Plasma Channel Radius Research Articles

ANALYSIS OF SPARK ERODED CRATER FORMED UNDER GROWING PLASMA CHANNEL IN ELECTRO-DISCHARGE MACHINING

ABSTRACT In electro-discharge machining, the occurrence of sparks cause material removal in the form of craters. These craters are due to melting and vaporization of workpiece over a localized area under the spark, which acts as the heat source. The crater under a single spark has been predicted by theoretical models adopting different approaches in solving the transient heat conduction equation, considering suitable assumptions with appropriate initial and boundary conditions. In the present work, a transient thermal model for a very large solid cylinder has been used to predict the size of the crater obtained under a single spark by determining the melting isotherm in both the axial and radial directions. An analytical study of the effect of plasma channel radius, heat flux, and pulse duration on the size of the crater has been made. Experiments are conducted using a commercial electro-discharge machine. The craters are measured under microscope and a comparison with theoretical results is presented. Subsequently, the nature of variation of crater diameter, crater depth and volume of material removed with respect to different machining parameters such as ‘ON’ time, ‘OFF’ time, and current have been explained by the theoretical results and it has been concluded that the plasma channel grows with respect to pulse duration such that at the end of the pulse the plasma channel radius becomes equal to the crater radius.

Pellet ablation studies on TORE SUPRA

The penetration of deuterium pellets into ohmically heated TORE SUPRA plasmas has been studied for various plasma conditions (ne = 1 × 1019-6 × 1019 m3, Te = 1-4 keV) and pellet characteristics (Np = 2 × 1020-1.3 × 1021 atoms/pellet, Vp = 0.6-2.4 km/s - i.e. an increase of about 1 km/s from the velocity range covered by the available data for pellet studies). The measured penetration depths compare well with the predictions of the NGS model. A refined NGPS model is presented, in which the plasma channel radius is computed self-consistently and the heating of the neutral cloud by the 'cold' plasma sheath is taken into account explicitly. When the value of ne is sufficiently high, it fits the experimental penetration values well, and the computed matter deposition profile compares well with the measured Hα signal. The same model has been shown to fit the experimental scaling laws deduced from the JET and ASDEX data

Relativistic electron-beam transport in curved channels

Collisionless single particle trajectories are modeled for a single plasma channel having one section curved in a circular arc. The magnetic field is developed by superposition of straight and curved channel segments. The plasma density gives charge and beam-current neutralization. High transport efficiencies are found for turning a relativistic electron beam 90° under reasonable conditions of plasma current, beam energy, arc radius, channel radius, and injection distributions in velocity and in position at the channel entrance. Channel exit distributions in velocity and position are found consistent with those for a straight plasma channel of equivalent length. Such transport problems are important in any charged particle-beam application constrained by large diode-to-target distance or by requirements of maximum power deposition in a confined area.

Use of diffusing inductive fields of a relativistic beam-plasma system to determine plasma conductivity

As an intense relativistic electron beam passes through neutral gas it produces a plasma channel. A technique to measure the conductivity profile of this plasma is discussed. The analysis shows that diagnosing the radial and temporal variation of inductive field strengths may be used to determine both the plasma conductivity and channel radius. The essence of the method is to measure magnetic diffusion time as a function of radial position, which fixes the resistive skin depth.