Saturation of Fishbone Instability by Self-Generated Zonal Flows in Tokamak Plasmas.

Gyrokinetic simulations of the fishbone instability in DIII-D tokamak plasmas find that self-generated zonal flows can dominate the nonlinear saturation by preventing coherent structures from persisting or drifting in the energetic particle phase space when the mode frequency down-chirps. Results from the simulation with zonal flows agree quantitatively, for the first time, with experimental measurements of the fishbone saturation amplitude and energetic particle transport. Moreover, the fishbone-induced zonal flows are likely responsible for the formation of an internal transport barrier that was observed after fishbone bursts in this DIII-D experiment. Finally, gyrokinetic simulations of a related ITER baseline scenario show that the fishbone induces insignificant energetic particle redistribution and may enable high performance scenarios in ITER burning plasma experiments.

Conceptual design of the ITER fast-ion loss detector.

A conceptual design of a reciprocating fast-ion loss detector for ITER has been developed and is presented here. Fast-ion orbit simulations in a 3D magnetic equilibrium and up-to-date first wall have been carried out to revise the measurement requirements for the lost alpha monitor in ITER. In agreement with recent observations, the simulations presented here suggest that a pitch-angle resolution of ∼5° might be necessary to identify the loss mechanisms. Synthetic measurements including realistic lost alpha-particle as well as neutron and gamma fluxes predict scintillator signal-to-noise levels measurable with standard light acquisition systems with the detector aperture at ∼11 cm outside of the diagnostic first wall. At measurement position, heat load on detector head is comparable to that in present devices.

Observation of confined current ribbon in JET plasmas.

We report the identification of a localized current structure inside the JET plasma. It is a field-aligned closed helical ribbon, carrying current in the same direction as the background current profile (cocurrent), rotating toroidally with the ion velocity (corotating). It appears to be located at a flat spot in the plasma pressure profile, at the top of the pedestal. The structure appears spontaneously in low density, high rotation plasmas, and can last up to 1.4 s, a time comparable to a local resistive time. It considerably delays the appearance of the first edge localized mode.

Active control of type-I edge-localized modes with n=1 perturbation fields in the JET tokamak.

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 field correction coils located far from the plasma. During the application of the n=1 field the ELM frequency increased by a factor of 4 and the amplitude of the D(alpha) signal decreased. The energy loss per ELM normalized to the total stored energy, DeltaW/W, dropped to values below 2%. Transport analyses shows no or only a moderate (up to 20%) degradation of energy confinement time during the ELM mitigation phase.

Production in food of 1,3-pentadiene and styrene by Trichoderma species.

The ability of two strains of Trichoderma, isolated from food, to produce the Volatile Organic Compounds 1,3-pentadiene and styrene was investigated. One of the strains had been implicated in a case of food spoilage involving the production of both compounds. In vitro in potato dextrose broth, the strains produced both 1,3-pentadiene and styrene within 5 days in the presence of sorbic acid and cinnamic acid. The taints were produced only in the presence of sorbic acid and cinnamic acid and were not synthesised de novo under the test conditions. Neither the conversion of cinnamic acid to styrene, nor the conversion of sorbic acid to 1,3-pentadiene by Trichoderma strains in foods has been previously reported. The range of organisms implicated in these types of spoilage is thus extended.

Probing internal transport barriers with heat pulses in JET.

The first electron temperature modulation experiments in plasmas characterized by strong and long-lasting electron and ion internal transport barriers (ITB) have been performed in JET using ion cyclotron resonance heating in mode conversion scheme. The ITB is shown to be a well localized narrow layer with low heat diffusivity, characterized by subcritical transport and loss of stiffness. In addition, results from cold pulse propagation experiments suggest a second order transition process for ITB formation.

Percutaneous transtracheal jet ventilation as a guide to tracheal intubation in severe upper airway obstruction from supraglottic oedema.

We report two cases of severe upper airway obstruction caused by supraglottic oedema secondary to adult epiglottitis and Ludwig's angina. In the former case, attempts to intubate with a direct laryngoscope failed but were successful once percutaneous transtracheal jet ventilation (PTJV) had been instituted. In the case with Ludwig's angina, PTJV was employed as a pre-emptive measure and the subsequent tracheal intubation with a direct laryngoscope was performed with unexpected ease. In both cases recognition of the glottic aperture was made feasible with PTJV by virtue of the fact that the high intra-tracheal pressure from PTJV appeared to lift up and open the glottis. The escape of gas under high pressure caused the oedematous edges of the glottis to flutter, which facilitated the identification of the glottic aperture. We believe that the PTJV should be considered in the emergency management of severe upper airway obstruction when this involves supraglottic oedema.

Monitoring Alfvén cascades with interferometry on the JET Tokamak.

A microwave interferometry technique is applied for the first time for detecting a discrete spectrum of Alfvén cascade (AC) eigenmodes excited with fast ions in reversed magnetic shear plasmas of the Joint European Torus. The interferometry measurements of plasma density perturbations associated with ACs show an unprecedented frequency and time resolution superior to that obtained with external magnetic coils. The measurements of ACs are used for monitoring the evolution of the safety factor and density of rational magnetic surfaces in the region of maximum plasma current.

Wavelength conversion of 1.53-microm-wavelength picosecond pulses in an ion-implanted multiple-quantum-well all-optical switch.

An ultrafast high-contrast all-optical switch produced from a metal-organic vapor phase epitaxy-grown wafer incorporating a 50-period InGaAsP/InGaAsP multiple-quantum-well (MQW) saturable absorber (SA) and a distributed Bragg reflector is described. Postgrowth implantation with 4-MeV nitrogen ions reduces the MQW free-carrier lifetime, and hence the switch recovery time, to 5.2 ps. Incorporation of the MQW SA in an optical cavity results in switching contrast ratios greater than 10 dB. The all-optical switch is used to perform wavelength conversion of 2-ps pulses.

Control of neoclassical tearing modes by sawtooth control.

The onset of a neoclassical tearing mode (NTM) depends on the existence of a large enough seed island. It is shown in the Joint European Torus that NTMs can be readily destabilized by long-period sawteeth, such as obtained by sawtooth stabilization from ion-cyclotron heating or current drive. This has important implications for burning plasma scenarios, as alpha particles strongly stabilize the sawteeth. It is also shown that, by adding heating and current drive just outside the inversion radius, sawteeth are destabilized, resulting in shorter sawtooth periods and larger beta values being obtained without NTMs.