Two wavelength laser interferometer for plasma diagnostics.
Plasma electron density measurement method using beat frequencies between two dual frequency lasers
ELECTRON DENSITY↗
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Rocket observations of electron densities in the night-time auroral E-region at Fort Churchill, Canada.
Rocket measured electron densities of nighttime auroral E region over Canada at different magnetic activity levels, noting frequency and plasma density relations
Matsushita, S.↗
Interplanetary magnetic holes: Theory
Magnetic holes in the interplanetary medium are explained as stationary, non-propagating, equilibrium structures in which there are field-aligned enhancements of the plasma density and/or temperature. Magnetic anti-holes are considered to be associated with depressions in the plasma pressure. In this model, the observed changes in the magnetic field intensity and direction are due to diamagnetic currents that are carried by ions which drift in a sheath as the result of gradients in the magnetic field and in the plasma pressure within the sheath. The thickness of the sheaths considered is approximately a few ion Larmor radii. An electric field is normal to the magnetic field in the sheath. Solutions of Vlasov's equation and Maxwell's equations are presented which account for several types of magnetic holes, including null-sheets, that were observed.
Burlaga, L. F.↗
Upper hybrid and Langmuir turbulence in the auroral E region
Oscillations at a frequency between the local upper hybrid and plasma frequencies have been detected in the upper E region of the morning auroral oval. The emission occurs in a narrow band of frequencies when the dipole antenna is nearly perpendicular to B but broadens when the antenna has a component parallel to B. The waves have a low-altitude cutoff at about 125-130 km, and their intensity increases in regions of low plasma density. No theoretical explanation yet exists for these waves, which may be the manifestation of a plasma instability process due to the suprathermal electron flux which accompanies collisional ionization in the auroral E region.
Kelley, Michael C.↗
Very Large Array-RATAN 600 observations of a solar active region
VLA-RATAN-600 observations of the sun around the partial solar eclipse in July 1990 are discussed. The relatively flat spectrum of the extended emission is attributed to the optically thin thermal bremsstrahlung of electrons trapped in a magnetic loop at coronal temperatures. Step-spectrum sunspot-associated emission is attributed to thermal gyroresonance radiation at different heights along the leg of a loop joining regions of positive magnetic polarity. Comparisons with predicted distributions of gyroresonance radio indicate that compact sunspot-associated sources lie at heights of 2500-17,500 km above the photosphere. Differences in the observed and predicted microwave emission suggest an inhomogeneous distribution of thermal plasma in the corona above the sunspot or the presence of localized flux tubes containing higher density plasma or nonpotential fields.
Bogod, V. M.↗
Wave-particle transport from density drift instabilities - A comparison of local and nonlocal theories
Second-order Vlasov theory is used to compute the dissipation rates of plasma irregularities with a variety of shapes. A derivation of the nonlocal dispersion equation using linearized Vlasov theory is presented. Expressions for the normalized amplitudes of the first-order plasma density and electrostatic potential fluctuations are derived. Expressions are given for the saturation amplitudes of the electrostatic eigenmodes. The wave-particle transport and irregularity dissipation rate are computed by using formulas whose derivation is presented. Computational results for specific density variations are shown, and conclusions on the validity of the local theory as opposed to the nonlocal theory are given.
Bernhardt, P. A.↗
Disentangling core and edge mechanisms of the density limit in DIII-D negative triangularity plasmas
The density limit is investigated in the DIII-D negative triangularity plasmas which lack a standard H-mode edge. We find the limit may not be a singular disruptive boundary but a multifaceted density saturation phenomenon governed by distinct core and edge transport mechanisms. Sustained, non-disruptive operation is achieved at densities up to 1.8 times the Greenwald limit ($n_\mathrm{G}$) until the termination of auxiliary heating. Systematic power scans show distinct power scalings for the core ($n_e \propto P_\mathrm{SOL}^{0.27\pm0.03}$) and edge ($n_e \propto P_\mathrm{SOL}^{0.42\pm0.04}$) density limits. The edge density saturation is triggered by the onset of a non-disruptive, high-field side radiation front and the associated cooling, which clamps the edge density below . In contrast, the core density continues to rise until it saturates, a state characterized by enhanced core turbulence. Core transport evolves from a diffusive to an intermittent, avalanche-like state, as indicated by heavy-tailed probability density functions (kurtosis ≈ 6), increased Hurst exponents, and a $1/f$-type power spectrum. These findings suggest that the density limit in the low-confinement regime is determined by a combination of edge radiative cooling and core turbulent transport. This distinction provides separate targets for control strategies aimed at extending the operational space of future fusion devices.
density limit↗
CRIT II electric, magnetic, and density measurements within an ionizing neutral stream
Measurements from rocket-borne sensors inside a high-velocity neutral barium beam show a-factor-of-six increase in plasma density in a moving ionizing front. This region was colocated with intense fluctuating electric fields at frequencies well under the lower hybrid frequency for a barium plasma. Large quasi-dc electric and magnetic field fluctuations were also detected with a large component of the current and the electric field parallel to B(0). An Alfven wave with a finite electric field component parallel to the geomagnetic field was observed to propagate along B(0), where it was detected by an instrumented subpayload.
Swenson, C. M.↗
Plasma flow generation and particle acceleration from expanding magnetic bubbles
Impulsive plasma dynamics in the laboratory are often driven by rising electric currents, yet their quantitative plasma response has not been well established. By means of fully kinetic particle-in-cell simulations and laser-driven capacitor-coil experiments, we show that a rising current expels plasma, forming an expanding magnetic bubble and accelerating particles. The expansion front velocity scales with the Alfvén speed determined by the magnetic field at its inner edge and the plasma density at its outer edge. This mechanism establishes impulsive current drive as a fundamental way that generates plasma flows and accelerates particles in laboratory plasmas, with potential relevance to astrophysics.
Zhang, Yang [Princeton University, NJ (United Stat↗
Plasma waves in the dayside polar cusp. I - Magnetospheric observations.
General survey of the Ogo 5 plasma-wave measurements for the dayside polar-cusp encounters of Nov. 1, 1968, and detailed analysis of the observations at the low-altitude (r approximately 3 to 5 earth radii) cusp boundaries. The survey section contains an overall discussion of the ULF magnetic-field wave levels and the VLF electric-field amplitude ranges measured from perigee out to 9 earth radii on Nov. 1, 1968. These cusp-associated observations are compared with those made on Oct. 27 and Nov. 6, 1968, when Ogo 5 traversed the dayside magnetosphere without encountering the cusp. It is shown that at the November 1 low-altitude cusp boundaries intense wave levels were detected over a broad spectral region at the steep gradients in cusp plasma density and thermal energy. The results are interpreted in terms of drift instabilities for low-beta plasmas with hot ions, and associated wave-particle and wave-wave interactions are briefly discussed.
Scarf, F. L.↗
Substorm-associated reconfiguration of the dusk side equatorial magnetosphere - A possible source mechanism for isolated plasma regions
A rapid reconfiguration of the dusk side magnetosphere was observed near the magnetic equator by particle and field experiments aboard Explorer 45 at 1715 UT on June 17, 1972. Following the onset of an 800-gamma negative bay in the auroral zone, Explorer 45, inbound at 1700 MLT and L about 5, observed a sharp dropout of outer zone electrons. Simultaneously, the plasma density dropped from a level typical of the plasmasphere to one typical of the ion trough, and plasma sheet proton fluxes increased, producing a 100-gamma depression in B, in a shift to a taillike configuration. Outer zone electrons with pitch angles near 45 deg returned with delay times consistent with injection near midnight at the time of dropout and eastward drift to the dusk meridian. Approximately 45 min after the reconfiguration, the satellite reentered the plasmasphere, and the electron fluxes returned to previous levels. In the next orbit, approximately 6 hours later, a region of isolated plasma was detected near apogee at 1400 MLT. There is therefore circumstantial evidence that the type of magnetospheric reconfiguration observed here is responsible for the detachment of regions of cold plasma from the plasmasphere.
Barfield, J. N.↗
Interpretation of neutral particle analyzer measurements on plasmas having azimuthal drift
The theoretical model accounts for drift and cyclotron components of ion motion in a partially ionized plasma. Density and velocity distributions are systematically prescribed. The flux into the neutral particle analyzer (NPA) from this plasma is determined by summing over all charge exchange neutrals in phase space which are directed into apertures. Calculation of the process is continued through the NPA using appropriate cross section data to obtain analyzer output distributions. Theoretical results were compared with NPA measurements on four plasma heating devices having radial electric, E, and axial magnetic, B, fields. Drift velocity, in the azimuthal direction is identified with E/B. Selection of randomized cyclotron velocity distributions about mean azimuthal drift yield energy distributions which compare well with experiment.
Englert, G. W.↗
Heating and cooling of the earth's plasma sheet
Magnetic-field models based on pressure equilibrium in the quiet magnetotail require nonadiabatic cooling of the plasma as it convects inward or a decrease of the flux tube content. Recent in situ observations of plasma density and temperature indicate that, during quiet convection, the flux tube content may actually increase. Thus the plasma must be cooled during quiet times. The earth plasma sheet is generally significantly hotter after the expansion phase of a substorm than before the plasma sheet thinning begins and cools during the recovery phase. Heating mechanisms such as reconnection, current sheet acceleration, plasma expansion, and resonant absorption of surface waves are discussed. It seems that all mechanisms are active, albeit in different regions of the plasma sheet. Near-earth tail signatures of substorms require local heating as well as a decrease of the flux tube content. It is shown that the resonant absorption of surface waves can provide both.
Goertz, C. K.↗
Evidence of auroral plasma cavities at Uranus and Neptune from radio burst observations
Radio bursts originating from the stronger magnetic polar regions of both Uranus and Neptune were detected by the planetary radio astronomy experiment during the Voyager 2 encounters with the planets. It has previously been demonstrated that these bursts are beamed into a broad, hollow emission pattern from their auroral sources. It is now shown that the bursts at both planets also manifest similar detailed patterns, with the waves beamed into two separate and distinct radiation cones at intermediate wave frequencies. This double-cone emission pattern is predicted by relativistic cyclotron resonance theory, and application of this theory to the observed emission pattern yields the plasma density structure within the radio source region. Calculations indicate that at both Uranus and Neptune the plasma-to-cyclotron frequency ratio can drop well below 0.01 within the active region. Such low values indicate that the southern auroral zones at both planets contain an auroral plasma cavity that is similar to that found in earth's nightside auroral zone.
Farrell, W. M.↗
Density drop at the divertor target in the prototype material plasma exposure eXperiment (Proto-MPEX)
The steady-state linear device “Material Plasma Exposure eXperiment” (MPEX) is currently under construction at Oak Ridge National Laboratory with the goal of enabling Plasma-Material Interaction studies at future fusion reactor relevant plasma conditions. In this work, a newly in-house developed hybrid Particle-In-Cell code-PICOS++ is applied to understand the experimental results obtained from the prototype of MPEX referred to as the “Proto-MPEX” during its helicon-only and helicon with ion cyclotron resonance heating (ICRH) experiments. This study explains the physics of the experimentally observed plasma density-drop at the divertor target in Proto-MPEX device during ICRH. In contrast to previous work on ICRH in MPEX, this study demonstrates that the mirror force plays a central role in the Proto-MPEX plasma transport during ICRH, which has new features not previously explored. Force balance analyses reveal that the temperature anisotropy produced by ICRH leads to a significant increase in the mirror force downstream of the resonance where the magnetic field is diverging. This force accelerates ions toward the target and leads to a drop in plasma density to ensure conservation of particle flux. Simulations with ICRH where the magnetic field divergence downstream of the resonance has been removed, do not produce plasma acceleration nor density drop at the target despite efficient ion heating at the resonance. Moreover, simulation results demonstrate that for a given ICRH power, lowering the source rate produces ions with increased perpendicular energy which interact with the mirror force to produce higher plasma acceleration which increases the strength of the density-drop at the target. The strength of the density drop appears to reach an asymptotic limit at a certain threshold ICRH power. Simulations show that this threshold power increases with increasing particle source rate.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Correcting for Background in Flowing Plasma Measurements
Movable langmuir probe measures charge-exchange plasma density and flow in vicinity of an ion engine. Angular dependence of probe current is utilized to determine plasma flow direction at probe location. By rotating target, data are shown to be independent of target-sputtered ions.
Carruth, M. R., Jr.↗
Results of the AEROS satellite program: Summary
Published literature reporting aeronomic data collected on two AEROS missions is summarized. The extreme ultraviolet solar radiation and other significant parameters of the thermosphere/ionosphere were investigated. Kinetic pressure, the quantity of atomic nitrogen, and partial densities of helium, oxygen, nitrogen, argon, and atomic nitrogen were determined. The thermal electron population, superthermal energy distribution, plasma density, ion temperature, and composition according to ion types were measured. The chief energy supply in the thermosphere was calculated. Aeronomic calculations showing that variations in the parameters of the ionosphere cannot be correlated with fluctuations of extreme ultraviolet solar radiation were performed. The AEROS data were compared with data from S3-1, ISIS, and AE-C satellites. Models of the thermosphere and ionosphere were developed.
Lammerzahl, P.↗
Model exospheres of the ringed planets
The theory of rotating ion exospheres in dipolar magnetic field geometries is used to predict certain effects of the rings on the inner plasmaspheres of the ringed planets Jupiter, Saturn, and Uranus. The analysis here assumes a purely ionospheric source. It is found that if rings affect only the trapped plasma, the cold plasma density at Saturn will be either reduced or increased by a factor of approximately 2 at L = 1.65, depending on whether the ring populates or empties the trapped trajectories. It is found that if all cold plasma particles on trapped orbits are absorbed and the rings are not a source of plasma, this simple exospheric theory can explain the ionospheric density profile inferred from the Pioneer 11 Saturn radio occultation experiment, in which a localized peak in the profile was observed on field lines threading the Guerin division between the C and D rings.
Luhmann, J. G.↗