Coherent Propagation of Polaritons in Semiconductor Heterostructures: Nonlinear Pulse Transmission in Theory and Experiment

The influence of coherent optical nonlinearities on polariton propagation effects is studied within a theory-experiment comparison. A novel approach that combines a microscopic treatment of the boundary problem in a sample of finite thickness with excitonic and biexcitonic nonlinearities is introduced. Light-polarization dependent spectral changes are analyzed for single-pulse transmission and pump-probe excitation

The operational space for divertor power exhaust in DEMO with a super-X divertor

SOLPS-ITER simulations of the European DEMO reactor with a Super-X divertor, which has larger major radius at the outer target and increased connection length, show an increased operational space for divertor power exhaust compared to the conventional single-null configuration. Using a multi-fluid approach with fluid neutrals and charge-state bundling of impurities, we assessed the existence and boundaries of the operational space in the single-null and Super-X configurations by carrying out fuelling, seeding and power scans. Compared to the conventional single-null divertor, the Super-X divertor offers lower impurity concentration (factor ∼2 lower) at the same main plasma density, and consistent with this, it has lower main plasma density at the same impurity concentration level. This observed difference is in line with the simple analytical Lengyel model predictions resulting from the increased connection length in the super-X configuration. DEMO with a Super-X divertor demonstrates remarkable robustness against increases in input power, and in this study is able to exhaust the maximum expected steady-state separatrix-crossing power of 300 MW while maintaining acceptable impurity concentration along the separatrix This is something that was not possible in the single-null configuration in this study. This robustness of the Super-X divertor lies mostly in its capability to sufficiently dissipate power in its divertor via argon (Ar) radiation at acceptable Ar concentration, which is related to two factors: long (with respect to single-null) parallel connection length from the upstream to the outer target and higher but tolerable extrinsic impurity concentration at higher input powers. Finally, consistent with neon-seeded simulations of ITER, it is observed in all our simulations that the plasma density drops with increasing Ar concentration given fixed power input. We find that as the Ar content increases, the accompanying enhancement of Ar radiation reduces the power available for deuterium (D) to be ionized, thus limiting the D ionization particle source, and consequently reducing the plasma density

Scoping the characteristics and benefits of a connected double-null configuration for power exhaust in EU-DEMO

A double-null configuration is being considered for the EU-DEMO, due to its potential benefits for power exhaust arising from the use of two active divertors and magnetically disconnected low- and high-field sides. Using systematic parameter scans in fluid simulations, we have investigated the divertor power exhaust in the EU-DEMO in a connected double-null configuration, and compared the edge plasma properties to those obtained in a single-null configuration under detached conditions anticipated for reactor operation. Neglecting drift effects and kinetic behaviour of the neutrals, no clear benefits of the double-null configuration could yet be identified for the radiation pattern and power mitigation on open field lines. Future work should address the aforementioned physics as well as the effect of the additional X-point on core radiation

Scoping the characteristics and benefits of a connected double-null configuration for power exhaust in EU-DEMO

A double-null configuration is being considered for the EU-DEMO, due to its potential benefits for power exhaust arising from the use of two active divertors and magnetically disconnected low- and high-field sides. Using systematic parameter scans in fluid simulations, we have investigated the divertor power exhaust in the EUDEMO in a connected double-null configuration, and compared the edge plasma properties to those obtained in a single-null configuration under detached conditions anticipated for reactor operation. Neglecting drift effects and kinetic behaviour of the neutrals, no clear benefits of the double-null configuration could yet be identified for the radiation pattern and power mitigation on open field lines. Future work should address the aforementioned physics as well as the effect of the additional X-point on core radiation

Contrasting H-mode behaviour with fuelling and nitrogen seeding in the all-carbon and metallic versions of JET

An all-metal ITER-Like Wall (JET-ILW), consisting of beryllium in the main chamber and tungsten surfaces in the divertor, has now been installed in JET to pursue low retention of fuel species and to explore the impact on next-step-relevant plasmas. Its implementation has offered a unique opportunity to compare behaviour with that in the previous all-Carbon lining (JET-C), notably for high-triangularity Type I H-modes with impurity seeding. This technique is recognised to be necessary for power handling both in ITER and in JET at full performance. Contrasting results are reported for closely-matched deuterium-fuelling plus nitrogen-seeding scans in each JET environment. Attention is focused upon neutral-beam-heated plasmas with total input power 15­17MW at 2.65T, 2.5MA, q95 3.5 , average triangularity d 0.4 , elongation k 1.7 and gas inputs spanning ranges 0.75 FD 3.3 , 0 FD 4.7 (1022 electrons / s assuming full ionisation). JET-C cases also included 1­2MW of central ion-cyclotron-resonance-frequency heating, so far absent from JET-ILW pulses, with possible consequences for respective core sawtooth and impurity-concentration results.Preprint of Paper to be submitted for publication in Proceedings of the 40th EPS Conference on Plasma Physics, Espoo, Finland 1st July 2013 - 5th July 201

SOLPS-ITER validation with TCV L-mode discharges editors-pick

This work presents a quantitative test of SOLPS-ITER simulations against tokamak a configuration variable (TCV) L-mode experiments. These simulations account for drifts, currents, kinetic neutrals, and carbon impurities providing the most complete edge transport simulations for TCV to date. The comparison is performed on nominally identical discharges carried out to assess the effectiveness of TCV's divertor baffles in the framework of the European Plasma Exhaust program and employs numerous edge diagnostics providing a detailed code-experiment benchmark for TCV. The simulations show a qualitative consistency, but the quantitative differences remain, which are assessed herein. It is found that, for a given separatrix density, the simulations most notably yield a colder, and denser, divertor state with a higher divertor neutral pressure than measured