SEPICA Science


Press Releases:

When the Sun Sneezes, ACE takes its temperature

(Pencil drawing by Daniela Möbius)


  • ACE News #60: Charge States of Energetic Particles in Corotating Interaction Regions (6 April, 2002)
  • ACE News #50: Relating Solar Wind Plasma to its Coronal Sources using In Situ Charge State Information (25 October, 2000)
  • ACE News #41: Heavy Ion Charge State Measurements over an Extended Energy Rangewith ACE and SOHO(31 January 2000)
  • ACE News #33: Charge State Variations between Impulsive and CME Related Solar Energetic Particle Events (7 July 1999)
  • ACE News #23: Ionic Charge States in 3He-rich Solar Energetic Particle Events (9 October 1998)
  • ACE News #14: Indication of Charge State Variation During the November 1997 Solar Particle Events (30 April 1998)
  • ACE News #4: Helium-3-Rich Solar Particle Events Observed by SEPICA (10 November 1997)

Scientific Papers:

Research Goals:

SEPICA is the main instrument on ACE responsible for the determination of the ionic charge states of solar and interplanetary energetic particles. The charge state of energetic ions is key data, needed to determine source temperatures, acceleration, fractionation, and transport processes for these particle populations. Ionic charge results from SEPICA's predecessor the ISEE ULEZEQ instrument have shown, for example:

Instrument Description:

To better understand the processes above, SEPICA was designed to provide superior charge state resolution and a larger geometric factor than ULEZEQ (see tables below). With these improved capabilities, individual charge states can now be resolved and counting statistics are more reliable.

Energy Range and Element Resolution

Energy Range



0.3 - 6 MeV/N (He) isotopic He
0.2-18 MeV/N (O) individual elements up to O
0.1-5.4 MeV/N (Fe) groups, deltaZ/Z approximately equals 2-3 up to Fe

Geometric Factor and Charge Resolution deltaQ/Q

Geometric Factor

less than or equal to 1 MeV/Q

less than or equal to 3 MeV/Q

0.2 cm2sr 0.3 1
0.03 cm2sr 0.1 0.3

To accurately measure the charge states of incoming ions SEPICA uses one high charge resolution sensor section and two low charge resolution sections. The charge resolution is achieved by focusing of the incoming ions through a multi-slit mechanical collimator, deflection in an elctrostatic analyzer with a voltage up to 30 kV, and measurement of the impact position in the detector system.

SEPICA schematic Schematic view of the SEPICA instrument
To determine the nuclear charge and energy of the incoming ions, thin-window flow-through proportional counters with isobutane as the counter gas, and ion-implanted solid state detectors are used. The counters provide for three independant deltaE (energy loss) verses E (residual energy) telescopes. The multi-wire proportional counter simultaneously determines the energy loss (deltaE) and the impact position of the ions. Supression of background noise from penetrating cosmic radiation is provided by an anti-coincidence system with a CsI scintillator and Si photodiodes. The data are compressed and formatted in the S3DPU, which is shared with SWICS and SWIMS.

Visit the Photo Gallery to see annotated photographs of SEPICA and ACE.

Movies for Public Outreach:

ACE and SEPICA Movies:

Related Topics:


Scientific Investigators:

Eberhard Möbius (lead) email:
Lynn Kistler email:
Mark Popecki email:
Eric Lund


Antoinette Galvin email:


Ken Crocker email:
Mark Granoff email: