J. S. Allcock
A5049687244- Magnetic confinement fusion research
- Fusion materials and technologies
- Laser-Plasma Interactions and Diagnostics
- Ionosphere and magnetosphere dynamics
- Superconducting Materials and Applications
- Laser-induced spectroscopy and plasma
- Fluid Dynamics and Turbulent Flows
- Particle accelerators and beam dynamics
- Scientific Measurement and Uncertainty Evaluation
- Plasma Diagnostics and Applications
- Flow Measurement and Analysis
Culham Centre for Fusion Energy
2020-2024
Culham Science Centre
2019-2024
CEA Cadarache
2024
United Kingdom Atomic Energy Authority
2024
Durham University
2019-2022
National Centre for Nuclear Research
2021
Australian National University
2020
University of Science and Technology of China
2020
Southwestern Institute of Physics
2020
We present the first analysis of atomic and molecular processes at play during detachment in MAST-U Super-X divertor using spectroscopy data. Our indicates can be separated into four sequential phases: First, ionisation region detaches from target onset leaving a increased densities downstream. The plasma interacts with these molecules, resulting ions ($D_2^+$ and/or $D_2^- \rightarrow D + D^-$) that further react leading to Molecular Activated Recombination Dissociation (MAR MAD), which...
Abstract In this work, we provide the first 2D spatially resolved description of radiative detachment in MAST-U Super-X L-mode divertor plasmas. The magnetic configuration was designed to achieve reduced heat- and particle loads at target compared conventional exhaust solutions. We use filtered camera imaging reconstruct emissivity profiles poloidal plane for multiple atomic molecular emission lines bands. A set deuterium fuelling scans is discussed that, together, span attached deeply...
Abstract The research program of the TCV tokamak ranges from conventional to advanced-tokamak scenarios and alternative divertor configurations, exploratory plasmas driven by theoretical insight, exploiting device’s unique shaping capabilities. Disruption avoidance real-time locked mode prevention or unlocking with electron-cyclotron resonance heating (ECRH) was thoroughly documented, using magnetic radiation triggers. Runaway generation high- Z noble-gas injection runaway dissipation...
The mega amp spherical tokamak (MAST) was a low aspect ratio device (R/a = 0.85/0.65 ~ 1.3) with similar poloidal cross-section to other medium-size tokamaks. physics programme concentrates on addressing key issues for the operation of ITER, design DEMO and future tokamaks by utilising high resolution diagnostic measurements closely coupled theory modelling significantly advance our understanding. An empirical scaling energy confinement time that favours higher power, lower collisionality...
Abstract Within the 9th European Framework programme, since 2021 EUROfusion is operating five tokamaks under auspices of a single Task Force called ‘Tokamak Exploitation’. The goal to benefit from complementary capabilities each machine in coordinated way and help developing scientific output scalable future largre machines. programme this ensures that ASDEX Upgrade, MAST-U, TCV, WEST JET (since 2022) work together achieve objectives Missions 1 2 Roadmap: i) demonstrate plasma scenarios...
Abstract 2D profiles of electron density and neutral temperature are inferred from multi-delay Coherence Imaging Spectroscopy data divertor plasmas using a non-linear inversion technique. The inference is based on imaging the spectral line-broadening Balmer lines can differentiate between Doppler Stark broadening components by measuring fringe contrast at multiple interferometric delays simultaneously. model has been applied to images generated simulated evaluate its performance. Typical...
Divertor detachment and alternative divertor magnetic geometries are predicted to be promising approaches handle the power exhaust of future fusion devices. In order understand process caused by volumetric losses in geometries, a Multi-Wavelength Imaging (MWI) diagnostic has recently been designed built for Mega Amp Spherical Tokamak Upgrade. The MWI will simultaneously capture 11 spectrally filtered images visible light emitted from plasmas provide crucial knowledge interpretation...
2D profiles of electron density and neutral temperature are inferred from multi-delay Coherence Imaging Spectroscopy data divertor plasmas using a non-linear inversion technique. The inference is based on imaging the spectral line-broadening Balmer lines can differentiate between Doppler Stark broadening components by measuring fringe contrast at multiple interferometric delays simultaneously. model has been applied to images generated simulated evaluate its performance. Typical mean...
A new Doppler coherence imaging spectroscopy interferometer has been developed on the HL-2A tokamak for scrape-off-layer impurity flow measurement. Its spatial resolution is estimated to be up ∼0.8 mm in horizontal direction and ∼9 vertical direction, with a field of view ∼34°. typical temporal about 1 ms. This salient feature allows time-resolved 2D measurements short-time phenomena HL-2A, such as edge localized modes. Group delay interference fringe pattern were calibrated dedicated...
In this paper, the pixelated phase mask (PPM) method of interferometry is applied to coherence imaging (CI)—a passive, narrowband spectral technique for diagnosing edge and divertor regions fusion plasma experiments. Compared previous CI designs that use a linear mask, PPM allows higher possible spatial resolution. The also observed give instrument contrast (analogous more narrow spectrometer function). A single-delay introduced as well multi-delay system uses combination both masks encode...
Abstract The beams of fast runaway electrons (RE), which are often produced during tokamak discharges, particularly dangerous and can induce serious damages the vacuum vessel internal components machine. proper diagnostics RE is essential for controlling discharge, e.g., by early mitigation disruptions potentially beams. usually based on measurements radiation emitted either these electrons, or as a result their interactions with plasma and/or walls. Such recorded means probes placed outside...
The MAST-U Super-X divertor provides the opportunity to study fusion plasma exhaust under novel conditions. However, in order these conditions, advanced diagnostics are required. Following development of Multi-Wavelength Imaging (MWI) diagnostic, we present installation a multi-delay coherence imaging spectroscopy (CIS) system within MWI, along with modifications made MWI for effective operation. This diagnostic will measure either carbon ion flow velocities and temperatures or electron...
2D electron density profiles obtained from coherence imaging spectroscopy in different MAST-U divertor conditions are compared. The data includes variations of strike point position, core density, and heating power. improved performance the long-legged divertors results a lower particle flux at target compared to configurations with smaller major radius, while also being characterized by temperatures deeper detachment. Comparisons against SOLPS simulations generally show good agreement...
Imaging birefringent interferometers are used to measure plasma flow in 2-D via the Doppler shift of a spectral emission line. Applications include physics study fusion energy experiments and Earth's upper atmosphere. We present new, best our knowledge, method for wavelength calibration that does not require measurement at rest targeted line, nor using tuneable laser source. This is useful when such light sources available. Fringes measured known wavelengths from lines gas-discharge lamps...