Critical Ionization Research Articles

A review of critical ionization velocity

This paper reviews the critical ionization velocity (CIV) phenomenon, with inclusion of recent research. CIV, suggested by Alfvén in 1954 as part of a larger cosmological theory accounting for the formation of the solar system, is controversial in that laboratory and space experiments to confirm its validity have yielded conflicting results. Theoretical analysis has suggested that the driving mechanism for CIV is some form of beam‐plasma instability, such as the lower hybrid instability, which leads to rapid energization of ambient electrons so that they gain enough energy to ionize the beam of neutral atoms by electron impact. The newly created beam ions energize the instability, thus fostering a cyclic process that may lead to an avalanche ionization. Because the implications of this process, if correct, are widespread, it has become important to establish a theoretical framework for its presence and its occurrence. This framework includes a variety of microscopic chemical and physicochemical processes, such as line excitation, formation of metastable states by electron impact, ionization of metastable states by electron impact, and ion‐electron recombination in the case of molecular ions. These reactions may occur in CIV experiments both in the laboratory and in space. Numerical computer models have been able to not only simulate CIV but also reveal details in nonlinear plasma evolution together with electron impact ionization of the neutral particles. Theories, laboratory experiments, and computer simulations have all shown CIV as feasible and reasonably understood, although all CIV experiments in space have yielded negative results with perhaps three exceptions. In the CIV experiments in space, not only the ionization yields were low, but also non‐CIV processes such as charge exchange, associative ionization, and stripping ionization may have occurred and may be easily mistaken as CIV. We also discuss the conditions under which the laboratory and the space experiments are carried out and highlight the differences, some of which may explain the different results.

H2 Formation in Low-Metallicity Galaxies

Abstract A possible formation mechanism of hydrogen molecules on a galactic scale is examined. We are interested especially in the role of hydrogen molecules for the formation and evolution of primordial galaxies. Thus, the formation process of hydrogen molecules in a very low-metallicity galaxy (I Zw 18; the most typical metal-deficient galaxy) is studied. Adopting a recent observational result of the absorption lines of hydrogen molecules in I Zw 18, we obtain the upper limit for the ionization degree in the case where hydrogen molecules can form via the $\mathrm{H}^{-}$-process, although they are generally believed to form on the surface of dust grains. Furthermore, we present a critical ionization degree, above which the $\mathrm{H}^{-}$-process can be dominant over the formation process on the surface of grains. Interestingly, this critical ionization degree is comparable to the upper limit of the ionization degree for I Zw 18. For determining the formation process of hydrogen molecules, future observational facilities can be useful. Thus, we examine the detectability in some wavelengths for metal-deficient galaxies. According to our estimate, the near-infrared line emission of hydrogen molecules is observable at the level of $10\,\mu\mathrm{Jy}$, the free–free radio emission is at the level of mJy, and the far-infrared emission from the dust on which hydrogen molecules form can also be detected at the 10-mJy level with its temperature of 16 K. The near-infrared line and the far-infrared continuum are feasible for ASTRO-F observations.

Temperature Dependence of Equilibrium and Transport Properties of Decyldimethylbenzylammonium Chloride in Aqueous Solutions

Apparent and partial molar volumes of decyldimethylbenzylammonium chloride (C10DBACl) at (15, 25, and 35) °C have been calculated from results of density measurements. The specific conductivities of the solutions have been determined at the same temperatures. The results served for the estimation of critical micelle concentration, cmc, ionization degree, β, and standard free energy of micellization, , of the surfactant. From equivalent conductivity measured at 25 °C in the low concentration range, the transport number of the C10DBA+ cation has been estimated. The aggregation number, n, of the micelles has been estimated from the conductivity data.

Particle acceleration mechanisms in space plasmas

There are many possible mechanisms for particle acceleration in space plasmas. Among these are two broadly defined types that may be characterised on the one hand by large scale electric field structures and on the other hand by stochastic mechanisms and enhanced wave activity. Double layers (DLs) are an example of the first type. They sustain a net potential difference, across which particles are accelerated. Crucial questions concern the generator maintaining the potential, the rate of energy transfer, equilibrium and matching conditions. Magnetic reconnection at an X-type neutral line is another example and shares many characteristics with DLs, such as the cutting of field lines and constraints set by external MHD motions. Particle acceleration by the growth of the modified two- stream instability (MTSI) is an example of the second type. The MTSI is driven by cross magnetic field ion motion and rapidly accelerates electrons. It has been seen as a link in the critical ionisation velocity (CIV) mechanism, which has been extensively studied both in experiments and theory. Crucial questions concern the evolution of the particle energy distribution, the wave source and the saturation of the driving instability.

An Electric Shock Model for Experiments on Critical Ionization Velocity

To describe the generation of the electric field by a discontinuity of the Hall current, an equation of the third order was obtained by using the electric charge conservation and Ohm's laws. Solutions to this equation are used to model the electric impulses detected in experiments aimed to verify the Alfven hypothesis on the critical ionization velocity in the process of the collision of neutral gas with magnetized plasma. A quantitative agreement with the experiment was attained, and the basic features of the measured signals were modeled under an assumption of strong anomalous resistance behind the discontinuity. Apparently, such an anomalous resistance occurs due to trapping of the current carriers by a small-scale modulation of the electric field.

Interactions between Poly(ethylene oxide) and Sodium Alkylcarboxylates As Studied by Conductivity and Gel Permeation Chromatography

The interactions between PEO and sodium alkylcarboxylates (octyl, decyl, and dodecyl) have been investigated by conductivity measurements and gel permeation chromatography (GPC). Also included in the study was sodium dodecyl sulfate. From the conductivity measurements the critical aggregation concentration, ionization degree, and binding ratios were determined; the binding ratio was also determined from GPC. PEO–surfactant interactions were observed for all the studied surfactants, except sodium octanoate. For the polymer–surfactant complexes the ionization degree was in all cases observed to be about 0.2 higher than the ionization degree for the corresponding aqueous micelles. Further, the binding ratio decreased somewhat with decreasing chain length of the alkylcarboxylate. The Gibbs free energy showed that the polymer–surfactant interaction decreases with decreasing chain length of the alkylcarboxylates and is weaker for alkylcarboxylate compared to alkylsulfate of similar chain length.

Keck Observations of the Hidden Quasar IRAS P09104+4109

We present imaging and spectropolarimetric observations of the ultraluminous infrared galaxy IRAS P09104+4109 using the Keck 10 m Telescope. We detect the clear presence of broad Hβ, Hγ, and Mg II λ2800 emission lines in the polarized flux spectra of the nucleus and of an extranuclear emission region ~4'' away, confirming the presence of a hidden central quasar. The polarization of the broad Mg II emission line is high (~29%), consistent with the remarkably high polarization (~30%–40%) observed in the extended continuum emission. This indicates that the off-nuclear continuum is dominated by light scattered from the hidden quasar, most probably by dust mixed with the line-emitting gas. The high polarizations, combined with the foreshortened morphology of the polarized brightness distribution, allow us to constrain the scattering biconical structure to be at inclination i ≈ 50° with a half-opening cone angle θc ≈ 40°. The narrow emission lines are polarized in a stratified fashion, with the high-ionization lines ([O III], [Ne V], [Fe VII]) being polarized 0.7%–1.7% and [O II] essentially unpolarized. The line polarizations are positively correlated with critical density, ionization potential, and velocity width of the emission lines. This indicates that, as is the case with the narrow-line radio galaxies, which also often contain powerful quasars, the narrow emission line region may be partially shadowed by the putative torus, with the higher ionization lines originating closer to the nucleus. One notable characteristic of the extranuclear knot is that all species of Fe are markedly absent in its spectrum, while they appear prominently in the nucleus. In addition, narrow Mg II is observed to be much weaker than predicted by ionization models. Our favored interpretation is that there is a large amount of dust in the extranuclear regions, allowing gaseous refractory metals to deposit. Near the nucleus, dust is destroyed in the strong radiation field of the quasar, inhibiting metal depletion onto grains. The extended emission regions are most likely material shredded from nearby cluster members and not gas condensed from the cooling flow or expelled from the obscured quasar. The higher temperature inferred from [O III] lines compared to that from [N II] and the general better agreement with models of line ratios, especially [O III] λ5007/λ4363 and He II/Hβ, provide strong evidence for matter-bounded clouds in addition to ionization-bounded clouds in the narrow-line region. Ionization by pure velocity shocks can be ruled out. Shocks with photoionizing precursors may be present but are probably not a dominant contributor to the energy input.

Observation of the CIV effect in interstellar clouds: a speculation on the physical mechanism for their existence

Observations of neutral hydrogen (H I) emission profiles produced by gas in the local interstellar medium are found to be characterized by four linewidth regimes. Dominant and pervasive features have widths on average of 5.2, 13, and 31 km/s, and a very broad component approximately 50 km/s wide. A striking coincidence exists between these linewidths and the magnitudes of the critical ionization velocities of the most abundant atomic species in interstellar space: 6 km/s for sodium and calcium; 13 km/s for carbon, oxygen, and nitrogen; 31 km/s for helium; and 51 km/s for hydrogen. The data relate to observations near neutral hydrogen structures that are filamentary.

EHD/EMHD Transport Processes and Electric Reconnection in Dusty and Dirty Plasmas

ABSTRACT: For dusty and dirty plasmas, fully or partially ionized, collisionless or collisional, containing dust grains or aerosols, charged and/or uncharged, an electrohydrodynamics (EHD)/electromagnetohydrodynamics (EMHD) is presented on the basis of a new equation of electric field transport in a charged fluid, supplemented by the equations of fluid vorticity, magnetic field, energy transport, and heat transfer extended for this new regime. The ‘electric Reynolds number’, RE=ɛμvL/T (ɛ: dielectric constant; μ: permeability; v: fluid velocity; L: characteristic length; T: characteristic time) plays an important role in the EHD/EMHD regime as a criterion of relative importance of convection, diffusion, dissipation, propagation, and radiation. The equation of electric field transport recovers the Kelvin‐Helmholtz theorem for high electric Reynolds numbers with a space‐charge related frozen‐in field concept. Tenuous cosmic plasmas where dust particles can be highly charged, need to be considered a multi‐component fluid, composed of electrons, ions, charged and/ or uncharged dust, and specifications are given briefly to a multi‐ component fluid model. By analogy with fluid vortex merging in the HD regime and magnetic reconnection in the MHD regime, electric reconnection is newly introduced in the EHD/EMHD regime. Following dust‐related electric reconnection, subsequent processes are divided into two cases, depending on whether the local electric fields on the grain surface are below or beyond the breakdown threshold of the background gas. For the former case, some of the electrostatic energy tends to be converted into the kinetic energy of the particle, leading to its rapid acceleration. For the latter case, a local surface discharge will take place due to sufficiently high local electric fields, forming a corona around the dust or object and leading to critical ionization flow in the form of streamer and leader followed by an eventual main discharge, or rarely by a plasma layer formation around the dust grain. Applications of EHD/EMHD and electric reconnection to a number of examples are indicated, including the formation of diffuse dust layers or dust distributions between the clouds and the ionosphere with reference to pre‐earthquake effects, natural and triggered lightning, tornadic thunderstorms, cloud‐to‐ionosphere discharges, ball lightning, nebular lightning, Chondrule production in meteorites, and a new universal electric‐cusp type plasma reactor.

Galactic Neutral Hydrogen Emission Profile Structure

Analysis of Galactic neutral hydrogen emission profiles that have been corrected for sidelobe radiation confirm the existence of three distinct component line width regimes identified by Verschuur & Magnani in 1994. In addition, a fourth becomes recognizable in the data in directions of low total column density. The line width regimes are around 50 km s-1 (component 1a), 31 km s-1 (component 1b), 13 km s-1 (component 2), and 5.2 km s-1 for the narrow lines arising from cool H I (component 3). In this paper, the new data are presented and compared with previously published results. The possible origin of the distinct line width regimes is briefly examined, and it is concluded that a new interpretation is needed, one that involves a plasma phenomenon known as the critical ionization velocity, which will be fully discussed in a subsequent paper.

Molecular model of phenolic polymer dissolution in photolithography

The resolution of photolithographic processes has advanced to the point that difficulties, such as line-edge roughness, associated with phenomena occurring at molecular length scales are becoming important. In order to control these phenomena, it is necessary to understand them. To that end, a numerical model has been used to simulate the dissolution of phenolic polymers in aqueous base. The simulation applies the Critical Ionization Model to a rectangular-lattice representation of the polymer matrix. The model has been adapted to describe the dissolution process that is responsible for photoresist function. Both continuum and molecular versions of the model are presented. The Continuum Model yields dissolution profiles that approximate the contours of the calculated spatial variations in chemical blocking (blocking profile). An algorithm has been developed to connect individual cells to form polymer chains, and to fill the lattice in a way that produces a Gaussian chain length distribution. The model employs only a single adjustable parameter, the time-step correction factor (assuming one can measure the probability of ionization once a site encounters the developer). The Molecular Model predicts a dissolution rate that decreases non-linearly with respect to degree of chemical blocking, as is observed experimentally. Dissolution profiles can be generated with the Molecular Model based either on this calculated dependence of the dissolution rate on blocking fraction or from direct application of the model to a blocking profile. The probabilistic nature of the model introduces edge roughness of the same degree as that observed experimentally. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2103–2113, 1999

Chemical Quantitative Analysis of Small Precipitates in the FE-SEM Using the Energy Distribution of Backscattered Electrons

Abstract Low voltage scanning electron microscopy with a field emission source allows characterization of materials with high spatial resolution. This high resolution comes from the low incident energy which gives a small interaction volume (about 10 nm in Fe at 1 keV ), from the field emission source which gives a small probe size (about 2.5 nm in the most recent FE-SEM) and from virtual, or through the lens, secondary electron detectors with gives high collection efficiency and eliminates some of the SEII and all the SEIII- For example, it has been shown that 10 nm NbC inclusions in steels can be imaged in such FE-SEM at 2 keV (this work was performed with a HITACHI S-4500). However, quantitative x-ray analysis of such precipitates are difficult because the critical ionization energy of the Nb Lα lines is equal to 2.37 keV, an incident electron energy of at least 5 keV must be used to get significant x-ray counts rates.

Ionization mechanisms in CRRES chemical releases: 1. In situ measurements and model results

The quadrupole ion mass spectrometer (QIMS) measured fluxes of barium and strontium ions during the CRRES G‐1 chemical release in full Sun and the G‐11b release in darkness. The barium ion fluxes detected in darkness were only a factor of 10 lower than the photoionization fluxes, indicating that the rate of nonsolar‐UV ionization was at least a factor of 8 higher than literature values of charge transfer and collisional ionization cross sections would suggest. Model calculations of the QIMS ion fluxes using new, state‐specific, calculations of the cross sections for ion‐pair formation and charge transfer [Wolf and Hunton, this issue] demonstrate that the large nonphotoionization rates are consistent with significant metastable excitation in the neutral cloud but not with a ground state population. Upper limits to the collisional ionization rates for the conditions of the releases are 4.3 × 10−3 s−1 for ion‐pair production and 2.2 × 10−3 S−1 for charge transfer. Collisions of high‐energy electrons with the neutrals early in the cloud expansion is suggested as a mechanism for producing the metastable metal atoms. A similar analysis of the strontium data indicates that photoionization, charge transfer, and collisional ion‐pair production alone cannot explain the large fluxes of strontium ions detected in the sunlit release. Associative ionization may therefore be an important ionization mechanism for that metal in sunlight. The implications of these results for analysis of space critical ionization velocity experiments are discussed.

Interaction of the Solar Wind with Comet Hale‐Bopp: Global Interaction and Microphysics

Comet Hale-Bopp, discovered at a heliocentric distance of ~7.2 AU, promises to become a striking spectacle as it approaches perihelion (~0.914 AU) on 1997 April 1. In this paper we describe the changes of the global interaction of the comet with the solar wind and some of the associated microphysics as the comet follows its trajectory from 4 AU to 1 AU from the Sun. Hale-Bopp's production rate of H2O at 4 AU is comparable to that of Halley's comet at the latter's encounter distance of ~0.9 AU. It is shown that while Hale-Bopp's H2O production rate may increase by 3.5-6 orders of magnitude in this range of heliocentric distances, depending on the assumed model of nuclear rotation, the dimensions of the region over which the solar wind is strongly perturbed as measured by the cometocentric distance of the cometary bow shock changes by only 1 order of magnitude. This effect primarily arises from the increasingly strong depletion effect of neutral particles ("neutrals") as the comet approaches the Sun. Because of this effect, the size of the shock at 1 AU is less than its size at 2 AU, despite the larger production rate of H2O at the smaller distance. Also, although this shock is always produced by mass loading of the inflowing solar wind by heavy cometary ions, its nature changes from "soft" or typically "comet-like" at large heliocentric distances to "hard" or "planet-like" near perihelion. This neutral depletion effect has important consequences for the microphysics as well. Strong Alfvén wave turbulence, which served as a distant precursor of the bow shock of Halley's comet, will not be generated by Hale-Bopp near perihelion. Also, downstream of the shock, the excitation of MHD waves, which led to the isotropization of "pick-up" cometary ions in the solar-wind frame near Halley's comet, will be suppressed, leading to a highly anisotropic (ring-type) distribution near Hale-Bopp. It is also shown that electron energization resulting from lower hybrid turbulence leads to observable X-ray emission, which will become progressively harder as the comet approaches the Sun. Finally, it is argued that the Townsend criterion for a discharge produced by energetic electrons is likely to be more easily fulfilled by comet Hale-Bopp at heliocentric distances of ≤3 AU than by Halley's comet at encounter, thereby leading to anomalous ionization of the neutral gas outflow by the so-called Alfvén or critical velocity ionization mechanism.

Spectra of High-Ionization Seyfert 1 Galaxies: Implications for the Narrow-Line Region

We present line profiles and profile parameters for the narrow-line regions (NLRs) of six Seyfert I galaxies with high-ionization lines: MCG 8-11-I1, Mrk 79, Mrk 704, Mrk 841, NGC 4151, and NGC 5548. The sample was chosen primarily with the goal of obtaining high-quality [Fe VII] λ6087 and, when possible, [Fe X] λ6374 profiles to determine if these lines are more likely formed in a physically distinct coronal line region" or are formed throughout the NLR along with lines of lower critical density (n_cr_) and/or ionization potential (IP). We discuss correlations of velocity shift and width with n_cr_ and IP. In some objects, lines of high IP and/or n_cr_ are systematically broader than those of low IP/n_cr_. Of particular interest, however, are objects that show no correlations of line width with either IP or n_cr_ In these objects, lines of high and low IP/n_cr_ are remarkably similar, which is difficult to reconcile with the classical picture of the NLR, in which lines of high and low IP/n_cr_ are formed in physically distinct regions. We argue for similar spatial extents for the flux in lines with similar profiles. Here, as well as in a modeling-oriented companion paper (Paper II), we develop further an idea suggested by Moore & Cohen that objects that do and do not show line width correlations with IP/n_cr_ can both be explained in terms of a single NLR model with only a small difference in the cloud column density distinguishing the two types of object. Overall, our objects do not show correlations between the full width at half- maximum (FWHM) and IP and/or n_cr_. The width must be defined by a parameter that is sensitive to extended profile wings in order for the correlations to result. In Paper II, we present models in which FWHM correlations with IP and/or n_cr_ result only after simulating the lower spectral resolution used in previous observational studies. The models that simulate the higher spectral resolution of our observational study produce line width correlations only if the width is defined by a parameter that is more sensitive to extended profile wings than is the FWHM. Our sample of six objects is in effect augmented by incorporating the larger sample (16 objects) of Veilleux into some of our discussion. This paper focuses on new interpretations of NLR emission-line spectra and line profiles that stem directly from the observations. Paper II focuses on modeling and complements this paper by illustrating explicitly the effects that spatial variations in electron density, ionization parameter, and column density have on model profiles. By comparing model profiles with the observed profiles presented here, as well as with those presented by Veilleux, Paper II yields insight into how the electron density, ionization parameter, and column density likely vary throughout the NLR.

Momentum coupling in the “CRIT II” critical ionization velocity experiment

A unified theory has been developed to explain the formation of a quasi‐dc electric pulse (ω ≤ Ωi) induced by an ionizing neutral barium beam across an ionospheric plasma. We obtained a generalized form for the dc electric field in the plane perpendicular to the magnetic field within a simplified slab barium cloud moving perpendicular to the geomagnetic fields. A current system associated with the quasi‐dc electric field was also proposed to provide a way to transfer the momentum between the streaming barium cloud and the ambient plasma. The characteristic time derived by using this model for momentum coupling between the streaming barium cloud and the ambient plasma is found to be in agreement with the previous result. The quasi‐dc electric field predicted by this model is reasonably consistent with the “CRIT II” critical ionization velocity measurements. On the basis of the constrains of the conservation of energy and momentum, we found that Alfvén's critical ionization velocity (CIV) effect is a self‐limiting ionization process in a finite extent neutral cloud. It may be the reason why the CIV effect took place in CRIT II but lasted only for a very short period, and it may have resulted in low ionization yields in most of space CIV experiments.

CRIT II electric and magnetic observations inside and outside an ionizing neutral jet

The full electric and magnetic field data set from the subpayload of the CRIT II sounding rocket experiment is presented for the first time. CRIT II was an ionospheric injection experiment aimed at studying the critical ionization velocity (CIV) effect. It consisted of two payloads located on nearly the same magnetic field line. By using the data from both payloads, we are able to reach a good understanding of the momentum transfer between the injected ions and the ambient ionosphere. The data also make it possible to resolve the conflict between the two competing models for the energy transfer from the newly created ions to hot electrons in the CIV process. The results give a natural coupling between the energy and momentum transfer processes in CIV experiments.

Far-Infrared Observations of the Radio Arc (Thermal Arches) in the Galactic Center

view Abstract Citations (23) References (56) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Far-Infrared Observations of the Radio Arc (Thermal Arches) in the Galactic Center Timmermann, Ralf ; Genzel, Reinhard ; Poglitsch, Albrecht ; Lutz, Dieter ; Madden, Suzanne C. ; Nikola, Thomas ; Geis, Norbert ; Townes, Charles H. Abstract We report far-IR spectroscopy in [O III] 52 and 88 μm, [N III] 57 μm, and [O I] 63 μm of the "sickle" (GO. 18-0.04) in the Galactic center radio arc. We also mapped the entire eastern region of the arched filaments, including the "banana" (GO. 10+0.02) in [O III] 88 μm. These observations and the recent detection of three near-IR He I/H I emission-line stars near the "sickle" strongly support the concept of a combined H II/photodissociation region (PDR). G0.18-0.04 is a low-density H II region with ne ≍ 600 cm-3 that is most likely excited by stars of type earlier than O8 located in the Quintuplet cluster. Ionization of the arched filaments and the "sickle" by fast shocks or the "critical ionization mechanism" can be ruled out. We derive a fractional abundance ratio for [N]/[O] = 0.30-0.35 consistent with observations of other H II regions in the vicinity of the Galactic center. Unusually wide [O III] 88 μm emission lines of widths FWHM = (70-110) km s-1 have been detected in the mapped region of GO.18-0.04. The large intrinsic line widths may be related to the interaction of the plasma with strong magnetic fields that are known to be present in the radio arc. Publication: The Astrophysical Journal Pub Date: July 1996 DOI: 10.1086/177506 Bibcode: 1996ApJ...466..242T Keywords: GALAXY: ABUNDANCES; ISM: INDIVIDUAL ALPHANUMERIC: G0.10+0.02; ISM: INDIVIDUAL ALPHANUMERIC: G0.15-0.05; ISM: INDIVIDUAL ALPHANUMERIC: G0.18-0.04; GALAXY: CENTER; ISM: H II REGIONS full text sources ADS | data products SIMBAD (11)

Micellar Properties of Sodium Sulfopropyl Alkyl Maleates in Aqueous SolutionA Time-Resolved Fluorescence Quenching Study

The aggregation behavior of four sodium sulfopropyl alkyl maleates with alkyl chain carbon numbers 12, 14, 16, and 18 has been investigated in aqueous solution as a function of surfactant concentration, added sodium chloride concentration, and temperature by means of electrical conductivity and time-resolved fluorescence quenching (TRFQ). Critical micelle concentration and micelle ionization degree decrease upon increasing chain length, exhibiting the classical behavior for straight alkyl chain surfactants, whereas the Krafft temperature, TK, increases. The aggregation numbers have been found to decrease with increasing temperature between TK and 65 °C, with the magnitude of decrease becoming higher for longer hydrophobic chains. The surfactants show micellar growth with surfactant and salt concentration. Whereas the increase of the aggregation number N with ionic strength I is generally weak and follows in good approximation the power law relation N ∝ Iβ, with a unique exponent β ≅ 0.13 below a surfactan...

The yield of ionization in critical ionization velocity space experiments

We compare the conditions in laboratory and space critical ionization velocity (CIV) experiments. One significant difference that comes to light is the rapid expansion of the neutral cloud in space experiments, which does not take place in the laboratory. This has important ramifications for the ultimate ionization yield if there is a time delay in the ignition of the CIV discharge. We find that a simple kinetic model implies that the delay time of CIV ignition is a critical factor in determining the ultimate yield of the experiment. Although the delay time is difficult to calculate precisely, we provide some estimates that predict low CIV yield for typical space experimental geometries, densities and expansion rates. We examine the possibility of the variation of experimental conditions to maximize yield, but find that natural limitations in the design of space experiments may lead to low yields in the best of circumstances. This implies that experiments to date neither prove nor disprove the relevance of the CIV process to cosmology.