H. Chuaqui

Ion beam emission in a low energy plasma focus device operating with methane

An investigation of ion beam emission from a low energy plasma focus (PF) device operating with methane is reported. Graphite collectors, operating in the bias ion collector mode, are used to estimate the energy spectrum and ion flux along the PF axis, using the time-of-flight technique. The ion beam signals are time correlated with the emission of soft x-ray pulses from the pinched focus plasma. The correlation of ion beam intensity with filling gas pressure indicates that the beam emission is maximized at the optimum pressure for focus formation at peak current. Ion beam energy correlations for operation in methane indicate that the dominant charge states in carbon ions are C+4 and C+5. The estimated maximum ion energy for H+, C+4 and C+5 are in the range of 200?400?keV, 400?600?keV and 900?1100?keV, respectively, whereas their densities are maximum for the energy range 60?100?keV, 150?250?keV and 350?450?keV, respectively. These results suggest that the ion beams are emitted from a high density, high temperature, short lived focus plasma, at a time which appears to precede the emission of soft x-ray pulses. The properties of the carbon ion beams are discussed in the context of potential applications in materials science.

Theoretical approach for plasma series resonance effect in geometrically symmetric dual radio frequency plasma

Plasma series resonance (PSR) effect is well known in geometrically asymmetric capacitively couple radio frequency plasma. However, plasma series resonance effect in geometrically symmetric plasma has not been properly investigated. In this work, a theoretical approach is made to investigate the plasma series resonance effect and its influence on Ohmic and stochastic heating in geometrically symmetric discharge. Electrical asymmetry effect by means of dual frequency voltage waveform is applied to excite the plasma series resonance. The results show considerable variation in heating with phase difference between the voltage waveforms, which may be applicable in controlling the plasma parameters in such plasma.

Investigation of the plasma jet formation in X-pinch plasmas using laser interferometry

A two-frame Mach–Zender interferometer is used to investigate the dynamics of X pinches formed from two 10 μm aluminum wires at current levels of 100 kA. Particularly, the columns of plasma that form on the interelectrode axis of the X pinch are studied quantitatively. It is demonstrated that the plasma which forms these columns does not come solely from expansion of the corona from the limbs of the X pinch but rather predominantly from the crossing point region. The results suggest that the plasma column is indeed a jet which consists of several components.

Measurements of time average series resonance effect in capacitively coupled radio frequency discharge plasma

Self-excited plasma series resonance is observed in low pressure capacitvely coupled radio frequency discharges as high-frequency oscillations superimposed on the normal radio frequency current. This high-frequency contribution to the radio frequency current is generated by a series resonance between the capacitive sheath and the inductive and resistive bulk plasma. In this report, we present an experimental method to measure the plasma series resonance in a capacitively coupled radio frequency argon plasma by modifying the homogeneous discharge model. The homogeneous discharge model is modified by introducing a correction factor to the plasma resistance. Plasma parameters are also calculated by considering the plasma series resonances effect. Experimental measurements show that the self-excitation of the plasma series resonance, which arises in capacitive discharge due to the nonlinear interaction of plasma bulk and sheath, significantly enhances both the Ohmic and stochastic heating. The experimentally ...

Experimental studies of ion beam anisotropy in a low energy plasma focus operating with methane

We have investigated, with time and space resolution, the ion beam emission from a plasma focus (PF) device, operating in methane, at 20 kV, with 1.8 kJ stored energy. A detector array is used to measure simultaneously the ion beams at five different angular directions with respect to the PF axis (0°, 10°, 15°, 20° and 90°), at a distance of 77 cm from the ion source. Ion beam energy correlations for operation in methane indicate that the dominant charge states on the detector are H+, C+4 and C+5, irrespective of the angular positions. The time integrated ion beam signal and the energy-dispersive x-ray analysis of a carbon films deposited on silicon surface shows the impurity emission from the PF electrode surface. Measured ion fluxes are maximum for the energy range of 15–40 keV, 50–100 keV and 100–300 keV, for H+, C+4, and C+5, respectively. Measurements of the angular distribution of hydrogen and carbon ions reveal a strong angular anisotropy. It is argued that the observed angular anisotropy of the ion beam emission can be explained in terms of ion Larmor radius effects during the z-pinch like plasma formation phase, which is characteristic of PF discharges.

Experimental studies of ionization processes in the breakdown phase of a transient hollow cathode discharge

The ionization process in the prebreakdown phase of a transient hollow cathode discharge (THCD) is investigated. The discharge is operated in H2 and N2 at pressures between 30 and 750 mTorr with applied voltages up to 30 kV. A capacitive probe array is used to measure the spatial and temporal evolution of plasma formation in the interelectrode spacing. The results obtained are consistent with the formation of a moving virtual anode. The growth and evolution of the virtual anode are closely linked to the formation of electron beams emitted from the hollow cathode region before and at the time of electric breakdown.

Hollow cathode effects in the pre-breakdown phase of a pulsed capillary discharge

Experimental observations of the hollow cathode effect (HCE) in an open end pulsed capillary discharge (PCD) are presented. In the HCE axial electron beams emitted from a pre-breakdown plasma produced spontaneously in the hollow cathode region (HCR) assist ionization growth in the interelectrode volume. The PCD operates in argon at 0.6?1.4?Torr, ~10?kV applied voltage. Time resolved spectroscopic measurements, with 15?ns time resolution, are used in conjunction with photomultiplier observations of light emission from the capillary ends, and Faraday cup measurements of axial electron beams, to characterize the pre- and post-breakdown processes in the HCR of the discharge. The HCR emission is found to be dominated by Ar?II lines. Comparison between measured and synthetic spectra indicates that the pre-breakdown HCR plasma is characteristic of a collisional low pressure, low density plasma, whereas the post-breakdown HCR plasma, tens of nanoseconds after breakdown, is due to plasma ejection from the capillary volume. Experimental evidence of a zippering effect in post-breakdown capillary plasma heating, due to an initial axial pressure gradient, as predicted by computer simulations, has been found.

Simple Faraday cup with subnanosecond response

A small Faraday cup of coaxial design for use in plasma physics experiments is presented. The construction permits an approximately 50‐Ω geometry to be maintained, allowing direct coupling to coaxial cable. The detector rise time is less than 0.4 ns, and is designed for beam currents of between 0.1 and 100 A. The design is well screened to reject spurious electrical noise.

Experimental observations in compact capillary discharges

We present experimental results on the characterization of a non-ablating fast pulsed capillary discharge, with a hollow cathode (HC) geometry, operating in argon below 1 Torr. Both the pre-breakdown and breakdown phase of the discharge are investigated with several diagnostics, which include electron beam monitoring, capacitive probe array and extreme ultraviolet (EUV) detector array. The pre-breakdown phase is found to be characterized by the emission of HC electron beams, which assist the propagation of a high speed ionization wave, with typical velocity in the 106–107 m s−1. Coinciding with electric breakdown a fast EUV radiation pulse is emitted. The leading edge of the radiation pulse is due to beam target emission by the HC electron beams. At the breakdown the radiation emission is mainly centered in the 5–15 nm spectral window, and is emitted from a capillary plasma which is being heated by a kiloampere level, 10 ns half-width current pulse.

Formation of hexagonal silicon carbide by high energy ion beam irradiation on Si (1 0 0) substrate

We report the investigation of high energy ion beam irradiation on Si (1 0 0) substrates at room temperature using a low energy plasma focus (PF) device operating in methane gas. The unexposed and ion exposed substrates were characterized by x-ray diffraction, scanning electron microscopy (SEM), photothermal beam deflection, energy-dispersive x-ray analysis and atomic force microscopy (AFM) and the results are reported. The interaction of the pulsed PF ion beams, with characteristic energy in the 60–450 keV range, with the Si surface, results in the formation of a surface layer of hexagonal silicon carbide. The SEM and AFM analyses indicate clear step bunching on the silicon carbide surface with an average step height of 50 nm and a terrace width of 800 nm.