Self-Consistent ICRH Distribution Functions and Equilibria in Magnetically Confined Plasmas

The deployment of high power radio frequency waves in the ion cyclotron range (ICRF) constitutes an important operational facility in many plasma devices, including ITER. Any charged particle describes a helical motion around a given magnetic field line, the so-called cyclotron motion. ICRF relies on the interaction between charged particles and an injected Radio Frequency (RF) wave, tuned to be at the same frequency as the helical cyclotron motion. It is applied not only for pure heating of the plasma, i.e. Ion Cyclotron Resonant Heating (ICRH), but also for the generation of non-inductive current through Ion Cyclotron Current Drive (ICCD). The numerical code package SCENIC has been developed for self-consistently simulating the effects of ICRH on the resonant ion species within the plasma, the resulting changes in the plasma equilibrium, and finally the back reaction onto the injected wave field. SCENIC is an iterated scheme, which advances the resonant ions' distribution function, the equilibrium and the wave field iteratively until a converged solution, representing a steady state, is reached. The constituents of SCENIC are the MagnetoHydroDynamic (MHD) equilibrium code VMEC,1 the full wave code LE-Man2 and the Hamiltonian guiding centre drift following code VENUS.3 All of these codes are capable of dealing with 3D geometries, and have recently been updated to handle pressure anisotropy, where the energy density parallel and perpendicular to the magnetic field differ. This is important since the RF field resonates mainly with the particle's motion perpendicular to the magnetic field, thus creating pressure anisotropy. After the introduction and description of the different codes and their interfaces, this work verifies the consistency of the numerical results with expected results for simple cases, and a benchmarking effort against the similar code package SELFO is shown. After this validation, SCENIC is applied to different heating scenarios, which are relevant to present (Joint European Torus, JET) and future (ITER) devices. Low power heating simulations with a 1% helium-3 minority in background deuterium plasmas demonstrate that a pressure anisotropy is induced. We show that the hot particle distribution function can be adequately approximated with a particular bi-Maxwellian for the equilibrium and wave field computations. For high power, 3% hydrogen minority heating scenarios, the heating scheme alters the background equilibrium state. This justifies one of the main novelties introduced in this work, namely the inclusion of the equilibrium computation in the self-consistent scheme. Effects due to asymmetric wave injection and different heating locations on the hot particle distribution function, the hot dielectric tensor and the equilibrium will be studied. Here, the emergence of a high energy tail in the minority species distribution function is shown explicitly, and some of its exotic features are observed via the RF driven current, the density and the pressure evolution

Self-consistent model of electron drift mode turbulence

The nonlinear dynamics of magnetic electron drift mode turbulence are outlined and the generation of large-scale magnetic structures in a non-uniform magnetized plasma by turbulent Reynolds stress is demonstrated. The loop-back of large-scale flows on the microturbulence is elucidated and the modulation of the electron drift mode turbulence spectrum in a medium with slowly varying parameters is presented. The wave kinetic equation in the presence of large-scale flows is derived and it can be seen that the small-scale turbulence and the large-scale structures form a self-regulating system. Finally, it is shown by the use of quasilinear theory that the shearing of microturbulence by the flows can be described by a diffusion equation in k-space and the corresponding diffusion coefficients are calculate

On the kinetic stability of magnetic structures in electron drift turbulence

The generation of large-scale magnetic fields in magnetic electron drift mode turbulence is investigated. The mechanism of magnetic Reynolds stress is elucidated with the help of kinetic theory, and a sufficient criterion in the form of Nyquist's criterion for the generation of zonal magnetic fields is developed. This criterion is then applied to a narrow wave packet, where an amplitude threshold due to finite width of the wave spectrum in k space is found

On the modulational stability of magnetic structures in electron drift turbulence

The generation of large-scale magnetic fields in magnetic electron drift mode turbulence is investigated. In particular, the mechanism of modulational instability caused by three-wave interactions is elucidated and the explicit increment is calculated. Also, a stability criterion similar to the known Lighthill criterion is found

Sustainability, systems thinking and professional practice

This article explores the impact of the new sustainability agenda on the occupational and professional needs of those who have taken educational and training programmes in the environmental field either at undergraduate or postgraduate level or through relevant professional institutions' continuing professional development programmes. It also describes a one-day workshop for the professionals on sustainable development, based on systems thinking and practice. The workshop provides a model for developing greater understanding and effective action in professional practice, by using dialogue and interprofessional learning to explore approaches to sustainability in a variety of business and professional contexts. It introduces the principles underpinning the concept of sustainability and provides tools to support the integration of sustainable development into professional practice and organisational change

Self-consistent model of electron drift mode turbulence

The nonlinear dynamics of magnetic electron drift mode turbulence are outlined and the generation of large-scale magnetic structures in a non-uniform magnetized plasma by turbulent Reynolds stress is demonstrated. The loop-back of large-scale flows on the microturbulence is elucidated and the modulation of the electron drift mode turbulence spectrum in a medium with slowly varying parameters is presented. The wave kinetic equation in the presence of large-scale flows is derived and it can be seen that the small-scale turbulence and the large-scale structures form a self-regulating system. Finally, it is shown by the use of quasi-linear theory that the shearing of microturbulence by the flows can be described by a diffusion equation in k-space and the corresponding diffusion coefficients are calculated

Large scale magnetic fields and coherent structures in nonuniform unmagnetized plasma

The properties of streamers and zonal magnetic structures in magnetic electron drift mode turbulence are investigated. The stability of such large scale structures is investigated in the kinetic and the hydrodynamic regime, for which an instability criterion similar to the Lighthill criterion for modulational instability is found. Furthermore, these large scale flows can undergo further nonlinear evolution after initial linear growth, which can lead to the formation of long-lived coherent structures consisting of self-bound wave packets between the surfaces of two different flow velocities with an expected modification of the anomalous electron transport properties

The Downward Influence of Sudden Stratospheric Warmings: Association with Tropospheric Precursors

Tropospheric features preceding sudden stratospheric warming events (SSWs) are identified using a large compendium of events obtained from a chemistryclimate model. In agreement with recent observational studies, it is found that approximately one-third of SSWs are preceded by extreme episodes of wave activity in the lower troposphere. The relationship becomes stronger in the lower stratosphere, where ~60% of SSWs are preceded by extreme wave activity at 100 hPa. Additional analysis characterizes events that do or do not appear to subsequently impact the troposphere, referred to as downward and non-downward propagating SSWs, respectively. On average, tropospheric wave activity is larger preceding downward-propagating SSWs compared to non-downward propagating events, and associated in particular with a doubly strengthened Siberian high. Of the SSWs that were preceded by extreme lower-tropospheric wave activity, ~2/3 propagated down to the troposphere, and hence the presence of extreme lower-tropospheric wave activity can only be used probabilistically to predict a slight increase or decrease at the onset, of the likelihood of tropospheric impacts to follow. However, a large number of downward and non-downward propagating SSWs must be considered (>35), before the difference becomes statistically significant. The precursors are also robust upon comparison with composites consisting of randomly selected tropospheric northern annular mode (NAM) events. The downward influence and precursors to split and displacement events are also examined. It is found that anomalous upward wave-1 fluxes precede both cases. Splits exhibit a near instantaneous, barotropic response in the stratosphere and troposphere, while displacements have a stronger long-term influence

Ion cyclotron resonance heating with consistent finite orbit widths and anisotropic equilibria

Minority ion cyclotron resonance heating is studied using the self-consistent numerical model SCENIC. This model includes 3D geometries with full shaping and anisotropic pressure effects, warm contributions to the dielectric tensor and full orbit effects. It evolves the equilibrium, wave field and hot particle distribution function iteratively until a self-consistent solution is found. We will show applications to JET-like two-dimensional equilibria with minority heating scenarios. The effects due to different heating locations on the hot particle distribution function, the hot dielectric tensor and the equilibrium will be studied for symmetric wave injection. Finally, the RF-induced particle pinch is investigated using asymmetric wave injection

Recovery of logged forest fragments in a human-modified tropical landscape during the 2015-16 El Nino

The past 40 years in Southeast Asia have seen about 50% of lowland rainforests converted to oil palm and other plantations, and much of the remaining forest heavily logged. Little is known about how fragmentation influences recovery and whether climate change will hamper restoration. Here, we use repeat airborne LiDAR surveys spanning the hot and dry 2015-16 El Nino Southern Oscillation event to measure canopy height growth across 3,300ha of regenerating tropical forests spanning a logging intensity gradient in Malaysian Borneo. We show that the drought led to increased leaf shedding and branch fall. Short forest, regenerating after heavy logging, continued to grow despite higher evaporative demand, except when it was located close to oil palm plantations. Edge effects from the plantations extended over 300 metres into the forests. Forest growth on hilltops and slopes was particularly impacted by the combination of fragmentation and drought, but even riparian forests located within 40m of oil palm plantations lost canopy height during the drought. Our results suggest that small patches of logged forest within plantation landscapes will be slow to recover, particularly as ENSO events are becoming more frequent. It is unclear whether tropical forest fragments within plantation landscapes are resilient to drought. Here the authors analyse LiDAR and ground-based data from the 2015-16 El Nino event across a logging intensity gradient in Borneo. Although regenerating forests continued to grow, canopy height near oil palm plantations decreased, and a strong edge effect extended up to at least 300m away.Peer reviewe