1,037 research outputs found
Self-consistent pedestal prediction for JET-ILW in preparation of the DT campaign
The self-consistent core-pedestal prediction model of a combination of EPED1 type pedestal prediction and a simple stiff core transport model is able to predict Type I ELMy (edge localized mode) pedestals of a large JET-ILW (ITER-like wall) database at the similar accuracy as is obtained when the experimental global plasma beta is used as input. The neutral penetration model [R. J. Groebner et al., Phys. Plasmas 9, 2134 (2002)] with corrections that take into account variations due to gas fueling and plasma triangularity is able to predict the pedestal density with an average error of 15%. The prediction of the pedestal pressure in hydrogen plasma that has higher core heat diffusivity compared to a deuterium plasma with similar heating and fueling agrees with the experiment when the isotope effect on the stability, the increased diffusivity, and outward radial shift of the pedestal are included in the prediction. However, the neutral penetration model that successfully predicts the deuterium pedestal densities fails to predict the isotope effect on the pedestal density in hydrogen plasmas
Microstability analysis of pellet fuelled discharges in MAST
Reactor grade plasmas are likely to be fuelled by pellet injection. This
technique transiently perturbs the profiles, driving the density profile hollow
and flattening the edge temperature profile. After the pellet perturbation, the
density and temperature profiles relax towards their quasi-steady-state shape.
Microinstabilities influence plasma confinement and will play a role in
determining the evolution of the profiles in pellet fuelled plasmas. In this
paper we present the microstability analysis of pellet fuelled H-mode MAST
plasmas. Taking advantage of the unique capabilities of the MAST Thomson
scattering system and the possibility of synchronizing the eight lasers with
the pellet injection, we were able to measure the evolution of the post-pellet
electron density and temperature profiles with high temporal and spatial
resolution. These profiles, together with ion temperature profiles measured
using a charge exchange diagnostic, were used to produce equilibria suitable
for microstability analysis of the equilibrium changes induced by pellet
injection. This analysis, carried out using the local gyrokinetic code GS2,
reveals that the microstability properties are extremely sensitive to the rapid
and large transient excursions of the density and temperature profiles, which
also change collisionality and beta e significantly in the region most strongly
affected by the pellet ablation.Comment: 21 pages, 10 figures. This is an author-created, un-copyedited
version of an article submitted for publication in Plasma Physics and
Controlled Fusion. IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
Characterisation of the L-mode Scrape Off Layer in MAST: decay lengths
This work presents a detailed characterisation of the MAST Scrape Off Layer
in L-mode. Scans in line averaged density, plasma current and toroidal magnetic
field were performed. A comprehensive and integrated study of the SOL was
allowed by the use of a wide range of diagnostics. In agreement with previous
results, an increase of the line averaged density induced a broadening of the
midplane density profile.Comment: 30 pages, 11 figure
Extrapolations of the fusion performance in JET
n preparation of the forthcoming high power campaign with the reactor-relevant deuterium-tritium (DT) fuel mixture in the Joint European Torus (JET), significant efforts are being devoted to DT scenario extrapolation using computer modelling. We report on simulations aimed at optimizing external heating using neutral beam injection (NBI) and radiofrequency waves in the ion cyclotron range of frequencies (ICRF) for high DT fusion yield. Our results show that by increasing external heating power to the maximum power available, the fusion neutron rate can be enhanced by a factor of 4-5 with respect to the recent record values. The comparison of two ICRF schemes using different resonant ion species, i.e. 3He and H minority ions, shows that the 3He minority heating scenario achieves a higher fuel ion temperature but not necessarily a better fusion performance. Finally, we study the dependence of the performance of external heating on key experimental parameters
Charge dependence of neoclassical and turbulent transport of light impurities on MAST
Carbon and nitrogen impurity transport coefficients are determined from gas
puff experiments carried out during repeat L-mode discharges on the Mega-Amp
Spherical Tokamak (MAST) and compared against a previous analysis of helium
impurity transport on MAST. The impurity density profiles are measured on the
low-field side of the plasma, therefore this paper focuses on light impurities
where the impact of poloidal asymmetries on impurity transport is predicted to
be negligible. A weak screening of carbon and nitrogen is found in the plasma
core, whereas the helium density profile is peaked over the entire plasma
radius.Comment: 17 pages, 7 figure
Challenges in the extrapolation from DD to DT plasmas: experimental analysis and theory based predictions for JET-DT
A strong modelling program has been started in support of the future JET-DT campaign
with the aim of guiding experiments in deuterium (D) towards maximizing fusion energy
production in Deuterium–Tritium (DT). Some of the key elements have been identified by
using several of the most updated and sophisticated models for predicting heat and particle
transport, pedestal pressure and heating sources in an integrated modelling framework. For the
high beta and low gas operational regime, the density plays a critical role and a trend towards
higher fusion power is obtained at lower densities. Additionally, turbulence stabilization
by E Ă— B flow shear is shown to generate an isotope effect leading to higher confinement
for DT than DD and therefore plasmas with high torque are suitable for maximizing fusion
performance. Future JET campaigns will benefit from this modelling activity by defining clear
priorities on their scientific program.EURATOM 63305
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