Strength Of Longitudinal Electric Field Research Articles

Enhanced polarized proton acceleration driven by femtosecond laser pulses irradiating a micro-structured solid–gas target

Herein, we propose a scheme based on collision-less shock acceleration (CSA) involving the use of composite targets comprising a micro-structured foil and a pre-polarized gas for obtaining high-energy polarized proton beams. Femtosecond laser pulses irradiate a microwire-array (MWA) target and efficiently heat the dense plasma, which moves toward the dilute plasma. Shocks are then introduced in the pre-polarized gas to accelerate upstream spin-polarized protons to relativistic velocities. Based on particle-in-cell simulations with added spin dynamics, protons with energies of 30–300 MeV are produced, and the polarization rate of protons in the high-energy region exceeds 90%. The simulations demonstrate an evident increase in the temperature and number of hot electrons owing to the presence of MWA structures, which increase both the longitudinal electric field strength associated with the shock and the energy of the reflected protons. During CSA, the bipolar magnetic field driven by hot-electron currents demonstrates a weak effect on the polarization level of the accelerated protons, resulting in a high polarization rate. The relationship between the energy of the polarized proton beam and the hot-electron temperature enables an optimization of the micro-structured target and other target components to enhance proton quality via the CSA process.

Parameters of Pulsed Discharge Plasma in High-Speed Gas Flows

The parameters of the plasma of a unsteady, pulsed, transverse-longitudinal discharge generated in subsonic and supersonic air flows are determined. It is shown that the longitudinal electric field strength, as well as the electron density and temperature in the anode part of the plasma loop, exceed the corresponding values in the cathode part of the loop. The effect of the gas flow rate and the discharge current on the electron temperature in the plasma of the pulsed discharge in air and the propane-air mixture is studied.

Fluid model of the positive column in argon‐oxygen direct current glow discharge

AbstractThe positive column of argon‐oxygen direct current (DC) glow discharge was investigated using a fluid model at pressures of around 410 Pa and discharge currents from 10 to 40 mA. The model was used to study the influence of an oxygen admixture on the properties of argon discharge. The simulated intensity of the electric field strength was compared with measured values at 5% and 100% of oxygen concentration. The one‐dimensional model in a cylindrical tube is based on the drift‐diffusion approximation of particle flux and the mean‐electron‐energy approximation is used to describe the electron interaction. The model takes into account the radial profile of particle concentration, the neutral gas kinetic temperature profile, and interactions with the wall in the cylindrical glass discharge tube. It was shown that 2% of the oxygen admixture causes a significant increase in longitudinal electric field strength and gas heating.

Analysis on the longitudinal field strength formed by tightly-focused radially-polarized femtosecond petawatt laser pulse.

Tight focusing of radially- or azimuthally-polarized electromagnetic waves becomes attractive because of the strong field generation in the longitudinal direction. In this paper, we investigate the strength of longitudinal electric field when a radially-polarized femtosecond PW laser pulse is tightly focused by a parabolic surface. From the calculation using the vector diffraction approach, it has been shown that the highest strength of 2.2 × 1013 V/cm can be reached for the longitudinal field with a radially-polarized 11.2-fs, 11.2-J uniform-beam-profile laser pulse. The difference in the strength of longitudinal field with different beam profile and the spectrum of a laser pulse has been also carefully examined. The propagation of a laser spot has been simulated under an extremely-tight-focusing condition (0.25 in terms of f-number) and an achievable field strength for a standing longitudinal field has been examined by colliding two radially-polarized fs PW-level laser pulses.

Positive Column of a High-Modulation Depth Discharge Current Without Stepwise Ionization

The positive column of a gas discharge in helium is investigated for high-modulation-depth discharge current without stepwise ionization. The electron energy distribution function for different discharge current oscillation phases, the electron concentration, and the longitudinal electric field strength are measured in helium gas-discharge plasma. The electric field modulation effect and the change of the electron energy distribution function over the period at frequencies less than the reciprocal ambipolar diffusion time are detected.

Direct current discharge with microparticles: The electrical characteristics and the plasma trap parameters

The electrical characteristics of the positive column of glow discharge were measured and simulated in pure neon and in plasma with micron size particles. The increment of the longitudinal electric field strength caused by the presence of dust structures was measured. Simulation was based on the diffusion-drift model of the positive column of glow discharge. Simulation was carried out using the measured values of dusty structure parameters and discharge characteristics. It was shown, that a dust structure maintained in a dc discharge represents a plasma trap for ions with ion concentrations more than three times higher than in a free discharge. The results can be used to calculate the traps for confinement of ions and dust particles in gas-discharge plasma.

Influence of dust particles on ionization and excitation in neon dc discharge

The influence of dust particles on the concentration of metastable neon atoms and ionization was investigated using the developed drift/diffusion model for plasma of positive column of glow discharge. The detailed de-excitation in neon was considered. In addition to usual plasma losses in dusty plasmas, the quenching of metastable atoms on dust particle surface was considered. The strong influence of dust particles on the ionization rate and concentration of metastable neon atoms in a positive column of glow discharge is shown to result from the change in the longitudinal electric field strength.

Characterization of laser-driven proton beams from near-critical density targets using copper activation

Copper activation was used to characterize high-energy proton beam acceleration from near-critical density plasma targets. An enhancement was observed when decreasing the target density, which is indicative for an increased laser-accelerated hot electron density at the rear target-vacuum boundary. This is due to channel formation and collimation of the hot electrons inside the target. Particle-in-cell simulations support the experimental observations and show the correlation between channel depth and longitudinal electric field strength is directly correlated with the proton acceleration.

Comparison of low-pressure DC glow discharge and dielectric barrier discharge in CO2-laser mixture by optical emission spectroscopy

Nowadays the CO2 lasers are used in many technologies, including medicine and material processing industry. Besides original low-pressure low-power lasers pumped by DC glow discharge, the attention is focused on the high power atmospheric pressure lasers. We use optical emission spectroscopy to study both low pressure (from 266 Pa to 1330 Pa) DC glow discharge (DC GD) and the dielectric barrier discharge (DBD) (from 5 kPa to 100 kPa) in mixtures of helium, nitrogen and carbon dioxide used in CO2 lasers.Considering the emission spectrum of the discharges mentioned above, we can find bands of the first and the second positive systems of the nitrogen molecule. From these bands it is possible to deduce energetic balance and the vibrational temperature [1].In our contribution, the vibrational temperature of nitrogen is determined by means of optical emission spectroscopy from the second positive system band of the nitrogen molecule for various discharge currents in DC glow discharge and for various gap widths in DBD. Using these two discharges we covered the whole pressure range from 266 Pa up to atmospheric pressure. The dependence of the vibrational temperature on N2 content in the mixture is also investigated. The vibrational temperature showed a steady decrease with increasing pressure in whole pressure range. It was found, that the vibrational temperature of nitrogen in the DC GD is twice as high as in the DBD, which was attributed to the different nature of discharges.Spectroscopic measurements were complemented with measurements of electric properties of discharges: the longitudinal electric field strength for DC glow discharge and Lissajous' figures for DBD [1,2].

Das toroidale schwachionisierte Magnetoplasma I

In a previous paper31 discrepancies between theory and experiment were found on investigating the positive column in a curved magnetic field. The approximation derived in 31 for the torus drift in a weakly ionized magnetoplasma is therefore checked here (Part I) with a refined theory which also yields the transverse electric field strength. Experimentally, both the transverse electric fields and the density profiles in the DC discharge were determined in addition to the longitudinal electric field strength. The discrepancies occurring in 31 are ascribed to the fact that the plasma concentrates at the cathode end of the magnetic field coils, this effect having a considerable influence on the form of the transverse density profile and on the stability behaviour. Part II later will show how the influence of this concentration can be eliminated and what effect in the current-carrying toroidal plasma causes a marked reduction of the charge carrier losses.

Ladungsträgerverluste in einem schwachionisierten stationären Gleichstromplasma im toroidalen Magnetfeld

For the particle losses of a weakly ionized plasma which result from the torus drift in a curved magnetic field, an expression is derived which is valid for certain parameters of the positive column of a gas discharge. To check this theory the “AMBIPOL” device was built. With this device it was possible to determine simultaneously the losses both in the toroidal and in the linear magnetic field by measuring the longitudinal electric field strength. As theory predicts, with growing magnetic field strength a weaker decrease of the longitudinal electric field was observed in the toroidal part of the discharge as compared to the linear part. The measured values of the relative electric field strength, however, exceed the theoretical limit, although the measurements of the electric field in the straight part and the measurements of the particle density and of the electron temperature in the curved part are consistent with theory. Moreover, contrary to the expectations, the onset of the KADOMTSEV instability occurs at lower critical magnetic fields in the toroidal part than in the straight part. Several possible explanations are discussed. In a later paper it will be attempted to make a choice among the three most probable ones.