Showing papers by "Ralf Srama published in 2005"

High-velocity streams of dust originating from Saturn

Abstract: As the Cassini-Huygens probe approached Saturn, the onboard dust detector revealed Saturn as a source of tiny grains moving faster than 100 km s−1. Most of these particles are now thought to originate from the edge of Saturn's outer dense ring. In situ analysis of the material in this region is not possible because the spacecraft would risk collision damage so close to the rings. But the new findings show that this can be achieved by proxy using the Cassini dust detector from a safe distance. And see the News pages for the remarkable first images of Titan from the Huygens part of the mission. High-velocity submicrometre-sized dust particles expelled from the jovian system have been identified by dust detectors on board several spacecraft1,2. On the basis of periodicities in the dust impact rate, Jupiter's moon Io was found to be the dominant source of the streams3. The grains become positively charged within the plasma environment of Jupiter's magnetosphere, and gain energy from its co-rotational electric field4. Outside the magnetosphere, the dynamics of the grains are governed by the interaction with the interplanetary magnetic field that eventually forms the streams5. A similar process was suggested for Saturn6. Here we report the discovery by the Cassini spacecraft of bursts of high-velocity dust particles (≥ 100 km s-1) within ∼70 million kilometres of Saturn. Most of the particles detected at large distances appear to originate from the outskirts of Saturn's outermost main ring. All bursts of dust impacts detected within 150 Saturn radii are characterized by impact directions markedly different from those measured between the bursts, and they clearly coincide with the spacecraft's traversals through streams of compressed solar wind.

Composition of saturnian stream particles.

Abstract: During Cassini's approach to Saturn, the Cosmic Dust Analyser (CDA) discovered streams of tiny (less than 20 nanometers) high-velocity (∼100 kilometers per second) dust particles escaping from the saturnian system. A fraction of these impactors originated from the outskirts of Saturn's dense A ring. The CDA time-of-flight mass spectrometer recorded 584 mass spectra from the stream particles. The particles consist predominantly of oxygen, silicon, and iron, with some evidence of water ice, ammonium, and perhaps carbon. The stream particles primarily consist of silicate materials, and this implies that the particles are impurities from the icy ring material rather than the ice particles themselves.

Velocity-dependent wave forms of piezoelectric elements undergoing collisions with iron particles having velocities ranging from 5 to 63 km/s

Abstract: A response from piezoelectric lead-zirconate-titanate elements was investigated by bombarding them with hypervelocity iron particles. The observed signal form was clearly dependent on the particle velocity during collisions. The signal form exhibited oscillations for particle velocities less than 6km∕s, whereas it changed drastically into a solitary pulse above 20km∕s. This behavior was exclusively classified based on the velocity. The rise time of the solitary pulse in the output form had a good correlation with the velocity at impact. The change in the form was discussed in terms of elastic and plastic states by regarding Young’s modulus as a criterion between both states. It is proposed that a single piezoelectric element has the potential to detect the velocity of particles in space.

Performance of AN Advanced Dust Telescope

Abstract: A Dust Telescope is a combination of aTrajectory Sensor with an analyzer for the elemental composition of micrometeoroids or space debris. Dust particle trajectories are determined by the measurement of the electric signals that are induced when a charged grain passes through a position sensitive electrode system. The position sensitive system consists of four planes of wires where each wire is connected to a separate charge sensitive amplifier. The amplifier is based on CMOS technology and was developed in cooperation with the ASIC Laboratory in Heidelberg. Furthermore, a 32 channel transient recorder (TR) running with 20 MHz and 10 bit resolution was developed and manufactured in order to store the individual signals. This system allows the accurate determination of the particle velocity vector. The elemental composition of particles is analyzed by a time-of-flight system for the ions which are generated upon the particle impact. The large area of this mass analyzer is 0.1 m and has a mass resolution above 100 for all possible impact locations. This paper describes the performances of the laboratory model of theTrajectory Sensor and shows the study results of the mass spectrometer.

In‐Situ Monitoring of Interstellar Dust in the Inner Solar System

Abstract: We present in this paper new interstellar dust data obtained in the inner solar system by the dust instruments on‐board the Cassini, Galileo and Helios spacecraft. While the Ulysses dust instrument provided an in‐situ monitoring of the interstellar dust stream at high ecliptic latitude between 3 AU and 5 AU, the new data cover an heliocentric distance range between 0.3 AU and 3 AU in the ecliptic plane. We show therefore in this paper the deep penetration of interstellar dust inside the Solar System. Furthermore, the data provide evidence of the interstellar dust stream alteration in the inner solar system, caused by radiation pressure forces and gravitation focusing.

Development of an ion-to-electron converter

Abstract: This article describes the design aspects of an ion-to-electron converter with a large area detector (approximately 450cm2). This converter was designed for a large area mass analyzer for the detection of cosmic dust particles. The design is based on the MM1 electron multiplier and the simulations were carried out using the software package SIMION 3D for the calculations of the electric field. Several dynode profiles were investigated in order to compare the time resolution and particle transmission. It is shown that the converter properties strongly depend on the dynode profile. Potential manufacturing processes are discussed briefly.

Empirical formulas for hypervelocity impact with a piezoelectric element and their application to a new real-time dust detector

Abstract: Hypervelocity collisions of microparticles with a lead-zirconate-titanate piezoelectric element are examined. The waveforms thus obtained depend on the velocities during collision, and are classified into three categories. In particular, the first cycle of the signal observed immediately after collision is essential to obtain information on the impact. In each category, experimental formulas that are functions of the impact velocity are established based on experimental data. It is concluded that a single piezoelectric element can potentially measure the velocity and/or momentum of hypervelocity microparticles in real time. In the abovementioned context, the new dust detectors are described.