About SEPICA Data

Sensor Full Name Measured Species Measured Quantities Typical Energy (MeV/nuc.) Measurement Technique


Solar Energetic Particle Ionic Charge Analyzer 1 <= Z <= 26 Q, Z, E 0.1 - 5.0 E/Q
dE/dx - E

The SEPICA Instrument on ACE

The Solar Energetic Particle Charge Analyser (SEPICA) is used to determine the 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. 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. 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.

For more information about the SEPICA instrument, visit the SEPICA Home Page, at the University of New Hampshire.

Due to failure of the valves that control gas flow through the instrument, active control of the SEPICA proportional counter is no longer possible. At this time, we do not expect to deliver any SEPICA data beyond Feb 4 2005, unless one of the valves opens by itself, as has happened a few times in the past.

SEPICA Data Description

Time Data
All level 2 data records for all ACE instruments contain timing information in the same format. The format of the timing information is described

Element Fluxes
SEPICA level 2 data is organized into 27-day time periods (Bartels Rotations - roughly one solar rotation period). For each Bartels Rotation, the level 2 data contains time averages of solar energetic particle fluxes over the following time periods:

Currently, spin-averaged flux data are available for 9 elements, in units of particles/(cm2*Sr*sec*MeV/nucleon), in a number of energy ranges. The energy ranges are different for each element - download this file of energy ranges. The elements for which data are available are:

Release notes for SEPICA level 2 data - provided by the SEPICA instrument team. All users of SEPICA data should read these notes.

The following other notes apply:

Flux Uncertainties
Flux data uncertainties are derived from statistical (counting) errors only. The uncertainties are fractional uncertainties, and are given as 1/sqrt(N), where N is the number of events in the averaging period. For no events, an uncertainty value of -999.9 is given.

Quality Information
up_time_fraction: a measure of the fraction of time the instrument was collecting data during a given averaging period.

number_of_records_120s: number of 120-second data records used in the averaging period (H and He only).

number_of_records_1hr: number of 1-hour data records used in the averaging period (heavier elements).

Our Email Address: asc@srl.caltech.edu

Last Updated:05 January, 1999

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