Journal of Fusion Energy最新文献

To resolve technical issues associated with the plasma-facing components (PFCs) such as the divertor to be installed in a steady state magnetic fusion DEMO reactor, employing high-temperature metals such as tungsten for the surface component, the use of liquid metals (LMs) such as molten lithium has been proposed and evaluated as a possible resolution over the past two or so decades, using plasma confinement devices as well as laboratory-scale experimental facilities. The present work is intended to explore the effect of forced convection in liquid metals on the transport behavior of particles and heat from divertor plasma bombardment. Laboratory-scale experiments have been conducted, using GaInSn and molten lithium as the liquid metal targets to be exposed to steady-state plasmas and infrared irradiation. Data clearly indicate that electromagnetically induced convection can enhance particles and heat transport in these liquid metals, proof-of-principle data for convected LM-PFCs.

Self-healing liquid metal divertors (LMDs) based on the Capillary Porous Structure (CPS) concept are currently being considered among the possible solutions to the power exhaust problem in future fusion reactors. Indeed, the passive replenishment of the plasma-facing surface by capillary forces and the self-shielding of the target via vapor emission can potentially improve the divertor lifetime and its resilience to transient loads. On the other hand, the LMD target erosion can be significant due to evaporation and thermal sputtering, on top of physical sputtering, possibly leading to unacceptable core plasma dilution/power losses (for a low-Z/high-Z metal such as Li and Sn, respectively). For this reason, it is necessary to assess whether an LMD is compatible with an European DEMO (EU-DEMO) plasma scenario. This requires a self-consistent model of the impurity emission from the target, the plasma in both the scrape-off layer (SOL) and the core regions and the transport of impurities therein. In this paper, an an integrated modelling approach is proposed, which is based on SOLPS-ITER and includes its coupling with a target erosion model written in FreeFem++ and a core plasma model (ASTRA/STRAHL). An application of the coupled SOL-target model to simulate experiments performed in the Magnum-PSI linear plasma device with a CPS target filled with Li is also included to provide a first demonstration of the capabilities of the approach. Results are promising, being in good agreement (within a few degrees) with the measured target temperature distribution. In perspective, the modelling framework presented here will be applied to the EU-DEMO with an Sn divertor.

The modelling of the edge lithium (Li) transport and heat flux deposition on divertor targets under different poloidal Li injections has been performed on EAST with the three-dimensional (3D) edge transport code EMC3-EIRENE. Four injected positions of Li impurity (including divertor and upstream injections) are investigated to check the Li density distribution and its impacts on the heat flux deposition profiles. The simulation results show that the Li injections near the strike points lead to small spatial amounts of Li ions compared to the upstream injections. The energy dissipation by Li impurity for different poloidal injections has been analysed by varying the upstream electron density. It is found that the increased upstream electron density leads to a slightly enhanced exhausted power of Li impurity for upstream injections while an evidently reduced energy loss for divertor injections. Moreover, the asymmetric distributions of heat flux deposition on target plates are obtained for divertor injections, while the symmetric distributions of heat flux are attained for upstream injections.

According to the European Fusion Roadmap, to demonstrate the feasibility of fusion energy, it is necessary to build a comprehensive database of materials properties to be used in future fusion power plants. This is the objective of the IFMIF-DONES facility, which will drive a deuteron beam on a liquid lithium target to produce high energy neutron fluxes for irradiating candidate fusion materials. Among the several ongoing activities in the frame of the EUROfusion Early Neutron Source Work Package (WPENS) project, deterministic accident analyses play an important role, since they help identifying a set of reference accident scenarios and related safety class components. Some of these scenarios are being studied with the MELCOR-fusion code, an integrated engineering code which is able to perform thermal-hydraulic transient calculations. In this work, the MELCOR-fusion code has been applied to two potential accident scenarios involving the degradation of the primary lithium loop of IFMIF-DONES. A rupture in the Quench Tank and a break in the inlet nozzle to the Target Vacuum Chamber were postulated as the two initiating events followed by a lithium spill into the Test Cell room. The purpose of this study was to obtain different key metrics, such as the maximum pressure and temperature loads reached in the TC room, the amount of the leaked lithium mass, and the time for lithium solidification. The computed results will help identify the safety requirements to be applied to the final design of the TC room.

We report sputtering yields of Li⁺, H⁻, O⁻, and OH_x⁻ ion species from an Li–O–H surface for H, D, He, Ne, and Ar ion irradiation at 45° incidence in the energy range of 30–2000 eV. A Li film was deposited on a stainless steel target using Li evaporators in the LTX-β vessel, using the LTX-β Sample Exposure Probe (SEP), which includes an ultrahigh vacuum suitcase for transferring targets without significant contamination from air exposure. The SEP was used to transfer the Li-coated target from LTX-β to a separate Sample Exposure Station (SES) to perform ion exposure measurements. The SEP was also used for characterization of the Li-coated target utilizing X-ray photoelectron spectroscopy in a different chamber, showing that the lithium film surface was oxidized. Ion exposures were performed using an electron cyclotron resonance plasma source in the SES. Sputtered/ejected species were sampled by a quadrupole mass spectrometer with capabilities for detecting positive and negative ions, and an energy filter for determining the mean kinetic energy of the ejected ion species. All ion irradiations caused Li⁺ ions to be ejected, while causing impurity ions such as H⁺, H⁻, O⁻ and OH⁻ to be ejected. Measured ion energies of Li⁺ ions from a Li–O–H surface suggested that the typical sheath potential on the divertor surface can trap sputtered Li⁺ ions, which were previously reported as ~ 60% of total sputtered Li species from Li targets (Allain and Ruzic in Nucl Fusion 42:202, 2002). Hence, our results for the sputtering yields of ejected ion species and their associated ion energies from a Li–O–H surface indicates that lithium sputtering is suppressed and impurity removal is enhanced due to the sheath potential at the divertor surface for fusion reactor applications.

The influence of a low-pressure argon arc with a hot tungsten cathode on the thin tin film with a negative bias voltage applied during the plasma treatment was investigated to study the tin film removal from the sample surface. Samples were prepared on a stainless-steel substrate using DC magnetron sputtering and hybrid HiPIMS assisted with electron cyclotron wave resonance (ECWR). During treatment an optical emission spectroscopy was employed to detect and characterize the emission line of tin spectrum and the electron density and temperature were measured by Langmuir probe. Morphological study by a scanning electron microscope helped to gain insight to the mechanism of tin removal from the substrate. In addition, elemental compositions of tin layer before and after treatment was measured by an energy dispersive X-ray spectroscopy. We believe that this study contributes to finding a proper treatment for tin removal from plasma facing surfaces of tokamaks using tin in the liquid metal divertor.

The primary performance index of the fast control power supply in the Experimental Advanced Superconducting Tokamak (EAST) is to quickly track the reference current signal, realize the excitation of the load coil with the output current, and feedback control the vertical displacement of the plasma. The current on the load coil of EAST fast control power supply is affected by various uncertain environmental factors, making it difficult to establish a standard mathematical model for prediction. Accurate object model is not required in grey prediction, and only a small amount of known information is needed to achieve short-term prediction of output current. Grey prediction has been studied and applied in EAST fast control power supply to some extent. To further improve prediction accuracy and accelerate output current response speed, an improved grey prediction algorithm is proposed to achieve output current prediction. Considering the control delay in digital control, the output current of the next period is predicted using the sampled original sequence. Following the principle of new information priority, an original sequence transformation operator is proposed to weight new information. The predicted output current in the next period is added to the original sequence while removing the oldest original sequence, to achieve rolling prediction of the output current in the next two periods. The control value of the output current is loaded one switching period in advance, further improving prediction accuracy while compensating for control delay. The output gain of proportional integral (PI) control is adaptively adjusted based on the error between the predicted current and the reference current, and the improved grey prediction variable gain PI control achieves fast and accurate control of the output current. Simulation and experimental results show that the proposed control method has high prediction accuracy. Compared to traditional PI control and grey prediction control, the proposed control method can effectively improve the output current response speed.

With direct symmetric laser illumination of a spherical target, there is the potential for high enough target gains to produce economically viable fusion power. Proposed solutions to the various laser-target physics problems have mostly relied upon modifications to the laser, while keeping the target relatively simple. Necessary but not sufficient laser constraints include a short laser wavelength, very uniform illumination of the target in both high and low spherical perturbation modes, a wide bandwidth, temporal pulse shaping, and a reduction of the focal spot size during the implosion. An electron-beam-pumped argon-fluoride gas laser best satisfies all of these constraints and has the potential for fusion energy gains that far exceed requirements for an economically viable power plant. Various diode-pumped solid-state laser concepts are reviewed. None can simultaneously satisfy most if not all of the constraints. For example, the recently proposed PolyKrōm design produces a set of narrowband discrete wavelengths. The intensity coherence time of this discrete set is too long, and it could not produce the required uniform laser illumination. It is also shown that solid state lasers cannot produce with sufficient efficiency the subnanosecond pulse that is required for the shock-ignition target design.

We propose a cost-effective polychromator with a single interference filter, because interference filters account for large parts of polychromator costs in the conventional Thomson scattering diagnostics with a Nd:YAG laser. Since the interference filters are used to transmit the scattered light in a specific wavelength range, one polychromator tends to have as many interference filters as its spectral channels, which makes high-resolution measurement with a number of polychromators expensive. However, we can save the number of interference filters and thus their costs by reentering reflected light from an interference filter into the same filter at different angles. This is possible, because the larger angle of incidence on the interference filter makes the wavelength of the transmitted light shorter. We measured dependence of transmitted wavelengths on the angles of incidence on one interference filter custom-ordered to transmit 1059 nm and developed the cost-effective polychromator using this dependence. The developed polychromator with a single filter successfully separated three different spectral channels (1043.2, 1051.9, and 1058.4 nm), enabling us to realize the cost-effective Thomson scattering diagnostics.