Electrons are measured from 0.2 to 10 MeV, primarily providing time markers for injections of solar particles. Hydrogen is measured from 1.4 to 120 MeV, and Helium is measured from 0.04 to 500 MeV/nucleon. The collection powers and energy ranges for heavier nuclei up to iron are ideal for observations of quiet-time populations such as particles accelerated by interplanetary shocks and the anomalous cosmic rays. The large collecting power available is ideal for observing 3He, 4He, and heavier nuclei in impulsive solar events. For the first time it may be possible to observe ultra heavy nuclei (Z> 30) in large solar events. Finally, there is also a telescope designed to measure isotopes from He to Fe, which is intended for solar particles, anomalous cosmic rays, and galactic cosmic rays. There will be important opportunities for combined studies with other spacecraft, such as SAMPEX, Ulysses, and Voyagers1 and 2.
LAUNCH The WIND spacecraft was launched at 04:30 EST on Nov. 1, 1994 aboard a Delta rocket. The orbit is designed to make several passes through the magnetosphere and then moving into a halo orbit around the L1 Lagrange point.
Overview
The EPACT investigation must make measurements over an extremely broad range of elements,
energies, and intensities. As a result, EPACT consists of multiple telescopes that also
provide a level of protection against single-point fialures. The Low Energy Matrix Telescope
(LEMT) consists of three identical telescopes, whereas ELITE consists of two Alpha-Proton-
Electron (APE) telescopes and an Isotope Telescope (IT). LEMT and ELITE have been designed,
built and tested by the Low Energy Cosmic Ray Group and the Electronics Systems Branch of the
Laboratory for High Energy Astrophycis at the NASA/Goddard Space Flight Center. Later, the
Suprathremal Energetic Particle telescope system (STEP) was added to EPACT. STEP contains two
identical telescopes. STEP was designed and built by the University of Maryland.
All the telescopes except for those in STEP use the dE/dx by E method of particle identification. Solid-state detectors are used throughtout for reliability and long-term stability. STEP measures time-of-flight and energy, from which particle mass can be obtained. Each STEP telescope includes a start and stop microchannel plate detector as well as a solid-state detector to measure the total energy.
Detector Subsystems
The Low Energy Matrix Telescope (LEMT)
The front dE/dx elements are 16 surface barrier detectors arrayed on a spherical dome
in order to minimize path-length variations. Each detector is nominally 1.75 cm^2 by 18 microns
thick. The residual E detector is an ion-implanted detector 36 cm^2 by 1000 microns thick. It is
subdivided into five 13.3 mm wide strips on each side.
The Electron Isotope System (ELITE)
The Alpha-Proton-Electron Telescopes
The primary purpose of the APE telescopes is to provide coverage of the lowest charge particles
over a wide range of incident energies up to very high rates. The APE telescopes do ovserve heavy nuclei
up through iron, however, and can resolve isotopes of the lighter elements without trajectory information.
APE-A consists of four detectors. The A1 and A2 detectors are circular silicon surface barrier detectors, nominally 150 microns thick by 8 cm^2. Double foils are used in front of the telescope to protect the A1 detector from sunlight and from high counting rates due to particles at energies just below the APE-A energy range. The A3 and A4 detectors are circular Lithium drifted detectors (LiDs) 3 mm thick by 17 cm^2. The telescope acceptance geometry is defined by a coincidence between the A1 and A2 detectors in anti-coincidence with the A4 detector. The geometry factor for the telescope is 1.2 cm^2 sr, independent of energy.
APE-B consists entirely of LiD detectors. The B1 and B2 detectors are curved (radius of curvature of 7.0 cm) to minimize path length variations. The maximum variation is 2.8 % for particles not passing through an edge of B1 or B2. Particles stopping in APE-B are identified by a coincidence condition of B1 * B2* ~C7 (~ means NOT). The geometry factor for stopping particles is 1.3 cm^2 sr. Particles stopping in B2 are referred to as 2-D particles, while those penetrating B2 and stopping in one of C1 through C6 are referred to as 3-D particles. Penetrating particles are also accepted for analysis. This expands the energy range to include minimum ionizing particles. Penetrating particles include both particles which enter through B1 and exit through D (forward particles) and those which enter D and exit B1 (backward particles). APE B has been mounted on a short tower with an unobstructed 180 degree view to allow both types of particles. The geometry factor for penetrating particles is 1.95 x 1.08 cm^2 sr, after allowing for 5% obstruction of the FOV by the spacecraft.
Isotope Telescope consists of 8 silicon detectors. The first two detectors are
two dimensional position sensitive detectors (PSDs). They are required so that path-length corrections
may be made for the angle of incidence and for nonuniformities in detector thickness. The electrodes on
each side of each PSD are segmented into 125 strips with a pitch of 0.5 mm and an inter-strip gap
of 35 microns. The strips are interconnected by 68 ohm chip resistors at the periphery of the detector
wafer. Preamplifiers connected to strips 1, 32, 63, 94, and 125 subdivide each PSD into 4 sections of
32 strips each. From the signal on the 5 preamplifiers, the particle position can be measured. This
technique works well for nuclei with charge Z > 2. For He, the isotopes are well separated, even with
poor spatial resolution. The next 5 detectors below the PSDs (E1 - E5) vary in thickness from 150
microns to 8 mm. Multiple dE/dx measurements are possible with this system.
The Suprathermal Energetic Particle System (STEP)
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