Runaway electron beams in the gas discharge for UV nitrogen laser excitation

The review of the methods for obtaining the runaway electron beams in the gas discharge is performed. The new method is offered, using which the beam is first formed in a narrow gap (∼1 mm) between the cathode and the grid and then it is accelerated by the field of the plasma column of the anomalous self-sustained discharge in the main gap (10–20 mm long). The electron beams with an energy of about 10 keV and current density of 10³ A/cm² at a molecular nitrogen pressure of up to 100 Torr have been obtained experimentally. The results of research of the UV nitrogen laser with an excitation via runaway electron beam and radiation of energy of ∼1 mJ are given. The UV nitrogen laser generation with the energy of ∼1 mJ has been obtained by the runaway electron beams.     

Diagnostics of plasma produced by femtosecond laser pulse impact upon a target with an internal nanostructure

X-ray diagnostics of the interaction of femtosecond laser pulses with intensities of 10¹⁶–10¹⁸ W/cm² with CO₂ clusters and frozen nanosize water particles is carried out. The stage of cluster expansion and the formation of a plasma channel, which governs the parameters of the formed X-ray radiation source and accelerated ion flows, is studied. The measurements are based on recording spatially resolved X-ray spectra of H- and He-like oxygen ions. Utilization of Rydberg transitions for spectra diagnostics makes it possible to determine plasma parameters on a time scale of t ∼ 10 ps after the beginning of a femtosecond pulse. The role of the rear edge of the laser pulse in sustaining the plasma temperature at a level of ∼100 eV in the stage of a nonadiabatic cluster expansion is shown. The analysis of the profiles and relative intensities of spectral lines allows one to determine the temperature and density of plasma electrons and distinguish the populations of “thermal” ions and ions that are accelerated up to energies of a few tens of kiloelectronvolts. It is shown that the use of solid clusters made of frozen nanoscale water droplets as targets leads to a substantial increase in the number of fast He-like ions. In this case, however, the efficiency of acceleration of H-like ions does not increase, because the time of their ionization in plasma exceeds the time of cluster expansion.     

Efficient generation of negative hydrogen ions in a low-voltage cesium-hydrogen discharge

The possibility of achieving the high density of negative hydrogen ions \(N_{H^ - } \) in a low-voltage cesium-hydrogen discharge is investigated. The \(N_{H^ - } \) density is determined experimentally from the absorption of laser radiation due to the photodetachment of electrons from H^? ions. The discharge plasma is investigated by the probe technique. The populations of the excited states of Cs atoms are determined from their emission intensities. With an input power of W≈(15–25) W/cm² in the discharge, densities of \(N_{H^ - } \sim (10^{12} - 10^{13} )cm^{ - 3} \) are achieved. The self-consistent calculations of the plasma parameters in the discharge gap agree well with the experimental results. The absorption of laser radiation due to the photoionization of Cs atoms is investigated. It is shown that the role of this absorption mechanism is negligible.     

Laser radiation scattering from the wires and fibers of imploding arrays on the Angara-5-1 facility

A method is developed for measurements of laser radiation scattering by wires and fibers in different types of imploding arrays in the initial stage of plasma production at discharge currents per wire of up to 2 kA for aluminum arrays and up to 8 kA for tungsten arrays. The experiments were carried out on the Angara-5-1 facility at a current density in the wires of 10⁸ A/cm² and current growth rate of ～10¹³ A/s. It is found that the indicatrix of laser radiation reflected from the wires (fibers) in cylindrical and conical arrays is modified at currents of 0.1–10 kA per wire (fiber). The experimental data on the reflection and scattering of laser radiation from wires and fibers are compared with the results of numerical simulations of their electric explosion in vacuum. It is proposed that the change in the reflection indicatrix of laser radiation is caused by the onset of thermal instabilities. The typical size of density and temperature inhomogeneities on the wire surface is in a range of 10–20 μm, which probably results in a transition from specular to diffuse reflection of laser radiation. A simultaneous abrupt (over 2–3 ns) reduction in the reflection intensity from several wires of an array indicates a homogeneous distribution of the discharge current over the irradiated wires. This closes the issue of the quality of the contact between the wires and the electrodes. The obtained experimental information is of considerable importance for the development of numerical codes for simulations of the implosion of wire arrays and the refinement of the wire parameters in the initial stage of plasma production.     

Melanin Granule Models for the Processes of Laser-Induced Thermal Damage in Pigmented Retinal Tissues. I. Modeling of Laser-Induced Heating of Melanosomes and Selective Thermal Processes in Retinal Tissues

The computer modeling was applied for investigation of the processes of laser-induced tissue damage. The melanin granule models for the processes of laser-induced thermal damage and the results of computer modeling of the optical, thermophysical, and thermochemical processes during selective laser interaction with melanoprotein granules (melanosomes) in retinal pigment epithelium are presented in this paper. Physical-mathematical model and system of equations are formulated which describe thermal interaction processes for “short” laser pulses of duration t _p<10⁻⁶ s and for “ long’ pulses of duration t _p10⁻⁶ s. Results of numerical simulation of the processes give the space–time distributions of temperature and degrees of thermodenaturation of the protein molecules inside and around melanosomes and in the volume of irradiated tissues. Energy absorption, heat transfer and thermochemical (thermodenaturation, coagulation) processes occurring during the interaction of laser pulses with pigmented spherical and spheroidal granules in heterogeneous tissues are theoretically investigated. The possibility for selective interaction of short laser pulses with pigmented granules is discussed which results in the formation of denaturation microregions inside and near the pigmented granules (granular thermodenaturation) without origination of a continuous macroscopic thermodenaturation lesion in tissue. Analytical model of heating of single spherical and spheroidal granule under laser pulse is presented. Simple equations for time dependencies of particle temperature are obtained. The presented results are of essential interest for laser applications in and can be used for investigation of laser interaction with pigmented tissues in different fields of laser medicine.     

Study of the generation of the 13.5-nm EUV radiation from Sn ions in a CO<Subscript>2</Subscript> laser-produced plasma

Results are presented from experimental and theoretical studies of the efficiency of using a CO₂ laser to create a high-power source of 13- to 14-nm EUV radiation for lithography. For a laser intensity of ∼2 × 10¹¹ W/cm², a conversion efficiency of k _EUV ≃ 1.5% was achieved on a plane solid Sn target. The calculated gas dynamics and population kinetics of Sn plasma ions agree qualitatively with experimental results.     

Effects of solar ultraviolet radiation on photochemical efficiency of <Emphasis Type="Italic">Chaetoceros curvisetus</Emphasis> (Bacillariophyceae)

To assess the short- and long-term impacts of Ultraviolet radiation (UVR, 280–400 nm) on the red tide alga Chaetoceros curvisetus, we exposed cells to three different solar radiation treatments–PAB:280–700 nm, PA:320–700 nm, and P:400–700 nm under 20°C incubated temperature. Short-term exposures were investigated: the photochemical efficiency (Φ_PSII) versus irradiance curves under six levels of solar radiation by covering the incubators with a variable number of neutral density screens (the irradiance thus varied from 100 to 3%) lasting 1 h, and long-term exposures were designed to assess how the cells acclimate to solar radiation (the growth, UV_abc and ratio of repair to damage rates of D1 protein were detected). A significant decrease in the photochemical efficiency (Φ_PSII) at high irradiance (100% of incident solar radiation, 261.6 Wm⁻²) was observed in short-term exposure (1 h). UVR-induced photoinhibition was reduced to 7% in 3% solar radiation (4.08 Wm⁻²), compared with 66% in 100% solar radiation (261.6 Wm⁻²). In long-term experiments (11 days) using batch cultures, cell densities during the first 6 days were relatively constant for treatment P, and decreased slightly under PA and PAB treaments, reflecting a change in the irradiance experienced in the laboratory to that of incident solar irradiance. Thereafter, cell density increased and UV-induced photoinhibition decreased with the following days, indicating acclimation to solar UV. At the end of experiment, cells were found to exhibit both higher ratios of repair to UV-related damage and increased concentrations of UV-absorbing compounds, whose maximum absorption was found to be at 329 nm. Our data indicate that C. curvisetus is sensitive to ultraviolet radiation, but was able to acclimate relatively rapidly (ca. 6 days) by synthesizing UV-absorbing compounds and by increasing the rates of repair processes of D1 protein in PSII.     

First results from plasma density measurements in the FTU tokamak by means of a two-frequency pulsed time-of-flight refractometer

A pulsed time-of-flight refractometer was developed and tested to determine the mean plasma density in the T-11M tokamak by measuring the propagation time of nanosecond microwave pulses in plasma. Later, it was also proposed to use such an instrument to measure and control the mean plasma density in the ITER tokamak by probing the plasma with an extraordinary wave, the electric field of which is perpendicular to the magnetic field in plasma, in the transparency window at frequencies of 50–100 GHz. To avoid the effect of the density profile shape on the measurement results in the nonlinear mode of refractometer operation (near the cutoff), a system operating at two different probing frequencies was developed and tested. Such a system provides two values of the time delay, which can be used to estimate the peaking factor of the density distribution α and correctly determine the linear density 〈Nl〉, regardless of the density profile (assuming a smooth density profile of the form of N(ρ) = N(0)(1 − ρ²)^α, where N(0) is the central plasma density and ρ = r/a is the normalized plasma radius). The first experiments on density measurements in the FTU tokamak performed with this refractometer are described, and results from these experiments are presented. The formation of a thin dense plasma layer in the zone of a strong magnetic field (the so-called MARFE layer) at a relatively low (for FTU) plasma density of ∼6 × 10¹⁹ m⁻³ was detected. The thickness of this layer, determined from the refractometry data, agrees well with the data obtained using a digital camera.     

Anomalous absorption of radiowaves by small-scale cylindrical irregularities stretched along the magnetic field

Results are presented from calculations of the anomalous absorption of an ordinary radiowave in the ionospheric plasma by a system of small-scale cylindrical density irregularities such that δN < 0. Account is taken of the effect of density perturbations on the propagation of excited cold waves and their conversion into plasma waves. It is shown that this effect attenuates the anomalous absorption of the radiowave. However, for sufficiently large density perturbations (about 6% or more), the absorption is substantial even for irregularities having comparatively large transverse sizes (about 5 m). The fluxes of cold and plasma waves excited by a radiowave in the anomalous absorption process are determined.     

Behaviors of impurity in ITER plasma with standard type I ELMy H-mode and steady-state scenarios

Self-consistent simulations of impurity behaviors in ITER plasmas in standard Type I ELMy H-mode and steady-state scenarios are investigated using 1.5D BALDUR integrated predictive modeling code. In these simulations, the plasma core transports, including electron and ion thermal, hydrogenic and impurity transports, are predicted using a linear combination of anomalous and neoclassical transports. An anomalous transport is calculated using a theory-based Multimode (MMM95) model; while the neoclassical transport is calculated using NCLASS model. The temperature and density boundary conditions are described at the top of the pedestal. Two different models for hydrogenic and impurity boundary density conditions are considered. The first model is called a “static boundary density model,” in which the hydrogenic and impurity densities at the boundary are fixed. For the second model, called a “dynamic boundary density model,” the hydrogenic and impurity densities at the boundary are assumed to be a large fraction of its line-averaged density. For simplicity, the pedestal temperature is assumed to be a constant in all simulations. The combination of a core transport model together with the boundary density models is used to simulate the time evolution of plasma current, temperature, and density profiles for ITER plasmas in standard type I ELMy H-mode and steady-state scenarios. As a result, the behaviors of impurity in ITER plasmas can be investigated. It is found in both ITER scenarios that the total amount of impurity, including beryllium and helium, in plasma core increases rapidly in early state and reaches a steady-state value. The level of impurity content in the steady state depends sensitively on the impurity boundary conditions. The effective charge at the edge is found to be about 1.4 and 1.1 using a static boundary density model and a dynamic boundary density model, respectively. It is also found that the hydrogenic and impurity transports in ITER plasmas for both scenarios is dominated by the kinetic ballooning modes, while the ITG and TEM modes provide the largest contributions for both thermal transports in most of region. In addition, a sensitivity study is carried out to investigate the impacts of pedestal temperature, pedestal density and line-averaged density on the impurity behaviors. It is found that increasing the pedestal temperature results in a reduction of the impurity content. On the other hand, increasing the pedestal density, line-averaged density or impurity influx result in an increase of the impurity content.     

Simulation of the generation of characteristic X radiation under vacuum heating of electrons by a femtosecond laser pulse

An analytic model of the generation of characteristic X radiation under vacuum heating of electrons at the surface of a massive target by a p-polarized nonrelativistic femtosecond laser pulse is considered. The results of calculations satisfactorily describe the measured data on the output of K _α radiation generated by laser pulses with a wavelength of 1.24 μm and peak intensities of 5 × 10¹⁶–2 × 10¹⁷ W/cm², incident at an angle of 45°.     

Visualization of plasma-induced processes by a projection system with a Cu-laser-based brightness amplifier

A novel method for visualization of the process of interaction of high-power energy fluxes with various surfaces is proposed. The possibility of the dynamic visualization of a surface covered with a ∼3-cm-thick plasma layer with a linear density of ∼10¹⁶ cm⁻² is demonstrated experimentally. A scheme of intracavity shadowgraphy of phase objects with the use of a laser projection microscope is developed. Shadow images illustrating the development of the plasma torch of an erosion capillary discharge in air are presented.     

Non-planckian equilibrium radiation of plasma-like media

Consideration of equilibrium radiation of plasma-like media shows that the spectral distribution of such radiation differs from that of Planckian equilibrium radiation (blackbody radiation). The physical reason for this difference consists in the impossibility of propagation of photons with the dispersion law ω = ck in systems of charged particles. The thermodynamics of equilibrium electromagnetic radiation in plasma is also considered. It is shown that the difference of the thermodynamic properties of such radiation from those of Planckian radiation is characterized by the parameter a = ℏΩ _p /T. This difference is especially pronounced in plasma media in which a ≥ 1. Applications of the results obtained to plasmas of metals (first of all, liquid metals in which charged particles have no distant order) and to the plasma model of the early Universe are discussed.     

Four-frequency polarizing microscope for recording plasma images in the wavelength range 0.4–1.1 μm

The optical scheme and design of a four-frequency polarizing microscope intended for simultaneous recording of plasma images in the wavelength range 0.4–1.1 μm with the spatial resolution 12 μm in the entire spectral range are described. The effectiveness of such a microscope in studies of plasmas produced on interaction of laser radiation with a target is demonstrated. The plasma images are obtained at the frequencies ω₀, (3/2)ω₀, 2ω₀, and (5/2)ω₀, where ω₀ corresponds to the frequency of heating radiation. The transformation coefficient that characterizes the efficiency of conversion of heating radiation into the 2ω₀, (3/2)ω₀, and (5/2)ω₀ harmonics generated in the plasma is determined.     

Experimental study of the excitation of rhodium isomer in a plasma produced by a picosecond laser pulse

Estimates and first experimental results on the excitation of a long-lived isomer state (E _m = 39.756 keV, J ^p = 9/2⁻, and T _1/2 = 56.114 min) of Rh¹⁰³ nuclei under the action of X radiation in a hot solid-state-density rhodium plasma produced by a picosecond laser pulse in the SOKOL-P laser facility are presented.     

Numerical 1D PIC-simulations of ion acceleration during laser-plasma interaction: Optimization of a two-component multilayered target structure

Ion beam acceleration is simulated using a one-dimensional 1D2P PIC code. The dependences of the maximum energy and width of the energy spectrum of the generated ion beams on the duration and intensity of laser radiation, as well as on the target parameters (thickness and number of layers, types and densities of atoms), are investigated. The optimal target configuration at which the energy of the accelerated ions is maximum (5–160 MeV for intensities of 5 × 10^{18 −5} × 10²⁰ W/cm²) is found. The optimal target configuration is shown to depend on the intensity and be independent of the laser pulse duration.     

Specific features of microheterogeneous plasma produced by irradiation of a polymer aerogel target with an intense 500-ps-long laser pulse

The properties of microheterogeneous plasma produced by irradiation of a polymer aerogel target with an intense (10¹⁴ W/cm³) short (0.5 ps) 1.064-μm laser pulse were studied. It is found that, even at plasma densities exceeding the critical density, a small fraction of the incident laser radiation penetrates through the plasma in which the processes of density and temperature equalization still take place. The intensification (as compared to plasmas produced from denser foams and solid films) of transport processes in such plasma along and across the laser beam can be caused by the initial microheterogeneity of the solid target. The replacement of a small (10% by mass) part of the polymer with copper nanoparticles leads to a nearly twofold increase in the intensity of the plasma X-ray emission.     

Influence of human biokinetics of strontium on internal ingestion dose of <Superscript>90</Superscript>Sr and absorbed dose of <Superscript>89</Superscript>Sr to organs and metastases

The objective of the present work is to apply the plasma clearance parameters to strontium, previously determined in our laboratory, to improve the biokinetic and dosimetric models of strontium-90 (⁹⁰Sr) used in radiological protection; and also to apply this data for the estimation of the radiation doses from strontium-89 (⁸⁹Sr) after administration to patients for the treatment of the painful bone metastases. Plasma clearance and urinary excretion of stable strontium tracers of strontium-84 (⁸⁴Sr) and strontium-86 (⁸⁶Sr) were measured in GSF-National Research Center for Environment and Health (GSF) in 13 healthy German adult subjects after intravenous injection and oral administration. The biological half-life of strontium in plasma was evaluated from 49 plasma concentration data sets following intravenous injections. This value was used to determine the transfer rates from plasma to other organs and tissues. At the same time, the long-term retention of strontium in soft tissue and whole body was constrained to be consistent with measured values available. A physiological urinary path was integrated into the biokinetic model of strontium. Parameters were estimated using our own measured urinary excretion values. Retention and excretion of strontium were modeled using compartmental transfer rates published by the International Commission on Radiological Protection (ICRP), the SENES Oak Ridge Inc. (SENES), and the Urals Research Center for Radiation Medicine (TBM). The results were compared with values calculated by applying our GSF parameters (GSF). For the dose estimation of ⁸⁹Sr, a bone metastases model (GSF-M) was developed by adding a compartment, representing the metastases, into the strontium biokinetic model. The related parameters were evaluated based on measured data available in the literature. A set of biokinetic parameters was optimized to represent not only the early plasma kinetics of strontium but also the long-term retention measured in soft tissue and whole body. The ingestion dose coefficients of ⁹⁰Sr were computed and compared with different biokinetic model parameters. The ingestion dose coefficients were calculated as 2.8 × 10⁻⁸, 2.1 × 10⁻⁸, 2.5 × 10⁻⁸ and 3.8 × 10⁻⁸ Sv Bq⁻¹ for ICRP, SENES, TBM and GSF model parameters, respectively. Moreover, organ absorbed dose for the radiopharmaceutical of ⁸⁹Sr in bone metastases therapy was estimated based on the GSF and ICRP biokinetic model parameters. The effective doses were 3.3, 1.8 and 1.2 mSv MBq⁻¹ by GSF, GSF-M, and ICRP Publication 67 model parameters, respectively, compared to the value of 3.1 mSv MBq⁻¹ reported by ICRP Publication 80. The absorbed doses of red bone marrow and bone surface, 17 and 21 mGy MBq⁻¹ calculated by GSF parameters, and 7.1 and 8.8 mGy MBq⁻¹ by GSF-M parameters, are comparable to the clinical results of 3–19 mGy MBq⁻¹ for bone marrow and 16 mGy MBq⁻¹ for bone surface. Based on the GSF-M model, the absorbed dose of ⁸⁹Sr to metastases was estimated to be 434 mGy MBq⁻¹. The strontium clearance half-life of 0.25 h from the plasma obtained in the present study is obviously faster than the value of 1.1 h recommended by ICRP. There are no significant changes for ingestion dose coefficients of ⁹⁰Sr using different model parameters. A model including the metastases was particularly developed for dose estimation of ⁸⁹Sr treatment for the pain of bone metastases.     

Pellet injection into H-mode ITER plasma with the presence of internal transport barriers

The impacts of pellet injection into ITER type-1 ELMy H-mode plasma with the presence of internal transport barriers (ITBs) are investigated using self-consistent core-edge simulations of 1.5D BALDUR integrated predictive modeling code. In these simulations, the plasma core transport is predicted using a combination of a semi-empirical Mixed B/gB anomalous transport model, which can self-consistently predict the formation of ITBs, and the NCLASS neoclassical model. For simplicity, it is assumed that toroidal velocity for ω _E×B calculation is proportional to local ion temperature. In addition, the boundary conditions are predicted using the pedestal temperature model based on magnetic and flow shear stabilization width scaling; while the density of each plasma species, including both hydrogenic and impurity species, at the boundary are assumed to be a large fraction of its line averaged density. For the pellet’s behaviors in the hot plasma, the Neutral Gas Shielding (NGS) model by Milora-Foster is used. It was found that the injection of pellet could result in further improvement of fusion performance from that of the formation of ITB. However, the impact of pellet injection is quite complicated. It is also found that the pellets cannot penetrate into a deep core of the plasma. The injection of the pellet results in a formation of density peak in the region close to the plasma edge. The injection of pellet can result in an improved nuclear fusion performance depending on the properties of pellet (i.e., increase up to 5% with a speed of 1 km/s and radius of 2 mm). A sensitivity analysis is carried out to determine the impact of pellet parameters, which are: the pellet radius, the pellet velocity, and the frequency of injection. The increase in the pellet radius and frequency were found to greatly improve the performance and effectiveness of fuelling. However, changing the velocity is observed to exert small impact.