Journal of Fusion Energy最新文献

The compact neutron emission spectrometers (CNES) system has enabled detailed and comprehensive characterization of fast ion confinement during the neutral beam injection heating in the Large Helical Device (LHD). Using high resolution neutron spectroscopy along both tangential and perpendicular lines-of-sight, CNES provides direct experimental access to deuterium–deuterium (D–D) reaction dynamics in velocity space, reflecting the behavior of fast ions injected by neutral beam injections. Significant Doppler shifts in D-D neutron energy were observed during intense tangential neutral beam injection, revealing the impact of the relative motion of the D-D reaction center-of-mass (CoM) with respect to the CNES sightline. An upshift in neutron energy was detected when the CoM moved toward the sightline, while a downshift occurred when it move away from the sighline. In plasmas heated by perpendicular neutral beam injection, a distinct double-humped neutron energy spectrum was observed, corresponding to the Larmor motion of helically trapped beam ions within the LHD’s magnetic ripple structure. The results demonstrate the capability of CNES to detect Doppler shifts in neutron energy associated with the direction and confinement of fast ions. By comparing experimental results with numerical simulations, the study confirms the reliability of both tangential and perpendicular CNESs sightline configuration in D-D neutron emission spectroscopy in LHD. The results improve our understanding of how fast ions generated by neutral beam injection affect D-D reaction.

In the Large Helical Device (LHD), plasma operation is possible with a helical divertor and inward-shifted configurations. For plasmas with a small distance between the divertor and the plasma, ultra-high neutral pressures of up to 2.4 Pa were measured in the helical divertor–ten times higher than theoretically predicted. This enables high particle exhaust rates, comparable to tokamaks such as ASDEX Upgrade and DIII-D, and is caused by a condensation instability near the divertor targets. Like a classical Marfe, it exhibits an asymmetric radiation pattern, but the new phenomenon is dominated by hydrogen radiation. We denote it as HYDRA, which stands for HYdrogen Dominated Radiation Asymmetry. The appearance of the HYDRA induces detachment of the divertor plasma, which, together with the ultra-high divertor neutral pressure, leads to a favorable divertor state for a fusion reactor based on the stellarator concept.

This is a review paper as a part of the special issue dedicated for Large Helical Device (LHD). The topic of this paper is long pulse discharges performed by Electron Cyclotron Heating (ECH) in LHD, and it is described based on the previously published papers related to the topic. The ECH system on LHD has been upgraded step by step, applying state of the art gyrotrons at the steps. The first long pulse discharge was achieved by applying 84 GHz, 110 kW continuous wave gyrotron. The pulse width was 65 min, with rather low line average electron density n_{e_ave} of 0.15 × 10¹⁹ m^− 3 and the central electron temperature T_e0 of 1.7 keV. Gradually applied 5 gyrotrons (three 77 GHz and two 154 GHz) took the place of the power source for the long pulse ECH discharges. Owing to the improvement in the ECH system, a stable 39 min discharge with much improved parameters, n_{e_ave} of 1.1 × 10¹⁹ m^− 3, T_e0 of over 2.5 keV, and a central ion temperature T_i0 of 1.0 keV was successfully performed with ~ 350 kW ECH power. Also, long pulse experiments have made progress in sustainment of improved electron confinement states (e-ITB) at the plasma core region. Sustainment of a plasma having e-ITB with n_{e_ave} of 1.1 × 10¹⁹ m^− 3 and T_e0 of ∼3.5 keV for longer than 5 min with 340 kW ECH power was successfully demonstrated.

Radiative collapse in neon (Ne) seeded plasmas has been detected using a two-dimensional radiation measurement (InfraRed imaging Video Bolometer, IRVB) and an AutoEncoder (AE) on the Large Helical Device (LHD). In divertor detachment for fusion reactors, while the divertor heat load is mitigated using impurity injection, excessive impurity injection induces radiative collapse. Therefore, it is important to detect the precursor of the radiative collapse for the control of the impurity injection amount to maintain stable divertor detachment. In this study, 1219 images measured with the IRVB were used for training. By using the AE model, in the discharges with moderate Ne pulses, radiative collapse was successfully detected as an increase of abnormality earlier than the Ne pulse just before the radiative collapse. Moreover, by investigating the anomalous radiation structure, it was found to remain at the edge plasma region when radiation increased without radiative collapse, whereas the anomalous radiation structure progressed toward the core plasma when radiative collapse occurred.

The Divertor Tokamak Test facility (DTT) is a fusion device under construction at the ENEA Research Centre in Frascati, Italy. DTT’s primary mission is to explore and test the physics and technology of concepts for the exhaust of the plasma thermal power, especially in the divertor region, in support to ITER and DEMO design. From this perspective, careful control of the total radiation emission will be essential for the operation of these next generation devices. This work focuses on the DTT bolometry system, which is currently in the design phase. Commercial foil bolometers have been selected to provide line-integrated measurements and enable tomographic reconstructions at this stage. The mechanical layout and integration into the machine have been defined, and the line-of-sights (LoS) configuration has been validated. However, preliminary thermo-mechanical analyses have revealed that the initial design did not fully meet all specifications. To address this, an actively cooled protective housing has been included to withstand the high thermal loads from the plasma, approximately 0.5 MW/m² for about 100 s in DTT. In this study, the equatorial bolometric camera simulations have been further refined, and the protective housing has been designed and fully integrated in the diagnostic port. A parametric thermal analysis has been performed, and the final design has been validated through finite elements simulations.

Second harmonic deuteron heating in the ion cyclotron range of frequency (ICRF) was evaluated based on neutron measurements newly installed before a deuterium experimental campaign of the LHD. In deuteron plasmas, it was confirmed that the neutron emission rate increased with higher ICRF injection power. Fast deuterons with energy above 500 keV could be measured by a diamond neutral particle analyzer, when the minority proton ratio was less than 1%. On the other hand, a significant increase in the neutron emission rate, due to fast deuterons produced by ICRF second harmonic heating, was not observed, even in the case of ICRF superimposing on neutral beam injection (NBI). In experiments when the ICRF resonance layer was located near the magnetic axis, fast-ion driven instabilities due to the ICRF heating were observed for the first time at the LHD.

This study presents a spectroscopic investigation of (text {Kr}^{24+}) ion, generated via a krypton impurity seeding experiment in the Large Helical Device, aimed at supporting Extreme Ultraviolet (EUV) diagnostics of high-temperature fusion plasma. EUV spectral lines corresponding to fine-structure transitions among the (text {2p}^{6}text {3s}^{2}text {,} , text {2p}^{6}text {3s3p,} , text {2p}^{6}text {3s3d,}) and (text {2p}^{6}text {3p}^{2}) configurations were observed in the 12–25 nm wavelength range. To systematically analyze the measured emission lines, extensive relativistic atomic structure calculations were carried out over a broad configuration space, spanning more than 40 configurations, including core-excited and correlation-dominated states up to (text {n}le {7}) and (ell le {4}). Bound-state wave functions were obtained using the relativistic many-body perturbation theory and configuration interaction method, implemented via the Flexible Atomic Code. Parallel calculations based on the relativistic multiconfiguration Dirac-Hartree-Fock method with configuration interaction were performed using the GRASP-2018 code to ensure numerical consistency. This article presents fine-structure-resolved excitation energies and transition parameters, including oscillator strengths and transition probabilities, for the relevant spectroscopic configurations up to (3ell). Moreover, electron impact excitation and ionization cross-sections from the ground state ((text {2p}^{6}text {3s}^{2} , {}^{1}text {S}_{0})) as well as from selected excited states to higher-lying levels were calculated using the relativistic distorted wave method from the respective thresholds over a wide energy range. The corresponding Maxwellian averaged rate coefficients for excitation, de-excitation, ionization, and three-body recombination were evaluated over fusion-relevant electron temperatures. The results are presented for the prominent spectroscopic transitions up to (3ell). These complete atomic and electron-collision datasets were incorporated into a suitable collisional-radiative model, accounting for the dominant population and depopulation processes, including electron impact excitation, de-excitation, ionization, radiative decay, and three-body recombination. The theoretically modeled EUV spectrum, calculated at (text {n}_text {e}text {=5.5}times text {10}^text {19} , text {m}^text {-3}) and (text {T}_text {e}text {=578} , text {eV}), shows good agreement with experimental observations, validating the accuracy of the calculated atomic structure, and electron-collision parameters. The resulting atomic dataset and modeling framework enable detailed spectral analysis of highly charged (text {Kr}^{24+}) ion under magnetically confined fusion plasma conditions.

Scheduled maintenance is likely to be lengthy and therefore consequential for the economics of fusion power plants. The maintenance strategy that maximizes the economic value of a plant depends on internal factors such as the cost and durability of the replaceable components, the frequency and duration of the maintenance blocks, and the external factors of the electricity system in which the plant operates. This paper examines the value of fusion power plants with various maintenance properties in a decarbonized United States Eastern Interconnection circa 2050. Seasonal variations in electricity supply and demand mean that certain times of year, particularly spring to early summer, are best for scheduled maintenance. Seasonality has two important consequences. First, the value of a plant can be 15% higher than what one would naively expect if value were directly proportional to its availability. Second, in some cases, replacing fractions of a component in shorter maintenance blocks spread over multiple years is better than replacing it all at once during a longer outage, even through the overall availability of the plant is lower in the former scenario.

Gamma ray diagnostics have been developed and installed in Large Helical Device (LHD) to study plasma physics, as well as to measure neutron fluence and spectrum in the LHD torus hall. LaBr₃:Ce scintillation and high purity Germanium (HPGe) detectors have been installed. LaBr₃:Ce scintillation detectors were used to measure gamma rays emitted from the plasma. Radiation shielding, composed of borated polyethylene and lead, was designed for the LaBr₃:Ce scintillation detector based on Monte Carlo radiation transport calculations. A gamma ray peak around 480 keV, believed to correspond to the ⁶Li(d, p’γ⁾⁷Li reaction, was observed. HPGe detectors were utilized for measuring the activity of metal foils. Using the activation analysis method, the thermal and epithermal neutron fluence distribution inside the LHD torus hall, the neutron spectrum, and the relationship between radioactivity and total neutron emission yield were determined.

One of the essential requirements for the future fusion power plants is the tritium self-sufficiency. Still, during transport from the breeding blanket towards the extraction system, a fraction of tritium permeates through the piping and containment walls, and it might escape into the outer environment. To reduce the amount of permeated tritium in the coolant, the obvious solution is coating of the tritium exposed surfaces with anti-permeation barriers. Stainless steels and EUROFER97 are the main materials for DEMO systems construction. While EUROFER97 is a reduced activation martensitic steel specially designed for the construction of fusion reactor blankets which will be exposed to neutron irradiation, stainless steels like 316(L) are used for constructing the other components and systems. Hydrogen isotopes in various gas mixtures are permanently circulated through the reactor systems as they are the fuel which drive it. This paper is a detailed analysis of different technologies and materials conceived for creating efficient barriers against hydrogen permeation through stainless steel and EUROFER97. This literature review presents some investigation of important aspects regarding the development of stable hydrogen permeation barriers in order to prevent adsorption in structural materials and permeation of hydrogen isotopes. These barriers will help avoid the corrosion and embrittlement effects, and also, they will prevent the migration of tritium towards other systems and environment which poses radiation protection issues.