A5074008035- Magnetic confinement fusion research
- Superconducting Materials and Applications
- Fusion materials and technologies
- Ionosphere and magnetosphere dynamics
- Particle accelerators and beam dynamics
- Laser-Plasma Interactions and Diagnostics
- Nuclear reactor physics and engineering
- Plasma Diagnostics and Applications
- Nuclear Physics and Applications
- Atomic and Subatomic Physics Research
- Numerical methods in engineering
- Laser-induced spectroscopy and plasma
- Solar and Space Plasma Dynamics
- Dust and Plasma Wave Phenomena
- Metal and Thin Film Mechanics
- Matrix Theory and Algorithms
- Advanced Numerical Methods in Computational Mathematics
- Time Series Analysis and Forecasting
- Electrostatic Discharge in Electronics
- Technology-Enhanced Education Studies
- Composite Structure Analysis and Optimization
- Particle Accelerators and Free-Electron Lasers
- Complex Systems and Time Series Analysis
- Atomic and Molecular Physics
- Semiconductor materials and devices
Imperial College London
1999-2025
Pancreas Centre (Canada)
2022
Center for Digestive and Liver Diseases
2022
East Asia School of Theology
2022
Culham Centre for Fusion Energy
2003-2014
Culham Science Centre
2002-2012
City University of Hong Kong
2003-2012
Fusion for Energy
2011
Queen's University Belfast
2005-2009
United Kingdom Atomic Energy Authority
2005-2008
Type-I edge-localized modes (ELMs) have been mitigated at the JET tokamak using a static external $n=1$ perturbation field generated by four error correction coils located far from plasma. During application of ELM frequency increased factor 4 and amplitude ${\mathrm{D}}_{\ensuremath{\alpha}}$ signal decreased. The energy loss per normalized to total stored energy, $\ensuremath{\Delta}W/W$, dropped values below 2%. Transport analyses shows no or only moderate (up 20%) degradation confinement...
A comparison of the L–H power threshold (Pthr) in JET with all carbon, JET-C, and beryllium/tungsten wall (the ITER-like choice), JET-ILW, has been carried out experiments slow input ramps matched plasma shapes, divertor configuration IP/BT pairs. The low density dependence threshold, namely an increase below a minimum ne,min, which was first observed MkII-GB C subsequently not current MkII-HD geometry, is again JET-ILW. At densities above Pthr reduced by ∼30%, ∼40% when radiation from bulk...
We present the results of experiments in JET to study effect plasma shape on high density ELMy H-modes, with geometry magnetic boundary similar that envisaged for standard Q = 10 operation ITER. The described are single lower null plasmas, q profile, neutral beam heating and gas fuelling, average triangularity δ calculated at separatrix ~0.45-0.5 elongation κ~1.75. In agreement previous obtained other divertor Tokamaks, thermal energy confinement time maximum achievable steady state a given...
A new technique has been developed to produce plasmas with improved confinement relative the H98,y2 scaling law (ITER Physics Expert Groups on Confinement and Transport Modelling Database ITER Basics Editors EDA 1999 Nucl. Fusion 39 2175) JET tokamak. In mid-size tokamaks ASDEX upgrade DIII-D heating during current formation is used a flat q-profile minimum close 1. On this leads q-profiles similar q but opposite other not an state. By changing method utilizing faster ramp temporary higher...
The neutral helium line intensity ratios 667.8 nm/728.1 nm and 728.1 nm/706.5 are measured at JET to provide essential information on the parallel radial profiles of electron density temperature both above divertor targets. accuracy derived values depends uncertainties in atomic data used calculate ratios. Work has been carried out assess sensitivity population calculations typical impact excitation rate coefficients using ADAS (Atomic Data Analysis Structure). We find that uncertainty 3s 1...
Results from the first measurements of a core plasma poloidal rotation velocity (upsilontheta) across internal transport barriers (ITB) on JET are presented. The spatial and temporal evolution ITB can be followed along with upsilontheta radial profiles, providing very clear link between location steepest region ion temperature gradient localized spin-up upsilontheta. an order magnitude higher than neoclassical predictions for thermal particles in region, contrary to close agreement found...
Abstract The dynamics of the L-H transition is not fully understood, with many parameters changing threshold power to enter H-mode and self-regulation between zonal flows turbulence in plasma edge. This paper primarily a presentation experimental results for DIII-D H-L transitions speculation on observations made. Power analysis measurements pedestal temperatures these are presented. A comparison made an comparable P sep exhibiting oscillatory behaviour, showing symmetry forward backward...
This paper describes experiments with highly shaped JET H-mode plasmas, which were directed to developing regimes where Type I ELMs are replaced by other edge relaxations, while maintaining the pedestal pressure of ELMy H-modes. It was found that II coexisted I, up densities order Greenwald limit, III appear, and good confinement lost. Only at highest collisionality it observed completely replace I. At high βp q95, 'grassy' completely. The MHD spectra characteristics for grassy significantly...
Pedestal and global plasma parameters are compared in conventional ELMy H-modes improved confinement discharges from ASDEX Upgrade (AUG), DIII-D, JET JT-60U with varying net input power. Both electron ion pedestal pressures studied. The top pressure pPED increases moderately power all tokamaks, broad agreement the dependence of IPB98(y, 2) scaling. Higher observed AUG high βpol at q95 ~ 6.5 triangularity. For machines scenarios a robust correlation between total thermal stored energy is...
Nine type-I ELMy H-mode discharges in diagnostic optimized configuration JET are analysed with the EDGE2D/NIMBUS package. EDGE2D solves fluid equations for conservation of particles, momentum and energy hydrogenic impurity ions, while neutrals followed two-dimensional Monte Carlo module NIMBUS. Using external boundary conditions from experiment, perpendicular heat conductivities χi,e particle transport coefficients D, v varied until good agreement between code result measured data is...
There is an increasing body of evidence that the energy lost from diverted tokamak plasmas due to edge localized mode (ELM) activity may not be confined solely deposition on divertor components. Plasma-facing surfaces in main confinement chamber also appear intercept significant fluxes. Whilst this no practical consequence for operation present day facilities, concerns are being raised over possible impact future devices, which ELMS carrying higher energies expected. A key parameter required...
The operational domain for active control of type-I edge localized modes (ELMs) with an n = 1 external magnetic perturbation field induced by the ex-vessel error correction coils on JET has been developed towards more ITER-relevant regimes high plasma triangularity, up to 0.45, normalized beta, 3.0, current 2.0 MA and q95 varied between 3.0 4.8. results ELM mitigation in triangularity plasmas show that frequency ELMs increased a factor 4 during application fields, while energy loss per ELM,...
The present status of understanding toroidal and poloidal momentum transport in tokamaks is presented this paper.Similar energy confinement times, i.e. τ E /τ φ ≈ 1 have been reported on several tokamaks.It more important though, to study the local both core edge plasma separately as, for example, plasma, a large scatter ratio effective diffusivity ion heat χ φeff /χ i,eff among different can be found.For value Prandtl number typically around 0.2 JET while still holds.Perturbative NBI...
Dedicated experiments on TF ripple effects the performance of tokamak plasmas have been carried out at JET. The was found to a profound effect plasma rotation. central Mach number, M , defined as ratio rotation velocity and thermal velocity, drop function amplitude (δ) from an average value = 0.40–0.55 for operations standard JET δ 0.08% 0.25–0.40 0.5% 0.1–0.3 1%. should be considered when estimating in ITER. With co-current injection neutral beam (NBI), were rotate direction. However,...
Recent JET experiments have been devoted to the study of (3He)–D plasmas involving radio frequency (RF) heating. This paper starts by discussing RF heating efficiency theoretically expected in such plasmas, covering both relevant aspects wave and particle dynamics. Then it gives a concise summary main conclusions drawn from recent that were either focusing on studying physics or adopting as tool plasma behavior. Depending minority concentration chosen, different physical phenomena are...
Results from recent experiments to study the effects of divertor geometry and increased plasma shaping on L–H transition threshold JET are reported. Equivalent septum configurations run with new replacement plate (SRP) in MkII Gas Box have shown that presence lowers power threshold, Pth, by 20%. For X-point virtual top distances less than 6 cm, SRP plasmas also demonstrate a significant decrease Pth pedestal electron temperature, Te reduced height. Although, plasma's remains above septum,...
This paper reports on the recent studies of toroidal and poloidal momentum transport in JET. The ratio global energy confinement time to is found be close τ E /τ ϕ = 1 except for low density or collisionality discharges where 2–3. On other hand, local analysis around 40 shows that effective diffusivity ion heat χ /χ i ≈ 0.1–0.4 (averaged over radial region r / a 0.4–0.7) rather than unity, as expected from times used often ITER predictions. apparent discrepancy versus can at least partly...
We report the identification of a localized current structure inside JET plasma. It is field-aligned closed helical ribbon, carrying in same direction as background profile (cocurrent), rotating toroidally with ion velocity (corotating). appears to be located at flat spot plasma pressure profile, top pedestal. The spontaneously low density, high rotation plasmas, and can last up 1.4 s, time comparable local resistive time. considerably delays appearance first edge mode.Received 23 November...
One of the most severe problems for fusion reactors is power load on plasma facing components. The challenge to develop operation scenarios, which combine sufficient energy confinement with benign heat loads radiative type-III ELMy H-mode seems a possible solution such an integrated ITER scenario. Nitrogen seeded H-modes standard inductive scenario and high beta stationary hybrid are investigated respect their transient steady-state fluxes divertor, properties, edge operational space, core...
Abstract DIII-D physics research addresses critical challenges for the operation of ITER and next generation fusion energy devices. This is done through a focus on innovations to provide solutions high performance long pulse operation, coupled with fundamental plasma understanding model validation, drive scenario development by integrating core boundary plasmas. Substantial increases in off-axis current efficiency from an innovative top launch system EC power, pressure broadening Alfven...
Since it is uncertain if ITER operation compatible with type-I edge localized modes (ELMs), the study of alternative ELM regimes an urgent issue.This paper reports on experiments JET aiming to find scenarios small ELMs and good confinement, such as type-II in ASDEX Upgrade, enhanced D-alpha H-mode Alcator C-mod or grassy JT-60U.The includes shape variations, especially closeness a double-null configuration, variations q 95 , density beta poloidal.H-mode pedestals without have been observed...
1 H-mode access studies under conditions of very low plasma density provide valuable information on the physics edge transport barrier formation and are an important part operational scenario development for next step fusion device, ITER. JET operation with a electron density, , MkII gas box septum divertor was found to have significant effect power threshold L–H transition, Pth. A sharp 'turning point' below which Pth increases decreasing is Ip/Bt values 2.5 MA/2.7 T, MA/2.6 MA/2.4 T 2.2 T....
This paper summarizes results of dimensionless identity experiments in JT-60U and JET, aimed at the comparison H-mode pedestal ELM behaviour two devices. Given their similar size, matched plasmas are also dimensional parameters (in particular, plasma minor radius a is same JET JT-60U). Power density scans were carried out values Ip, providing q scan (q95 = 3.1 5.1) with fixed (and matched) toroidal field. Contrary to initial expectations, match between devices was quite difficult achieve. In...