Electron cyclotron resonance heating in a short cylindrical plasma system

Electron cyclotron resonance (ECR) plasma is produced and studied in a small cylindrical system. Microwave power is delivered by a CW magnetron at 2.45 GHz in TE¹⁰ mode and launched radially to have extraordinary (X) wave in plasma. The axial magnetic field required for ECR in the system is such that the first two ECR surfaces (B = 875.0 G andB = 437.5 G) reside in the system. ECR plasma is produced with hydrogen with typical plasma density n^e as 3.2 × 10¹⁰ cm^-3 and plasma temperature T^e between 9 and 15 eV. Various cut-off and resonance positions are identified in the plasma system. ECR heating (ECRH) of the plasma is observed experimentally. This heating is because of the mode conversion of X-wave to electron Bernstein wave (EBW) at the upper hybrid resonance (UHR) layer. The power mode conversion efficiency is estimated to be 0.85 for this system. The experimental results are presented in this paper.     

Formation of hollow heavy ion beams in plasma lens

Hollow cylindrical high-energy heavy ion beams are an efficient driver for target irradiation to achieve highly compressed matter. This paper is devoted to the study of how hollow beams form with the use of a plasma lens. Calculations and measurements were performed with a 200 MeV/amu C⁺⁶ beam.     

Current-induced implosion of a multiwire array as a radial plasma rainstorm

We present our experimental results of the X-ray radiography of fast radiating Z-pinches based on cylindrical multiwire tungsten arrays. The experiments were carried out at the Angara-5-1 facility at an electrical power of up to 4 TW with a discharge current of up to 4 MA rising at a rate on the order of 5×10¹³ A s^?1. The linear mass of single and composite arrays reached 500 µg cm^?1, the initial radius was 4–10 mm, and the wire diameter was 5–8 µm. We have experimentally shown that for the current-induced implosion of multiwire tungsten arrays, significant azimuthal and axial plasma inhomogeneities result from discharge cold start and prolonged plasma production, which determine the subsequent course of the implosion. The Z-pinch structure also remains spatially inhomogeneous at the time of intense X-ray radiation. The generated inhomogeneous plasma collapses toward the array axis in the form of numerous radially elongated plasmoids with relatively small diameters. The stream of plasmoids is called a radial plasma rainstorm. As the plasmoids contract toward the array axis, they decrease in radial size and merge into isolated plasma current filaments, which are elongated mainly along the discharge axis. We critically discuss the models of a radiating Z-pinch in plasma composed of matter with a large atomic number that disregard the cold-start and prolonged plasma-production effects.     

Low-Power RF plasma sources for technological applications: III. helicon plasma sources

The third part of the paper is devoted to an investigation of the so-called helicon plasma sources. These are RF devices operating with a relatively weak external magnetic field, which is, at the same time, strong enough for the resonant electron gyrofrequency to be much higher than the industrial frequency (ω=8.52×10⁷ s⁻¹). As in [1, 2], a study is made of elongated cylindrical plasma sources in a longitudinal (directed along the cylinder axis) magnetic field and planar disk-shaped plasma sources in a transverse (perpendicular to the plane of the disk) magnetic field. A comparison of the present results with the results that were obtained in [3] without using the helicon approximation leads to the conclusion that elongated helicon sources hold great promise for plasma technologies.     

K-shell aluminum resonance line ratios for plasma diagnosis using spot spectroscopy

Using a detailed atomic model of K shell aluminum ions, we have calculated four diagnostic resonance line ratios as a function of temperature and density for cylindrical aluminum plasmas of diameter 50 and 100 μm, assumed in collisional-radiative equilibrium. The ion densities vary from 10¹⁹ cm^-3 to 10²¹ cm^-3, the temperatures range from 200 to 700 eV. The conditions are applicable to experiments using the spot spectroscopy technique for plasma diagnosis.     

Electron cyclotron resonance breakdown studies in a linear plasma system

Electron cyclotron resonance (ECR) plasma breakdown is studied in a small linear cylindrical system with four different gases — hydrogen, helium, argon and nitrogen. Microwave power in the experimental system is delivered by a magnetron at 2.45 ± 0.02 GHz in TE₁₀ mode and launched radially to have extra-ordinary (X) wave in plasma. The axial magnetic field required for ECR in the system is such that the fundamental ECR surface (B = 875.0 G) resides at the geometrical centre of the plasma system. ECR breakdown parameters such as plasma delay time and plasma decay time from plasma density measurements are carried out at the centre using a Langmuir probe. The operating parameters such as working gas pressure (1 × 10⁻⁵−1× 10⁻² mbar) and input microwave power (160–800 W) are varied and the corresponding effect on the breakdown parameters is studied. The experimental results obtained are presented in this paper.      

Anomalous plasma phenomena of hollow cathode arc discharge

Magnetically confined argon plasma produced by hollow cathode arc discharge has been studied in different experimental conditions, with discharge current from 10–50 A, vessel argon pressure between 10^–3 and 10^–4 torr (1 torr=133·32 Pa) and axial magnetic field up to 0·12 T. The plasma density measured by a cylindrical Langmuir probe is found to be 10¹⁹ to 4 × 10¹⁹ m^–3 and the electron temperatureT _e varies between 2·5 and 4·8 eV. When an external axial magnetic field is applied the plasma temperature decreases with the increase in the magnetic field intensity until it reaches a minimum value at 0·075T and then increases with the same rate. This has been interpreted as high frequency waves excitation due to electron beam-plasma interaction, which explains the electron density jumps with the magnetic field intensity. Enhanced plasma transport across the magnetic field is studied and classified as anomalous diffusion.     

Non-equilibrium plasma production by pulsed laser ablation of gold

A gold target has been irradiated with a Q-switched Nd:Yag laser having 1064?nm wavelength, 9?ns pulse width, 900?mJ maximum pulse energy and a maximum power density of the order of 10¹⁰?W/cm². The laser–target interaction produces a strong gold etching with production of a plasma in front of the target. The plasma contains neutrals and ions having a high charge state. Time-of-flight (TOF) measurements are presented for the analysis of the ion production and ion velocity. A cylindrical electrostatic deflection ion analyzer permits measurement of the yield of the emitted ions, their charge state and their ion energy distribution. Measurements indicate that the ion charge state reaches 6⁺ and 10⁺ at a laser fluence of 100?J/cm² and 160?J/cm², respectively. The maximum ion energy reaches about 2?keV and 8?keV at these low and high laser fluences, respectively. Experimental ion energy distributions are given as a function of the ion charge state. Obtained results indicate that electrical fields, produced in the plume, along the normal to the plane of the target surface, exist in the unstable plasma. The electrical fields induce ion acceleration away from the target with a final velocity dependent on the ion charge state. The ion velocity distributions follow a “shifted Maxwellian distribution”, which the authors have corrected for the Coulomb interactions occurring inside the plasma.     

Low-power rf plasma sources for technological applications: I. Plasma sources without a magnetic field

A general analytical theory is developed and numerical simulations are carried out of cylindrical plasma sources operating at an industrial frequency of f=13.56 MHz ω=8.52×10⁷ s⁻¹). Purely inductive surface exciters of electromagnetic fields (exciting antennas) are considered; the exciters are positioned either at the side surface of the cylinder or at one of its end surfaces. In the latter case, the plasma flows out of the source through the opposite end of the cylinder. A study is made of both elongated systems in which the length L of the cylinder exceeds its diameter 2R and planar disk-shaped systems with L<2R. The electromagnetic fields excited by the antenna in the plasma of the source are determined, and the equivalent plasma resistance, as well as the equivalent rf power deposited in the plasma, is calculated.     

Resonant decay of a Langmuir wave in the presence of dust grains in a cylindrical plasma

The resonant parametric decay of a Langmuir wave into a backward propagating Langmuir wave and an ion acoustic (IA) wave is studied in a cylindrical dusty plasma. The analysis shows that the frequency of the IA mode decreases with the parameter δ_c (where δ_c is the ratio of the ion density to the electron density) for negatively charged dust grains. The growth rate of the resonance decay instability (RDI) and the threshold required for its onset also decrease with δ_c and are strongly dependent on the electron to ion temperature ratio for both positively and negatively charged dust grains. The results obtained also illustrate the dependence of the threshold of the resonance decay instability (μ_th) on the plasma cylinder radius.     

Influence of a plasma jet on different types of tungsten

The influence of a plasma producing nonstationary thermal loads akin to edge-localized modes in a tokamak on different types of tungsten is investigated. Tungsten is irradiated by a jet of a hydrogen plasma generated in a plasma gun. The plasma density and velocity are on the order of 10²² m^?3 and 100–200 km/s, respectively, and the irradiation time is 10 μs. Two plasma flux densities, 0.70 and 0.25 MJ/m², are used. Structural modifications in irradiated single-crystal and hot-rolled tungsten samples, as well as in V-MP and ITER_D_2EDZJ4 tungsten powders, are examined. It is found that the plasma generates a regular crack network with a period of about 1 mm on the surface of the single-crystal, hot-rolled, and V-MP powder samples, while the surface of the ITER_D_2EDZJ4 powder is more cracking-resistant. The depth of the molten layer equals 1–3 μm, and the extension of intense thermal action is 15–20 μm. The material acquires a distinct regular structure with a typical grain size of less than 1 μm. X-ray diffraction analysis shows that irradiation changes the crystal lattice parameters because of the melting and crystallization of the surface layer. The examination of the V_MP tungsten powder after cyclic irradiation by a plasma with different energy densities shows that high-energy-density irradiation causes the most significant surface damage, whereas low-energy-density irradiation generates defects that are small in size even if the number of cycles is large.     

The nonlinear transformation of an ion beam in the plasma lens

The plasma lens can carry out not only sharp focusing of ions beam. At those stages at which the magnetic field is nonlinear, formation of other interesting configurations of beams is possible. Plasma lens provides formation of hollow beams of ions. Application of the several plasma lenses allow to get a conic and a cylindrical beams. The plasma lens can be used for obtaining a beams with homogeneous spatial distribution. Calculations and measurements were performed for a C⁺⁶ and Fe⁺²⁶ beams of 200?C300 MeV/a.u.m. energy. The obtained results and analysis are reported.     

Self-focusing and nonlinear acceleration process in laser produced plasma

Ruby laser intensities exceedingI ^* - 10¹⁴ W/cm² create a predominant acceleration of dense plasma due to nonlinear collisionless interaction resulting mainly from collective effects. Recoil causes confinement of the plasma interior in the form of a superlinearly increased radiation pressure. Similar nonlinear forces produce self-focusing in plasmas at a threshold laser power of only 10⁵ to 10⁶ W. The resulting filaments have intensitiesI ^*, from which their diameter can be determined in agreement with measurements of Korobkin and Alcock. These high intensities should allow some observed properties of laser produced plasmas (keV ions, linear increase of the ion charge) to be interpreted on the basis of the nonlinear acceleration described.     

On the oscillations of the plasma atmosphere in gamma-ray bursts

One of the possible hypotheses implies that cosmic gamma-ray bursts can arise when two neutron stars or black holes merge together. These bursts sometimes continue for several tens of seconds, but the time dependence of their intensity often exhibits ～10²–10³ almost periodic small peaks with a period of ～10 ms. A model of oscillations in the lower plasma shell, which arises in cosmic gamma-ray bursts and is located near a neutron star, is proposed; the greater part of arising plasma in the form of an “upper” shell continues to expand into the surroundings. Other possible interpretations of periodicity of the “small peaks” are also analyzed.     

Ar plasma waveguide produced by a low-intensity femtosecond laser

Using the interaction of a low-intensity femtosecond laser pulse (30 fs, 6 × 10¹⁵ Wcm^? 2) with argon cluster jet produced from a slit nozzle, we experimentally probe the formation of a uniform plasma waveguide by the interferogram analysis. The results about evolution of plasma channel demonstrate that it is feasible to produce the plasma waveguide for an fs laser pulse of low-intensity. It takes tens of nanoseconds to form a plasma waveguide. The simulation by one-dimensional Gaussian plasma hydrodynamic expansion model indicates that the temperature of plasma channel is not high under this condition. Thus it takes tens of nanoseconds to form a plasma waveguide.     

Development of a new atmospheric pressure cold plasma jet generator and application in sterilization

This paper reports that a new plasma generator at atmospheric pressure, which is composed of two homocentric cylindrical all-metal tubes, successfully generates a cold plasma jet. The inside tube electrode is connected to ground, the outside tube electrode is connected to a high-voltage power supply, and a dielectric layer is covered on the outside tube electrode. When the reactor is operated by low-frequency (6 kHz--20 kHz) AC supply in atmospheric pressure and argon is steadily fed as a discharge gas through inside tube electrode, a cold plasma jet is blown out into air and the plasma gas temperature is only 25--30℃. The electric character of the discharge is studied by using digital real-time oscilloscope (TDS 200-Series), and the discharge is capacitive. Preliminary results are presented on the decontamination of E.colis bacteria and Bacillus subtilis bacteria by this plasma jet, and an optical emission analysis of the plasma jet is presented in this paper. The ozone concentration generated by the plasma jet is 1.0×10¹⁶cm^-3 which is acquired by using the ultraviolet absorption spectroscopy.     

Nonlinear plasma spectroscopy of the hydrogen balmer-α line

The plasma line broadening of H_α fine-structure lines is investigated with Doppler-free saturation and polarization spectroscopy in He-H gas and are discharges at plasma densities of 10⁸ cm^?3 <N?1.4×10¹⁴ cm^?3. With a single-mode laser, the shift and broadening of four resolved H_α fs lines are measured in a low pressure discharge forN<10¹¹ cm^?3. With an intense, broadband multi-mode laser the plasma effects of H_α are investigated up toN=1.4×10¹⁴ cm^?3 in a hollow cathode are. Calculations in the classical phase shift and impact approximations can explain the experimental data and peculiarities of the low-density plasma effects and show that the ions are the dominant perturbers. Ion dynamical effects, perturber mass and temperature dependence, are observed and interpreted. Applications of the nonlinear techniques to other H and D lines, other atoms, and for H and D plasma diagnostics are discussed.     

Hydrogen plasma absorption coefficients at laser frequencies

Detailed numerical calculations of hydrogen-plasma absorption coefficients are performed for a number of laser wavelengths between 0·3371 and 10·6 μ, in a wide range of plasma densities (10¹⁶-10²¹ cm^-3) and temperatures (0·5–10⁵ eV). The numerical data are then utilized to determine plasma temperatures in pulsed linear discharge experiments which measure CO₂-laser i.r. absorption. Some features of dense plasma laser-heating are also discussed.     

High sensitivity HCN laser interferometer for plasma electron density measurements

This paper describes a high sensitivity 337 μm HCN laser interferometer for plasma electron density measurements. The plasma phase shift is transferred to a low frequency signal obtained by slightly shifting the frequency of the 337 μm radiation in the reference beam of the interferometer. The frequency shift is produced by diffracting the radiation of a cylindrical rotating blazed grating. A phase shift is deduced from the time variation of the zero crossings of the low frequency signal, giving a result which is independent of amplitude fluctuations. Using pyroelectric detectors, the interferometer has a time resolution of 100 μsec and a sensitivity of 10^-2 fringe.     

Analysis of plasma photonic crystal with a tunable band gap using parallel method

This paper presents a parallel frequency-dependent finite-difference time-domain ((FD)²TD) method for plasma in the dispersive media. Results obtained with parallel and serial algorithms verify that parallel (FD)²TD has the same precision as the serial (FD)²TD, while the parallel approach could reduce the CPU time efficiently. A tunable filter is analyzed based on a one-dimensional photonic crystal containing a plasma defect by this method. The tunability of the photonic crystal filter can be achieved by adjusting the defect layer parameters instead of changing the dimension of photonic crystal.