Mutual interactions between plasma filaments in a tokamak evidenced by fast imaging and machine learning.

Magnetically confined fusion plasmas are subject to various instabilities that cause turbulent transport of particles and heat across the magnetic field. In the edge plasma region, this transport takes the form of long filaments stretched along the magnetic field lines. Understanding the dynamics of these filaments, referred to as blobs, is crucial for predicting and controlling their impact on reactor performance.

Investigation on the origin of hot electrons in laser plasma interaction at shock ignition intensities.

Shock Ignition is a two-step scheme to reach Inertial Confinement Fusion, where the precompressed fuel capsule is ignited by a strong shock driven by a laser pulse at an intensity in the order of [Formula: see text] W/cm[Formula: see text]. In this report we describe the results of an experiment carried out at PALS laser facility designed to investigate the origin of hot electrons in laser-plasma interaction at intensities and plasma temperatures expected for Shock Ignition. A detailed time- and spectrally-resolved characterization of Stimulated Raman Scattering and Two Plasmon Decay instabilities, as well as of the generated hot electrons, suggest that Stimulated Raman Scattering is the dominant source of hot electrons via the damping of daughter plasma waves.

Novel concept suppressing plasma heat pulses in a tokamak by fast divertor sweeping.

One of the remaining challenges in magnetic thermonuclear fusion is survival of the heat shield protecting the tokamak reactor vessel against excessive plasma heat fluxes. Unmitigated high confinement edge localized mode (ELM) is a regular heat pulse damaging the heat shield. We suggest a novel concept of magnetic sweeping of the plasma contact strike point fast and far enough in order to spread this heat pulse.

High-heat flux ball-pen probe head in ASDEX-Upgrade.

A new high heat flux ball-pen probe head installed on the midplane manipulator is currently being used in ASDEX-Upgrade (AUG). The probe was designed to withstand high heat fluxes making possible the investigation of the plasma edge under harsh conditions, such as low power H-mode. Composed of seven pins (four Langmuir probes, mounted in two Mach probe pairs, and three ball-pen probes), the new probe head allows us to measure several plasma parameters simultaneously and with high temporal resolution.

Demonstration of Safe Termination of Megaampere Relativistic Electron Beams in Tokamaks.

For the first time it is experimentally demonstrated on the JET tokamak that a combination of a low impurity concentration bulk plasma and large magnetohydrodynamic instabilities is able to suppress relativistic electron beams without measurable heat loads onto the plasma facing components. Magnetohydrodynamic simulations of the instability and modeling of the postinstability plasma confirm the prompt loss of runaways and the absence of regeneration during the final current collapse. These surprising findings motivate a new approach to dissipate runaway electrons generated during tokamak plasma disruptions.

Real-time feedback control of the impurity emission front in tokamak divertor plasmas.

In magnetic confinement thermonuclear fusion the exhaust of heat and particles from the core remains a major challenge. Heat and particles leaving the core are transported via open magnetic field lines to a region of the reactor wall, called the divertor. Unabated, the heat and particle fluxes may become intolerable and damage the divertor.

Phase, Composition and Structure Changes of CoCrNi-Based Concentrated Alloys Resulting from High Temperature Oxidation.

In this work, CoCrNi, FeCoCrNi and CoCrFeMnNi concentrated alloys with a Y-Ti oxide particle dispersion were prepared by mechanical alloying and Spark Plasma Sintering. The alloy consists of an FCC Ni-based matrix with a Y-Ti oxide dispersion and additional phases of CrC and CrO. The effect of Fe, Mn, and Y-Ti oxide particles on the formation of oxide scales and the composition of the adjacent CoCrNi and FeCoCrNi alloys was studied.

Phase control of a z-current-driven plasma column.

A dynamic mitigation is presented for sausage and kink instability growths of a z-current-driven magnetized plasma column. In this Rapid Communication we found that a wobbling motion of the z-current electron axis induces a phase-controlled perturbation, so that the growths of the sausage and kink instabilities are successfully and remarkably mitigated. In general, plasma instabilities emerge from perturbations, and the perturbation phase is normally unknown.

Electromagnetic Burst Generation during Annihilation of Magnetic Field in Relativistic Laser-Plasma Interaction.

We present the results of theoretical studies of formation and evolution of the current sheet in a colliosionless plasma during magnetic reconnection in relativistic limit. Relativistic magnetic reconnection is driven by parallel laser pulses interacting with underdense plasma target. Annihilation of laser created magnetic field of opposite polarity generates strong non-stationary electric field formed in between the region with opposite polarity magnetic field accelerating charged particles within the current sheet.

Micro-Faraday cup matrix detector for ion beam measurements in fusion plasmas.

Atomic beam probe is an extension of the routinely used beam emission spectroscopy diagnostic for the plasma edge current fluctuation measurement at magnetically confined plasmas. Beam atoms ionized by the plasma are directed to a curved trajectory by the magnetic field and may be detected close to the wall of the device. The arrival location and current distribution of the ions carry information about the plasma current distribution, the density profile, and the electric potential in the plasma edge.

Peculiar behavior of Si cluster ions in a high-energy-density solid Al plasma.

Peculiar behavior is found in a Si cluster ion, moving with a speed of ∼0.22c (c: speed of light) in a solid Al plasma in the context of cluster-ion beam driven inertial confinement fusion: The Si ion, moving closely behind the forward-moving Si ion for a distance of several Å in the cluster, feels the wake field generated by the forward Si. The acceleration interaction force on the rear Si ion by the forward-moving ion may balance with the deceleration backward force in the longitudinal-moving direction.

Fast density reconstruction of Li-BES signal on the COMPASS tokamak.

This article describes a fast and automatic reconstruction of the edge plasma electron density from the radiation of energetic Li atoms of the diagnostic beam on the COMPASS tokamak. Radiation is detected by using a CCD camera and by using an avalanche photo-diode system with a temporal resolution of 20 ms and 2 s, respectively. Both systems are equipped with a 670.

High magnetic field test of the ITER outer vessel steady-state magnetic field Hall sensors at ITER relevant temperature.

The ITER outer vessel steady-state magnetic field sensor diagnostics consist of sixty sensor units. Each sensor unit features a pair of ceramic-metal Hall sensors with a sensing layer made of bismuth. The sensors were tested simultaneously in the magnetic field ranging from -12 T to +12 T at the temperature range from 27 to 127 °C.

Observation and evaluation of the alignment of Thomson scattering systems.

Concerning plasma diagnostics based on Thomson scattering (TS), precise adjustment and proper alignment is of great importance in order to provide reliable and accurate measurements. Any misalignment could result in an incorrectly determined plasma density or prevent the measurement with this type of diagnostic altogether. Suitable means of alignment monitoring should be integrated into each TS diagnostic system.

Steady state magnetic sensors for ITER and beyond: Development and final design (invited).

The measurements of the magnetic field in tokamaks such as ITER and DEMO will be challenging due to the long pulse duration, high neutron flux, and elevated temperatures. The long duration of the plasma pulse makes standard techniques, such as inductive coils, prone to errors. At the same time, the hostile environment, with repairs possible only on blanket exchange, if at all, requires a robust magnetic sensor.

The Influence of Milling and Spark Plasma Sintering on the Microstructure and Properties of the Al7075 Alloy.

The compact samples of an Al7075 alloy were prepared by a combination of gas atomization, high energy milling, and spark plasma sintering. The predominantly cellular morphology observed in gas atomized powder particles was completely changed by mechanical milling. The continuous-like intermetallic phases present along intercellular boundaries were destroyed; nevertheless, a small amount of Mg(Zn,Cu,Al)₂ phase was observed also in the milled powder.

Nanocrystalline Al7075 + 1 wt % Zr Alloy Prepared Using Mechanical Milling and Spark Plasma Sintering.

The microstructure, phase composition, and microhardness of both gas-atomized and mechanically milled powders of the Al7075 + 1 wt % Zr alloy were investigated. The gas-atomized powder exhibited a cellular microstructure (grain size of a few µm) with layers of intermetallic phases along the cell boundaries. Mechanical milling (400 revolutions per minute (RPM)/8 h) resulted in a grain size reduction to the nanocrystalline range (20 to 100 nm) along with the dissolution of the intermetallic phases.

Spark Plasma Sintering of a Gas Atomized Al7075 Alloy: Microstructure and Properties.

The powder of an Al7075 alloy was prepared by gas atomization. A combination of cellular, columnar, and equiaxed dendritic-like morphology was observed in individual powder particles with continuous layers of intermetallic phases along boundaries. The cells are separated predominantly by high-angle boundaries, the areas with dendritic-like morphology usually have a similar crystallographic orientation.

Degradation of phospholipids under different types of irradiation and varying oxygen saturation.

The effects of different types of radiation on the formation of peroxide forms of 2-dioleoyl-sn-glycero-3-phosphocholine were studied under various conditions. For the irradiation, an aqueous solution of small unilamellar vesicles was prepared. Variations in parameters such as the dose rate and molecular oxygen saturation levels were evaluated.

Filamentary probe on the COMPASS tokamak.

This paper describes a new filamentary probe recently introduced on the COMPASS tokamak. It allows the measurement of electrostatic and magnetic properties of the filaments and their changes in dependence on distance from the separatrix in the region between a divertor and midplane. The probe head is mounted on a manipulator moving the probe radially on a shot-to-shot basis.

Fitting of the Thomson scattering density and temperature profiles on the COMPASS tokamak.

A new technique for fitting the full radial profiles of electron density and temperature obtained by the Thomson scattering diagnostic in H-mode discharges on the COMPASS tokamak is described. The technique combines the conventionally used modified hyperbolic tangent function for the edge transport barrier (pedestal) fitting and a modification of a Gaussian function for fitting the core plasma. Low number of parameters of this combined function and their straightforward interpretability and controllability provide a robust method for obtaining physically reasonable profile fits.

High magnetic field test of bismuth Hall sensors for ITER steady state magnetic diagnostic.

Performance of bismuth Hall sensors developed for the ITER steady state magnetic diagnostic was investigated for high magnetic fields in the range ±7 T. Response of the sensors to the magnetic field was found to be nonlinear particularly within the range ±1 T. Significant contribution of the planar Hall effect to the sensors output voltage causing undesirable cross field sensitivity was identified.