urn:nasa:pds:context:instrument:ice.ici 1.0 1.11.0.0 Product_Context urn:nasa:pds:context:instrument:ici.ice 2021-02-24 1.0 Changed inst LIDs from u:n:p:c:i:instID.scID to u:n:p:c:i:scID.instID And per "Guide toPDS4 Context Products" v1.7, changed all lidvid_reference to lid_reference urn:nasa:pds:context:instrument_host:spacecraft.ice instrument_to_instrument_host Coplan, M.A., K.W. Ogilvie, P.A. Bochsler, and J. Geiss, Ion Composition Experiment, IEEE Trans. Geosci. Electron., GE-16, 185-191, 1978. reference.COPLANETAL1978 ION COMPOSITION INSTRUMENT Spectrometer not applicable not applicable Instrument Overview =================== The Ion Composition Instrument is a novel spectrometer for measuring the ionic composition of the solar wind from the ICE (ISEE-C, ISEE3) spacecraft. The resolution and dynamic range of the instrument are sufficient to be able to resolve up to twelve individual ions or groups of ions. This will permit the solution of a number of fundamental problems related to solar abundances and the formation of the solar wind. The spectrometer is composed of a stigmatic Wien filter and hemispherical electrostatic energy analyzer. The use of curved electric field plates in the filter results in a substantial saving of weight with respect to a conventional filter of the same resolution and angular acceptance. The spectrometer is controlled by a microprocessor based on a special purpose computer which has three modes of operations: full and partial survey modes and a search mode. In the search mode, the instrument locks on to the solar wind. This allows four times the time resolution of the full survey mode and yields a full mass spectrum every 12.6 min. SCIENTIFIC OVERVIEW =================== ION COMPOSITION studies in the solar wind are essential for understanding the dynamics and energetics of the solar wind acceleration region, and are an important source of solar abundance information. The ion composition of the solar wind is, however, poorly known because of the technical difficulties associated with the separation of the different ions over the wide dynamic range involved. With electrostatic energy analyzers, the He+2 /H+ abundance ratio has been studied extensively in the solar wind, and large variations found. During quiet low-temperature conditions, ions other than H+ and 4He+2 have been separated with this technique and the presence of heavy ions has been demonstrated. In addition, some information about abundances and charge state distributions has been obtained. The foil collection technique has been used to determine the abundances of the isotopes of He, Ne, and Ar in the solar wind. Although this method has yielded precise abundance data, its time resolution is limited. The ICE spacecraft will be continuously in the solar wind and thus affords an opportunity for a comprehensive uninterrupted composition study. With a continuous record of such a large number of ions, fundamental problems concerning the origin of the solar wind and solar composition can be investigated. Some of these are discussed below. 1) A number of momentum transfer mechanisms for the acceleration of heavy ions into the solar wind have been proposed. Under the inferred conditions in the solar wind source region, coulomb collisions would be sufficient to transfer momentum from protons to heavy ions with high Z**2/M ratios. Momentum transfer by waves has also been proposed as an efficient mechanism. To assess the relative importance of the various mechanisms, measurements of solar wind ions over a large range of M and Z under varying conditions in the corona and solar wind are necessary. 2) Bame et al. (1978) have recently proposed that the He/H ratio of 0.04-0.05 typically found in fast solar wind streamers be equated with the He/H ratio in the outer convective zone of the sun. This is a factor of two lower than the generally accepted value and, if correct, would reduce the calculated boron neutrino flux. A comprehensive investigation of the ion abundance variations should lead to a better understanding of ion fractionation processes in the solar corona, and in turn should yield accurate estimates of the He/H ratio. 3) A correlation between the He/H ratio and solar wind speed has been observed but the mechanism is unknown. By extending correlation studies to other ions it may be possible to uncover the mechanism. 4) Local temperatures and temperature gradients in the corona can be estimated from measurement of the charge distribution of Fe ions and the charge states of 0 and Si. To test the validity of the various solar wind expansion models, the experimentally derived temperatures and gradients can be compared to those derived from the models. 5) An average 4He/3He ratio of 2350 +- 120 has been derived from the five Apollo solar wind foil experiments , however, the ratio appears to be highly variable. In one instance, a ratio of 500 was observed over a two-day period With the mass spectrometer on ICE (ISEE-C), 3He will be continuously monitored, permitting an accurate determination of the solar surface abundance of this cosmologically important nucleus. The relation between anomalous 3He abundances in the solar wind and the small 4 He/3He ratios in some solar flares can also be studied. Calibration =========== The sensor was calibrated at the test facility of the Physikalisches Institut of the University of Bern. This facility consists of a vacuum chamber in which a homogeneous monoenergetic mass separated beam of ions can be produced and directed at the sensor mounted on a test platform which can be rotated about two axes perpendicular to the direction of the ion beam. Sweep circuits were used to synchronously change the voltages on the plates of the filter and analyzer while the outputs of each of the three CEM's strobed a multi-channel analyzer operating in the pulse-height-analysis mode. Calibrations were performed with H2+ and He+ at nominal velocities of 300, 400, 500, and 600 km/s. The orientation of the sensor with respect to the incident ion beam was changed in small increments over a range of +- 8 degree in the horizontal plane and +- 14 degree in the vertical plane. Angular acceptances derived from these functions are in good agreement with theory, whereas the experimental resolution always exceeds that predicted. The absolute values of the transmission determined at normal incidence for H2+ and 4He+ at the four different values of ion velocity are in excellent agreement with theory. The ability of the instrument to reject stray ions which create ghost peaks by scattering from the outside plates of the analyzer and contribute to the background was measured. In all cases, the ratio of ghost peak counts to counts in the main peak was less than 10**-4 with the ghost peaks always appearing at energy values 7 percent less than those of the corresponding main peaks. Because of the large difference in M/Z between 4He and 3He, interference of 4He+2 at the position of the 3He+2 peak is less than 10**-5 of the 4He signal. Operational Considerations ========================== The input voltages to the power supplies which provide the potential to the electric field plates of the Wien filter and energy analyzer are obtained from 12-bit digital-to-analog converters. The digital inputs to the converters come from the microcomputer-based processor. The full parameter range covered by the experiment is 300-600 km/s in velocity, 840- 11720 eV/Z in energy per charge, and 1.5-5.6 in mass per charge. The velocity range is divided into n steps and the energy per charge range into m steps, with both being logarithmically related. V(1s), (n, m) = R1**(m-1)*R2**(n-1)*V1(1,1), energy analyzer V(2s),(n) = R2** (n -1)*V2 (1), Wien filter 1 < n < 24, 1 <m <-40 (15) where V1s, and V2s, are the digital values of the voltages applied to the inputs of the power supplies, V1(1, 1) and V2(1) are the voltages for the velocity step n = 1 and the mass step m = 1, and R1 and R2 are constants. There are three modes of operation which are selectable by ground command. In mode 1, m is varied from 1 to 40. For each value of m, n is varied over its complete range. This mode is useful for surveying the solar wind. In mode 2, minimum and maximum values of m and n are chosen, so that only a part of the fuli parameter range is scanned; this mode will be for particular MIZ ratio determinations. Mode 3 is a search mode. The value of n corresponding to the velocity of the solar wind is determined by varying n from I to 24 while holding m constant at the value corresponding to that for 4 He until the value of n corresponding to the maximum counting rate is found. A scan is then made from n = n (solar wind) - 3 to n = n (solar wind) + 3 varying m between specified minimum and maximum values. This mode is intended for normal operations, as it yields the most data per unit time. In general, after each spin of the spacecraft a step is taken, but provisions have been made for holding a step for s = 2, 4, or 8 rotations of the spacecraft. The telemetry contains details of the mode, specified by the values of VI(l, 1), V2(l), mmin, mmax, nmin, nmax, s, R1, R2, and the counts from each of the detectors (separately logarithmically compressed above 127) for the corresponding values of m and n. At the minimum time resolution, a spectrum is obtained every 24 X 40 X 3 s (spin period = 3 s), or 48 min. Use of the search mode reduces this to approximately 12 X 3 + 6 X 40 X 3 s = 12 min, 36 s. Detectors ========= The basic requirements of the instrument were that it be capable of measuring ionic abundances over the M/Z range of 1.5-5.6 (3He+2 - 56Fe+10) at velocities from 300 to 600 km/s. To keep the dynamic range near 1x10**4 , H+ is not measured. The geometric factor g of the instrument is related to the ion flux F and count rate N by g = N/F (1) In order that N be at least one count per second for the least abundant ion species under consideration, g must be of order 10**-3 cm2. The dimensions of the apertures and angular acceptances in the plane of the spacecraft rotation and perpendicular to it determine g. The combination of a Wien filter and an electrostatic energy analyzer is a well-known means for determining the velocity and the energy per charge and, hence, the mass per charge of ions. Low resolution mass spectrometers of this type have been flown in the solar wind and in the inner magnetosphere. The spherical electrostatic energy analyzer is of conventional design. Care was taken to insure that the height and spacing of the plates were sufficient to accommodate the maximum angular divergence of entering ions; the analyzer constant is 5.86 eV/V, and its energy resolution is 50. With this design, the energy analyzer will transmit virtually all ions at the tuned energy independent of the angle with which they leave the Wien filter and enter the analyzer. It was thus assumed that the transmission function for the tuned analyzer is unity. Filters ======= It has been shown that the Wien filter can be made to focus along the direction of the magnetic field as well; as perpendicular to it by using cylindrical electrical plates. When this is done, the focusing length will be longer than for the parallel plate filter by a factor of 2**-1/2 however, the height of the filter can be reduced by up to a factor of 2. The result is a filter with volume and approximate weight 2**-1/2 that of a conventional filter of comparable resolution and geometric factor. Three important parameters are 1) Ion Optics; 2) Transmission Properties; 3) Velocity Resolution; and 4) Angular Acceptance. Measured Parameters =================== The table below details a description of the Wien filter and energy analyzer parameters. An approximation to the geometric factor is g = s * h * T * (delta alpha) (1/2)/180 (14) where s and h are the width and height of the Wien filter entrance aperture, (delta alpha) (1/2) is the acceptance angle in the x-z plane, and T is the transmission. Using the data from Coplan et al. (1978) Table II at a speed of 450 km/s, g is typically 1.7 x 10**-3 CM**2 for 3He and 4x 10**-4 CM**2 for the Fe ions, results which are close to the design goal. To achieve the theoretical resolution, the magnetic field in the working gap of the Wien filter was made homogeneous to better than +-l percent by the use of shaped pole pieces. The magnets used are sintered samarium cobalt, and a contoured yoke of vanadium pennendur provides a flux path for the internal magnetic field and serves as the principal structural element of the filter. To reduce the joint area (which contributes to flux leakage), the yoke was fabri- cated with only one open end. A shield of high permeability material further attenuates the external magnetic field to acceptable levels. The electric field in the Wien filter is produced by plates of gold plated aluminum with shims on top and bottom of each to correct for fringing fields. The plates of the electrostatic analyzer were roughened and plated with copper sulfide black in order to reduce ion scattering and UV reflectivity. A grounded high-transmission grid covers the exit aperture to reduce field distortion inside the analyzer. Ions leaving the exit aperture of the analyzer are detected by three identical channeltron electron multipliers (CEM's) mounted on ceramic circuit boards which also contain pre- amplifiers and discriminators. The multipliers are operated in the saturated pulse mode and the discriminators are set at a level corresponding to approximately 10**-13 C of charge per pulse. A grid, maintained at the potential of the CEM input, is placed directly in front of the detectors to increase counting efficiency by ensuring that all secondary electrons are collected. The relative count rates in each of the detectors depend on the angular distribution of the ions entering the filter and can be used to obtain the direction of the bulk motion of each species and some temperature information. Counts are only registered during 12 percent of the spin period of 3 s, giving a total background count rate of 0.02 per spin period. By comparison, the count rate for each of the Fe charge states (flux, 3 X 10**3 CM**-2 S**-1 ; geometric factor, 4 X 10**-4 CM**2) i s estimated to be 4 counts per spin period. TABLE INSTRUMENT PARAMETERS Wier, Filter (Stigmatic) Working Gap Length 180 mm Working Gap Cross-Section 11 mm 33 mm Average Magnetic Field 0.1454 W/m**2 Zero equipotential Radius of Curvature in (x,y)-plane 30.8 mm Entrance nd Exit Aperture Dimensions 2 mm X 15 mm Transmission 26-50% Resolution (V(0)/delta V) 20-30 Angular acceptance in ecliptic plane 0.5 - 3.6 deg Angular acceptance vertical to ecliptic plane 3 - 12 deg Weight 2.7 kg Electrostatic Energy Analyzer (spherical) Radius of zero equipotential 50.0 mm Radius of outer plate 54.7 mm Radius of inner plate 46.1 mm Sector Angle 167 deg Entrance and exit aperture dl-nsi.ns 2 mm x 15 mm Resolution (EIAE) 50 Weight 0.178 kg Massspctrometer (Filter and Analyzer) Range 3He - Fe Dynamic range 10**4 - 10**5 Overall gemtric factor 4x10**-4 - 1.7x10**-3 CM**2 Weight of sensor (without electronics) 4.ZB kg Total weight of instrument 5.6 kg