Ion Bursts Research Articles

The spatial distribution of energetic ions and electrons in the magnetotail

The spatial distributions of energetic ion and electron bursts observed on the IMP 7 and 8 satellites in the Earth's magnetotail were studied. It was found that the ion bursts were more frequently detected in the dusk than in the dawn quarter of the neutral sheet whereas the electron bursts, more frequently in the dawn than the dusk quarter. The degree of dawn-dusk asymmetry is however energy dependent; the distribution for higher energy particle bursts exhibits higher degree of asymmetry. The morphologies of the distributions manifest themselves as seasonal variations of the most probable solar ecliptic latitudes at which the ion and electron bursts were observed. The amplitudes of the variations are about 25° with the seasonal variation for ions leading that for electrons by about 2 months.

Spectral analysis of ion-acoustic soliton excitation

The evolution of the frequency spectrum of a velocity modulated burst of ions from a fine mesh grid in a plasma is measured and interpreted. Initial frequency modulation close to the grid indicates a ‘‘klystron bunching’’ of the ions. The measured spectrum far from the grid indicates the excitation of an ion-acoustic soliton.

Plasmoid‐associated energetic ion bursts in the deep geomagnetic tail: Properties of the boundary layer

Energetic (>35 keV) ion bursts in the deep geomagnetic tail associated with the passage of 37 plasmoids are examined using data from the energetic particle anisotropy spectrometer (EPAS) instrument on ISEE 3. These bursts can usually be divided into four distinct phases: (1) strongly tailward streaming ions observed in the lobe for a few minutes prior to plasmoid entry, commencing ∼25 min after geomagnetic substorm onset; (2) the plasmoid interval, when the energetic ions have a broader tailward angular distribution arising from convection with the plasmoid; (3) the “post‐plasmoid” plasma sheet, where more strongly tailward streaming ions are observed in the plasma sheet on field lines disconnected from the earth at the substorm neutral line; and (4) a strongly tailward streaming ion population extending into the lobe for a few minutes after exit from the plasma sheet. We concentrate here on the streaming ion “boundary layers” observed in the lobe at the leading and trailing edges of these bursts. In a majority of these layers, a clear dawn‐dusk gradient anisotropy and energy dispersion are evident at the leading edge, and a similar gradient anisotropy with “reverse” dispersion is evident at the trailing edge. It is shown however that the dispersion at onset is not consistent with simple time of flight from a near‐earth neutral line or from a neutral line retreating tailward during substorm recovery. Instead, observations of 90° pitch angle ions with a time resolution of 16 s are used to infer that the ion onset is due to a layer of energetic ions expanding outward from the tail center plane and engulfing the spacecraft. At the trailing edge of the burst, this layer contracts back across the spacecraft toward the center plane. Mean expansion and contraction speeds are 94±74 km s−1 and 99±100 km s−1 respectively, with boundary layer thicknesses of ∼3 RE. From these observations, it is concluded that the expansion of the ion layer is caused predominantly by the ion layer being swept across the spacecraft by the arrival of the plasmoid in the deep tail, contributing ∼60 km s−1 to the expansion speed, rather than by a thickening of the region of lobe field lines disconnected at the substorm neutral line which expands at ∼35 km s−1. The energy dispersion at the leading edge can be reconciled with a near‐earth neutral line in this case. Using this dispersion and the measured expansion speed of the layer, the electric field along the near‐earth substorm neutral line is deduced. Values derived from layer expansions and contractions are both ∼0.4 mV m−1, equivalent to ∼110 kV across a ∼40‐RE tail width.

Localized auroral disturbance in the morning sector of topside ionosphere as a standing electromagnetic wave

An intense, localized auroral disturbance observed by Intercosmos-Bulgaria-1300 satellite in the morning sector at the altitude 850 km is analyzed in detail. The disturbance is characterized by strong “jumps” of electric and magnetic fields reaching ∼ 80 mV/m and ∼ 100 nT, fluctuations of ion density ( Δn/ n ∼ 70%) and bursts of downward and upward energetic electron fluxes. Electric and magnetic disturbances display a distinct spatial-temporal relationship typical for the standing quasi-monochromatic wave ( ƒ ∼ 1 Hz, λ x ∼ 10 km ). The ratio of amplitudes of electric and magnetic fluctuations is equal to Alfvén velocity ( ΔE/ ΔB ∼ v A / c). However, a strong parallel component of the electric field (∼ 30 mV/m) and large ion density fluctuations indicate significant changes of plasma properties (the effects of anomalous resistivity are possible).

Energetic particles in the comet Halley environment

An overview is presented of electrons, protons and heavier ions (E > 20 keV) recorded by the energetic particle detector EPONA in the Comet Halley environment, 12–15 March, 1986. Pick-up ions were detected at distances of up to at least 7.5 × 10 6 km from the nucleus. Estimates of the energies that typical cometary ions may be expected to acquire from the solar wind pertaining at Encounter show that the pick-up process is insufficient to account for the energies of the particles detected. An additional mechanism must thus be postulated to account for the observed particle signatures. Preliminary correlations with magnetic and plasma wave data from other instruments suggest that the presence of MHD turbulence at several million kilometers upstream of the bowshock may have contributed to the acceleration of the first pick-up ions observed. The bowshock boundary (inbound) does not appear to have constituted a location where particle acceleration to high energies took place. Downstream of the shock boundary, hardening of the energy spectrum and the development of less anisotropic particle streaming was observed to occur when the spacecraft was in a turbulent environment ∼ 1 × 10 6 km from the nucleus. The waxing influence of mass loading as a mechanism for reducing energetic particle fluxes as well as the depletion of energetic ions due to their escape along open field lines and to charge exchange collision with neutrals in a progressively more stagnant solar wind, may be inferred in a regime (seen on the magnetometer data to be largely non-turbulent) traversed by the spacecraft from ≀ 5 × 10 5 km from the nucleus to within the magnetic pile-up region. A major burst of ions and electrons (not yet established to be of cometary origin) occurred when the spacecraft was close to the Contact Surface. A population of high energy electrons (from 180 keV to at least 300 keV) was detected for about one hour before Closest Approach and for several hours thereafter. Also an energetic beam of electrons was identified exiting from a location at about 1 × 10 6 km from the nucleus (outbound). Finally, differences between inbound and outbound particle signatures are described.

On grid launched linear and nonlinear ion-acoustic waves. II

For pt.I, see ibid., vol.24, p.1483 (1980). A series of experiments is described on grid excited ion-acoustic solitons. Particular attention is paid to ion bursts which are accelerated through the grid by the exciting potential and their role in launching the soliton. It is found that the soliton is launched a finite distance in front of the grid. A mechanism for excitation is proposed.

Energetic particle transport in the upstream region of Jupiter: Voyager results

Using Voyager 1 and 2 energetic (≳ 30 keV) ion measurements near the magnetopause, in the magnetosheath, and immediately upstream of the Jovian bow shock, the available ion compositional patterns have been examined together with typical energy spectra in each of these regions. Field‐aligned, highly anisotropic ion bursts occurring early in most upstream events have relatively low fluxes of electrons and heavy ions associated with them. Characteristic spectral changes are found late in long‐lived ion events at the same time that heavy ion and energetic electron fluxes are enhanced. The interplanetary magnetic field is always connected toward the dawn side of the planet late in this subset of upstream events at the time that relativistic electrons and heavy ions are high. A model emphasizing energetic particle escape in the prenoon part of the Jovian magnetosphere late in events is presented to explain many of the upstream region features.

The generalized function solution of the Fokker–Planck equation for monoenergetic charged particle transport

The solution of the Fokker–Planck equation describing the motion of an isotropic burst of ions originating at the center of an infinite medium and undergoing small angle deflections is obtained in terms of generalized functions using the multiple collision approach. The resulting solution can be shown to define a functional on the test function space Sβα for α≥ 1/2 and β≤ 1/2 and the space of polynomials specifying the dynamic moments.

Formation of Ion Phase-Space Vortexes

The formation of ion phase space vortexes in the ion two stream region behind electrostatic ion acoustic shocks are observed in a laboratory experiment. A detailed analysis demonstrates that the evolution of such vortexes is associated with ion-ion beam instabilities and a nonlinear equation for their initial evolution is derived. The results are supported by a numerical particle simulation. Also the possibility of vortex excitation by ion bursts and coalescence of two vortexes are demonstrated. The effects of finite ion temperature, particle trapping and charge exchange collisions are discussed and the results related to ionospheric observations.

Multipurpose Beam Pulsing System for the 12UD Pelletron Tandem Accelerator at the University of Tsukuba

A beam pulsing system has been developed for a 12 MV tandem accelerator. The system consists of a pre-acceleration chopper, a klystron buncher and a post-acceleration chopper. The pre-acceleration chopper comprises a slow chopper and a fast travelling-wave chopper. Pulsed beams with widths in the range from 10 µs to ∼2 s are obtained with the slow chopper, and the repetition periods can be varied from 70 µs to 4 s. The fast chopper produces ion bursts having widths between 0.05 and 0.8 µs with a duty factor of ∼10%. The buncher is operated with the two choppers to obtain beam pulses as narrow as a few nanoseconds. Time-of-flight measurements yielded pulse widths 2–4 ns (FWHM) wide for ions in the mass range 1≦A≦28. The ratio of the dark to peak ion current was usually of the order of 10-4.

Current sheet acceleration of ions in the geomagnetic tail and the properties of ion bursts observed at the lunar distance

Recent analyses of measurements obtained from the Rice University Apollo 14 SIDE on the lunar surface have revealed the frequent appearance of fast tailward-streaming ion “bursts” near the centre plane of the geomagnetic tail. In this paper the properties of these “bursts” are tested for compatibility with tail current sheet tangential stress balance conditions assuming that they are produced by current sheet acceleration of tail lobe plasma downstream and tailward of a magnetic neutral line. Calculations are performed taking the ions to be either protons or singly charged oxygen, the latter possibility being directly suggested by several recent observations. When “burst” bulk parameters are calculated by assuming that the ion distribution functions are convecting isotropic Maxwellians, the results are found to be difficult to reconcile with current sheet stress balance conditions for either protons or oxygen. Use of a different ion distribution based on theoretical expectations and observations in the near-Earth tail, however, results in number density estimates being increased by factors of around an order of magnitude. When the revised densities and ion distribution functions are taken into account, reasonable agreement between observed and expected ion bulk speeds is obtained. In some cases the agreement is better assuming oxygen ions rather than protons, but not by a large factor.

The distant interplanetary wake of Venus: Plasma observations from Pioneer Venus

In June 1979 the Pioneer Venus orbiter made its first series of passes through the distant solar wind wake of Venus at distances of 8–12 Rv behind the planet. During this period the plasma analyzer aboard the spacecraft detected disturbed magnetosheath plasma that intermittently disappeared and reappeared, suggesting a tattered, filamentary cavity trailing behind the planet. The magnetosheath dropouts almost always occurred inside the region of ‘magnetotail’ observed by Russell et al. Sporadic bursts of energetic ions (E/q ≳ 4 kV) are detected inside and, occasionally, outside the magnetotail; all such bursts are consistent with identification of the ion as O+ of planetary origin moving at the local magnetosheath flow speed. The morphology of the plasma dropouts and of the O+ bursts is analyzed in detail. The cavity appears to contract at times of high solar wind dynamic pressure. The intensity of the O+ component is highly variable, and appears not to be strongly correlated with solar wind dynamic pressure. The most intense bursts correspond to a flux ≲107 ions cm−2 s−1. This maximum flux, if steady and filling a cylinder 1 Rv in radius would correspond to a mass loss rate of ≲1025 ions s−1; the intermittency and variability of the flux suggest that the true mean loss rate is very much lower. The kinetic temperature of the O+ component is estimated as 105–106 K in order of magnitude.

A time-of-flight mass spectrometer for measurement of secondary ion mass spectra

A time-of-flight mass spectrometer has been constructed at the University of Manitoba. In this instrument, bursts of alkali-metal ions of ∼10 ns duration strike a thin layer of organic material deposited onto a metal backing. The secondary ions produced are accelerated across a fixed potential ⩽10 kV, then travel down a flight tube 1.6 m long. Measurement of the time of flight determines the mass-to-charge ratio of the ions. Mass spectra from biomolecules with masses up to 1355 u have been measured with the instrument. They exhibit significant quasimolecular ion peaks.

A direct-inlet mass spectrometer for real-time analysis of airborne particles

A surface-ionization mass spectrometer has been developed for real-time analysis of particles in air. The spectrometer is equipped with an efficient inlet for transmitting air-borne particles directly to the ionizing filament in the ion source, a dispersive mass analyzer for simultaneous measurement of multiple ion beams, and an ion detecting and measuring system which can integrate ion bursts from individual particles over a three-decade size range. The desk-sized instrument requires only electrical power for operation and can be transported to different locations.

Plasma rest frame distributions of suprathermal ions in the Earth's foreshock region

We present rest frame ion distributions computed from three‐dimensional observations of upstream suprathermal ions gained by the University of Iowa Quadrispherical Lepedea on ISEE‐1. The observations are for a single inbound, midmorning pass starting upstream from the ion foreshock and continuing across the quasiparallel bow shock into the magnetosheath. The crossing of the ion foreshock boundary is marked by a several minute burst of ions of temperature 100–200 eV moving along the IMF away from the bow shock at 500 km/s relative to the solar wind. The observation of these ‘reflected’ ions is followed by an extended interval of ‘diffuse’ ions of temperatures 2‐3 keV flowing at ∼250 km/s relative to the solar wind and persisting until the bow shock is crossed. The diffuse ion β has a value of approximately 6 in the region of the suprathermal ions, exceeding the normal thermal ion β of the solar wind by roughly an order of magnitude. Both types of suprathermal ions constitute roughly 2% of the total ion density and carry a parallel heat flux of ∼2 × 10−2 ergs cm−2 s−1. When integrated over an assumed 10 × 10 RE bow shock emission area, this implies an upstream dissipation that may approach 1017 to 1018 ergs/s, comparable to a modest substorm.

Observations of transient H+ and O+ bursts in the equatorial magnetosphere

Twenty‐two days of data from the Lochkeed ion mass spectrometer aboard the Scatha satellite were used to perform a statistical study of short‐lived H+ and O+ bursts observed in the equatorial magnetosphere. The results of the study indicate that the ion bursts were transient phenomena occurring primarily in the nighttime sector during periods of enhanced geomagnetic activity. The average energy of the bursts, 〈W〉, was 1 keV, although the bursts were found to occur over any portion of the instrument's 100‐eV to 32‐keV energy range. Over one third of the observed bursts were associated with field‐aligned electrons flowing from the same hemisphere as the bursts. The energy width (ΔW/〈W〉 ≃1) and the pitch angle width (as great as 30°) of the bursts suggest that the ions had undergone substantial velocity space diffusion close to the geomagnetic equator.

Geos-2 magnetopause encounters: Low energy (

The Suprathermal Plasma Analysers (SPA's) flown on the ESA GEOS spacecraft are well suited to measurements of the plasma populations in the magnetosheath and boundary layer regions. During August 1978 enhancements in solar wind pressure have caused major compressions of the magnetosphere such that on at least 15 occasions, plasma of magnetosheath origin has been observed with the geostationary GEOS-2. Encounter times of up to four hours provide rare opportunities for detailed study of this storm displaced boundary. Intense fluxes of electrons and protons with characteristic energy spectra identify magnetosheath and boundary layer transitions - electron densities exceeding 100 cm −3 result from high solar wind density and the consequent compression. Local heating is evident in the boundary layer but this complex and dynamic region is difficult to characterise; dense bursts of cold plasmapheric ions are observed here in the wake of each compression. The local time pattern of the encounters indicate a strong asymmetry, the post-noon magnetosphere being more resistant to the solar wind impulse than is the morningside. At solar maximum the magnetopause is driven inside 7 Re on the order of 25 times per year.

Ion Heating Due to Double-Layer Disruption in a Plasma

A new mechanism is presented for ion heating in a plasma penetrated by an electron beam. Oscillating potentials comparable to the electron-beam energy are observed below the threshold of the stable double-layer formation. These fluctuations (formation and disruption of double layers) accelerate, trap, and detrap thermal ions, resulting in highly energetic ion bursts, which form a tail on the ion-energy distribution function.

Comment on ‘Magnetosheath burst of predominantly medium nuclei observed with Imp 8 on February 16, 1974’ by T. P. Armstrong, S. M. Krimigis, and R. P. Lepping

Armstrong et al. (1978) report the observation of a unique series of charged particle bursts with an unusually high content of Z >2 particles and a high degree of collimation from the direction of the sun. These bursts were observed only with their CPME (charged particle measurement experiment) instrument on Imp 8, while not with the CPME on Imp 7. No indication has been seen for heavy ion bursts comparable in intensity to those reported by Armstrong et al. (1978) with the ULET (ultralow energy telescope) instrument of the University of Maryland/Max‐Planck‐Institut experiment on Imp 8 at the same time. It is noted that the ULET counting rates observed on Imp 8 are fully compatible with the CPME rates observed on the Imp 7 spacecraft. We conclude that the CPME and the ULET data from Imp 8 during these periods do not agree, and this casts doubt on the correctness of the CPME results for these special events.

Solar wind ion injections in the morning auroral oval

Energy versus time dispersion of precipitating ion bursts was observed during two rocket flights in the morning auroral oval. Individual bursts lasted about 20 seconds and repeated on a time scale of 100 seconds. The dispersion is interpreted as energy‐dependent time‐of‐flight delay which provides identification of ion charge‐to‐mass ratio as well as injection source distance. The data are consistent with injections of magnetosheath ions with injection distances ranging from 7 to 19 earth radii. Individual events extended over a region of at least several degrees of magnetic longitude and 0.3 degrees of invariant latitude. It is suggested that these events are associated with turbulent plasma entry into the magnetospheric entry layer.