Amount Of Charged Particles Research Articles

Analysis of the Transition Time between the Space-Charge-Limited and Inverse Regimes

Accumulation of cold ions trapped within a space-charge-limited sheath collapses the sheath, causing a transition to the inverse sheath mode. A driving mechanism creating trapped ions is charge-exchange collisions which occur between fast ions and cold neutrals. Due to the complex nature of the temporally evolving sheath, it is difficult to predict how long the transition takes. Depending on the properties of the plasma, emitted electrons, and neutrals, the time scale can range from microseconds to hours. For experimental situations, it is important to understand whether the sheath will transition to an inverse mode within the observation time allotted. In this paper, we establish a theoretical basis for defining transition time of the sheath in terms of plasma properties. Calculations include an analytical approximation for the length of the virtual cathode, the amount of charged particles in each layer of the space-charge-limited sheath, and a time for its transition to the inverse sheath. The theoretical model is then compared to 1D kinetic simulations of a space-charge-limited sheath with charge-exchange collisions present. The results are applied to estimate transition time scales for applications in laboratory plasma experiments, the lunar sheath, and tokamaks.

An ion source using laser ablation

This article describes the measurement of the fractional ionization in an ablated plume produced by excimer laser, and the application of the plume as an ion source. Laser ablation of iron, aluminum, and tantalum with a KrF excimer laser was performed in a vacuum chamber. The ablated plume was caught by a cup type electrode used to measure the amount of charged particles as current wave forms. Applying electrostatic potential larger than 40 V, the current wave forms were separated into electropositive and electronegative peaks. Each peak indicates ions and electrons, respectively. The amount of ions, 6×1013 ions/pulse, was estimated by integrating the electropositive peak. The ionization degree of 1.7% was also estimated by a series of analyses. For an aluminum target, the ion current reached 2 A at the peak and 1 mA on average at 60 kJ/m2, 500 mJ, and 50 Hz.

Formation and Growth of Sio2 Particlesin Low Pressure H2/O2/Ar Flames Doped with Sih4

Low pressure premixed H2/O2Ar flames (H2/O2 = 1.69, 1.04 ⩽ Ar/(H2 + O2) ⩽ 1.36) were doped with small amounts of SiH4 (131 ppm ⩽ SiH4/(H2 + O2 + Ar) ⩽ 524 ppm) and were stabilized on a flat, water-cooled sintered bronze plate at pressures 27.5 mbar ⩽ p ⩽ 30 mbar. Particles formed during the flame reaction process were extracted at different heights from the flame zone by a molecular beam sampling technique, which is part of a particle mass spectrometer. PMS. This instrument, which was developed earlier in this laboratory, generates a particle beam in a high vacuum containment. From direct measurements of both, the kineticenergy and the velocity of charged particles, their mass was directly determined. As the amount of naturally charged particles in the SiH4-doped H2/O2/ Ar flame was nearly zero. small amounts of C2H2 (about 5 ppm) was added to the flame, which changes the charging situation drastically. The PMS measurements indicate a strong formation rate of charged particles at flame co-ordinate x ⩾ 20 mm, which were in the mass range 3.7 10-20 g ⩽ mp, ⩽ 58.3 1O-20g. The equivalent particle size determined with a material density of ρ = 2.65 g cm- 3 was 3.0 nm⩽ dp ⩽ 7.6 nm. The absolute particle mass depends on the amount of SiH4 on the dilution ratio, and is a function of the flame co-ordinate. J;. An increasing amount of C2H2 added to the H2/O2/Ar + SiH4 flame results in an increase in the amount of charged particles by more than one order of magnitude. The experimental results on SiO2 particle formation were verified by a theoretical model. It includes the futl homogeneous H2/O2 and SiH4/O2 kinetics as well as transport properties of burner stabilised flames. The particle formation was described based on homogeneous nucleation of SiO2-vapour and Brownian coagulation, simulated both by a monodisperse as well as by a sectional model. Considering the size dependent charging probability of neutral particles by chemo-ions, good agreement in particle size and size distribution between the experimental results and the computer simulations was obtained.