Influence Of Plasma Effects Research Articles

Multimodal Nonlinear Microscopy for Therapy Monitoring of Cold Atmospheric Plasma Treatment.

Here we report on a non-linear spectroscopic method for visualization of cold atmospheric plasma (CAP)-induced changes in tissue for reaching a new quality level of CAP application in medicine via online monitoring of wound or cancer treatment. A combination of coherent anti-Stokes Raman scattering (CARS), two-photon fluorescence lifetime imaging (2P-FLIM) and second harmonic generation (SHG) microscopy has been used for non-invasive and label-free detection of CAP-induced changes on human skin and mucosa samples. By correlation with histochemical staining, the observed local increase in fluorescence could be assigned to melanin. CARS and SHG prove the integrity of the tissue structure, visualize tissue morphology and composition. The influence of plasma effects by variation of plasma parameters e.g., duration of treatment, gas composition and plasma source has been evaluated. Overall quantitative spectroscopic markers could be identified for a direct monitoring of CAP-treated tissue areas, which is very important for translating CAPs into clinical routine.

Short-pulse laser ablation of materials at high intensities: Influence of plasma effects

AbstractThe paper is devoted to the study of plasma effects, which are present in laser ablation at relatively high intensity (I ≥ 1012 W/cm2). We start from the classical “two temperature model” of laser ablation (“cold solid approximation”) and we extend it to higher intensities where laser-induced heating and laser-induced changes in the background material become relevant. The new model is also compared to experimental results on laser ablation of solid targets from short pulse lasers at high intensities (up to 1014 W/cm2). Finally, we consider the effects on laser-ablation of laser-generated fast electrons.

Kinetic theory of radiation in non-equilibrium relativistic plasmas

Many-particle QED is applied to kinetic theory of radiative processes in many-component plasmas with relativistic electrons and non-relativistic heavy particles. Within the framework of non-equilibrium Green’s function technique, transport and mass-shell equations for fluctuations of the electromagnetic field are obtained. We show that the transverse field correlation functions can be decomposed into sharply peaked (non-Lorentzian) parts that describe resonant (propagating) photons and off-shell parts corresponding to virtual photons in plasmas. Analogous decompositions are found for the longitudinal field correlation functions and the correlation functions of relativistic electrons. As a novel result a kinetic equation for the resonant photons with a finite spectral width is derived. The off-shell parts of the particle and field correlation functions are shown to be essential to calculate the local radiating power in relativistic plasmas and recover the results of vacuum QED. The influence of plasma effects and collisional broadening of the relativistic quasiparticle spectral function on radiative processes is discussed.

Plasma Effects in Three-body Recombination of High-Z Bare Ions with Electrons

The influence of plasma effects on three-body recombination of bare ions with electrons in cold plasma in the electron cooler is discussed in context of recombination “enhancement” observed in storage ring experiments. We show that for high-Z bare ions and low electron temperatures and densities the cooler plasma becomes “nonideal”, leading to the enhancement of the three-body recombination rates. This effect is described in terms of the Debye screening length within the “rigid shift” approximation. We demonstrate, that in cold (T ≈ 1–10 K) anisotropic plasma the screening effect substantially enhances the three-body recombination rates for very high n-states. The relaxation of high Rydberg states below the field ionization cut-off, set in storage ring experiments, is discussed. The calculations are confronted with the experimental results obtained in storage ring experiments.

The influence of plasma effects on the timing properties of surface-barrier detectors for heavy ions

Detecting ions from He to Xe at various accurately determined energies with surface-barrier detectors, the dependence of the timing signal on field strength, resistivity, area and thickness of the detector has been studied. Deviations of the measured time-of-flight from the calculated one in the order of up to several ns have been found for slow heavy ions. A variation of the field strength may also cause a time shift of several ns, depending on mass and velocity of the detected ions and the properties of the detector. Above a critical field F min a linear decrease of this “plasma delay” with increasing field strength has been observed. By linear extrapolation to infinite field strength a value for the minimum charge-collecting time of each detector has been determined. The experimental data allow to extract a set of empirical formulae that are able to describe the “plasma delay” as a function of the energy, mass and effective charge of the detected ions and of the thickness, area and resistivity of the detector.

Influence of the plasma effects on the energy spectra

Proton and helium energy spectra are observed under influence of plasma effects in a silicon detector. For heavier particles, it is shown that the plasma density along the trajectory of the incident particles into silicon is more serious than the length of its ionized track for the pulse height defect. The pulse height defect and the width of the spectra are proportional to the inverse square of the applied field 1/ E 2, and the electric field erosion into plasma plays an important role in the plasma effects.

The influence of plasma effects on the timing of fission fragments with semiconductor detectors

For fission fragments incident on surface-barrier detectors of low resistivity (ϱ ≈ 400Ω cm) the dependence of the fast current signal on field strength and local resistivity variations of the basic material has been studied. It is well known that with the fast signal as timing reference a time shift is observed when varying the bias voltage. This is due to a change in plasma time. The additional variation of plasma time with mass and/or energy of the heavy ions necessitates a time-walk correction in fission-fragment time-of-flight studies, which has been determined by two independent methods to be about ± 200 ps for the mean light and heavy fragment of binary fission from 252Cf. Local resistivity changes of the silicon wafer the detectors are made from, give rise to local plasma-time shifts, which spoil the time resolution of large-area detectors. For a narrow well-collimated beam of fission fragments an optimum time resolution of 215 ps has been obtained.