Instrument Description

Instrument Overview Instrument Overview

Principle of Operation Principle of Operation of CODIF

CODIF Instrument Paper CODIF Instrument Paper


Instrument Overview

The Cluster Ion Spectrometer (CIS) is a comprehensive ionic plasma spectrometry package onboard the four Cluster spacecraft, capable of obtaining full three-dimensional ion distributions with one spin (4 second) time resolution and with mass-per-charge composition determination. The CIS package consists of two different instruments, the time-of-flight ion Composition Distribution Function analyzer (CODIF, CIS-1), and the Hot Ion Analyzer (HIA, CIS-2), plus a sophisticated dual-processor based instrument control and data processing system (DPS), which permits extensive onboard data-processing.

The CIS experiment is a collaborative effort of many international institutions, under the principal responsibility of CESR (Toulouse, France). The Max-Planck-Institut für extraterrestrische Physik (MPE) contributed to CODIF the analog electronics for time and position determination, the post-acceleration high voltage, the microchannel plates, the electronic box, the carbon foils, mechanical components for the time-of-flight section and support for integration, test, and calibration.

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Principle of Operation

Fig. 1: CODIF-schematic

Principle of Operation of CODIF

The instrument combines the selection of incoming ions according to energy per charge by electrostatic deflection in a toroidal analyzer with post-acceleration by up to 20 keV/e and subsequent TOF analysis.The electrostatic analyzer (ESA) is of a toroidal top-hat type with a uniform response over 360° of polar angle. As illustrated in Fig. 1, the analyzer consists of an inner toroid, to which a variable negative potential is applied, an outer toroid with a cut-out at the top, and a top-cap lifted above the outer toroid. Both, the outer toroid and the top-cap are normally held at ground potential, thereby exposing no high voltage to the outside world. A beam of parallel ion trajectories entering the aperture is focused to a certain location at the exit plane of the analyzer. This location determines the incident polar angle of the ions. With a cross-plate voltage of 2-5200 V (varied with logarithmically spaced steps), the energy range is 15-40000 eV/e. The analyzer has an intrinsic energy resolution of dE/E ~ 0.13. It is surrounded by a cylindrical collimator which serves to define the acceptance angles. The full polar angle of the analyzer is divided into 16 pixels of 22.5° each. The full energy sweep will be performed 32 times per spin. Thus a two dimensional cut through the distribution in polar angle with 11.25° resolution in azimuthal angle is obtained every 1/32 of a spin period. The entrance apertures of CODIF provides two different geometrical factors in order to maximize the dynamic range of the instruments, with the geometric factor in the second half attenuated by a factor of 100 using an array of pin holes.

Behind the electrostatic analyzer the ions are accelerated by a voltage of -10 to -20 kV, such that the ions have a minimum energy before entering the TOF section. The energy per charge E/Q as selected by the ESA plus the energy e . UACC gained by post-acceleration and the measured time-of-flight t through the length d of the TOF unit are combined into the mass per charge M/Q of the ion according to:

M/Q = 2ß(E/Q + e . UACC)/(d/t)2.

The quantity ß represents the effect of energy loss in the thin carbon foil
(3 µg/cm2) at the entry of the TOF section and depends on particle species and incident energy. The start signal is provided by secondary electrons, that are emitted from the carbon foil during the passage of the ions. The electrons are accelerated and deflected onto the start portion of the microchannel plate (MCP) by the appropriate potential configuration. The secondary electrons also provide the position information for the angular sectoring. The stop signal is provided by secondary electrons generated by the ions hitting the stop portion of the same MCP.

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CODIF Instrument Paper

CODIF Instrument Paper

In addition to CLUSTER, a similar time-of-flight plasma analyzer system has been flown as ESIC (Equator-S Ion Composition instrument) on  Equator-S, and as  TEAMS (Time-of-flight Energy Angle Mass Spectrograph) on  FAST. For a full description of the CODIF sensor on these missions see the  CODIF Instrument Paper .

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© Max-Planck-Institut für extraterrestrische Physik

last update 12/8/2004
by Rosmarie Mayr-Ihbe,

Contact Person: Berndt Klecker,