FREJA / Cold Plasma Analyzer

Launched successfully October 6, 1992 @06:20:02UT

The Swedish satellite FREJA (name pronounced fray-ya) was launched October 6th, 1992 from the Gobi Dessert in Central China. It carried a Canadian Cold Plasma Analyzer (designated F3C), the development of which was led by Dr. Brian Whalen of the Herzberg Institute for Astrophysics in Ottawa and built by COM DEV Ltd. in Cambridge, Ontario. This instrument was designed to measure cold plasma. F3C was able to discern energy per unit charge (E/Q) of ions or electrons in the range 0 < E/Q < 200 Volts and complemented measurements made by the F3H hot plasma experiment. Funding for the construction of F3C was provided by the National Research Council of Canada - Space Division, which later became the Canadian Space Agency. CSA funded final development and operations of the CPA. Support for scientific work was initially generated by the National Research Council's Herzberg Institute and then by the Natural Science and Engineering Research Council of Canada. .

Data from F3C were telemetered to receiving stations at Esrange, Sweden, Prince Albert, Saskatchewan, and at the Japanese base SYOWA in Antarctica. CPA operations were handled by Institute for Space and Atmospheric Studies at the University of Saskatchewan in Saskatoon, while the data analysis has been done at the U of C following the arrival in 1995 the CPA's PI for data analysis (David Knudsen) following Dr. Whalen's retirement.

The CPA operated from January 1993 through May 1994, and had two new capabilities that made it unique: 1) True 2-D energy/angle-of-arrival imaging capability and 2) unprecedented spatial resolution. The latter feature has led to observations which show that intense ion heating is often confined within narrow regions of intense, low-frequency electromagnetic perturbations only a few hundred metres across, and which have been identified as solitary kinetic Alfven waves (SKAW's). Future studies using CPA will seek to uncover the exact mechanisms by which SKAW's energize ions, and to characterize the larger-scale plasma environment in which these small-scale particle energization structures are embedded (see Publications below).

Sweden's third satellite, FREJA, was launched into a 62° inclination orbit on October 6th, 1992 at 06:20:02 UT from the Gobi Desert in China. Its primary purpose was to investigate the physical plasma processes occurring on medium altitude (approx 13000 km) auroral field lines. Previous observations made with the S3-3 satellite (at lower altitudes than FREJA) and the Dynamics Explorer satellite (at higher altitudes) have shown this region to be the site of a number of fundamentally important plasma processes including the acceleration of particles both into and out of the auroral ionosphere, wave-particle interactions and the generation of parallel electric fields.

Cold Plasma Analyzer Design

The Cold Plasma Analyzer (CPA) Instrument is composed of three major elements (subsystems): the Sensor Assembly (SA), the Boom Assembly(BA), and the Power and Controller Unit (PCU).

Sensor Assembly

The sensor assembly contains an electrostatic analyser and electronics to accumulate pulses from theMicrochannel Plate (MCP) detector and transmits the results to the PCU. It also contains a sun sensor subsystem to determine the attitude of the SA, and a temperature sensor and SA heater which is controlled by the PCU.

In the SA, energy analysis is performed by a spherical plate electrostatic analyser which focuses a parallel beam of charged particles incident in the plane perpendicular to the sensor axis of symmetry onto a high-speed MCP. The analyser disperses energy in the radial direction and angle of incidence in the azimuthal direction. Thus, for one setting of the analyser electrodes, simultaneous energy/angle of incidence information may be derived in one plane. Thus, the instrument provides a near instantaneous image of the particle distribution function in a plane and a complete (4 pi ) image in one-half a spacecraft rotation. The imaging capability is utilized to provide high temporal (spatial) resolution information in the image plane. These data are derived from two independent "pulse" and "current mode" (low and high frequency) signal processing paths.

A high count rate MCP is used as the image plane sensor and is operated with bias currents adequate to maintain a linear response at count rates in excess of 30 MHz (summed over the MCP active area). When the sensor is operated near the maximum count rate, statistically significant estimates of electron or ion densities, temperatures and drift velocities may be derived in approximately 0.1 ms. Any combination of the above parameters may be selected to be telemetered to ground, resulting in a maximum temporal resolution (for any one parameter) of approximately 0.1 ms.

An Automatic Count Rate Control (elecrostatic gating) system is included in the sensor entrance aperture to increase the dynamic range of the instrument. This gate is also used to perform a coarse mass analysis of the incident thermal ion population.

To support the plasma density observations, the SA is electrically isolated from the boom. The surface may be biased and the current to the surface monitored by electronics in the SA.

Boom Assembly

Since the analyser has been designed specifically for thermal and suprathermal energies, the sensor must be deployed on a boom to avoid the perturbing effects associated with the spacecraft. Also, to control (or offset) spacecraft charging, the potential of the external surface of the sensor is adjustable and the surface material is carefully selected to reduce contact potential problems inherent in verylow-energy charged particle observations.

The boom, which is a ``Stacer'' mechanism, will deploy the CPA to a distance of two meters from the spacecraft, which should place the sensor outside the Freja sheath using reasonable assumptions about the local plasma distribution. We note that the SA will from time to time enter the wake of the spacecraft, allowing the CPA to sample these perturbations, which is an interesting study in itself. In general, the sensor should be in a good position to sample the unperturbed medium.

Langmuir probe response tests will also be conducted using the SA skin as a probe while simultaneously observing the particle distributions arriving at the probe surface. These data will be used to test a computer model of the particle trajectories in the SA sheath, which is both a scientifically interesting and technically challenging problem.

Power And Control Unit

The PCU contains the high- and low-voltage power converters and instrument controller. The converters operate in the 100 to 150 kHz frequency range, are programmed by the controller and externally switched by a hardwired (safety) command decoder. The controller unit is composed of two microprocessors (8085) and peripherals, a 32 Kbit program ram, and a 1 Mbit storage ram.

The definitions of the CPA operation modes are contained in sequencing files which define all the sensor electrical parameters, the data collection and compression algorithms, parameter looping, telemetry format and sequence between operation modes which are time tagged to the Freja clock. A number of sequencing files are contained in the program ram and these may be changed by ground command.

FREJA Parameters

Parameter	Value
Inclination	63.0 Degrees
Apogee altitude	1763 km
Perigee altitude	597 km
Orbital Period	108 minutes
Stabilization	Spin Stabilized
Spin Period	10 rpm
Control	Magnetic Field
Orientation	Sun Oriented +/- 30 degrees.
Size	2.2m x 0.5m
Launch Mass	256 kg
Orbit Mass	241 kg
Payload Mass	73.1 kg (incl. booms and antennas)
High Rate Telemetry	262/524 kbps (S-Band 2208MHz)
Low Rate Telemetry	1200 bps (400.55MHz)
Uplink	1200 bps (400.55MHz)
Downlink Stations	Esrange, Prince Albert, Syowa
Downlink Time	Up to 30 minutes per pass
On-Board Storage	None
Storage	15 Mbyte time-tagged command queue
Solar Cells	1.08 m²
Max Power	137 W
Payload Usage	66.1 W
Expected Lifetime	2 years
Mission Lifetime	4 years

Experiment	Information
Project Scientist	Rickard Lundin, Swedish Institute of Space Physics (IRF), Kiruna, Sweden
F-1 Electric Field	Göran Marklund, Alfvén Laboratory, Royal Institute of Technology (KTH), Stockholm, Sweden Measures potential difference between opposing probes. Maximum Field 1 V/m Minimum Field ~0.03 mV/m Sampling Rate: 768 /s Normal mode; 6144 /s Burst mode Also provides satellite potential information, indicating relative plasma density variations of the ambient plasma.
F-2 Magnetic Field	Larry Zanetti, Applied Physics Laboratory (APL), John Hopkins University, Laurel, MD, USA Measures Earth's Magnetic Field in 3 dimensions. Range +/- 65,000 nT Sampling Rate 128 vector samples/second Measures 3-axis waves from 1.5 Hz to 64 Hz bandpassed. including polarization, ellipticity, etc of the wave field. Range +/- 500 nT at Sampling Rate of 128 vector samples/second
F-3H Hot Plasma / Energetic Particles	Lars Eliasson, Swedish Institute of Space Physics (IRF), Kiruna, Sweden Electron Spectrometer measures the angular and energy distributions of electrons with high temporal and spacial resolution. Range 0.1 keV - 120 keV Sampling time 10 ms/energy-angle matrix Ion Composition Spectrometer measures hot and cold ion distributions. Energy Range 0.5 - 15000 eV/q Mass Range 1 - 40 AMU/q Sampling time 10 ms/mass-angle matrix
F-3C Cold Plasma / Particles	Brian Whalen, Hertzberg Institute for Astrophysics (HIA), Nationa Research Council of Canada, Ottawa, Canada. Electro-static analyser detects ions and electrons. Energy Range 0 < E/Q < 200 eV Dynamic Range 100 < n < 100000 per cubic cm Sampling Rate 10 ms typical, 0.1 ms maximum.
F-4 Wave Experiment	Bengt Holback, Swedish Institute of Space Physics (IRF), Uppsala, Sweden Measures electric, magnetic, density and electron temperature wave fields and turbulence as well as backround plasma density and background electron temperatures.
F-5 UV auroral imagers	Sandy Murphree, Institute for Space Research, University of Calgary, Calgary, Canada Two CCD imagers with passbands 1235A--1600A and 1340A--1800A Sample rate typically 1 image every 6s Telemetry HIGH 88.064 kbits/s, LOW 44.032 kbits/s
F-6 Electron Beam Instrument	Götz Paschmann, Max Plank Institut für Extraterr. Phisik, Garching, Germany Measures electric field by sensing drifts in an electron beam Sampling rate 64 /s minimum 640 /s maximum. Dynamic range > 10 mV/m
F-7 Electron Spectrometer and Correlator	Manfred Boehm, Max Plank Institut für Extraterr. Phisik, Garching, Germany Measures electron distribution. Dynamic Range 10 eV to 25 keV Energy steps - 32 normal 64 maximum. Angular Channels - 32 evenly spaced Sampling Rate 1 ms

SII/TEI Development Team (UofC)

Peter Smith

Tim Cameron

Greg Enno

Kaare Berg

Johnathan Burchill

Ivan Weavers

Andrew Yau

David Knudsen

Peter King

Cliff Marcellus

Publications

Whalen, B., A., D. J. Knudsen, A. W. Yau, A. M. Pilon, T. A. Cameron, J. F. Sebesta, D. J. McEwan, J. A. Koehler, N. D. Lloyd, G. Pocobelli, J. G. Laframboise, W. Li, R. Lundin, L. Eliasson, S. Watanabe, and G. S. Campbell, The Freja F3C Cold Plasma Analyzer, Space Sci. Rev., 70, p.541-561, 1994.

Knudsen, D. J., B. A. Whalen, A. W. Yau, M. J. Greffen, A. I. Eriksson, N. Lloyd, M. Boehm, J. Clemmons, and L. G. Blomberg, Sub-kilometer thermal plasma structure near 1750 km altitude in the polar cusp/cleft, Geophys. Res. Lett., 21, 1907, 1994.

Knudsen, D.J., J.H. Clemmons, and J.-E. Wahlund, Correlation between core ion energization, suprathermal electron bursts, and ELF plasma waves, J. Geophys. Res., 103, 4171, 1998.

Knudsen, D.J., and J.E. Wahlund, Core ion flux bursts within solitary kinetic Alfvén waves, J. Geophys. Res., 103, 4157, 1998.

Knudsen, D.J., P.O. Dovner, A.I. Eriksson, and K.A. Lynch, The effect of lower hybrid cavities on core plasma observed by Freja, J. Geophys. Res., 103, 4241, 1998.

Knudsen, D. J., T. D. Phan, M. D. Gladders, M. Greffen, and B. A. Whalen, Thermal electron temperature measurements from the Freja Cold Plasma Analzyer, AGU Monograph on Measurement Techniques for Space Plasmas, edited by Borovsky, Pfaff, and Young, American Geophysical Union, Washington, D.C., 1998.

Wahlund, J.-E., A.I. Eriksson, B. Holback, M.H. Boehm, J. Bonnell, P.M. Kintner, C.E. Seyler, J.H. Clemmons, L. Eliasson, D.J. Knudsen, P. Norqvist, L.J. Zanetti, Broadband ELF plasma emission during auroral energization, 1, Slow ion acoustic waves, J. Geophys. Res., 103 , 4343, 1998.