The configuration diagram for CPI-HS is shown in
Figure 2. The Hot Plasma Analyzer is
equipped with three spherical-segment plates. The outer and inner plates
are grounded, and the center plate is supplied with a programmable series
of voltages, 65 mV to 2.4 kV, in order to provide E/Q analyses of the
ions and electrons. The radius of curvature R of the center plate is 10.2
cm and the analyzer constant, R / (2 × dR), is 20 for electrons and
positive ions. The 64 E/Q passbands for the range are identified in Table 1. The inner and outer
channels are the positive ion and electron analyzers, respectively. Each
of these two analyzers is serviced with 9 continuous-channel electron
multipliers in order to divide the fan-shaped acceptance angle into 9
individual segments. These sensors are Galileo Electro-Optics Spiraltrons
with either 1 mm or 3 mm diameter acceptance apertures, the outputs of
which are fed into individual AMPTEK Inc. model A111F PAD
amplifier-discriminators. The Spiraltron bias voltages are controlled by
ground commands to any one of 32 voltage levels between +1690 to +3400 V
(electron sensors) and -1718 to -3450 V (positive ion sensors).
Considerable design effort was expended in shaping the analyzer
fields-of-view and in maintaining approximately equal geometric factors
and E/Q resolutions for the two sets of nine sensors. These goals were
accomplished with a fence at the entrance apertures of the electrostatic
analyzers, tailored angular length (analyzer arc angle) from entrance to
exit apertures, and aperture plates at the sensors. In addition the
concave surfaces of the spherical-segment plates were machined with
sawtooth serrations of 1-mm depth in order to suppress the ultraviolet
(primarily solar Lyman) and
electron scattering along the plates into the sensors.
The fields-of-view, energy resolutions and provisional geometric factors are derived from ray tracing and laboratory calibrations and are tabulated in Table 2.. The provisional geometric factors are to be refined with postlaunch data. The latitude is taken with respect to the spin axis of the spacecraft with 0° in a direction parallel to the spin axis and viewing generally toward the south ecliptic pole. The azimuthal range of ø is given in the spacecraft spherical coordinate system. The meridional plane at ø = 0° is parallel to the normal to the entrance aperture of the electrostatic analyzers. For example, the instantaneous field-of-view for electron sensor E1 is the solid angle within and . Note that the total coverage of latitude is 4° to 176° and allows sampling of all but 0.3% of the sr solid angle for particle velocity vectors at the spacecraft position. This is an important feature for accurate determination of the three-dimensional velocity distributions.
The operation of the Hot Plasma Analyzer, and the other two analyzers to be described below, is extremely flexible and is controlled by uplinked commands to the instrument microprocessors. A frequent operating mode for measuring the three-dimensional velocity distributions of positive ions and electrons is the division of one spacecraft rotation period (3 s) into eight equal intervals (azimuthal sectors). Four E/Q passbands are consecutively sampled in each of these azimuthal sectors. Every other passband in the range 22.2 V to 48.2 kV (see Table 1) is used. Thus a 1728-sample determination of each of the ion and electron intensities over the above E/Q range is acquired in 18 s. The repetition rate is 21 s because 2304 samples each of the ion and electron velocity distributions, , are gathered each 192 s in order to characterize the spacecraft potential, the secondary electron environment, and ambient cold plasmas.
The configuration of the Solar Wind Ion Analyzer is also shown in Figure 2. The twelve sets of sensors and amplifier-discriminators are the same types as those employed for the Hot Plasma Analyzer. The bias voltage for the Spiraltrons can be varied from -1975 V to -3940 V in 32 increments by ground command. The analyzer arc angle is 75° and the analyzer constant is 42. A programmed series of potentials ranging from 3.4 V to 163 V on the outer plate with the inner plate grounded provides measurements of positive ions with within a maximum of 64 passbands. These passbands are listed in Table 3. The total latitudinal span of the field-of-view is which is divided into 12 equal, contiguous segments of 5° with the use of 12 sensors at the exit aperture of the electrostatic analyzer. The angular coverages, energy resolutions, and provisional geometric factors for the 12 sensors are tabulated in Table 4.
Operation of the Solar Wind Ion Analyzer is flexible via ground commands. A current operating mode provides division of the azimuthal (spin) sector øs = 303.75° to 56.25° into 42 equal, contiguous segments where øs = 0° is the direction to the sun. Thus the field-of-view consists of 504 contiguous solid angles, 12(latitude) × 30(azimuth). These fields-of-view and the E/Q passbands are interleaved to achieve 7560 samples of the ion velocity distribution once each 48 s. The odd-numbered passbands as listed in Table 3 are employed for this particular mode of operation.