IMPACT

In-situ Measurements of Particles And CME Transients

IMPACT (In-situ Measurements of Particles And CME Transients) is a suite of seven instruments that will sample the 3-D distribution of solar wind plasma electrons, the characteristics of the solar energetic particle (SEP) ions and electrons, and the local vector magnetic field.

	Science objectives
	The Instrument IMPACT SIT
	MPS contribution
	The Team at MPS
	Project status
	Related links
	IMPACT publications by MPS members

Science objectives

IMPACT will be one of the STEREO mission's four measurement packages whose principal objective is to understand the origin and consequences of coronal mass ejections (CME's). CME's are the most energetic eruptions on the Sun. They are responsible for essentially all of the largest solar geomagnetic storms. The PI of the IMPACT package is Dr. Janet Luhmann.

The Instruments

IMPACT

IMPACT consists of 7 instruments:

• SWEA (Solar Wind Electron Analyzer)
• STE (Suprathermal Electron Telescope)
• MAG (Magnetometer)
• SEPT (Solar Electron Proton Telescope)
• SIT (Suprathermal Ion Telescope)
• LET (Low Energy Telescope)
• HET (High Energy Telescope)

The first three of these are located on the IMPACT boom/mast that extends a total of 4.5 meters antisunward on each spacecraft. (MAG is 3 meters from the spacecraft, SWEA is at the end of the boom, at 4.5 meters).
The latter four instruments make up the SEP subsystem which is mounted on the spacecraft body. The SEP instruments are packaged together except for a part of the SEPT instrument mounted on the spacecraft at a different location for field-of \-view reasons.

Figure 2: The location of the IMPACT instrument on one of the two STEREO spacecraft

SIT

The Suprathermal-Ion-Telescope (SIT) is part of the 'In-situ Measurements of Particles and CME Transients' (IMPACT) investigation on board the two STEREO spacecraft. Each SIT sensor is a time-of-flight (TOF) mass spectrometer, designed to measure the ions, protons through iron, from 20 keV/nucleon up to several MeV/nucleon in energy.

In-situ observations of solar and interplanetary energetic particles help us to understand the important processes involved in the acceleration and transport of energetic particles. Since energetic particles are produced throughout the universe, these processes are relevant not only in the heliosphere but also in more exotic, astrophysical sites, where in-situ measurement are not possible.

SIT is designed to measure energetic particles produced by a wide variety of phenomena, including particles accelerated by CME driven shocks in the solar corona and in interplanetary space, solar flares, and corotating interaction regions (CIRS). Because the shocks associated with CMEs are often quite weak at 1 AU, the energy spectra produced by these shocks are usually soft and do not extend into the MeV energy range. The large geometric factor (0.3 cm2 sr) and low energy response of SIT makes it well suited for observing energetic particles produced locally by these events.

Another advantage of SIT is that good mass resolution allows the composition of the particles to be measured, thus helping to determine the source population of the particles. Composition measurements, for instance, are useful in distinguishing particles that are accelerated in the corona, in interplanetary space, or at the site of solar flares.

Figure 3: Schematic diagram of the SIT sensor

MPS contribution on the IMPACT/SEP/SIT

SIT is an international project and part of the IMPACT instrument. SIT is led by Glenn Mason, Univ of Maryland, College Park, Greenbelt, MD. USA. The hardware contribution from the MPS includes the following parts:

• electronic board for two amplifiers and two Constant-Fraction discriminators for Start- and Stop pulses
• electronic board for Time to Digital Converter (TDC), Coincidence Check plus event counter (contract: Inst. f. Datenverarbeitung, Braunschweig)

The Team at MPS

Axel Korth	Lead Investigator
Urs Mall	Co-Investigator
Radoslav Bucik	Guest Scientist
Klaus Heerlein	Engineers and Technicians

Project status

The Engineering Model (EM) is tested and is working satisfactorily. The two Flight Model (FM1, FM2) were delivered in February and May 2004 to the University of Maryland, Greenbelt, USA. The Flight Spare Model (FS) was delivered in December 2004 to the same instution. The launch is planned for August 2006 from Cape Canaveral, FL, USA.

Related links

	IMPACT at SSL in Berkeley (with a list of the team members)
	SIT description document