Soft x-ray tomography on the high field spherical tokamak ST40.

As part of its roadmap to developing commercial fusion plants, Tokamak Energy Ltd. operates the high field spherical tokamak ST40. Studies on this device will help to expand the high field spherical tokamak physics basis by characterizing confinement and the fusion triple product. In support of this, bolometers and broadband and x-ray sensitive diodes can provide information on key energy loss mechanisms of the plasma. These mechanisms include core magnetohydrodynamic activity that deteriorates confinement, such as sawtooth crashes that can be used to characterize relaxations in the q-profile. In addition, combinations of these diagnostics can be used to infer the total radiated power losses and plasma composition. Here, we present results from a new, midplane, tangential, Be-filtered diode with 16 channels spanning the radial extent of the plasma. The system is shown to resolve magnetohydrodynamic instabilities (up to 100 kHz) and be able to provide radiation profiles through tomography. The tomographic inversion routine is compared against other diagnostics on ST40 and provides emissivity measurements across a variety of operating scenarios. Finally, we look ahead to implementing multiple soft x-ray cameras on ST40 and the improvements this will have on the diagnostic capabilities.

Design and commissioning of resistive foil bolometer diagnostics on the ST40 tokamak.

Following successful campaigns on the compact high field spherical tokamak ST40, resistive gold foil bolometers have now been installed to measure the radiated power profile. Positioned on the midplane, two bolometer cameras offer perspectives of the horizontal and vertical planes, while the third camera, situated above the midplane, provides a vertical view of the top divertor plates, including the X-point and the strike points. These cameras use a commercial off-the-shelf data acquisition platform with modules specifically designed for bolometers in a Wheatstone bridge configuration, providing both phase sensitive detection and in situ calibration. This paper presents an overview of the design and functionality of all three cameras and the commissioning of the horizontal plane camera. The commissioning of the horizontal camera shows data from a range of plasma pulses, presenting a positive correlation between the relative profiles measured from the bolometer camera and an absolute extreme ultraviolet diode camera viewing along similar lines of sight.

Narrow bandwidth, low-emittance positron beams from a laser-wakefield accelerator.

The rapid progress that plasma wakefield accelerators are experiencing is now posing the question as to whether they could be included in the design of the next generation of high-energy electron-positron colliders. However, the typical structure of the accelerating wakefields presents challenging complications for positron acceleration. Despite seminal proof-of-principle experiments and theoretical proposals, experimental research in plasma-based acceleration of positrons is currently limited by the scarcity of positron beams suitable to seed a plasma accelerator. Here, we report on the first experimental demonstration of a laser-driven source of ultra-relativistic positrons with sufficient spectral and spatial quality to be injected in a plasma accelerator. Our results indicate, in agreement with numerical simulations, selection and transport of positron beamlets containing N e + ≥ 10 5 positrons in a 5% bandwidth around 600 MeV, with femtosecond-scale duration and micron-scale normalised emittance. Particle-in-cell simulations show that positron beams of this kind can be guided and accelerated in a laser-driven plasma accelerator, with favourable scalings to further increase overall charge and energy using PW-scale lasers. The results presented here demonstrate the possibility of performing experimental studies of positron acceleration in a laser-driven wakefield accelerator.

Paradental cysts: a role for food impaction in the pathogenesis? A review of cases from Northern Ireland.

We present the clinical, radiographic and histological findings of 15 paradental cysts. These were the second most common type of cyst associated with mandibular third molars, comprising 25% of all lesions at this site. Ten patients were aged 30 years or younger and 13 gave a history of pericoronitis. There was a close relationship between the site of the cyst and the angle of the impacted tooth; the cyst lay mesially to two mesioangularly impacted teeth, buccal to two vertically impacted teeth and distal/distobuccal to the remainder, all but one of which were distoangular in impaction. The pericoronal follicular space was preserved in nine cases, a useful diagnostic sign. Most cysts were lined with epithelium that resembled that seen in radicular cysts, although the lining of three cysts resembled that of unicystic ameloblastoma, a potential diagnostic pitfall. We propose that the relation between location of cyst and angle of impaction points to a role for food impaction in the pathogenesis of paradental cysts.

An overview of economics.

Economics influences health care at every level. Part of that influence is the result of the interaction of buyers and sellers in markets. Another part is the interaction among aggregates of different markets, the government, and international actors. This article provides a short, non-technical introduction to basic theories of both micro and macro economics as a necessary precursor to the understanding of more complex theories and debates about the economics of health care.