Los Alamos research in nozzle based coaxial plasma thrusters

The topics are presented in viewgraph form and include the following: research approach; perspectives on efficient magnetoplasmadynamic (MPD) operation; NASA and DOE supported research in ideal magnetohydrodynamic plasma acceleration and flow, electrode phenomena, and magnetic nozzles; and future research directions and plans

Serpent neutronics model of Wendelstein 7-X for 14.1 MeV neutrons

In this work, a Serpent 2 neutronics model of the Wendelstein 7-X (W7-X) stellarator is prepared, and an response function for the Scintillating-Fibre neutron detector (SciFi) is calculated using the model. The neutronics model includes the simplified geometry for the key components of the stellarator itself as well as the torus hall. The objective of the model is to assess the 14.1 MeV neutron flux from deuteron-triton fusions in W7-X, where the neutrons are modelled only until they have slowed down to 1 MeV energy. The key messages of this article are: demonstration of unstructured mesh geometry usage for stellarators, W7-X in particular; technical documentation of the model and first insights in fast neutron behaviour in W7-X, especially related to the SciFi: the model indicates that the superconducting coils are the strongest scatterers and block neutrons from large parts of the plasma. The back-scattering from e.g. massive steel support structures is found to be small. The SciFi will detect neutrons from an extended plasma volume in contrast to having an effective line-of-sight.</p

通过 3-D 建模分析 Wendelstein 7-X 启动情景的螺旋刮层中的热通量特性

International audienceA crucial topic for the stellarator W7-X is the power dissipation by impurities for future island divertor scenarios. The investigation of the related heat flux distribution and profiles including the radial power fall-off length λq in the 3D stellarator SOL is less straight forward as in toroidally symmetric tokamaks. Studies with the 3D plasma edge transport code EMC3-Eirene predicted a modulation of plasma parameters with LC and correlated heterogenous heat and particle loads onto the limiters during start-up operation. The relative simple start up geometry at W7-X allows for a detailed analysis of the heat fluxes in separate helical transport channels featuring different ∥ to ⊥ transport ratios. It is shown that the SOL has two characteristic fall off domains - a near SOL and a far SOL domain which both have different power decay lengths. An increase of λq with LC in the order of ~1-1.5cm in the near SOL and ~1.8-2.8cm in the far SOL for a power scan in the range of P=0.5-2MW at nLCFS=2×1018m−3 has been found. First comparisons with IR camera data will be discussed.Un sujet crucial pour le stellarator W7-X est la dissipation de puissance par les impuretés pour les futurs scénarios de divertor insulaire. L'étude de la distribution et des profils de flux de chaleur associés, y compris la longueur de chute de puissance radiale λq dans le SOL du stellarator 3D, est moins simple que dans les tokamaks à symétrie toroïdale. Des études avec le code de transport de bord de plasma 3D EMC3-Eirene ont prédit une modulation des paramètres du plasma avec LC et des charges de chaleur et de particules hétérogènes corrélées sur les limiteurs pendant le démarrage. La géométrie de démarrage relativement simple à W7-X permet une analyse détaillée des flux de chaleur dans des canaux de transport hélicoïdaux séparés présentant différents rapports de transport ∥ à ⊥. Il est montré que le SOL a deux domaines de décroissance caractéristiques - un domaine SOL proche et un domaine SOL lointain qui ont tous deux des longueurs de décroissance de puissance différentes. Une augmentation de λq avec LC de l'ordre de ~1-1,5 cm dans le SOL proche et de ~1,8-2,8 cm dans le SOL lointain pour un balayage de puissance dans la plage de P=0,5-2MW à nLCFS=2×1018m−3 a été trouvé. Les premières comparaisons avec les données des caméras IR seront discutées

通过 3-D 建模分析 Wendelstein 7-X 启动情景的螺旋刮层中的热通量特性

International audienceA crucial topic for the stellarator W7-X is the power dissipation by impurities for future island divertor scenarios. The investigation of the related heat flux distribution and profiles including the radial power fall-off length λq in the 3D stellarator SOL is less straight forward as in toroidally symmetric tokamaks. Studies with the 3D plasma edge transport code EMC3-Eirene predicted a modulation of plasma parameters with LC and correlated heterogenous heat and particle loads onto the limiters during start-up operation. The relative simple start up geometry at W7-X allows for a detailed analysis of the heat fluxes in separate helical transport channels featuring different ∥ to ⊥ transport ratios. It is shown that the SOL has two characteristic fall off domains - a near SOL and a far SOL domain which both have different power decay lengths. An increase of λq with LC in the order of ~1-1.5cm in the near SOL and ~1.8-2.8cm in the far SOL for a power scan in the range of P=0.5-2MW at nLCFS=2×1018m−3 has been found. First comparisons with IR camera data will be discussed.Un sujet crucial pour le stellarator W7-X est la dissipation de puissance par les impuretés pour les futurs scénarios de divertor insulaire. L'étude de la distribution et des profils de flux de chaleur associés, y compris la longueur de chute de puissance radiale λq dans le SOL du stellarator 3D, est moins simple que dans les tokamaks à symétrie toroïdale. Des études avec le code de transport de bord de plasma 3D EMC3-Eirene ont prédit une modulation des paramètres du plasma avec LC et des charges de chaleur et de particules hétérogènes corrélées sur les limiteurs pendant le démarrage. La géométrie de démarrage relativement simple à W7-X permet une analyse détaillée des flux de chaleur dans des canaux de transport hélicoïdaux séparés présentant différents rapports de transport ∥ à ⊥. Il est montré que le SOL a deux domaines de décroissance caractéristiques - un domaine SOL proche et un domaine SOL lointain qui ont tous deux des longueurs de décroissance de puissance différentes. Une augmentation de λq avec LC de l'ordre de ~1-1,5 cm dans le SOL proche et de ~1,8-2,8 cm dans le SOL lointain pour un balayage de puissance dans la plage de P=0,5-2MW à nLCFS=2×1018m−3 a été trouvé. Les premières comparaisons avec les données des caméras IR seront discutées

Recent progress on the National Spherical Torus Experiment (NSTX)

Recent upgrades to the NSTX facility have led to improved plasma performance. Using 5MW of neutral beam injection, plasmas with toroidal {beta}{sub T} (= 2{mu}{sub 0}&lt;p&gt;/B{sub T}{sup 2} where B{sub T} is the vacuum toroidal field at the plasma geometric center) &gt; 30% have been achieved with normalized {beta}{sub N} (={beta}{sub T}aB{sub I}/I{sub p}) {approx} 6% {center_dot} m {center_dot} T/MA. The highest {beta} discharge exceeded the calculated no-wall {beta} limit for several wall times. The stored energy has reached 390kJ at higher toroidal field (0.55T) corresponding to {beta}{sub T} {approx} 20% and {beta}{sub N} = 5.4. Long pulse ({approx}1s) high {beta}{sub p} ({approx}1.5) discharges have also been obtained at higher B{sub {phi}} (0.5T) with up to 6MW NBI power. The highest energy confinement times, up to 120ms, were observed during H-mode operation which is now routine. Confinement times of {approx} 1.5 times ITER98pby2 for several {tau}{sub E} are observed during both H-Mode and non-H-Mode discharges. Calculations indicate that many NSTX discharges have very good ion confinement, approaching neoclassical levels. High Harmonic Fast Wave current drive has been demonstrated by comparing discharges with waves launched parallel and anti-parallel to the plasma current

Infrared imaging systems for wall protection in the W7-X stellarator (invited)

Wendelstein 7-X aims at quasi-steady state operation with up to 10 MW of heating power for 30 min. Power exhaust will be handled predominantly via 10 actively water cooled CFC (carbon-fiber-reinforced carbon) based divertor units designed to withstand power loads of 10 MW/m2 locally in steady state. If local loads exceed this value, a risk of local delamination of the CFC and failure of entire divertor modules arises. Infrared endoscopes to monitor all main plasma facing components are being prepared, and near real time software tools are under development to identify areas of excessive temperature rise, to distinguish them from non-critical events, and to trigger alarms. Tests with different cameras were made in the recent campaign. Long pulse operation enforces additional diagnostic design constraints: for example, the optics need to be thermally decoupled from the endoscope housing. In the upcoming experimental campaign, a graphite scraper element, in front of the island divertor throat, will be tested as a possible means to protect the divertor pumping gap edges during the transient discharge evolution