Atomic Physics Processes Research Articles

Self-similar hydrodynamic flow in the laser light to x-ray conversion layer of a laser-heated solid

Intense short-wavelength laser light may be converted into thermal soft x rays in the dense plasma formed by irradiation of a solid high-Z material. Under certain conditions, the hydrodynamic flow in the conversion layer is self-similar, and profiles of the hydrodynamic variables may be readily calculated by solving the appropriate hydrodynamic equations. It is found that the structure of the conversion layer depends on the type of equilibrium that determines the atomic physics processes of radiation emission. Varying the conditions between the limits of local thermodynamic equilibrium (LTE) and coronal equilibrium (CE) shows, that in the latter case, the radiation comes mainly from a thin layer in the dense part of the conversion layer.

A short mean-free path, coupled neutral-ion transport description of a tokamak edge plasma

The ion and neutral densities and temperatures in the edge region of a diverted plasma can vary over two or more orders of magnitude causing atomic physics processes to modify the usual short mean-free path transport descriptions of magnetized plasmas. The short-mean-free path ordering is particularly relevant to the rather cold, moderately dense plasmas of interest in gas target divertor operation. Under such conditions, charge-exchange, ionization, and recombination couple the ions to the neutrals and alter the transport coefficients of both species. The coupling modifications to the ions are evaluated in the short mean-free path limit by a minor adjustment in standard procedures when neutral–neutral collisions are negligible. The short-mean-free path coupling modifications to the neutrals are evaluated by assuming the charge-exchange rate coefficient is velocity independent. A closed neutral-ion fluid description is obtained by assuming temperatures sufficiently high that ion energy and momentum exchange with the electrons is unaffected by atomic processes and densities sufficiently low that electron–neutral collisions may be neglected.

Geometrical, kinetic and atomic physics effects in a two dimensional time dependent fluid simulation of ablating fuel pellets

The ablation process of hydrogen fuel pellets in hot magnetized plasmas is investigated using a newly developed two dimensional time dependent hydrodynamics code, P2D. Surface evaporation and ablated fluid flow are evolved, coupled with a kinetic calculation of the non-local heating due to slowing down of hot Maxwellian background electrons in the cold ablated plasma. Results of the neutral gas shielding model of pellet ablation are extended to include effects due to non-spherical ablation flows, proper treatment of scattering in the kinetic calculation of the hot electron heat deposition, and atomic physics processes in the ablation cloud and at the pellet surface. These effects have been considered previously, though never as a comprehensive whole. The non-spherical nature of the ablation flow reduces the ablation rate by about a factor of two, while the use of a full Maxwellian distribution for the hot electrons increases ablation by a factor of about four. With Maxwellian hot electrons, atomic physics effects (principally due to dissociation and sublimation) can reduce the ablation rate by up to a factor of two. These effects are systematically quantified using simple physical arguments and code results. For comparison with experiment, we give a simple fit to the code ablation rate results for spherical deuterium pellets: G2DGS approximately=1.65*1015Rp(cm)1.26ne(cm-3)0.35Te(eV)1.87 atoms/s, where Rp is the pellet radius and ne (Te) is the plasma density (temperature). This fit is compared with measured local ablation rates in Ohmic discharges on TFTR and JET. Predicted ablation rate profiles agree well with those on TFTR, but poorly with those on JET; pellet penetration depths agree well on both machines. Probable causes of the observed discrepancies (both experimental and theoretical) are discussed; in particular, transport processes in the post injection plasmas are shown to be able to account for some of the differences

Atomic physics effects on dissipative toroidal drift wave stability

The effects of atomic physics processes such as ionization, charge exchange, and radiation on the linear stability of dissipative drift waves are investigated in toroidal geometry, both numerically and analytically. For typical Tokamak Fusion Test Reactor (TFTR) [Plasma Physics and Controlled Nuclear Fusion Research, 1986 (IAEA, Vienna, 1987), Vol. 1, p. 51] and Texas Experimental Tokamak (TEXT) [Nucl. Technol. Fusion 1, 479 (1981)] edge parameters, overall linear stability is determined by the competition between the destabilizing influence of ionization and the stabilizing effect due to the electron temperature gradient. An analytical expression for the linear marginal stability condition, ηcrite, is derived. The instability is most likely to occur at the extreme edge of tokamaks with a significant ionization source and a steep electron density gradient.

Time-dependent collisional radiative model of ionizing and recombining plasmas

A time-dependent collisional radiative model, based on a five-charge state at any spacetime point in the plasma, is elaborated in order to follow the basic atomic physics processes in a plasma undergoing ionization and recombination. This model can either be used independently or be included in a magnetohydrodynamics code of a transient plasma. In the latter case, the efficiency of the model makes it particularly useful in saving computing time of hydrodynamic codes developed in connection with ion-driven fusion.

Parity nonconserving asymmetries in resonance scattering and nuclear reactions induced by polarized protons.

The parity-nonconserving nucleon-nucleon interaction studied in nuclear systems provides a unique window on \ensuremath{\Delta}S=0 hadronic weak processes. To check the predictions concerning the interactions between weak hadronic currents, low-energy nuclear physics processes appear to be very suitable. Considering the nuclear reactions induced by polarized protons as low-energy nuclear processes, we derive expressions for the longitudinal and irregular transverse parity-nonconserving analyzing powers, when the reactions take place via parity mixed resonances. Applications for $^{13}\mathrm{C}$(p\ensuremath{\rightarrow},p${)}^{13}$C, $^{15}\mathrm{N}$(p\ensuremath{\rightarrow},p${)}^{15}$N, and $^{15}\mathrm{N}$(p\ensuremath{\rightarrow},\ensuremath{\alpha}${)}^{12}$C resonance reactions are done.

Time-dependent Hartree-Fock theory of multiphoton ionization: Helium.

The multiphoton ionization of helium has been determined for a number of laser wavelengths and intensities using the time-dependent Hartree-Fock model. Conclusions about the ionization dynamics for very-short-pulse, high-intensity lasers are discussed. The limits and characteristics of the time-dependent Hartree-Fock method for atomic physics processes are also evaluated.

Ionization and charge transfer in high-energy ion-atom collisions

Electron capture and loss by fast highly charged ions in a gas target, and ionization of the target by passage of the fast projectile beam, are fundamental processes in atomic physics. These processes, along with excitation, can be experimentally studied separately (“singles”) or together (“coincidence”). This paper is a review of recent results on singles measurements for electron capture and loss and for target ionization, for velocities which are generally high relative to the active electron, including recent ionization measurements for a nearly relativistic projectile.

Book reviews

Book reviews

Zero-dimensional energy balance modelling of the CTX spheromak experiment

A zero-dimensional time-dependent energy balance model is used to explore the energy loss mechanisms of the CTX spheromak experiment at Los Alamos National Laboratory. A coupled set of model equations representing electron, ion, neutral, and impurity particle balance, electron and ion temperature, and magnetic field decay, are solved from initial values and the results compared to the time behaviour of experimentally measured average densities, temperature, and magnetic field. The energy balance model considers all the major atomic physics processes, especially the effects of radiation from a non-equilibrium distribution of impurity charge states evolving in time. The model includes the effects of a strong neutral-particle source which replaces by ionization the plasma being lost by a short particle confinement time. The neutral source is required in experiments to prevent the sudden termination of the discharge associated with low densities. A major new conclusion is that all the data from resistively decaying spheromaks can be effectively modelled, when the flux loss effects of a resistive flux conserver are also included, using plasma resistivity increased by a factor of 3.2 ± 0.6 over the Spitzer-Härm value evaluated with the volume-average temperature. This factor appears to be constant for all discharges at all times. The analysis has determined that the power density associated with the particle replacement is the most important loss in the warm, non-radiation-dominated CTX spheromaks.

Kaon Factories

Kaon factories would provide beams 100-1000 times more intense than those available from present accelerators in the 10-30 GeV range. More intense or cleaner secondary beams of kaons, antiprotons and neutrinos would be of particular interest for high precision experiments and studies of rare processes in both particle and nuclear physics, e.g. symmetry violations in K-decay, neutrino scattering, meson and baryon spectroscopy, hypernuclei, exotic atoms, K <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> studies of nuclear density and resonance propagation in nuclei. The various accelerators proposed include both fastcycling synchrotrons providing 100 μA proton beams at 15 to 32 GeV and superconducting isochronous ring cyclotrons giving 100-400 μA at up to 15 GeV. This paper describes these designs and the various technical problems associated with them.

High Oxygen Abundance in a Bright Filament of the Crab Nebula

Detailed stationary photoionization models with homogeneous chemical composition were constructed for a bright filament of the Crab Nebula centered ~42″ W-SW of the pulsar. So far this filament is the only one which has been observed in the ultraviolet (Davidson et al, 1982), in the visual (Miller, 1978; Davidson et al, 1982) and in the near-infrared (Dennefeld and Péquignot, 1982), so that numerous constraints and meaningful tests of the models exist. On the other hand the computer program used in the calculations includes recently introduced atomic physics processes (charge exchange reactions and “low-temperature” di-electronic recombinations) and was tested and calibrated by means of models of the high-excitation planetary nebula NGC 7027 whose line spectrum shares some characteristics with that of the Crab Nebula.

High Sensitive Scintillation Gamma-Ray Spectrometry

Characteristics of low level scintillation spectrometer operating in various coincidence modes are reviewed. A comparison of results shows that the most sensitive mode is the beta-gamma-gamma spectrometer. The high sensitivity obtained enables to investigate rare decay processes in nuclear physics, to perform nondestructive measurements of cosmogenic nuclides in extraterrestrial samples, e.g. lunar and meteorite samples, as well as to perform low level radioactivity measurements in the environment.

Biochemistry

RETURN TO ISSUEPREVNewsNEXTBiochemistryJEFFREY L. FOXView Author Information C&EN WashingtonCite this: Chem. Eng. News 1979, 57, 33, 22–23Publication Date (Print):August 13, 1979Publication History Published online7 November 2010Published inissue 13 August 1979https://doi.org/10.1021/cen-v057n033.p022Copyright © 1979 American Chemical SocietyArticle Views6Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (180 KB) SUBJECTS:Biochemistry,Genetics,Nuclear magnetic resonance spectroscopy,Physical and chemical processes Get e-Alerts

Collisional Atomic Physics with Molecular Projectiles

Many collisional atomic physics processes are altered when solid targets are bombarded by molecular, compared to atomic, projectiles. We present energy and angular distribution measurements of exiting particles when 50-300 keV H+2 and HeH+ molecules are incident on thin (1.8-5 ?g/cm2) solid carbon targets. We find that the ratio of molecular to atomic projectile energy loss is velocity and transit time dependent, and ranges from ~ 0.8 to 1.3. The energy distribution of the exiting charged, neutral, and molecular particles are compared and found to be consistent with the assumption that protons of a velocity ? v0 do not have bound states while moving in solids.

Ionospheric heating by radio waves: Predictions for Arecibo and the satellite power station

The effect of resistive heating by radio waves on ionospheric temperatures, electron densities, and airglow emissions is examined by using numerical ionospheric structure and heat balance codes. Two cases are studied: (1) a 3‐GHz, 10‐GW microwave beam from a proposed satellite power station and (2) 1‐MW and 3‐MW beams of 15‐MHz radio waves launched by the Arecibo antenna. By intent, these two cases have similar intensities and geometries of resistive heating. The most dramatic heating effects are predicted to occur in the E region, where a thermal runaway will take place. The E region electron temperature will increase from 200°K to roughly 1000°K, and the E region electron density will increase by a factor of about 3. In the F region, where thermal conductivity plays an important role, temperature increases of 200°–500°K will appear along magnetic field lines passing through the radio wave beams. Enhanced emissions in airglow and molecular infrared lines will also occur. Radio wave heating, when combined with the diagnostic capabilities of the Arecibo incoherent scatter radar, will generate new opportunities to measure the rates of atomic physics processes and neutral atmosphere temperatures and composition at D and E region altitudes.

Review

Abstract Scattering Theory (Aspects of Scattering Processes in Atomic, Nuclear and Particle Physics) Edited by A. O. Barut Gordon and Breach Science Publishers Inc., 1969, pp. viii + 431.