Role Of Energetic Electrons Research Articles

Detailed Thermal and Nonthermal Processes in an A-class Microflare

How microflares behave and differ from large flares is an important question in flare studies. Although they have been extensively investigated, microflares are not fully understood in terms of their detailed energy release processes and the role of energetic electrons. A recent study on an A-class microflare suggests the existence of a nonthermal component down to 6.5 keV, indicating that accelerated electrons play an important role in microflares, as in large flares. Here, we revisit this event, and present a comprehensive, quantitative analysis of the energy release and plasma heating processes. Using careful differential emission measure (DEM) analysis, we calculate the thermal X-ray fluxes. By subtracting this multithermal component from the observed data, we confirm the existence of the remaining nonthermal component. In addition, we analyze the clear evaporation process and report the first imaging evidence for a low-energy cutoff of energetic electrons in EM maps of >10 MK plasma, which first appeared as two coronal sources significantly above the chromospheric footpoints. Detailed calculations of electron transport, based on the electron parameters and the evolution of loop dynamics, provide strong evidence of a beam-driven plasma heating process with a low-energy cutoff consistent with that derived independently from DEM analysis. This study reveals the important role of electron thermalization and low-energy cutoffs in the physical processes of microflares.

Role of energetic electrons during current ramp-up and production of high poloidal beta plasma in non-inductive current drive on QUEST

A scenario for non-inductive current ramp-up has been demonstrated using electron cyclotron waves in the spherical tokamak QUEST. The configuration was characterized by a high toroidal magnetic mirror ratio of 2 and a steady vertical magnetic field of more than 10% of the toroidal magnetic field. The generation and confinement of energetic electrons having energy greater than 10 keV were studied using hard x-rays. Because of the energetic electron pressure, a natural divertor formed with an inboard poloidal field null at the high poloidal beta (approximately 3–4).

The role of energetic electrons in self-oscillations of a discharge plasma

The role of energetic electrons in periodic self-oscillations of a discharge plasma has been studied by measuring the spatiotemporal evolution of plasma potential, electron density, and electron velocity distribution function. It is found that the self-oscillation involves the instabilities of sheaths, propagation of a double layer and competition between the ionization, thermalization, and diffusion. The energetic electrons are the key factor which links these processes to form the oscillation cycle. The time interval of each phase in the cycle is estimated according to the physical process and the calculations are in agreement with experimental measurements. The study of the probe perturbation effect on the oscillations indicates that the length of the oscillation period is related to the amount of energetic electrons; the more energetic electrons, the shorter the period.

Nonequilibrium volume plasma chemical processing

A review is presented of plasma chemical processes occurring in the volume part of electrical nonequilibrium discharges. The role of energetic electrons as initiators of chemical reactions in a cold background gas is discussed. Different discharge types of (glow, corona, silent, RF, and microwave discharges) are investigated with respect to their suitability for plasma processing. Emphasis is placed on the requirements of initiating and maintaining the discharge and, at the same time, optimizing plasma parameters for the desired chemical process. Using large-scale industrial ozone production as an example, the detailed process of discharge optimization is described. Other applications of volume plasma processing include other plasma chemical syntheses as well as decomposition processes such as flue gas treatment and hazardous waste disposal. The author only deals with plasmas which are not in equilibrium. >

Characteristics of the white-light source in the 1981 April 24 solar flare

Observations of the white-light solar flare event of April 24, 1981 are presented. The observations were carried out in the optical, hard X-ray, and radio wavelengths from land-based observatories and from the International Sun-Earth Explorer (ISEE-3) satellite. Time-intensity profiles were derived for three lines of continuum emissions. The derived profiles are interpreted in terms of the energetics of the flare, and the role of energetic electrons in the production of optical continuum emission is examined in detail.

The possible role of energetic electrons in the production of surges

Energetic electrons, which play a major role in the explosive phases of flares, are proposed as the energy source for the production of surges. Flare data from a two-year interval are analyzed to show that the probability of having surges associated with flares is greater when there are accompanying decimeter type III bursts or impulsive 8800 MHz bursts. The model of chromospheric heating by impulsive electrons proposed by Hudson is examined and shown to provide an adequate explanation for the origin of flare surges. The proposed surge model is consistent with the temporal evolution of the flare-surge event and the required surge energy. Surges not accompanied by flares can also probably be explained by the model.

The role of energetic electrons in the correlation of meter and decimeter type III bursts with 4 keV X-ray emission

The correlation of type III burst-groups with 4 keV solar X-ray emission is examined. A total of 151 burst-groups reported by the Fort Davis Observatory were compared with X-ray emission observed by the Naval Research Laboratory experiment on the OGO-5 satellite. A higher X-ray correlation is found for type III burst-groups when: (1) the bursts are observed on the decimeter band and (2) the bursts are more intense. The bremsstrahlung flux resulting from the proposed coronal loss of the E< 10 keV type III electrons is shown to be below the detection threshold of the OGO-5 experiment. No fine structure is found in the correlated impulsive X-ray bursts with a time scale on the order of one second. It is proposed that electrons are accelerated over a time of 10–100 s or more and that the type III bursts are the result of the occasional escape of a small fraction of the energetic electrons from the acceleration region.