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Polar Diagram Polar
Instrument Descriptions

Plasma Wave Instrument

Donald A. Gurnett
Department of Physics and Astronomy
University of Iowa
Iowa City, IA 52242

For additional information see the University of Iowa Plasma Wave Investigators Home Page

The primary goal of the Polar Plasma Wave Investigation (PWI) is to provide comprehensive measurements of plasma wave phenomena in the high latitude auroral zones, in the dayside magnetic cusp regions, and in the plasmasphere and plasmasheet. Coordinated measurements will be made with the plasma, energetic particle, imaging, and magnetic field measurements to study local processes with an emphasis on wave-particle interactions. These studies will be performed in conjunction with measurements from the other GGS and COSTR spacecraft in order to determine the mechanisms of mass, momentum, and energy flow through geospace.

Known natural plasma wave phenomena to be investigated include MHD velocity turbulence associated with magnetospheric plasma convection, magnetic pulsations, electrostatic and electromagnetic ion cyclotron waves, lion roars in the magnetosheath and cusp, magnetic noise bursts and turbulence along auroral field lines, chorus and hiss, whistlers, electrostatic cyclotron harmonics, continuum radiation, and kilometric radiation. These wave phenomena are closely associated with the transport and acceleration of plasma in the earth's magnetosphere. Wave phenomena also provide measurements of important local and remote plasma parameters such as the electron density.

The specific objectives of the Polar Plasma Wave Investigation include the following:

  • Comprehensive measurements of spectral and wave vector characteristics of naturally occurring electromagnetic and electrostatic plasma waves over the frequency range from 0.1 Hz to 800 kHz for wave electric and magnetic fields.
  • Measurement of spectral and wave vector characteristics of electromagnetic and electrostatic plasma waves generated by ground-based active experiments.
  • Analysis of plasma wave measurements in collaboration with other Polar investigations in order to characterize wave-particle processes associated with the auroral zone, the magnetic cusp, the dayside magnetosheath, and the nightside equatorial plasmasheet.
  • Participation in a coordinated effort with investigators on Wind, the Japanese Geotail spaceeraft, Cluster, ground-based experiments, and other ISTP experiments to study global mechanisms of mass, momentum, and energy flow in geospace plasmas.
The Polar Plasma Wave Investigation employs seven distinct sensors for detecting the electric and magnetic fields of plasma waves. These sensors consist of: a pair of orthogonal two-sphere electric antennas in the spin plane of the spacecraft with sphere-to-sphere separations of 100 meters and 130 meters respectively, shared with the Electric Field Instrument (EFI); a short two-sphere electric antenna aligned along the spacecraft spin axis with a sphere-to-sphere separation of 14 meters, also shared with EFI; a triaxial magnetic search coil mounted on the end of a rigid stacer boom, shared with EFI; and a magnetic loop antenna mounted on the same boom and oriented parallel to the 100-meter electric antenna in the spin plane.

The spheres on the electric antennas are 9 cm in diameter and each contains a high-impedance preamplifier that provides signals to the boom deployment mechanisms. Amplifiers in the deployment mechanisms buffer signals to EFI and PWI independently. Each of the three magnetic search coils consists of two bobbins mounted on high permeability micro-metal cores 40cm long. Each bobbin is wound with 10,000 turns of #40 wire. The coil outputs are amplified by a preamplifier in the search coil housing to provide a low-impedance signal to the main electronics box. The search coil sensitivity constant is 70 micro V/nT-Hz and the resonance frequency is approximately 10 kHz. The loop antenna is similar to the magnetic loop antenna on Dynamics Explorer A and is designed to detect magnetic fields over a frequency range from 25 Hz to 800 kHz. The loop sensitivity constant is 385 micro V/nT-Hz and the resonance frequency is 45 kHz.

Hot Plasma Analyzer

Jack D. Scudder
Department of Physics and Astronomy
University of Iowa
Iowa City, IA 52242
For additional information, see the HYDRA home page. HYDRA is a plasma experimental investigation to be performed on the POLAR spacecraft of the GGS program. The scientific objectives fall into three broad categories:
  • to observe the expected kinetic and magnetohydrodynamic signatures of magnetic reconnection in the cusp region; to quantify the energy released to the plasma and the rate of mass flux into the magnetosphere implied; and to understand what external parameters control the rates of reconnection of magnetic flux;
  • to understand the role of field aligned currents in the auroral zone, their relation to auroral forms and terrestrial kilometric radiation, and their response to magnetotail and solar wind stimuli as monitored by the other OPEN spacecraft; to ascertain the altitude dependence of the associated electrical potential and the parameters which control its size
  • a quantitative, high time resolution definition of the regions associated with the cusp and entry layer including a study of the mass and momentum transfer between magnetosheath and entry layer plasmas.

Magenetic Fields Experiment

Christopher T. Russell
Institute of Geophysics and Planetary Physics
University of California, Los Angeles
Los Angeles, CA 90024-1567
(310) 825-3188
For additional information see the UCLA POLAR Magnetometer Team Home Page

The Magnetometer on the Polar Spacecraft is a high precision instrument designed to measure the magnetic fields in the high and low altitude polar magnetosphere. This instrument will be used to investigate the behavior of field-aligned current systems and the role they play in the acceleration of particles and the dynamics of the fields in the polar cusp, magnetosphere, and magnetosheath. The instrument design has been influenced by the needs of the other instruments for immediately useable magnetic field data and high rate (100+ Vectors/Sec) data distributed on the spacecraft. The design provides a fully redundant instrument with enhanced measurement capabilities depending on available spacecraft power.

Toroidal Ion Mass Spectrographs

William K. Peterson
LASP, University of Colorado
1234 Innovation Drive
Boulder, CO 80303
(303) 492-0686 or (303) 492-6444
For additional information see the TIMAS Home Page

The Toroidal Imaging Mass-Angle Spectrograph (TIMAS) instrument measures the full three-dimensional velocity distribution functions of all major magnetospheric ion species with one-half spin period time resolution. The TIMAS is a first order double focusing (angle and energy), imaging spectrograph that simultaneously measures all mass per charge components from 1 AMU/e to greater than 32 AMU/e over a nearly 360 degrees by 10 degree instantaneous field-of-view in 20 milliseconds. Mass per charge is dispersed radially on an anular microchannel plate detector and the azimuthal position on the detector is a map of the instantaneous 360 degrees field of view. With the rotation of the spacecraft, the TIMAS sweeps out a 4pi solid angle image in a half spin period. The energy per charge range from l5eV/e to 32 keV/e is covered in 28 non-contiguous steps spaced approximately logarithmically with adjacent steps separated by about 30%. In order to handle the large volume of data within the telemetry limitations the distributions are compressed to varying degrees in angle and energy, log-count compressed and then further compressed by a lossless technique. This data processing task is supported by two SA3300 microprocessors. The voltages (up to + 5 kV) for the tandem toroidal electrostatic analyzers are supplied from common high voltage supplies using optically controlled series-shunt regulators.

Electric Fields Instrument

Forrest S. Mozer
Space Sciences Laboratory
University of California, Berkeley
Berkeley, CA 94720
The Electric Field Instrument (EFI) on the Polar spacecraft measures the three components of the ambient vector electric field and the thermal electron density. The results are used to study:
  • Parallel and perpendicular electric fields and density variations in double layers, electrostatic shocks, and other time domain structures found in the auroral acceleration region and at other locations in the Polar orbit.
  • The high latitude convection electric field.
  • The electric field and plasma density structure on field lines connected to the high latitude magnetopause, polar cusp, and plasma mantle.
  • Correlations of electric fields with those measured by other ISTP spacecraft at different points along the same magnetic field line or along a common boundary, or in different regions of the magnetosphere.
  • Modes, phase velocities and wavelengths of propagating waves and spatial structures.
The electric field and plasma density measurements are made over a frequency range of DC to above 20 kHz. The dynamic range of the electric field measurement is 0.02 to 1000 mV/m, while the plasma density will be measured at least over the range of 0.1 to 100 particles per cubic centimeter. A by-product of the experiment is measurement of the floating potential of the spacecraft over the range of about +1 to +90 volts.

An important component of the Electric Field Instrument is a two megabyte burst memory that allows storage of high time resolution field and plasma density measurements, allowing study of rapid variations of non-linear spatial structures and waves.

The EFI sensors are arranged as three orthogonal sphere pairs whose potential differences and Langmuir probe characteristics are measured. Two of these sphere pairs are in the satellite spin plane on the ends of wire booms that provide tip to tip sphere separations of 100 and 130 meters respectively, while the third pair is aligned along the spacecraft spin axis with a 14 meter tip to tip separation that is provided by rigid stacer booms.

The electric field preamplifiers have frequency responses to above one mHz to accommodate their use by the Plasma Wave Instrument. In addition, the Electric Field Instrument interfaces on the spacecraft with the Magnetic Field Expirement (which provides information for deciding when to trigger bursts of data collection), the Hydra plasma experiment (in order that both instruments collect high time resolution data simultaneously), and the low energy plasma experiment, Tide, (which wants to know when the Electric Field Instrument is collecting data in the burst mode).

The heritage for the Electric Field Instrument encompasses instruments previously flown on the S3-3, GEOS, ISEE-1, Viking, and CRRES satellites, as well as experiments being built for the Freja, FAST, and Cluster satellites.

For more information see the EFI Home Page

Thermal Ion Dynamics Experiment

Thomas E. Moore
Code 692
Goddard Space Flight Center
Greenbelt, MD 20771
(301) 286-5236
The Thermal Ion Dynamics Experiment (TIDE) and Plasma Source Instrument (PSI) have been developed in response to the requirements of the ISTP Program for three-dimensional plasma composition measurements capable of tracking the outflow of ionospheric plasma throughout the magnetosphere. This plasma is in part lost to the downstream solar wind and in part recirculated within the magnetosphere, participating in the formation of the diamagnetic hot plasma sheet and ring current plasma populations. Significant obstacles which have previously made this task impossible include the low density and energy of the outflowing ionospheric plasma plume and the positive spacecraft floating potentials which exclude the low-energy plasma from detection on ordinary spacecraft. Based on a unique combination of focusing electrostatic ion optics and time of 3 flight detection and mass analysis, TIDE provides the unprecedented sensitivity (seven channels at 0.1 cm2 sr each) and resolution required for this purpose. PSI will produce a low energy plasma locally at the POLAR spacecraft which will provide the ion current required to balance the photoelectron current, along with a low temperature electron population, thus regulating the spacecraft potential at a few tenths of a volt positive relative to the space plasma. Thus it will be possible with TIDE/PSI to:
  1. investigate the extent to which ionospheric ions are recirculated within the distant magnetotail neutral sheet or lost to the solar wind.
  2. investigate the mass dependent degree of energization achieved as ionospheric plasma flows antisunward on merged flux tubes through the lobes and into the distant tail.
  3. thereby investigate the ionosphere as a source of plasma to the plasma sheet and ring current. For additional information see the TIDE Homepage

Ultraviolet Imager

UVI logo

George K. Parks
Geophysics Program
University of Washington
Seattle, WA 98195
(206) 543-0953

The Ultraviolet Imager (UVI) is a two dimensional imager sensitive to far ultraviolet wavelengths. With its 8 degree circular field of view, it will image the sunlit and nightside polar regions of the earth. The UVI is able to detect and provide images of very dim emissions with a wavelength resolution never achievable before. The highly sensitive instrument will conduct observations of both the sunlit and nightside polar regions in the far ultraviolet wavelengths. The resulting images will help quantify the overall effects of solar energy input to the earth's polar regions. Its scientific objectives are to image to aurora simultaneously, to measure the total energy and characterize the energy that is deposited in the auroral regions, to characterize the space and time variations of the aurora, and to help correlate events in the auroral regions to other regions in the magnetosphere. The key wavelengths that will be imaged are:

FilterWavelenth Range
OI 1304130.4 nm
OI 1356135.6 nm
LBH short140 - 160 nm
LBH long160 -175 nm
Solar175 - 190 nm

The UVI PI institution is the University of Washington under the direction of Dr. G. Parks. For additional information, see the UW UVI home page. The UVI lead hardware institution is NASA Marshall Space Flight Center. For additional information see the UVI MSFC home page.

Visible Imaging System

L. A. Frank
Department of Physics and Astronomy
University of Iowa
Iowa City, IA 52242
(319) 335-0804

The Visible Imaging System (VIS) is a set of three low-light-level cameras to be flown on the POLAR spacecraft of the International Solar-Terrestrial Physics (ISTP) program. Two of these cameras share primary and some secondary optics and are designed to provide images of the nighttime auroral oval at altitudes ~1 to 8 RE (Earth radius) as viewed from the eccentric, polar orbit of the spacecraft. A third camera is used to monitor the directions of the fields-of-view of the auroral cameras with respect to the sunlit Earth. The auroral images are to be gained with filters with narrow passbands at visible wavelengths. The emissions of interest include those from N2+ at 391.4 nm, Ol at 557.7 and 630.0 nm, Hl at 656.3 nm and OII at 732.0 nm. The primary scientific objectives of this imaging instrumentation, together with the in situ measurements from instruments on board the ensemble of ISTP spacecraft, are (1) quantitative assessment of the dissipation of magnetospheric energy into the auroral ionosphere, (2) an instantaneous reference system for the above in situ observations, (3) development of a substantial model of the energy flow within the magnetosphere, (4) investigation of the topology of the magnetosphere, and (5) delineation of the responses of the magnetosphere to substorms and variable solar wind conditions.

For additional information see the VIS Homepage

Polar Ionospheric X-ray Imaging Experiment

David L. Chenette
Space Physics Laboratory
Lockheed Martin Advanced Technology Center
3251 Hanover Street
Palo Alto, CA 94034

The Polar Ionospheric X-ray Imaging Experiment (PIXIE) to be included in the payload of the POLAR spacecraft is described. The PIXIE instrument will measure the spatial distribution and temporal variation of x-ray emissions in the energy range 3 to 60 keV from the earth's atmosphere. From these x-ray measurements, the morphology and spectra of energetic electron precipitation and its effects upon the atmosphere can be derived.

Energetic electrons are thought to play a key role in the transfer of energy within the earth's magnetosphere. They are a major source of ionization of the upper atmosphere and therefore a controlling factor in ionospheric conductivity, which in turn has important implications for the global magnetospheric electrical circuit. Although a variety of possible mechanisms for accelerating these particles has been hypothesized, global measurements with good energy resolution to determine where and when the mechanisms operate have not yet been made.

Particle spectrometers can measure electron fluxes directly, but only in the immediate vicinity of a spacecraft. Remote observations detect secondary photons associated with the electron flux; for example, the bremsstrahlung x-rays produced when the electrons enter the upper atmosphere. The Polar Ionospheric X-ray Imaging Experiment (PIXIE) will provide global measurements of the spatial distribution and temporal variation of bremsstrahlung x-ray emissions from the earth's atmosphere. From these x-ray measurements, the morphology and spectra of energetic electron precipitation and the effects upon the atmosphere can be derived. The measurements can be used to estimate the total rate of electron energy deposition and the energy distribution of the precipitating electrons. The electron energy distribution can then be used to compute the altitude profile of ionization and electrical conductivity. All of these quantities will be derived for the entire auroral zone simultaneously. PIXIE x-ray measurements can be made on the day side of the earth as well as the night, and the precipitating electron intensities and energy spectra can be derived from the x-ray images. These are unique capabilities that cannot be duplicated by optical or UV devices. Images of atmospheric bremsstrahlung emission will be obtained over the energy range of 3 to 60 keV with good spatial and energy resolution, and with sufficient time resolution (a few minutes) to generate movies of the dynamical variations of auroral luminosities and associated atmospheric effects.

The design of an instrument for mapping bremsstrahlung x-rays and the plans for on-orbit operations and data analysis should be based on actual measurements of bremsstrahlung x-rays at satellite altitudes. For these purposes, we have formulated representative spectra and intensities based on the only existing sets of satellite bremsstrahlung data. (These data were acquired by the Lockheed and Aerospace groups - Imhof et al., 1974, 1981, 1985; Datlowe et al., 1988; Mizera et al., 1978, 1984; Gorney, 1987) . Previous instruments viewed a relatively small region below a low-altitude spacecraft and, therefore, do not give a global picture, but the data can be taken as representative of certain classes of auroral events. The two physical parameters that are crucial in determining global upper atmospheric processes are the total energy input to the high latitude regions of the atmosphere and the spectrum of the precipitating electron fluxes which provide a highly variable and significant portion of that energy. Based on our data taken from low-altitude polar orbiting satellites, bremsstrahlung x-rays can be used to deduce these parameters.

For additional information see the PIXIE Home Page.

Charge and Mass Magnetospheric Ion Composition Experiment

Theodore A. Fritz
Center for Space Physics
Boston University
725 Commonwealth Ave
Boston, MA 02215

The objective of the Charge and Mass Magnetospheric Ion Composition Experiment (CAMMICE) is the unambiguous determination of the composition of the energetic particle populations of the Earth's magnetosphere over the range of 6 keV/Q to 60 MeV per ion in order to identify mechanisms by which these charged particles are energized and transportcd from their parent source populations to the magnetosphere.

There are two main sources of particles for the magnetosphere: the solar wind and the ionosphere. Measurements of the following ion flux ratios: (2)H/(1)H, (3)He/(4)He, (12)C/(16)O, (l4)N/(16)O, (4)He/(20)Ne, (20)Ne/(36)Ar, and (24)Mg/(16)O, and the following charge state density ratios: He++/H+, He+/H+, O+/H+, and O++/O+ at different locations and over a wide energy range will serve as the principal tracers of plasma origin. The energy dependence of the flux ratios will indicate the relative strength of the sources throughout the magnetosphere and the as yet undetermined coupling between the magnetosphere and the two source regions. The excellent energy coverage of the CAMMICE instruments will permit elemental and isotopic abundance determination of energetic ions known to be produced, energized, transported, and lost during substroms and main phase magnetic storms, as well as those of energetic solar particles from flares and solar cosmic rays. These instruments will also permit studies of ion composition dependent boundary layer processes, identification of radiation belt regions by their dominant composition and differentiation of transport mechanisms which are mass and mass-per-charge dependent. Early versions of the instrument have operated successfully both within the radiation belts (CRRES) and within the high latitude boundary regions (Viking).

The CAMMICE consists of two types of sensor systems: the Magnetospheric Ion Composition Sensor (MICS), and the Heavy Ion Telescope (HIT). Each sensor performs a multiple-parameter measurement of the composition of magnetospherically trapped and transient ion populations over a combined energy range from 6 keV/Q to 60 MeV per ion (a range of over 4 orders of magnitude) and for elements from hydrogen through iron.

See also CAMMICE WWW page

Comprehensive Energetic Particle Pitch Angle Distribution

J. Bernard Blake
Space Sciences Department
The Aerospace Corporation
P.O. Box 92957
Los Angeles, CA 90009
(310) 336-7078

The CEPPAD consists of three packages. Two are spacecraft body mounted and the third is located on the despun platform. The first body-mounted package consists of the Imaging Proton Sensor (IPS) and the Digital Processing Unit (DPU). The second consists of the Imaging Electron Sensor (IES) and the High Sensitivity Telescope (HIST). The single despun platform package is the Source/Lose-Cone Energetic Particle Spectrometer (SEPS). The IPS, IES and HIST all use the body-mounted DPU. The SEPS sensor is independent of the body mounted sensor and contains a separate digital processing unit. This approach was taken because of the limitations inherent in communicating between the spacecraft body and despun platform.

The IPS measures protons over the enagy range from ~10 keV to 1 MeV using a spectrometer which incorporstes a Microstrip Solid State Detector (MSSD) hsving a planar configuration with six individual elements. The IES measures electrons over the energy range from ~ 25 to 400 keV using a spectrometer which incorporates a Microstrip Solid State Detector (MSSD) having a 0.5 x 2.1 cm planar configuration with five individual elements. The MSSD forms the image plane for a sensor segment with a "pin-hole" aperture. The MSSD has a thick "dead layer" and thus does not respond to protons with energies below ~ 250 keV. However the dead layer is sufficiently thin as that it allows the IES to be sensitive to electrons with enagies ~ 25 KeV or more. The "pin-hole" aperture accepts electrons over a 60 degrees angular segment in a plane containing the satellite spin axis. Each of the five detector e1ements in the MSSD detects electrons in a ~12 degrees angular sub-interval of the 60 degrees field-of-view (FOV). The complete IES system has a nominal geometric factor of 6 x 10^-3 cm2. The nominal angular resolution of a detector element is 12 degrees x 12 degrees and its elemental geometric factor is approximately 3.8 x 10^-4. Three of these detector segments provide the desired electron measurements over a FOV of +/- 12 degrees x 180 degrees. The satellite spin is used to obtain measurements over the full 4p steradians.

All detector elements in each segment are attached to a dedicated preamplifier. In the normal mode of operation, the detector elements with fields of view perpendicular, parallel and antiparallel to the spin axis are connected to a dedicated amplifier chain at all times. There are a total of 6 amplifier and pulse height analyzer chains in the IES signal conditioning unit (SCU). The remaining four detector elements in each sensor segment are then sampled on a time-share basis. Each of the remaining three amplifier chains are attached to one of the four detector elements in each segment under DPU control. In general, the DPU can control which 6 of the 15 detector elements are being sampled at any given time by the amplifier chains. The responses of the selected detector elements are pulse-height analyzed by 8-bit Analog-to-Digital Converters (ADCs) to obtain the energy for each detected partical.

The DPU samples the 5 detector elements in each ES segment according to pre-programmed sampling schemes which utilize the sectored satellite spin to obtain data samples over the unit sphere. In the normal mode of operation, the combined data from the 3 dedicated detector elements and the 3 program-control sampled detectors strips are used to build a three dimensional (3D) "image" of the medium energy electron angular distribution. For each electron detected, the polar and azimuthal angular sector and energy are known. The DPU accumulates the result into an array which contains the electron fluxes in 15 (polar) by 32 or 16 (azimuthal) angular intervals for each of up to 12 energy ranges. Within 24 seconds (4 spin periods), the complete 4p steradians can be sampled and within one spin period a 2D distribution function can be obtained.

See also CEPPAD WWW page and the SEPS WWW page.

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