CDA carries an integrated time-of-flight mass spectrometer (22 cm drift length) in order to analyze the elemental composition of an impinging dust particle. The fast sampling rate of 100 MHz at the multiplier enables this channel to record a time of flight mass spectrum of mass resolution M/AM =50. The resolution is high enough to identify the major elemental composition.

3.2. Cometary and Interstellar Dust Analyser, CIDA

The CIDA instrument on board Stardust [27] is a high resolution time-of-fhght mass spectrometer. The drift tube of the time-of-flight spectrometer CIDA is folded and has a total length of 56 cm. The reflector compensates for different initial starting energies of the ions and thus increases the mass resolution. Amplifiers connected to the multiplier allow the measurement of the TOF spectrum. The useful target size is 120 mm in diameter. For an impact angle of 40° from the target normal, this corresponds to a sensitive area of 0.009 m2. CIDA is a direct derivative of the highly successful PIA and PUMA instruments flown on the Giotto and Vega spacecraft [9]. However, it has about 10 times larger sensitive area (0.009 m2) and twice its mass resolution (M/AM = 250).

3.3. Dust Detector System, D2S

The D2S instrument consists of an impact detector of the type flown on Vega [28] and a trajectory analyzer of charged dust grains, similar to the charge measurement sub-system of Cassini CDA [26]. The proposed large surface area dust detector consists of an array of 7 individual D2S detectors. Each D2S detector will apply two sets of parallel grids for position, charge and velocity sensing, a shield grid in front of the charge sensing stage, and a PVDF film for mass determination at the bottom of the instrument.

The detection principle of the charge-sensing trajectory detectors is based on charge induction by the dust particle's electrical charge [8] [29] [30]. Two parallel grids are connected to a single charge sensitive amplifier. When a charged dust grain passes through these grids, it induces a charge on the grids, and this can be measured as a function of time. The amplitude of the signal is proportional to the charge on the dust particle, and the duration of the signal contains information on the velocity of the grain. Two sets of parallel grids are inclined in perpendicular directions. Thus, a particle's instantaneous position is measured in two perpendicular planes, and the trajectory of the charged particle can be reconstructed. Several dust charge signals (of > 10'15 C) obtained by Cassini CDA proved the principle.

The detection principle of the PVDF film detectors is based on the depolarisation signal a dust particle generates, when penetrating a permanently polarised PVDF thin film [28] [31]. Dust grains penetrating the thin PVDF film remove dipoles along their trajectory producing a fast electric charge pulse without requiring bias voltages. The produced signal is a function of the particle mass and velocity. PVDF film dust detectors have been extensively tested and calibrated in laboratory experiments.

3.4. Momentum sensor, ISIDE

The Impact Sensor for Interstellar Dust Exploration (ISIDE) is aimed at monitoring the dust mass flux, measuring the momentum of the impacting grains and their velocity. ISIDE is formed by an array of four sensor plates. ISIDE sensing elements are similar to the subsystems used in the GIADA experiment, for ESA's Rosetta mission.

The instrument uses piezoelectric transducers (PZT) as impulse sensors. PZTs have been used successfully in high velocity impact sensors since the Explorer I mission and have given excellent results in the Giotto cometary mission (DIDSY experiment) and on the Mir space station. As an example, thanks to DIDSY, it was possible to monitor for the first time the dust flux at comet lP/Halley during flyby with a relative velocity of 68 km/s [32],

Each ISIDE sensing element is formed by a 12 x 12 cm aluminum diaphragm equipped with five piezoelectric sensors placed at the four corners and at its center, and thus able to detect the grain impact. The geometry of the plate has been chosen to have a propagation frequency close to the resonating frequency of the sensing crystals and to damp reflected waves from the sensor edges, which would increase the noise.

3.5. Plasma Monitor, PLASMON

PLASMON is a plasma monitor consisting of a magnetometer, a simple electrostatic plasma analyser and a Faraday cup. All three sensors are integrated in the spherical PLASMON sensor which has a diameter of 15 cm. The PLASMON instrument will be mounted at the dust baffle. The sensors are controlled by a single DPU which serves as the interface to the spacecraft. All three sensor types are well space-proven. A similar instrument, the ROMAP, was developed and tested for the Rosetta Lander. Assuming a radial solar wind bulk velocity, all major plasma parameters such as electron and proton densities, and temperatures and proton bulk velocity can be derived.

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