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Instrument: SEPICA : Solar Energetic Particle Charge Analyzer
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SEPICA is one of nine instruments aboard the ACE spacecraft. Its mission is to
collect information about particles emanating from the Sun. SEPICA detects the
ionic charge state, kinetic energy, and nuclear charge of ions coming from the
Sun, and with that information, one can determine not only the type of ions
present, but also the history of those ions within the Sun. This aids
scientists in their understanding of the Sun and the processes that take place
within it.

The SEPICA instrument is the prime sensor on ACE, which is used to determine
charge state distribution of energetic particle distributions. SEPICA is
designed to measure the ionic charge state, Q, the kinetic energy, E, and the
nuclear charge, Z, of energetic ions above 0.2 MeV/Nuc (Stone et al., 1990).
This includes ions accelerated in solar flares as well as in interplanetary
space during energetic storm particle (ESP) and co-rotating interaction region
(CIR) events. For low mass numbers SEPICA will also separate isotopes -- for
example, 3He and 4He. During solar quiet times, SEPICA should also be able to
directly measure the charge states of anomalous cosmic ray nuclei, including H,
N, O, and Ne, which are presumed to be singly-charged. With the capability to
differentiate the charge states of ions, the instrument will also be able to
separate neutral atoms (Q = 0) from ions. Thus it may be able to identify
energetic neutrals created through charge exchange.

The instrument is based on the design of the ULEZEQ (Ultra Low Energy Z E Q
Analyzer) sensor flown on the ISEE spacecraft (Hovestadt et al., 1978). The
sensor combines the determination of the electrostatic deflection of incoming
ions in a collimator-analyzer assembly by the measurement of the impact
position in the detector plane and a dE/dx - E telescope with a proportional
counter solid state detector combination. The background from penetrating
radiation is suppressed by the use of an anti-coincidence detector. The
scientific objectives of the ACE mission call for significant improvements over
the ULEZEQ sensor in the following parameters of the instrument:

1. Increase of the geometrical factor by at least a factor of 10 (to improve
the measurement statistics significantly)

2. Improvement of the charge resolution to deltaQ/Q 0.1 below 0.7 MeV/nucleon
(to allow resolution of individual charge states for elements up to oxygen.

SEPICA was built as a collaboration between the UNH Space Science Group and the
National Aeronautics and Space Administration (NASA). SEPICA's mission was
proposed in 1986. The project was kicked off into Phase B in May of 1991, with
the development and implementation of Phase C started in January, 1994.
Satellite integration and testing (Phase D) was carried out through 1996 and
1997. ACE itself was launched on 25 August, 1997, on a Delta II launch vehicle,
from the Kennedy Space Center in Florida. Since then, SEPICA has been returning
data on the solar wind.


Online Resources

Instrument Logistics
Data Rate: 0.604 kbps
Instrument Start Date: 1997-08-25
Instrument Owner: University of New Hampshire, Space Science Group