A5044802412- Magnetic confinement fusion research
- Particle accelerators and beam dynamics
- Gyrotron and Vacuum Electronics Research
- Cold Atom Physics and Bose-Einstein Condensates
- Plasma Diagnostics and Applications
- Laser-Plasma Interactions and Diagnostics
- Superconducting Materials and Applications
- Quantum, superfluid, helium dynamics
- Microwave Engineering and Waveguides
- Ionosphere and magnetosphere dynamics
- Nonlinear Waves and Solitons
- Image and Signal Denoising Methods
- Electromagnetic Launch and Propulsion Technology
- Solar and Space Plasma Dynamics
- Digital Filter Design and Implementation
- Fusion materials and technologies
- Atomic and Subatomic Physics Research
- Nonlinear Photonic Systems
- Electromagnetic Simulation and Numerical Methods
- Energy Load and Power Forecasting
- Pulsed Power Technology Applications
- Mathematical Analysis and Transform Methods
- Seismic Imaging and Inversion Techniques
- Advanced SAR Imaging Techniques
- Marine and coastal ecosystems
University of Oxford
2023-2025
Tokamak Energy (United Kingdom)
2025
Princeton University
2018-2025
Kaw Nation
2023
American University of the Middle East
2022
Massachusetts Institute of Technology
2014
University of Waikato
2013
Varian Medical Systems (United States)
1983-1986
With the increased urgency to design fusion pilot plants, fast optimization of electron cyclotron current drive (ECCD) launchers is paramount. Traditionally, this done by coarsely sampling 4-D parameter space possible launch conditions consisting (1) location (constrained lie along reactor vessel), (2) frequency, (3) toroidal angle, and (4) poloidal angle. For each initial condition, a ray-tracing simulation performed evaluate ECCD efficiency. Unfortunately, approach often requires millions...
The ability to model the interplay between core and edge of tokamak plasmas is crucial designing both plasma operating scenario a fusion pilot plant design itself. Scrape-off-layer (SOL) models that are tailored integrated modeling need have fast turn-around time minimal computational burden enable wide parameter-space coverage for scoping. SOL 0-D Box reduced based on global power particle balance captures essential physics transport with little cost. usage in core-edge coupled simulations...
High-beta magnetised plasmas often exhibit anomalously structured temperature profiles, as seen from galaxy cluster observations and recent experiments. It is well known that when such are collisionless, gradients along the magnetic field can excite whistler waves efficiently scatter electrons to limit their heat transport. Only recently has it been shown parallel also in collisional plasmas. Here, we develop a Wigner–Moyal theory for instability starting Braginskii-like fluid equations slab...
Abstract With the increased urgency to design fusion pilot plants, fast optimization of electron cyclotron current drive (ECCD) launchers is paramount. Traditionally, this done by coarsely sampling 4-D parameter space possible launch conditions consisting (1) location (constrained lie along reactor vessel), (2) frequency, (3) toroidal angle, and (4) poloidal angle. For each initial condition, a ray-tracing simulation performed evaluate ECCD efficiency. Unfortunately, approach often requires...
The phenomenon of focusing microwave beams in a plasma near turning-point caustic is discussed by exploiting the analytical solution to Gaussian beam-tracing equations two-dimensional (2-D) linear-layer problem. location maximum beam and width at that are studied terms initial conditions. This must be taken into account interpret Doppler backscattering (DBS) measurements. We find filter function characterises scattering intensity contribution along path through inversely proportional width,...
The design and optimization of radiofrequency-wave systems for fusion applications is often performed using ray-tracing codes, which rely on the geometrical-optics (GO) approximation. However, GO fails at wave cutoffs caustics. To accurately model behavior in these regions, more advanced computationally expensive ``full-wave'' simulations are typically used, but this not strictly necessary. A new generalized formulation called metaplectic geometrical optics (MGO) has been proposed that...
The results of tests on a Varian 140 GHz CW gyrotron are presented. In initial pulse the tube, an output power 100 kW was achieved at 28% efficiency in desired TEU0 031 cavity mode. Under operating conditions, tube level 75 31% efficiency. This is highest ever obtained frequency above microwave tube. During tests, measurements ohmic losses interaction circuit were made and temperature window monitored. These measurements, as well those efficiency, presented compared with theoretical...
A recent paper by Davies et al. [Phys. Plasmas 28, 012305 (2021)] presents rational interpolants for the resistive (α) and thermoelectric (β) transport coefficients as functions of Hall parameter χ ion charge state Z. Here, this discussion is augmented showing that, at least in Lorentz limit Z→∞, proposed α⊥ β⊥ can be made even more accurate over a larger range making slight modifications to ensure exact asymptotic limits are preserved. Although authors do not discuss conductivity (κ)...
Geometrical optics (GO) is often used to model wave propagation in weakly inhomogeneous media and quantum-particle motion the semiclassical limit. However, GO predicts spurious singularities of wavefield near reflection points and, more generally, at caustics. We present a new formulation GO, called metaplectic geometrical (MGO), that free from these can be applied any linear equation. MGO uses sequenced transforms wavefield, corresponding symplectic transformations ray phase space, such...
Abstract For the first time, a Varian 60 GHz gyrotron designed specifically to generate microwaves in single output mode has been operated at power levels up 200 kW CW. Using mode-specific directional couplers, measurements of content indicated that greater than 95% microwave was desired TE02 with only small percentages neighbouring TE01 and TE03 circular electric modes. High output-mode purity is required for efficient utilization gyrotrons as high-power sources electron cyclotron resonance...
We describe an effective theory of interaction between pairs dark matter particles (denoted $\chi$) and $W$ bosons. Such could accommodate $\chi\bar{\chi}\rightarrow WW$ processes, which are a major focus indirect experiments, as well $pp \rightarrow W\rightarrow W\chi\bar{\chi}$ would predict excesses at the LHC in $W$+MET final-state. reinterpret ATLAS analysis hadronic mode translate bounds to space detection signals. also terms graviton through processes $W\rightarrow WG$ $Z\rightarrow...
The optimization of radio frequency-wave (RF) systems for fusion experiments is often performed using ray-tracing codes, which rely on the geometrical-optics (GO) approximation. However, GO fails at caustics such as cutoffs and focal points, erroneously predicting wave intensity to be infinite. This a critical shortcoming GO, since caustic quantity interest, e.g., RF heating. Full-wave modeling can used instead, but computational cost limits speed optimizations performed. We have developed...
As an approximate theory that is highly regarded for its computational efficiency, geometrical optics (GO) widely used modeling waves in various areas of physics. However, GO fails at caustics, which significantly limits applicability. A new framework, called metaplectic (MGO), has recently been developed allows caustics certain types to be modeled accurately within the framework. Here, we extend MGO most general case. To illustrate our theory, also apply it several sample problems,...
Weather pattern anomalies and climate change have greatly impacted human activities the environment in varying ways. Whether induced naturally or by anthropogenic activities, it remains a menace to global public health. A foreknowledge of weather/climate can help mitigating impact disasters emanating from these changes. Upper-air meteorological data play an exceptionally large role weather prediction. However, there is paucity ground truth Nigeria many parts Africa. Consequently, need...
Metaplectic geometrical optics (MGO) is a recently developed ray-tracing framework to accurately compute the wavefield behavior near caustic (turning point or focal point), where traditional breaks down. However, MGO has thus far been restricted having real-valued wavevectors. This disadvantageous because often upon crossing from “illuminated” region “shadow” region, two rays coalesce into one complex-valued ray corresponding transition propagating evanescent behavior. One can distinguish...
The metaplectic transform (MT), also known as the linear canonical transform, is a unitary integral mapping which widely used in signal processing and can be viewed generalization of Fourier transform. For given function $\psi$ on an $N$-dimensional continuous space $\textbf{q}$, MT parameterized by rotation (or more generally, symplectic transformation) $2N$-dimensional phase $(\textbf{q},\textbf{p})$, where $\textbf{p}$ wavevector dual to $\textbf{q}$. Here, we derive pseudo-differential...
The effects of space-charge field on velocity spread in the drift tube regions gyro devices which use either magnetron injection guns (MIG) or Pierce gun/wigglers (PW) are investigated using computer simulation codes. It is shown that changes occur while beam makes a transition from an essentially coherent laminar state to incoherent mixed state.
In spherical tokamaks, the electron plasma frequency is greater than cyclotron frequency. Electromagnetic waves in range of frequencies are unsuitable for directly heating such plasmas due to their reduced accessibility. However, mode-conversion extraordinary wave Bernstein (X-B mode-conversion) at upper hybrid resonance makes it possible efficiently couple externally-launched electromagnetic energy into an overdense core. Traditional models describe X-mode propagating a potential containing...
The metaplectic transform (MT), a generalization of the Fourier sometimes called linear canonical transform, is tool used ubiquitously in modern optics, for example, when calculating transformations light beams paraxial optical systems. MT also an essential ingredient geometrical-optics modeling caustics that we recently proposed. In particular, this application relies on near-identity (NIMT); however, NIMT approximation so far not exactly unitary and leads to numerical instability. Here,...
A wave near an isolated turning point is typically assumed to have Airy function profile with respect the separation distance. This description incomplete, however, and insufficient describe behavior of more realistic fields that are not simple plane waves. Asymptotic matching a prescribed incoming field generically introduces phase front curvature term changes characteristic from hyperbolic umbilic function. function, which one seven classic "elementary" functions catastrophe theory along...
Aims. We consider the influence of viscous dissipation on "spine" reconnection solutions in coronal plasmas. It is known from 2D and 3D "fan" studies that losses can be important. extend these arguments to solutions.
The scrape-off layer parallel heat flux decay lengths measured at ST40, a high field, low aspect ratio spherical tokamak, have been observed to bifurcate into two groups. wide group matches closely with the scale of ion poloidal Larmour radius and follows existing H-mode scalings, while narrow falls up 10 times below on total radius. onset width is be associated suppressed magnetic fluctuations, suggesting reduced electromagnetic turbulence levels in SOL.
High-beta magnetized plasmas often exhibit anomalously structured temperature profiles, as seen from galaxy cluster observations and recent experiments. It is well known that when such are collisionless, gradients along the magnetic field can excite whistler waves efficiently scatter electrons to limit their heat transport. Only recently has it been shown parallel also in collisional plasmas. Here we develop a Wigner--Moyal theory for instability starting Braginskii-like fluid equations slab...