Minor Radius Research Articles

Ellipsoidal Trajectory Optimization for Minimizing Latency and Data Transmission Energy in UAV-Assisted MEC Using Deep Reinforcement Learning

Due to their flexible deployment and movement capability, unmanned aerial vehicles (UAVs) are being utilized as flying mobile edge computing (MEC) platforms, offering real-time computational resources and low-latency data processing for a wide range of applications. This article aims to explore a UAV-assisted MEC system where multiple UAVs provide MEC services to mobile devices (MDs) using an ellipsoidal trajectory. Depending on the position, size, and orientation of the ellipsoidal trajectories, the coverage area of the UAV, the energy consumption, and the task transmission latency of MDs change. This has rarely been investigated in the existing works. Furthermore, unlike other studies, we consider that each MD has varying task offloading rates, which, together with varying user densities, makes the problem more challenging. Therefore, we formulate an optimization problem that finds the center position, major radius, minor radius, and rotation angle of the ellipsoidal trajectory of UAV-assisted MEC servers, to minimize the total transmission latency and energy consumption of mobile devices while taking into account the required data transmission rate, task transmission time, and energy consumption constraints. Then, we transform this optimization problem into a Markov decision process and propose a deep Q-learning-based ellipsoidal trajectory optimization (DETO) algorithm, to resolve it. The results from our simulations demonstrate that DETO efficiently computes the optimal position and trajectory for each UAV, and can achieve better performance compared to other baselines, leading to the reduced data transmission latency and energy consumption of mobile devices across a range of simulation scenarios.

Unprecedented confinement time of electron plasmas with a purely toroidal magnetic field in SMARTEX-C

Confinement time of electron plasmas trapped using a purely toroidal magnetic field has been found to exceed {100}, hbox {s} in a small aspect ratio (R_{o}/a sim {1.59}, R_o and a are device major and minor radius, respectively), partial torus. It improves upon the previously reported confinement time by nearly two orders of magnitude. Lifetime is estimated from the frequency scaling of the linear diocotron mode launched from sections of the wall, that are also used for mode diagnostics. Confinement improves as neutral pressures are reduced to < 5 times 10^{-10} hbox{mbar} in the presence of a steady state magnetic field of 200 Gauss (sim {60}, hbox {s} with droop < 0.1%) at {100}, hbox {V} electron injection energies. With reduced pressures the role of (ion driven) instability diminishes and loss mechanisms resulting from elastic electron–neutral (e–n) and the ubiquitous electron–electron (e–e) scattering seem to play an important role which suggests low electron temperatures. The contribution to electron population resulting from the ionization of background neutral gas at these temperatures and pressures are expected to be insignificant and is corroborated in our experiments.

Near-perfect turning of robot-based 3D printing continuous carbon fiber reinforced nylon composites based on fiber-scale internal stress characterization

Mechanical metamaterials based on continuous fiber reinforced composites exhibit excellent mechanical properties. Continuous fiber 3D printing is counted as an ideal manufacturing approach for mechanical metamaterials. Currently, most metamaterial lattice structures are printed at centimeter-scale. The significant change in the width of the printed filament caused by fiber twist and shift during steering is an obvious defect when turning with minor radius. Near-perfect turning is proposed herein as a turning under the smallest possible printing radius, and the printed filaments present superior width retention rate. The key to printing high-precision composite lattice structures below centimeter-scale is to assess the near-perfect turning radius. Therefore, a fiber near-perfect turning placement model was established and the near-perfect turning radius ra was assessed by measuring the fiber-scale internal stress required in the model. The precision evaluations show that the near-perfect turning radius calculated by the model is in good agreement with the experimental value, proving the model’s validity. In the case of the Robot-based printing platform and Nylon-carbon fiber composites, the near-perfect turning radius is 2.0 mm. This study establishes a solid process foundation for metamaterial manufacturing below the centimeter scale.

Photo and temperature responsive novel surface active ionic liquid-based polymeric hydrogel

Integrating more than two properties into a single polymeric hydrogel to introduce the multi-functionality has been a challenge for the scientific community in recent times. In order to impart photo and temperature responsive characteristics added with adjustable mechanical properties into the polymeric hydrogel, herein we have added newly synthesized photo-responsive ionic liquid (IL) into the polymeric (κ-carrageenan) hydrogel. The IL used is having morpholine-based ester functionalized long chain cation and azobenzene based anion that exhibited trans to cis transformation when irradiated by light of 465 nm for 50 min and show surface-active properties with CMC of 6.83 mM. IL with such photo and temperature responsive properties when mixed with the hydrogel of κ-carrageenan in KCl solution gives the photo and thermo-responsive hybrid hydrogel. The three-dimensional network structure of hydrogel made up of the ellipsoidal aggregates with major and minor axis radius of 9.3 A0 and 1.6 A0, respectively is made up of a fibrous porous structure and gets disrupted through the light irradiation and initiated the gel to sol transition, studied through the SEM images, DLS data and rheological measurements. The (IL) based hydrogel gets disrupted after light irradiation as the anion of the IL starts transforming from trans to cis isomerization. Also, the thermo-reversible transition of hydrogel within room temperature to 54 °C is also shown by rheology. Kinetics of the trans to cis transformation, controlled strain and stress measurement and thermal stability of the hydrogel are assessed here. The studied photo and temperature responsive hydrogel could start a new range of smart materials.

Nonlinear microtearing modes in MAST and their stochastic layer formation

First nonlinear gyrokinetic simulations of microtearing modes in the core of a MAST case are performed on two surfaces of the high-collisionality discharge used in Valovič et al (2011 Nucl. Fusion 51 073045) to obtain the favorable energy confinement scaling with collisionality, . On the considered surfaces microtearing modes dominate linearly at binormal length scales of the order of the ion Larmor radius. While the effect of electron collision frequency is moderate in linear simulations, a strong dependence on this parameter is found in nonlinear simulations at , where r and a are the surface and tokamak minor radius, respectively. The dynamics of magnetic islands generated by microtearing modes is analysed, showing that the radial extent of the stochastic region caused by islands overlapping plays an important role in determining the saturation level of the microtearing mode driven heat flux. Local nonlinear gyrokinetic simulations show that the microtearing mode driven heat flux, , is largely dominated by magnetic flutter and depends strongly on the magnetic shear, . Comparing two surfaces, and , reveals that is negligible at (), with the electron temperature gradient (ETG) driven heat flux, , comparable to the experimental electron heat flux, , while is significantly larger and comparable to and at (). Microtearing modes cause more experimentally significant transport in higher regions and may influence (together with ETG modes) the observed scaling of energy confinement time with collisionality (Valovič et al 2011 Nucl. Fusion 51 073045).

Gyro orbit simulations of neutral beam injection in Wendelstein 7-X

Simulations exploring neutral beam operation in Wendelstein 7-X (W7-X) at reduced magnetic field are performed using a newly implemented gyro orbit model in the BEAMS3D code. Operation at field strengths below the nominal 2.5 T are seen as a path to explore both high beta plasmas and as a means to access magnetic configurations not possible at 2.5 T. As the field strength becomes smaller, the gyro radius for 55 keV fast protons grows from at 2.5 T to at 0.75 T in a device with minor radius bringing into question the applicability of the gyro center approximation. To address this a gyro orbit model was implemented in the BEAMS3D code. Agreement is found between the gyro center and gyro orbit models in a circular cross section tokamak equilibrium at high field. A set of W7-X equilibria are assessed with fixed density and temperature profiles but decreasing magnetic field strength (increasing plasma beta). Neutral beam deposition is found to be mostly unaffected with changes in the core of the plasma associated with the Shafranov-shift. In general good agreement is found between gyro orbit and gyro center simulations at 2.5 T. Both models indicate increasing losses with decreasing magnetic field strength with the gyro orbit losses being higher at all field strengths. Gyro orbit simulations to the first wall of W7-X show a change in loss pattern with decreasing magnetic field strength. A preliminary assessment of losses to fast ion loss detectors are made.

Development of compact tokamak fusion reactor use cases to inform future transport studies

The OMFIT STEP (Meneghini et al., Nucl. Fusion, vol. 10, 2020, p. 1088) workflow has been used to develop inductive and steady-state H-mode core plasma scenario use cases for a $B_0 = 8 \, {\rm T}$ , $R_0 = 4 \, {\rm m}$ machine to help guide and inform future higher-fidelity studies of core transport and confinement in compact tokamak reactors. Both use cases are designed to produce 200 MW or more of net electric power in an up-down symmetric plasma with minor radius $a = 1.4 \, {\rm m}$ , elongation $\kappa = 2.0$ , triangularity $\delta = 0.5$ and effective charge $Z_{{\rm eff}} \simeq 2$ . Additional considerations based on the need for compatibility of the core with reactor-relevant power exhaust solutions and external actuators were used to guide and constrain the use case development. An extensive characterization of core transport in both scenarios is presented, the most important feature of which is the extreme sensitivity of the results to the quantitative stiffness level of the transport model used as well as the predicted critical gradients. This sensitivity is shown to arise from different levels of transport stiffness exhibited by the models, combined with the gyroBohm-normalized fluxes of the predictions being an order of magnitude larger than other H-mode plasmas. Additionally, it is shown that although heating in both plasmas is predominantly to the electrons and collisionality is low, the plasmas remain sufficiently well coupled for the ions to carry a significant fraction of the thermal transport. As neoclassical transport is negligible in these conditions, this situation inherently requires long-wavelength ion gyroradius-scale turbulence to be the dominant transport mechanism in both plasmas. These results are combined with other basic considerations to propose a simple heuristic model of transport in reactor-relevant plasmas, along with simple metrics to quantify coupling and core transport properties across burning and non-burning plasmas.

New Scheme of Microlens Fiber Array for High Coupling Efficiency in Si-Photonics Module

A new scheme of microlens 4-fiber array (M4FA) for high-coupling efficiency in Si-photonics module employing automatic packaging a silicon V-groove array and microlens fibers is demonstrated. The silicon V-groove array was fabricated by KOH wet etching. The microlens fibers were precisely controlled by automatic grinding and calibrated spin-on-glass (SOG) liquid electrostatic coating to achieve the required minor radius of curvature of 1.3- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> for achieving high coupling efficiency. In comparison with other microlens fabrication by mechanical grinding and multiple fusing techniques, the proposed M4FAs enable to adjust the fiber offset, radius of curvature, and alignment tolerance by SOG coating after fiber grinded, resulting in high-average coupling efficiency of 60% from Si-photonics module to M4FA. The newly developed M4FA by automatic grinding and calibrated SOG coating is beneficial for the applications of Si-photonics modules use in many low-cost and high-performance light-wave interconnections.

Global gyrokinetic simulations of the impact of magnetic island on ion temperature gradient driven turbulence

The effect of island width on the multi-scale interactions between magnetic island (MI) and ion temperature gradient (ITG) turbulence has been investigated based on the global gyrokinetic approach. It is found that the coupling between the island and turbulence is enhanced when the MI width (w) becomes larger. A vortex flow that is highly sensitive to the width of the MI can be triggered, ultimately resulting in a potent shear flow and a consequent reduction in turbulent transport. The shearing rate induced by the vortex flow is minimum at the O-point while it is maximum at both of the two reconnection points of the island, i.e. the X-points, regardless of the island width. There exists a nonmonotonic relationship between zonal flow (ZF) amplitude and island width, showing that the ZF is partially suppressed by medium-sized MIs whereas enhanced in the case of large island. A larger MI can tremendously damage the ITG mode structure, resulting in higher turbulent transport at the X-point whereas a lower one at the O-point, respectively. Such phenomenon will be less distinct at very small island widths below w/a ∼ 8% ≈ 12 (a is the minor radius and the ion gyroradius), where it shows that turbulence near the X-point is hardly affected although it is still suppressed inside the island. Furthermore, the influence of different island sizes on turbulence transport level is also discussed.

Design of superconducting tokamak magnet systems and applications to HTS

In this paper we illustrate a self-consistent procedure to design the superconducting Toroidal Field (TF) and Central Solenoid (CS) magnet systems starting from the basic plasma dimensioning parameters. By defining the plasma major radius and minor radii, as well as the inboard TF coil neutron shielding radial built, we proceed by sizing the TF Winding Pack (WP), its case and the CS modules. The ITER magnets design philosophy and criteria are adopted throughout the study. A key outcome of this work is to illustrate the inter-play between machine size, magnetic field and availability of inductive flux for burn. In doing so we investigate the advantages brought by high field tokamak design compared the more conventional (ITER-like) Nb3Sn based magnet design solutions.

Statistical analysis of similarity of plasma parameters profiles at quasi-stationary stage of discharge in JET tokamak

A statistical analysis is carried out of the similarity of profiles of plasma parameters: electron temperature T e, density n e, and pressure P e, at the stage of quasi-stationary plasma current (the so called flat-top stage) of about 9000 discharges in the JET tokamak, among the discharges from #84458 to #99419 that covers almost the entire database of successful discharges in the JET ITER-like wall machine. For all these parameters, the existence of universal profiles is shown as functions of the normalized minor radius of the plasma column ρ. The discharge universal profiles (DUPs) are obtained by dividing the space-time-dependent profile by its value at the center of the plasma column or by the space-averaged value of this parameter in the region ρ ⩽ ρ max = 0.5–1, and subsequent averaging over time at the flat-top stage of each discharge. The machine universal profiles (MUPs) are obtained by averaging over time of flat-top stage of all discharges. It is shown that for 86% of the discharges, the time-averaged relative root-mean-square deviation of P e profile from the DUP is less than 20% at ρ ⩽ 0.8, and for the MUP, it is less than 17%. A similar picture is observed for the profiles of T e and n e/√T e. An auxiliary heating, P aux ⩾ 1 MW or 10 MW, was present at, respectively, 44% and 21% of the total duration of the flat-top stage of discharges. It is shown that large, ∼100% in magnitude, jumps of T e at ρ = 0, caused by the switch-on of auxiliary heating, can be described with a ∼20% accuracy by the jumps of the space-averaged temperature if the DUP is used to describe the stationary shape of the temperature spatial profile. The results obtained illustrate the degree of plasma self-organization in tokamaks.

Scenario trajectory optimization and control on STEP

In this paper we present optimized actuator trajectories, evolving in time and space, of non-inductive ramp-up scenarios for the Spherical Tokamak for Energy Production (STEP). These trajectories are computed by solving a non-linear, multi-objective, constrained, finite-time optimal control problem. A method unique to STEP ramp-up studies that provides an alternative to existing trajectory search strategies which rely on manually adjusting trajectories to reach a desired state. To navigate a non-linear parameter space which is densely populated with local minima, we demonstrate an iterative objective function construction process whereby costs and constraints are included successively and re-optimized after each inclusion to improve convergence and feasibility. This method is particularity useful when the initial trajectory is far from the desired operating space. We use the RApid Plasma Transport simulatOR (RAPTOR) code to self-consistently solve four coupled, 1-D state equations; poloidal flux, electron temperature, ion temperature and electron density. Our STEP actuator trajectories lasting 1500s, consist of 8 Gaussian electron cyclotron heating and current drive beams distributed across the minor radius, a Deuterium/Tritium particle source and plasma current. We also introduce a modified transport Bohm–gyroBohm model and a new actuator module to RAPTOR which were required to adequately simulate the STEP operating scenarios.

Transition from ITG to MTM linear instabilities near pedestals of high density plasmas

Investigation of linear gyrokinetic ion-scale modes ( k θ ρ s = 0.3) finds that a transition from ion temperature gradient to microtearing mode (MTM) dominance occurs as the density is increased near the pedestal region of a parameterized DIII-D sized tokamak. H-modes profile densities, temperatures, and equilibria are parameterized utilizing the OMFIT PRO_create module. With these profiles, linear gyrokinetic ion-scale instabilities are predicted with CGYRO. This transition (nMTM) has a weak dependence on radial location in the region near the top of the pedestal ( ρ = 0.7 − 0.9), which allows simulating single radii to examine the approximate scaling of nMTM with global parameters. The critical nMTM is found to scale with plasma current. Additionally, increasing the minor radius by decreasing the aspect ratio and increasing the major radius are found to reduce nMTM. However, any relationship between nMTM and density limit physics remains unclear as nMTM increases relative to the Greenwald density with larger minor radius and with larger magnetic field, suggesting that the transport due to MTM may be less important for a reactor. Additionally, nMTM is sensitive to the pedestal temperature, the local electron and ion gradients, the ratio of ion to electron temperature T i / T e, and the current profile. MTMs are predicted to be the dominant instability in the core at similar Greenwald fractions for DIII-D, NSTX, and NSTX-U H-mode experiments, supporting the results of the parameterized study. Additionally, MTMs continue to be the dominant linear instability in a DIII-D L-mode after an H–L transition as the plasma approaches a density limit disruption despite the large change in plasma profiles.

Parametric study of the kinematic evolution of coronal mass ejection shock waves and their relation to flaring activity

Context.Coronal and interplanetary shock waves produced by coronal mass ejections (CMEs) are major drivers of space-weather phenomena, inducing major changes in the heliospheric radiation environment and directly perturbing the near-Earth environment, including its magnetosphere. A better understanding of how these shock waves evolve from the corona to the interplanetary medium can therefore contribute to improving nowcasting and forecasting of space weather. Early warnings from these shock waves can come from radio measurements as well as coronagraphic observations that can be exploited to characterise the dynamical evolution of these structures.Aims.Our aim is to analyse the geometrical and kinematic properties of 32 CME shock waves derived from multi-point white-light and ultraviolet imagery taken by the Solar Dynamics Observatory (SDO), Solar and Heliospheric Observatory (SoHO), and Solar-Terrestrial Relations Observatory (STEREO) to improve our understanding of how shock waves evolve in 3D during the eruption of a CME. We use our catalogue to search for relations between the shock wave’s kinematic properties and the flaring activity associated with the underlying genesis of the CME piston.Methods.Past studies have shown that shock waves observed from multiple vantage points can be aptly reproduced geometrically by simple ellipsoids. The catalogue of reconstructed shock waves provides the time-dependent evolution of these ellipsoidal parameters. From these parameters, we deduced the lateral and radial expansion speeds of the shocks evolving over time. We compared these kinematic properties with those obtained from a single viewpoint by SoHO in order to evaluate projection effects. Finally, we examined the relationships between the shock wave and the associated flare when the latter was observed on the disc by considering the measurements of soft and hard X-rays.Results.We find that at around 25 solar radii (R⊙), the shape of a shock wave is very spherical, with a ratio between the lateral and radial dimensions (minor radii) remaining at aroundb/a ≈ 1.03 and a radial to lateral speed ratio (VR/VL)≈1.44. The CME starts to slow down a few tens of minutes after the first acceleration and then propagates at a nearly constant speed. We revisit past studies that show a relation between the CME speed and the soft X-ray emission of the flare measured by the Geostationary Operational Environmental Satellite (GOES) and extend them to higher flare intensities and shock speeds. The time lag between the peak of the flare and of the CME speed is up to a few tens of minutes. We find that for several well-observed shock onsets, a clear correlation is visible between the derivative of the soft X-ray flux and the acceleration of the shock wave.

Theoretical investigation of braking of tearing mode rotation by resistive walls in ITER

The locking of the 2/1 tearing mode to the resistive wall in the ITER tokamak (15 MA inductive scenario 2) is investigated theoretically using a cylindrical asymptotic matching model. The model takes into account the fact that ITER plasmas will effectively be surrounded by two walls; the inner blanket module layer with a time constant of about 23 ms, and the outer vacuum vessel with a time constant of about 380 ms. The model also takes cognizance of the fact that neither the blanket module layer nor the vacuum vessel can be accurately described as “thin” walls (in the ordinarily accepted sense). The model incorporates changes in both the plasma poloidal and the toroidal angular velocity profiles, in response to the electromagnetic braking torque that develops at the rational surface, because it turns out that neoclassical poloidal flow-damping is not strong enough to completely suppress changes in the poloidal velocity. Finally, the model accurately calculates changes in the poloidal and toroidal plasma angular velocity profiles by evolving the full angular equations of motion, taking the electromagnetic braking torque, plasma inertia, plasma viscosity, and poloidal flow-damping into account. The time required for the 2/1 tearing mode to grow from a small amplitude to a sufficient one to lock to the walls is found to be about 3.5 s. The critical full radial island width at which wall locking is triggered is found to be about 9% of the plasma minor radius.

Coherent mode induced by supersonic molecular beam injection in EAST Ohmic plasmas

A coherent mode (CM) induced by the supersonic molecular beam injection (SMBI) was observed in Ohmic plasmas of EAST tokamak. The CM existed in the spectra of the electron temperature fluctuation and density fluctuation, but not in the spectrum of Mirnov fluctuation. The radial location of the CM was about 10 cm inside the separatrix (normalized minor radius ). In most cases, the CM has multiple discrete frequencies between with an interval of ∼1 kHz. Occasionally, there is only one dominant frequency. The poloidal scale of the CM (poloidal wavenumber , poloidal mode number ) is between that of typical ion turbulence and macroscopic magnetohydrodynamic activities. Statistical analysis results suggest that the onset of the CM requires a high temperature gradient and a relatively low density gradient. Furthermore, the transport analysis shows that the SMBI-caused perturbation propagates inward faster in plasmas with stronger CM, which implies that the CM might be correlated to a high local transport level. However, the impact of the CM on macroscopic plasma parameters including stored energy, energy confinement time, and SMBI-caused mean density fluctuation is too weak to be found in comparison with the random fluctuation and the measurement errors, which suggests that the CM does not have a clear influence on the global confinement.

Research on Magnetic-Induced Error of Small-Sized Fiber Optic Gyro Fiber Coil in Space Environment

Spacecraft is severely limited in weight and volume, resulting in a small bending radius of the fiber coil used by IFOG (Interference Fiber Optic Gyroscope). The fiber coil has such a size that the influence of bending on fiber birefringence cannot be ignored. In this paper, we research magnetic-induced errors of small-sized IFOG working in low orbit space. Firstly, we use the Jones matrix to analyze the effects of radial magnetic field and axial magnetic field on IFOG. Secondly, we establish a three-dimensional model for the radial magnetic-induced errors and magnetic-induced errors of minor radius fiber coil. Using the finite element method, we analyze the magnetic-induced error between different levels of the fiber coil. Combined with the birefringence distribution of the minor radius fiber coil, an accurate three-dimensional magnetic-induced error model is established. Thirdly, in the experiment, we design the magnetic-induced error test platform that includes the Fluke standard current source, transconductance amplifier, and Helmholtz coil. The experimental results show that, compared with the traditional calculation method, the three-dimensional magnetic-induced error model reduces the RMSE (Root Mean Square Error) of the radial magnetic field by 56.9% and the RMSE of the axial magnetic field by 35.7%, respectively.

Simulation and risk assessment of hydrogen leakage in hydrogen production container

In this paper, the hydrogen leakage and diffusion characteristics analysis and risk assessment are carried out on the container where a 2 Nm3/h alkaline hydrogen production device is located. Firstly, the transient and steady process of hydrogen leakage from hydrogen production container is analyzed. Secondly, the dynamic balance of combustible hydrogen cloud is analyzed, the concept of critical ventilation flow is put forward. It was found that in order to reduce the flammable volume by 85%, the installed ventilation can only cover the leakage flow of 1.0 Nm3/min. Finally, TNT equivalent method is used to evaluate the hazard degree of hydrogen leakage. It is found that the existed hydrogen production container ventilation device can only exhaust the hydrogen-air cloud with small flow leakage, while the accumulation of gas cloud still exists in large flow leakage. Under the critical ventilation flow, the minor injury radius can be reduced from 4.8 m to 2.78 m. The effect of critical ventilation flow was verified.

An optical-input Maximum Likelihood Estimation feedback system demonstrated on tokamak horizontal equilibrium control

A readily parallelized Maximum Likelihood Estimation (MLE) algorithm with linear computational complexity is demonstrated in real time using only measurements from an extreme ultraviolet (EUV) diagnostic to control the horizontal position of a tokamak plasma. A set of trial emissivity profiles are parameterized by the control quantity of interest (Rm), and the MLE is identified from the profile which minimizes the signal reconstruction residual. The algorithm depends on an empirically determined likelihood function with exponential form. EUV emission (λ≈ 15 eV-1 keV) is captured in a poloidal plane by four 16-channel AXUV diodes mounted at different poloidal angles with radial and angular resolution sufficient to discern plasma equilibrium evolution in HBT-EP. Calculations of the plasma major radius by the system are consistent within diagnostic uncertainty for the majority of the discharge with those of: a weighted average of vertical soft X-ray or EUV chords, magnetic sensors, and an equilibrium reconstruction. The feedback system corrects for a horizontal displacement of the major radius equal to 20% of the plasma minor radius by adjusting the vertical field produced from 40 in-vessel control coils in real time. The MLE calculation is performed on a GPU in a 15μs cycle, with similar performance in this application to a simple weighted average of vertical chords. Results demonstrate horizontal position control using magnetic actuators and an optical observer.

Non-monotonic radial structures of fluctuating temperatures and densities associated with fishbone activities in KSTAR

General characteristics of a fishbone mode in KSTAR are investigated. Fishbone activities are observed with a Mirnov coil, an electron cyclotron emission radiometer (from the core to the edge of plasmas) and an beam emission spectroscopy system (core or edge plasmas) which are measuring fluctuations of poloidal magnetic fields, electron temperatures, and densities, respectively. Temporal evolutions of these fluctuations are similar to the observations from other tokamaks. An interesting and notable feature found in KSTAR fishbone modes is that radial coherence structures of electron temperature and density with respect to magnetic fluctuations are non-monotonic that they have a local minimum at r/a∼0.7 and a maximum at r/a∼0.9 in addition to the usual global peak near the q = 1 surface, where r/a is the normalized minor radius and q is the safety factor. Furthermore, the associated temporal evolution of the electron temperatures in slow-time scale, i.e., less than 1 kHz, with the fishbone activities show that there exist a drop in temperature or increase in temperature depending on inside or outside the q = 1 surface, respectively, from the core to the edge plasmas except that there are almost no temperature changes in the intermediate region which seems to be correlated with the non-monotonic coherence profile. Such a non-monotonic structure and the slow temporal evolution of temperatures are explained with barely trapped resonating fast ions with the banana orbit widths of the order of the minor radius, so that they transit the core and the edge regions simultaneously without trespassing the mid-plane intermediate region.