Recombination of a Xenon Plasma Jet

28th Plasmadynamics and Lasers Conference, 1997

Results from experimental and numerical investigations of the mechanism of ionizational nonequilibrium in recombining plasmas of air, nitrogen/argon, and air/argon are presented. Measurements of electron and excited state concentrations in plasmas produced with a 50 kW RF torch operating at atmospheric pressure are compared with numerical simulations performed with three reaction mechanisms widely used for air plasma kinetics. It is shown that, as electron recombination in molecular plasmas occurs primarily through inherently fast two-body dissociative recombination, ionizational nonequilibrium is ultimately caused by slow three body neutral recombination. The rates of the controlling three-body neutral recombination reactions are assessed through a comparison between the predictions of the kinetic models and the measured nonequilibrium concentrations of electrons, of the A, C, and D states of NO, of the B and C state ofN 2 , and of the A state of OH.

Physics Letters A, 1996

Recombination of hydrogen plasma in the divertor volume can be considered as a simple explanation of divertor plasma detachment phenomena experimentally observed on many tokamaks. As will be shown in this report, the presence of rotationally and vibrationally excited molecules significantly enhance the conventional three-body recombination of plasma and expand the plasma temperature and density range responsible for plasma recombination to much higher temperatures and/or lower densities. The effective rate coefficient for plasma recombination due to chemical reactions with molecules, calculated on the basis of generalized collisional-radiative model (CRAMD code), was found be about 10-10 cm 3 /s in the wide range of plasma temperatures T, = 1-3 eV and densities

Arxiv preprint physics/ …, 2004

In a new divertor simulator, an ultra-cold (T e <1 eV) high density recombining magnetized laboratory plasma is studied using probes, spectroscopic measurements, and ultra-fast imaging of spontaneous emission. The Mistral-B device consists in a linear high density magnetized plasma column. The ionizing electrons originate from a large cathode array located in the fringing field of the solenoid. The ionizing electrons are focused in a 3 cm diameter hole at the entrance of the solenoid. The typical plasma density on the axis is close to 2.10 18 m-3. The collector is segmented into two plates and a transverse electric field is applied through a potential difference between the plates. The Lorentz force induces the ejection of a very-low temperature plasma jet in the limiter shadow. The characteristic convection time and decay lengths have been obtained with an ultra-fast camera. The study of the atomic physics of the recombining plasma allows to understand the measured decay time and to explain the emission spectra.

High Energy Density Physics, 2011

Radiative shock waves play a pivotal role in the transport energy into the stellar medium. This fact has led to many efforts to scale the astrophysical phenomena to accessible laboratory conditions and their study has been highlighted as an area requiring further experimental investigations. Low density material with high atomic mass is suitable to achieve radiative regime, and, therefore, low density xenon gas is commonly used for the medium in which the radiative shock propagates. In this work the average ionization and the thermodynamic regimes of xenon plasmas are determined as functions of the matter density and temperature in a wide range of plasma conditions. The results obtained will be applied to characterize blast waves launched in xenon clusters.

Nuclear Fusion, 1998

Evidence for volume recombination in the JET divertor has been obtained from the population ratios of the excited states of neutral hydrogen. The ratio of the Balmer series lines Dγ/Dα has been used to identify recombination at both the inner and the outer divertor target. At the outer target the onset of recombination is well correlated with the plasma detachment as observed with Langmuir probes in the divertor target. While Te obtained from the target probe characteristics falls to ∼2 eV, Te from the population distribution of the excited states is 0.8 ± 0.1 eV. The peak plasma density viewing across the outer divertor leg just above the target exceeds 2.5 × 10 20 m -3 . When the plasma becomes partially detached from the outer target, the radial distribution of recombination shows a maximum close to the outer divertor strike point.

2010

A study of ternary recombination of He2 + ions with electrons is presented. The experiment was carried out using flowing afterglow apparatus equipped with axially movable Langmuir probe (FALP). The flow tube was cooled down to 77 K and the number density of helium buffer gas was varied in the range of 1×10 17 cm -3 - 5×10 17 cm -3 . At these conditions, there are three main processes of recombination - dissociative recombination, ternary recombination (helium assisted) and collisional radiative recombination - CRR (the third particle is an electron). We observed the dependence of effective recombination rate coefficient αeff on helium buffer gas density with the ternary rate coefficient KHe = (9.0 ± 3.0)×10 -26 cm 6 s -1 while the extrapolation of this dependence towards low helium density gives the value of ternary recombination rate coefficient of CRR of He2 + ions with electrons KCRR = (2.2 ± 0.8) × 10 -17 cm 6 s -1 . These results are in good agreement with theoretical

Astronomy and Astrophysics, 2004

We have calculated dielectronic recombination rate coefficients for 22 ions of the boron isoelectronic sequence, between C + and Xe 49+ , within the generalized collisional-radiative framework, as outlined by Badnell et al. (2003). Calculations have been performed from both ground and metastable initial states, in both LS-and intermediate-coupling, allowing for ∆n = 0 and ∆n = 1 core-excitations. Results are presented and discussed for a selection of ions from the sequence. Results which are not presented here can be accessed from the Atomic Data and Analysis Structure (ADAS) database (Summers 2003) or from the Oak Ridge Controlled Fusion Atomic Data Center (http://www-cfadc.phy.ornl.gov). Comparison is made with the results of other existing theoretical calculations.

Measurements of recombination rate coefficients of binary and ternary recombination of H þ 3 and D þ 3 ions with electrons in a low temperature plasma are described. The experiments were carried out in the afterglow plasma in helium with a small admixture of Ar and parent gas (H 2 or D 2 ). For both ions a linear increase of measured apparent binary recombination rate coefficients ( eff ) with increasing helium density was observed: eff From the measured dependencies, we have obtained for both ions the binary ( BIN ) and the ternary (K He ) rate coefficients and their temperature dependence. For the description of observed ternary recombination a mechanism with two subsequent rate determining steps is proposed. 3 ) is formed. In the following step H Ã 3 (or D Ã 3 ) collides with a He atom of the buffer gas and this collision prevents autoionization of H Ã 3 (or D Ã 3 ). Lifetimes of the formed H Ã 3 (or D Ã 3 ) and corresponding ternary recombination rate coefficients have been calculated. The theoretical and measured binary and ternary recombination rate coefficients obtained for H þ 3 and D þ 3 ions are in good agreement.

Journal of Applied Physics, 2001

Electron production rate and electron density in cold optically pumped CO-Ar and CO-N 2 plasmas in the presence of small amounts of O 2 and NO have been measured using a Thomson discharge probe and microwave attenuation. Nonequilibrium ionization in the plasmas is produced by an associative ionization mechanism in collisions of highly vibrationally excited CO molecules. It is shown that adding small amounts of O 2 or NO ͑50-100 mTorr͒ to the baseline gas mixtures at Pϭ100 torr results in an increase of the electron density by up to a factor of 20-40 ͑from n e Ͻ10 10 cm Ϫ3 to n e ϭ(1.5-3.0)ϫ10 11 cm Ϫ3 ). This occurs while the electron production rate either decreases ͑as in the presence of O 2 ͒ or remains nearly constant within a factor of 2 ͑as in the presence of NO͒. It is also shown that the electron-ion recombination rates inferred from these measurements decrease by two to three orders of magnitude compared to their baseline values ͑with no additives in the cell͒, down to ␤Х1.5ϫ10 Ϫ8 cm 3 /s with 50-100 mTorr of oxygen or nitric oxide added to the baseline CO-Ar mixture, and ␤Х(2 to 3)ϫ10 Ϫ7 cm 3 /s with 75-100 mTorr of O 2 or NO added to the baseline CO-N 2 mixture. The overall electron-ion removal rates in the presence of equal amounts of O 2 or NO additives turn out to be very close, which shows that the effect of electron attachment to oxygen at these conditions is negligible. These results suggest a novel method of electron density control in cold laser-sustained steady-state plasmas and open a possibility of sustaining stable high-pressure nonequilibrium plasmas at high electron densities and low plasma power budget.