Transient buildup and dissipation of a compressed plasma shockwave in arc-discharge plasma beams

Electric propulsion offers the advantage of a high specific impulse through a large exhaust velocity and has seen significant progress in space flight applications. Recently, we observed a transient plasma shockwave during pulsed plasma thruster operation when the plasma beam impacted a probe surface. However, details regarding the plasma shockwave formation are still unknown. This work is an experimental investigation of the compression-induced plasma shockwave in the presence of a planar obstruction. To study the complete shockwave buildup and dissipation process, an ultra-high-speed imaging system was set up to visualize the time-resolved shockwave morphology at a sub-microsecond level. In addition, the local magnetic field and plasma density were measured using 2-D magnetic coils and a triple Langmuir probe, respectively. The successive images of the shockwave give us a comprehensive understanding of the shockwave buildup process. During the 12 μs operational period of the thruster, two shockwaves were formed during the first cycle of the discharge. It is also interesting to note that there is a 1 μs dissipation period between the two shockwaves with the same cloud of plasma compressing against the probe surface. A shockwave model is also developed to predict the appearance of the two shockwaves. The implication is that the local magnetic field strength can be a key indicator for the plasma shockwave buildup and dissipation process.

HELIUM RELEASE FROM 12Cr18Ni10Ti STAINLESS STEEL AFTER IMPACT OF STEADY STATE GLOW DISCHARGE He PLASMA

The thermal desorption experiments were carried out to study the process of helium outgassing from the stainless steel 12Cr18Ni10Ti after exposure to a steady state glow discharge (GD) plasma in He atmosphere. The currentvoltage characteristics in different plasma regimes have been measured and estimation of He ions energy has been made. Measurements of He release from the stainless steel probes showed the saturation of probe surface with He after the fluencies of ~ 4 ∙ 1019 ion/cm2. The value of He outgassing strongly depends on the regime of GD plasma: pressure of work gas, discharge voltage, etc. Several maximums, including the maximum at the temperature of 100…150 °C, were registered in the He desorption curves that indicated different He atom states on the surface and in the nearest surface bulk. Physical mechanisms of such He outgassing are discussed.

Semiconductor surfaces

This chapter discusses the electronic, phononic and atomic behavior at surfaces. Symmetry breaking at the surface causes the emergence of new properties as the state description changes. Starting with an introduction of the semi-classical view, a bulk-based view of workfunction and electron affinity and cautions related to them, toy models are employed to explore the evolution of states at the surface. For electrons, propagating Bloch states persist to the surface but there are also states that are confined. Properties of these confined states and surface states are explored. The implications of stress and of surface reconstruction are discussed to elucidate the atomic rearranging that arises in semiconductors of interest when symmetries change. The state evolution approach is then extended to probe surface phonons. Again, bulk modes persist up to the surface, but there can also be surface-confined modes as well as surface-propagating modes.

Laser hardening influence of metal surfaces

In this paper we analyze the influence of the number of laser pulses on the hardness of the metal. We have shown that the hardness increases with the number of laser pulses due to the increase in the probe surface temperature, especially by increasing the superficial absorption of laser radiation. Optical microscopy was analyzed by the metallographic aspects of the target in OLT 65, Al, Cu, laser irradiated.