The ISEE-C Plasma Wave Investigation

IEEE TRANSACTIONS ON GEOSCIENCE ELECTRONICS, VOL. GE-16, NO. 3, JULY 1978 191

state of the interplanetary plasma," J. Geophys. Res., vol. 73, spectrometer for space plasmas," Rev. Sci. Instr., vol. 39, p. 441, p. 5485, 1968. 1968. [19] I. Iben, "The 37 Cl solar neutrino experiment and the solar helium [25] K. W. Ogilvie and J. Hirshberg, "The solar cycle variation of the abundance," Am. Phys., vol. 54, p. 164, 1969. solar wind helium abundance," J. Geophys. Res., vol. 79, p. 4959, of a Wien filter with 1974. [20] D. loanoviciu, "Ion optics inhomogeneous [26] D. E. Robbins, A. J. Hundhausen, and S. J. Bame, "Helium in the fields," Int. J. Mass Spectrom. Ion Phys., vol. I1, p. 169, 1973. solar wind," J. Geophys. Res., vol. 75, p. 1178, 1970. [21] C. Jordan, "The ionization equilibrium of elements between car- [27] E. G. Shelley, R. D. Sharp. R. G. Johnson, J. Geiss, P. Eberhardt, bon and nickel," Mon. Notic. Roy. Astron. Soc., vol. 142, p. 501, H. Balsiger, G. Haerendel, and H. Rosendauer, "Plasma Composi- 1969. tion Experiment on ISEE -A," this issue, pp. 266-270. [22] C. E. Kuyatt and J. A. Simpson, "Electron monochromator de- (28] E. G. Shelley, R. G. Johnson, and R. D. Sharp, "Satellite observa- sign," Rev. Sci. Instr., vol. 38, p. 103, 1967. tions of energetic heavy ions during a geomagnetic storm," J. [23] W. Legler, "Ein modifiziertes Wiensches Filter also Elektronen- Geophys. Res., vol. 77, p. 6104, 1972. monochromator," Z. Phys., vol. 171, p. 424, 1963. [29] R. V. Wagoner, "Big-Bang nucleosynthesis revisited," Astrophys. [24] K. W. Ogilvie, T. Mcllrath, and T. D. Wilkerson, "A mass energy J.,vol. 179,p. 343, 1973.

The ISEE-C Plasma Wave Investigation

F. L. SCARF, R. W. FREDRICKS, D. A. GURNETT, AND E. J. SMITH

Abstmct-The ISEE-C plasma wave investigation is designed to pro- discontinuity, and this provides a nonlocal wave-particle vide comprehensive information on interplanetary wave-particle interaction mechanism. interactions. Three spectrum analyzers with a total of 19 bandpass 2) to analyze the basic interplanetary instabilities asso- channels cover the frequency range 0.3 Hz to 100 kHz. The main analyzer, which uses 16 continuously active amplifiers, gives two ciated with thermal anisotropy and heat conduction that complete spectral scans per second in each of 16 filter channels. The cause the solar wind to behave as an effective fluid even when instrument sensors include a high-sensitivity magnetic search coil, and the mean free path becomes large near 1 AU. electric antennas with effective lengths of 0.6 and 45 m. 3) to study the energy loss and wave-wave conversion mechanisms for suprathermal electrons and protons by corre- INTRODUCTION lating particle distribution data with wave measurements. This study will involve effects associated with solar-radio T HE ISEE-C plasma wave instrument will provide high- bursts. sensitivity measurements of interplanetary wave phe- 4) to determine the effective transport coefficients (heat nomena over the spectral range extending from below 1 Hz conductivity, electrical conductivity, viscosity) associated to 100 kHz. The wave electric-field and magnetic-field with wave-particle scattering in the solar wind. are a electric components detected using long body-mounted 5) to search for local wave-particle acceleration processes dipole (90 m, tip-to-tip), a short boom-mounted electric in the solar wind. dipole (0.6 m, effective length), and a high-sensitivity magnetic search coil. The signal processing units in the plasma We will also try to evaluate local plasma parameters by wave electronics box and in the dc magnetometer utilize analyzing plasma wave data, search for interplanetary whistler- three distinct spectrum analyzers that cover a total of 19 mode signals that should develop whenever (T_lTI )e exceeds different frequency channels with varying time resolution. unity, and study the dynamical energy dissipation processes The main analyzer, with 16 continuously active channels, that can cause large amplitude MHD waves in the solar wind provides two complete spectral scans per second. to steepen into collisionless shocks. The primary scientific objectives of the ISEE-C plasma wave investigation can be summarized as follows: INSTRUMENT CHARACTERISTICS The basic elements of the ISEE-C plasma wave instrument 1) to determine the roles that plasma waves play at inter- are in 1. line in center planetary discontinuities and at stream-stream interaction shown Fig. The drawing the depicts the spacecraft with all booms and antennas deployed. The fronts. Some wave energy must propagate away from the 90-m, tip-to-tip, balanced dipole antenna along the U-axis Manuscript received April 3, 1978. has been designated as the primary long electric-field sensor F. L. Scarf and R. W. Fredricks are with TRW Defense and Space for the plasma wave instrument, and the V-axis dipole antenna Systems Group, Redondo Beach, CA 90278. is the primary in-ecliptic sensor for the radio-astronomy D. A. Gurnett is with the Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242. investigation. However, these two wave instruments have E. J. Smith is with Jet Propulsion Laboratory, Pasadena, CA 91103. been designed with a capability to operate together using

0018-9413/78/0700-0191$00.75 1978 IEEE Authorized licensed use limited to: The University of Iowa. Downloaded on June 29,2010 at 15:31:35 UTC from IEEE Xplore. Restrictions apply. 192 IEEE TRANSACTIONS ON GEOSCIENCE ELECTRONICS, VOL. GE-16, NO. 3, JULY 1978

TABLE I ISEE-C PLASMA WAVE INSTRUMENT CHARACTERISTICS Sensors: Long electric dipole (90 meters, tip-to-tip); the U-axis antennas *re assigned to the plasma w ve Investigation, but the radio astronomy (STH) and plasm wave (SCH) groups can share the U-or V-axis systms, if necessary. Short electric antenna (0.6 meter effective length), on the minus X-axis hard bow. Search coml, on the minus X-axis hard boon.

Sixteen-channel spectrum nalyzer, 17 Hz to 100 kHz: 16 filters, 16 AGC aplifiers, 2 scans per second [E(long) or E(short) or S1. Eight-channel spectrum analyzer, 17 Hz to I kHz: 8 filters, one AGC Mlpiifier, I scan per 16 seconds [E(short) or B]. Three-channel spectrum analyzer, 0.316 Hz to 8.8 Hz: using SMH electronics, I scan per 32 seconds [B only].

Short Electric: 0.25 kg Search Coil; 0.3 kg Unity tain Preaps: 0.09 kg (x4) Main Electronics: 2.64 kg Subtotal 3.55 kg

[Each ator-driven antenna eleeent: 2.4 kg (x2)1

Power: 3.8 Watts

parable to the mean settling time of each AGC amplifier, and switching transients are absent. The 16-channel spectrum analyzer can be used with any of the wave sensors (long U, long V, short electric, or search coil). The 8-channel analyzer covers the range 17 Hz to 1 kHz with a set of filters that correspond to the lower frequency ones in the main analyzer, but this secondary analyzer utilizes a single AGC amplifier. The commutator switches the ampli- Fig. 1. Top: The magnetic search coil (left) and the short electric antenna (right). Center: Drawing of ISEE-C with all booms and fier from one frequency channel to another after every four antennas deployed. Bottom: One of the four identical unity gain measurements (covering 2 s) and the entire 8-channel scan is preamplifiers used with the long wire antennas (left), and the main electronics unit (right). repeated every 16 s. This second spectrum analyzer is designed to be used with the magnetic search coil or the short the V-axis or the U-axis dipoles in case one or more of the electric antenna. four individual 45-m wire antenna elements fails to deploy The third spectrum analyzer, which covers the range below properly. This redundancy was achieved by designing sepa- 17 Hz, is located within the electronics unit of the Vector rate radio-astronomy and plasma wave preamplifiers that Helium Magnetometer [6]. A cable from the plasma wave can operate together on any individual antenna element. A instrument brings the output of the magnetic search coil to set of these preamplifier pairs is mounted near the base of the SMH box, and the low-frequency spectrum is analyzed each 45-m antenna/motor unit. The photograph in the lower once per 32 s using three relatively broad filters that cover left shows one of the four long electric unity gain plasma the range 0.316-8.8 Hz. The lowest of these channels is wave preamplifiers, each of which is basically identical to the centered about the nominal ISEE-C spin frequency, and units built by the University of Iowa for operation on ISEE-A since the search coil is mounted at an angle to the boom, and ISEE-B [1]. The two additional sensors are the magnetic the 0.316-Hz output will provide a low-resolution backup search coil (upper left) and the short electric antenna (upper measurement of the dc magnetic-field component in the plane right), which are mounted together on the 3-m minus-X perpendicular to the spacecraft spin axis. boom, as indicated in the central drawing. A photograph of The ISEE-C spectral coverage for plasma waves is sum- the main electronics unit for the plasma wave instrument is marized in the left-hand part of Fig. 3. This panel compares shown in the lower right, and the instrument specifications the response curves for the 15-percent bandwidth filters used are in Table I. in the two high-frequency analyzers with the spectral responses Fig. 2 contains a simplified block diagram of the ISEE-C of the three wave channels in the Vector Helium Magnetometer plasma wave instrument. The signals from the wave sensors unit. It can be seen that the full instrument will measure are processed using three spectrum analyzers. The main many aspects of E and B fluctuations over the complete 16-channel analyzer covers the range 17 Hz to 100 kHz range extending from 0.3 Hz to 100 kHz, although the ability with a separate continuously active automatic gain control of the instrument to perform highly comprehensive measure- (AGC) amplifier following each of the 16 bandpass filters. ments does vary over this range. From 17 Hz to 1 kHz the This spectrum analyzer provides essentially continuous in- capability is optimum since the 8 continuously active channels formation since the time between samples (500 ms) is com- can be used to measure characteristics of short- or long-

Authorized licensed use limited to: The University of Iowa. Downloaded on June 29,2010 at 15:31:35 UTC from IEEE Xplore. Restrictions apply. SCARF et al.: PLASMA WAVE INVESTIGATION 193

16 FILTERS, 16 AMPLIFIERS TO 16 ANALOG MINOR FRAME WORDS

*ATOR

*- WORD GATE AND RESET PULSES

8 FILTERS, 1 AMPLIFIER TO 1 ANALOG TO VECTOR HELIUM MINOR FRAME WORD MAGNETOMETER (SMH)

ISEE-C PLASMA WAVE INSTRUMENT (SCH) Fig. 2. Block diagram.

16-C HANNEL ANALYZER

RADIO WAVES (SPEED OF LIGHT)

I U

z PLASMA 0l WA VES

Fig. 3. Left: Filter response curves for the ISEE-C plasma wave investigation. Right: Some characteristic phase speed versus frequency plots for typical interplanetary conditions (B = 5 gamma, N = 5 protons/cm3).

wavelength electric fields or magnetic fluctuations, while many of the lower frequency modes have V(phase) < V(wind), the second spectrum analyzer can be used to compare E and hence Doppler shifts will have to be accounted for in the and B measurements, or to compare long- and short-wave- analysis of data obtained from the ISEE-C observing platform. length E-field observations. For the 8 continuously active However, in a very general sense, Fig. 3 does show that the channels covering the range 1.7 kHz to 100 kHz, there is still ISEE-C plasma wave instrument will provide excellent cov- considerable flexibility, but the capability to compare outputs erage for all important local wave modes above the ion cyclo- from various wave sensors is absent here. tron frequency. Since electromagnetic ion cyclotron oscilla- The right-hand side of Fig. 3 contains frequency versus tions will be detectable in the magnetometer data, the full phase speed plots for many characteristic interplanetary wave ISEE-C payload should provide valuable information for modes (assuming B = 5 gamma, N = S protons/cm3 ). For a many new studies involving interplanetary wave-particle nominal solar wind speed near 400 km/s, it can be seen that interaction phenomena.

Authorized licensed use limited to: The University of Iowa. Downloaded on June 29,2010 at 15:31:35 UTC from IEEE Xplore. Restrictions apply. 194 IEEE TRANSACTIONS ON GEOSCIENCE ELECTRONICS, VOL. GE-16, NO. 3, JULY 1978

In---I r

IMP-7 (LOOP) _. EXPECTED IN-FLIGHT THRESHOLD lo-2 (MINIMUM ISEE-A NOISE LEVEL; SHORT ELECTRIC; S/C IN SUN)

10 SHORT ELECTRIC ANTENNA: HAWKEYE-I Z THRESHOLDS FOR WAVES (SEARCH COIL) WITH X O > 0.7 METERS lo-3 \ IMP-7 lo-5 MAGNETIC SENSORS, \ t IMP-6 (LOOP) (LOOP) ISEE-C IN-FLIGHT THRESHOLD Z\ J T HRESHOLD SPECTRAL DENSITY, SPECTRAL DENSITIES HELIOS-1 (PRE-LAUNCH) 106_6 (SEARCH COIL) 112 GAMMA/(Hz)1/2 - volts/M( Hz) 10 ISEE-C SEARCH COIL lo-7 _

HELIOS \ /SEARCH COIL CUTOFF 10-9

-1- .-,* lU- ~~~~~~~I 1% ,I -,,,1 .-2 -6 10 100 1000 10 10- 103 104 105 FREQUENCY, Hz FFREQUENCY, Hz Fig. 4. Anticipated threshold sensitivities of the ISEE-C plasma wave investigation.

SENSOR CHARACTERISTICS AND ANTICIPATED mechanical changes have been incorporated for ISEE. The SENSITIVITIES most important of these improvements involve: a) the use of The Search Coil low-noise, high-impedance field-effect transistors in the input circuits; b) the use of an input capacitive voltage divider that The ISEE-C search coil is a high sensitivity version of the greatly reduces the effect of any sheath fluctuation on the sensor con- magnetic designed for ISEE-A, -B [1]. The flux sensor response; c) the use of grounded metallic tape wrap centrating core, made of high permeability nickle-iron alloy, around each fiberglass antenna stem, to satisfy the ISEE is 39.4 cm in length, with a square cross section (0.48 cm on electrostatic cleanliness specification. a side). The coil has 80 000 turns of AWG 47 wire and the The short electric antenna has an effective length of 0.61 m, effective loop area is 2100 m2 for signals below 500 Hz. The and the intrinsic sensitivity is given by the solid upper curve entire unit is 40.6 cm long, the coil constant is 13 ,V/gamma/ on the right side of Fig. 4. Early post-launch data from Hz, and the rolloff above 500 Hz is approximately 6 dB per ISEE-A, -B indicate that low-frequency spacecraft-associated octave. noise is always detected on the electric antennas except when The anticipated in-flight sensitivity of the ISEE-C search each ISEE is in the earth's shadow. This noise is most likely coil is plotted as a function of frequency in the left side of to be coupled to the plasma through the current systems that Fig. 4. The other curves shown here are adapted from a draw- flow in the illuminated solar panels, and we expect similar ing in a recent report by Neubauer et al. [3] . The comparisons low-frequency spacecraft interference to be present on ISEE-C. indicate that the ISEE-C search coil will be at least as sen- Thus the actual in-flight threshold will probably be elevated sitive as any magnetic sensor flown previously, and if the at low frequencies as given by the dashed line, which is based spacecraft noise levels are sufficiently low, the ISEE-C in- on actual ISEE-A measurements in the quiet solar wind. On strument will be able to detect very low wave levels with the basis of achievable thresholds from previous interplanetary the magnetic sensor. missions that used solar-panel spacecraft, these in-flight Short Electric Antenna interference levels are not at all unexpected. For instance, on Helios-2, with an antenna-effective length of 16 m, the to well- The short electric antenna is designed provide 30-Hz in-flight threshold was near 2 X 10-4 V/m(Hz) /2. for such defined measurements of signal amplitudes modes, The ISEE-A minimum level at 30 Hz is a factor of 10 higher can short wave- as ion acoustic oscillations, which have very than the Helios-2 level, as would be expected if comparable taken to be lengths. The minimum wavelength is nominally voltage ripples were present, and we therefore anticipate that 27TXD where XD [= (KT/47rNe2)1/2] is the Debye length, but the ISEE -C noise environment will also be roughly comparable and in waves with this cutoff is not well defined principle, (in voltage ripple) to that found on Helios. X < (2ITXD) can also be generated; in fact, Scarf [5] presented evidence that waves with )X (2ITXD)/2 were detected by the Electric Antenna IMP-7 plasma wave instrument at the September 15, 1974 Long interplanetary shock, when XD was approximately 6 m. Since The long electric antenna is designed to provide optimum small values of XD are commonly expected near interplanetary E-field sensitivity for the long-wavelength electromagnetic stream interfaces and shocks, an E-field sensor with l(eff) = modes (solar radio bursts, whistler-mode signals, etc.). The effective length <

Authorized licensed use limited to: The University of Iowa. Downloaded on June 29,2010 at 15:31:35 UTC from IEEE Xplore. Restrictions apply. IEEE TRANSACTIONS ON GEOSCIENCE ELECTRONICS, VOL. GE-16, NO. 3, JULY 1978 195 intrinsic sensitivity of the ISEE-C instrument, using the large with the design, fabrication, integration, and pre-launch data electric antennas. This assumes that no solar array noise reduction tasks. They are indebted to S. Mosier of Goddard effects are present and that the waves have X >> 45 m. In Space Flight Center for representing their interests with the fact, the early ISEE-A measurements indicate that some wire antenna design, procurement, and integration. They finite solar panel noise is also detected on the long electric are also very grateful for the outstanding support and con- antennas, although the voltage interference effect is less tinuing cooperation of the many members of the ISEE Project significant because the antenna length is so much longer. Staff, and their associates at Fairchild Space and Electronics Moreover, it appears that for the long antennas on ISEE-A, Company. the noise rolls off more rapidly with frequency than for the short antennas. Since we do not yet know how to scale these effects as functions of varying antenna length, we do not show REFERENCES an anticipated spacecraft noise effect in connection with the [1] D. A. Gurnett, et al., IEEE Trans. Geosci. Electron., this issue, long electric antenna curve of Fig. 4; it is likely that the pp. 225-230. [2] J. P. Heppner, et al., IEEE Trans. Geosci. Electron., this issue, effect will be small, in comparison with the in-flight noise pp. 253-257. enhancement shown on the upper curve. [3] F. M. Neubauer, G. Musmann, and G. Dehmel, "Fast magnetic fluctuations in the solar wind," J. Geophys. Res., vol. 82, p. ACKNOWLEDGMENT 3201, 1977. [4] F. L. Scarf, R. W. Fredricks, I. M. Green, and G. M. Crook, "Ob- P. Virobik, the TRW Project Manager for the ISEE-C Plasma servations of interplanetary plasma waves, spacecraft noise, and was the of a effort a sheath phenomena on IMP-7," J. Geophys. Res., vol. 79, p. 73, Wave Instrument, leader large involving 1974. number of cooperating institutions. The authors are very [51 F. L. Scarf, "Wave-particle interaction phenomena associated grateful for his dedicated efforts and they especially thank with shocks in the solar wind," in Proc. of the DeFeiter Symp. J. E. and I. Green of D. Odem on Study of Traveling Int. Phenom., Noordwijk, The Nether- Atkinson, Vrem, (all TRW), lands: Reidel Publishing Company, pp. 259-275, 1977. and R. Shaw (of the University of Iowa), and A. Frandsen [6] D. A. Gurnett, et at., IEEE Trans. Geosci. Electron., this issue, and J. van Amersfoort (of JPL) for their invaluable assistance pp. 225-230.

The ISEE-C Vector Helium Magnetometer

ALLAN M. A. FRANDSEN, BENJAMIN V. CONNOR, JAN VAN AMERSFOORT, AND EDWARD J. SMITH

Abstract-The ISEE-C vector helium magnetometer is a slightly stability of the instrument together with the cost-saving po- modified instrument that originally served as the spare unit for the tential of using existing hardware made this approach very Pioneer 10 and 11 missions to Jupiter. The essential features of the instrument are described and the speciflcations are tabulated. Sci- attractive. Only minor modifications were necessary to sat- entific objectives and minor modifications needed for the ISEE mission isfy the ISEE-C interface and environmental requirements. are discussed briefly. Integration into the spacecraft was made possible by a project- supplied data processing unit (DPU), a specifically designed buffer which makes ISEE appear Pioneer-like to the VHM. INTRODUCTION IN THE EARLY YEARS of planetary exploration, a magne- SCIENTIFIC OBJECTIVES tometer was developed for use on Mariner missions to Mars The ISEE-C magnetometer will make continuous observa- and Venus [1], [2]. The instrument, the vector helium mag- tions of the interplanetary magnetic field near 1 AU. The netometer (VHM), was subsequently developed to meet the measurement of the three field components will reveal the requirements of the Pioneer 10 and 11 missions to Jupiter and interplanetary sector structure, the instantaneous direction Saturn [3]. A flight-spare VHM identical to those now operat- of the field, including the polarity of the very important ing on Pioneer 10 and 1 1 was selected for the ISEE-C magnetic north-south component, and the field magnitude, which field investigation. The proven reliability, sensitivity, and will be computed from the three components. It will be possible to identify and study the whole range of dynamic Manuscript received April 3, 1978. This report represents one aspect phenomena that have been disclosed on previous missions, of research carried out by Jet Propulsion Laboratory for NASA under such as interplanetary shocks, hydromagnetic discontinuities, Contract NAS7-100. The authors are with the Jet Propulsion Laboratory, California In- and Alfven waves [4]. Because the separation between the stitute of Technology, Pasadena, CA. spacecraft and Earth is less than the typical correlation length 0018-9413/78/0700-0195$00.75 © 1978 IEEE Authorized licensed use limited to: The University of Iowa. Downloaded on June 29,2010 at 15:31:35 UTC from IEEE Xplore. Restrictions apply.