterium–tritium neutron emission rate (Sn_DT). Drop of Sn_DT increases substantially with EIC amplitude to the third power and reaches up to 30%. The relation shows that not only tritons confined in confined-loss boundary, but also tritons confined in the inner region of a plasma, are substantially transported.journal articl
Correlation Analysis between Density and Magnetic Field Low Frequency Fluctuations in Improved Confinement Mode on LHD
Get PDFA plasma density fluctuation signal was measured by the recently-installed Beam Emission Spectroscopy (BES). A time-dependent analysis was performed for a discharge in the Large Helical Device (LHD) and compared with the magnetic fluctuation. While the fundamental frequency peak shows a high correlation between the density fluctuation and the magnetic fluctuation, the higher harmonic components have smaller or even negligible correlation. As a possible mechanism that makes the density fluctuation and the magnetic fluctuation different, the relation between the MHD mode and the transport is discussed.journal articl
Demonstration of High-Speed Data Replication Relay Across Multiple Repository Sites Using a Global Loop Path
Get PDF0000-0001-6388-4489Technical verification has been progressing for high efficiency data replication between ITER and the Remote Experimentation Centre (REC) in Japan. Transferring a huge amount of data simultaneously to multiple destinations might cause excessive loads and network bandwidth on the sender so that daisy-chained relay transfer would be a considerable solution. This study demonstrates how efficiently the replication relay could be realized for the next-generation fusion experiments, such as ITER and JT-60SA. All the LHD data were consecutively sent to the REC through the global loop path (GLP: Toki - Gifu - Tokyo - Amsterdam - New York - Los Angeles - Tokyo - Aomori - Rokkasho) on SINET5 L2VPN, whose round-trip time is almost 400 ms. MMCFTP was used for the data transferring application. In both the Japan domestic path and the GLP cases, every transfer shows a very stable flattop speed as the preset 8 Gbps. However, longer gap times were needed in MMCFTP initial negotiation to establish numerous sessions. The performance optimized NVMe and iSCSI striped storages have shown higher throughputs than the ITER estimated initial data rate of 2 GB/s. Those knowledge enable the design optimization of not only the sender/receiver servers with their storages but also the intermediate relay server system.journal articl
Simulation of Impurity Transport and Deposition in the Closed Helical Divertor in the Large Helical Device
Get PDF0000-0003-0655-7347Long pulse discharges in the Large Helical Device have often been interrupted by large amounts of dust particle emission from the divertor region caused by the exfoliation of carbon-rich mixed material deposition layers. The plasma wall interaction code ERO2.0 has provided the simulation results of the three-dimensional distribution of the carbon flux density in the divertor region which is quite reasonable with the observed distribution of the carbon-rich deposition layers. The code has also succeeded in reproducing the reduction of the carbon deposition layers on dome plates by changing the target plate configuration in the divertor region. The ERO2.0 simulations have also successfully explained dust particle emission from the inboard side near the equatorial plane for the new target plate configuration at the termination of a long pulse discharge. These simulation results prove that the ERO2.0 code is applicable to predicting the possible position from where the dust particles are released, and to designing an optimized divertor configuration for performing stable long pulse discharges with controlled dust particle emission.journal articl
Neutron Emission Rate Characteristics of an Electron Cyclotron Heated Large Helical Device Deuterium Plasma
Get PDF0000-0003-4555-1837The total neutron emission rate (Sn) characteristics of electron cyclotron heated plasma were surveyed in the Large Helical Device in order to exhibit the thermonuclear performance of helical plasma. The dependence of Sn on electron density showed that Sn increased with an electron density of power of 3.1. To understand Sn, characteristics in the electron cyclotron heated plasma, a numerical simulation considering thermal deuterium-deuterium fusion reactions was performed. Although the numerical simulation overestimated Sn in a relatively low Sn region, calculated Sn matched the experimental result for a relatively high Sn region. A possible reason for the disagreement in the low Sn region is that effective charge due to the impurities such as carbon is changed because of the low density.journal articl
Extending the total neutron emission rate of steady-state deuterium large helical plasma guided by a data-driven approach
Get PDF0000-0003-4555-1837A 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