Impact ionization of high-velocity cosmic dust particles has been used as a basic principle for dust detectors in space for many decades. It has provided optimum means to gain insight into the dust environment in the solar system. The Ulysses Dust Detector System provided for the first time impact ionization-based detection of interstellar dust (ISD) in the solar system and discovered surprisingly heavy ISD particles with sizes up to a few microns. Studies based on astronomical observations of the local interstellar medium, on the other hand, sug-gested a much smaller upper limit of around 0.25 mu m (silica) or 1 mu m (graphite) for the size distribution of ISD particles. Therefore, it has been suggested that low-density fluffy dust particles may mimic the impact signals of heavier compact particles. In this work, we discuss a series of impact experiments that have been performed at the Heidelberg dust accelerator facility with the Cosmic Dust Analyzer flight spare unit, to compare the high-velocity impact ionization properties of compact and hollow silicate particles, and carbon aerogel particles with each other and with literature data. The experiments indicate differences in the collected total amount of impact charges and how quickly the charges are collected, between impacts from compact particles and their non-compact coun-terparts. The results of this first study suggest that fluffy particles generate less ions upon impact than their compact counterparts, opposite to the suggested explanation for the heavy ISD particles. Data from the performed impact experiments indicate that a secondary process (e.g. secondary impacts from ejecta or more target material ionization) could be the main cause for the observed differences. These results imply that the previously detected heavy ISD particles may be real. We identify the key problems with the performed dust experiments and advise that future impact ionization instruments should additionally be calibrated with improved low-density fluffy dust particles that better represent the properties of cosmic dust particles.

The Venetia Burney Student Dust Counter (SDC) is an in situ dust detector on board the New Horizons spacecraft measuring the interplanetary dust particle (IDP) distribution for grains with mass m > 10−12 g. SDC provides a near-continuous measure of the interplanetary dust environment, with recent results spanning beyond 50 au. This coverage includes the Edgeworth–Kuiper Belt (EKB), suggested by numerical models to be the dominant source of IDP in the outer solar system. Here we present the updated dust density distribution to 50 au and compare estimated flux values to existing theoretical models. SDC observes peak dust flux and densities near 42 au, and we expect a decay with increasing heliocentric distance. Based on SDC measurements, we also discuss the effects of IDP generation, transport, and loss on the evolution of the surfaces of EKB objects, the continual intermixing of their surface material, and the general tendency to homogenize their spectral properties. Continued SDC measurements remain critical for revealing the large-scale structure of the EKB and to guide the interpretation of dust disks around other stars. Additionally, we consider the potential of an interstellar dust (ISD) and “outer” Kuiper Belt contribution to SDC measurements and its effect on anticipated SDC flux values beyond 50 au, and we show that the inclusion of either source to the predicted model results in a noticeable deviation in anticipated SDC measurements beyond 50 au. Current and future SDC measurements also serve to constrain the relative contribution of ISD to SDC’s flux and density estimates.

Faraday cups can measure velocity distribution functions of space plasmas and are frequent instruments on heliophysics missions. A new version of a Faraday cup instrument is in development for the Luna 26 mission and will be used for fast monitoring of the solar wind plasma parameters. The prototype of this instrument is exposed to dust impacts in a velocity range of 0.2–60 km s−1 using an electrostatic dust accelerator. The collected data are used to evaluate the sensitivity and detection efficiency of dust particles on two different surfaces. The results indicate that the sensitivity is sufficient for detection of the interplanetary dust as well as for the registration of the dust lifted from the lunar surface. A simple modification of the FC electronics would increase the detection efficiency by an order of magnitude.

Introduction: Water ice is prevalent in the solar system, and there have been numerous studies of the effects of radiation and charged particle bombardment of water ice in laboratory settings [1-6]. However, many questions yet remain concerning the effect of interplanetary dust particle (IDP) bombardment on icy surfaces and bodies, as IDP impacts into ice have not been heavily investigated. This is despite the fact that IDP impacts are expected to be at least as important as radiation and charged particle bombardment [7]. Since liquid water is regarded as a prerequisite for life, icy ocean worlds such as Europa and Enceladus are the focus of several planned NASA and ESA fly-by missions [8-9]. Water plumes erupting from Enceladus's surface have been observed [10], and analysis of the plume using impact ionization time of flight (TOF) mass spectrometry from the Cosmic Dust Analyzer (CDA) on the Cassini spacecraft strongly indicate that the plume originated from the subsurface ocean [11]. There have also been observations of what appear to be similar water plumes on Europa [12-14]. These observations indicate that the environment around these bodies is rich with dust from both the ice surface and the subsurface oceans, and that fly-by spacecraft with TOF spectrometers will be able to study surface and subsurface chemistry in situ without landing. Isotopic ratios have been used as metrics for solar system formation and evolution models, and the deuterium-hydrogen (D-H) ratio is of particular importance in studying the formation of planetary bodies. Temperature-dependent chemical processes result in deuterium-enrichment of water ice relative to hydrogen at low-temperatures [15]. Such enrichment processes enable measurements of D-H ratios in outer solar system bodies to be used to constrain the time and location that planetary bodies formed in the solar system as well as other geophysical phenomena [16-18]. While laboratory work has been performed to match CDA flight spectra, these studies have used laser ablation of flowing liquid sources rather than actual dust impact into actual ice surfaces [19]. However, the University of Colorado dust accelerator at the Institute for Modeling Plasma, Atmospheres, and Cosmic Dust (IMPACT, impact.colorado.edu), paired with a cryogenic target capable of creating H2O ice mixtures, allows for unique and tightly controlled experiments to study hypervelocity dust impact into ice. Such experiments will answer significant questions about the long term chemical evolution of icy bodies under dust bombardment as well as the survivability and detectability of certain types of chemistry in icy dust grains, be they isotopic ratios or complex organics, studied by impact ionization TOF instruments on flyby spacecraft. Experimental Setup: The IMPACT dust accelerator at the University of Colorado uses a 3 MV linear electrostatic potential to launch micron-sized dust particles at velocities up to 100km/s [20]. The accelerator features non-destructive inline beam detectors that record particle mass, velocity, charge, and radius. Active particle down-selection is provided by an FPGAcontrolled particle selection unit. This unit prevents impact of particles outside of a user-defined mass, velocity, radius, or radius parameter space. Selected particles are impacted onto the ice target, shown in Fig. 1.

The detection efficiency and durability of a microchannel plate (MCP) detector to direct impacts of high-velocity dust particles is investigated experimentally. A new type of in situ time-of-flight cosmic dust analyzer instrument has been developed, where the ion detector is exposed to occasional impacts of cosmic dust particles. The dust accelerator facility operated at the University of Colorado is used to directly measure the effect of dust impacts on a commercial, off-the-shelf microchannel plate (MCP) detector. The MCP is exposed to approx. 480 dust particle impacts from wide size and velocity ranges of 0.05-1.6 mu m radii and 2-35 km/s, respectively. The dust impact events are registered with 96% efficiency. Of these, 57% of the output signals are single charge pulses, and 43% are more complex signals that suggest ion feedback mechanisms within the detector. For all dust detection events, the output charge pulse is significantly larger than those from the detection of single ions or photons. The gain of the MCP detector shows no apparent degradation after the bombardment. In the investigated size/velocity range, the dust particles do not pose a risk of damaging the MCP. Scanning electron microscope images show that the impact generated craters are small, on the order of the size of the impacting particles. The performed measurements and the extrapolation of the results to the worst case expected to occur for the duration of a spaceflight mission indicate that MCP detectors require protection from dust impacts in order to reduce the risk of detector damage for these types of dust analyzer instruments, and a mechanism for providing protection is described.

Acharge pickup detector was developed at the University of Colorado for use in classroom demonstrations and in the dust accelerator at the Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT). The detector can be used in a physics classroom to help high school and introductory-level physics students connect electromagnetic phenomena with measurement techniques that are common to experimental physics and in electronics courses to demonstrate the use of a charge-sensitive amplifier (CSA). Construction of a similar detector would develop students’ basic machining and electronics skills, which are crucial in most undergraduate experimental physics opportunities. The detector is designed to nondestructively determine the velocity and charge of particles. The detector is compact (8.6 cm x 5.4 cm x 4.1 cm), simple, and lightweight. It is built with off-the-shelf components with simple machining, resulting in a low-cost (∼$100) detector that maintains the high sensitivity (0.2 fC) necessary for characterization of most hypervelocity dust particles, as well as a wide variety of other applications accessible to introductory-level physics students such as charged particles in a dust storm, pith balls, or charged raindrops. This paper focuses on both characterization of the detector using the accelerator at IMPACT and the basics of the undergraduate-level physics principles, electronics principles, mechanical design, and lab applications.

Permanently polarized Polyvinylidene Fluoride (PVDF) films have been used on a variety of spacecraft as in situ dust detectors to measure the size and spatial distributions of micron and sub-micron dust particles. The detectors produce a short electric pulse when impacted by a hypervelocity dust particle. The pulse amplitude depends on the mass and relative speed of the dust grain. This relationship has been studied both empirically and numerically to better understand the film’s principle of operation, as well as the effects of film thickness, film temperature, and particle penetration depth. However, little work has been done to constrain the effects of varying particle density and incidence angle despite the frequent occurrence of such configurations in most space-based applications. We present calibrations of non-penetrating impacts on 28 μm thick films at varying incidence angles ranging from 0° to 75° for iron and aluminum particles in the mass and speed range of 10−12 ≤ m ≤ 10−8 g and 0.5 ≤ v ≤ 7 km/s, respectively. The study was carried out at the 3 MV dust accelerator laboratory at the University of Colorado at Boulder. The results show that PVDF signals are largely independent of particle density and incidence angle up to 75° for non-penetrating impacts.

Charge sensitive amplifiers (CSAs) are electronic integrating circuits frequently used for detecting quick charge pulses such as those produced in semiconductor detector devices and electron multipliers. One of the limitations of highly sensitive CSA circuits is the accuracy with which they can be calibrated due to the necessity of using injection capacitors on the order of a few pF, which are difficult to calibrate and to disentangle from other stray capacitance in calibration circuits. This paper presents an alternate method for calibrating the electronics for CSAs with conductive detectors, referred to as the “external conductor” method, using the detector itself to form the injection circuit. The external conductor method is compared to the traditional injection capacitor method for an example detector. The new method results in an increase to the calibration factor of up to 70% over the value derived from a traditional injection capacitor, with an uncertainty in the new value of 2%. Finally, the results from the external conductor method are compared to a third, independent approach, which uses reference charged particles as calibration sources in the Colorado dust accelerator. The results of the charged particle approach corroborate the external conductor calibration to within the stated uncertainty.

The solar system currently possesses two remnant debris disks leftover from the planetary formation era in the form of the asteroid belt and the Edgeworth-Kuiper Belt (EKB). Similar to other stellar systems, these debris disks continually generate submillimeter-sized dust grains through processes such as mutual collisions, interstellar dust grain bombardment, and sublimation/sputtering of larger grains. Here, we use recent in situ measurements by the New Horizons Student Dust Counter and an interplanetary dust dynamics model to constrain the overall structure and magnitude of the solar system's debris disk, including the disk mass, optical depth, and surface brightness in both scattered light and thermal emission. We find that similar to 99% of the solar system's dust disk mass (grains with diameter <1 mm) is contained within EKB and Oort Cloud cometary grains outside of 30 au, with the remaining similar to 1% mass in the form of Jupiter-family cometary dust within 5 au. The total disk mass is estimated to be similar to 8 x 10(-7) M-circle plus with a total fractional luminosity of similar to 5 x 10(-7), confirming our solar system as a relatively dust-poor system compared to debris disks around similar-aged FGK stars. Finally, we estimate that Kuiper Belt Object collisional events such as that which created the Haumea family could transiently increase the current surface brightness of our debris disk by a factor of only similar to 6, far less than median brightnesses seen in other nearby disks. This further supports the idea that the EKB has been largely depleted of its primordial mass relative to other stellar systems by instabilities triggered by planetary migration.

Recent space experiments suggest that electron and ion energy analyzers using microchannel plates (MCPs) as detectors are also registering direct hits by nanodust particles. To allow the analysis and interpretation of these putative dust events, the detection efficiency of MCPs has to be characterized. We report on a series of experiments to investigate the detection efficiency of MCP detectors to direct impacts for both positively and negatively charged micron and submicron sized iron particles. A double-stack MCP detector in a chevron configuration was mounted as a target in a dust accelerator. A range of particle velocities and masses were used for a comprehensive examination. The MCP detected and produced definite signals associated with confirmed particle impacts of the MCP for both positively and negatively charged dust particles. The detection efficiency was found to be (6 +/- 1)% for positively charged dust and (9 +/- 3)% for negatively charged dust particles with a characteristic mass of 6.0 x 10(11) mu (10(-15) kg) and speed of 100 m/s. The examined particle velocity range accurately replicates Rosseta's interaction with dust grains emanating from comet 67P/ Churyumov-Gerasimenko's nucleus. Additionally, the MCP detection efficiency for low velocity particles shows a possible underestimate of higher speed nanograin signals from Cassini's electron plasma spectrometer during its flyby through Enceladus' active south pole.

The Dust Coordinate Sensor (DCS) is a dual detector instrument located on the beamline of the 3 MV hypervelocity dust accelerator at the University of Colorado Institute for Modeling Plasma, Atmospheres and Cosmic Dust (IMPACT). This instrument non-destructively measures the three-dimensional trajectories of charged, hypervelocity (3-8 km/s), micron-sized dust particles in flight by utilizing the image charge induced on grids of wire electrodes. Where previous peak detection was typically limited to dust particles carrying charges >similar to 100 fC, new signal processing techniques developed for DCS allow for effective trajectory measurements on particles carrying charges as small as 6 fC. The new signal processing also effectively eliminates false signal detections completely. The position measurements are matched by timestamp to the charge and velocity for each launched dust particle. Verification of the system was performed with independent impact location measurements on a target placed in the beamline. These measurements agree to within 1 mm(2) of the predicted locations using DCS trajectories. This study demonstrates the capability of the instrument including new processing methods. Precise trajectory measurement along the beamline enables new options for instrument calibration, scientific experiments, and improvement of the accelerator performance.

The Student Dust Counter (SDC) is an in-situ dust detector aboard the New Horizons spacecraft observing the distribution of interplanetary dust particles (IDPs) with mass > 10(-12) g or approximately 0.5 mu m in radius. New Horizons was launched on January 19th, 2006 and performed a fly-by of the Pluto system on July 14th, 2015. SDC has nearly continuously mapped the dust density distribution along the trajectory of New Horizons, and it continues to operate providing measurements of the IDP in the Edgeworth-Kuiper Belt (EKB). We present results of the dust density distribution from 1 to 38 AU and compare these measurements to existing theoretical models.

High-speed tracking of hot and molten microparticles in motion provides rich information about burning plasmas in magnetic fusion. An exploding-wire apparatus is used to produce moving high-temperature metallic microparticles and to develop four-dimensional (4D) or time-resolved 3D particle tracking techniques. The pinhole camera model and algorithms developed for computer vision are used for scene calibration and 4D reconstructions. 3D positions and velocities are then derived for different microparticles. Velocity resolution approaches 0.1 m/s by using the local constant velocity approximation.

Ice is prevalent throughout the solar system and beyond. Though the evolution of many of these icy surfaces is highly dependent on associated micrometeoroid impact phenomena, experimental investigation of these impacts has been extremely limited, especially at the impactor speeds encountered in space. The dust accelerator facility at the Institute for Modeling Plasmas, Atmospheres, and Cosmic Dust (IMPACT) of NASA's Solar System Exploration Research Virtual Institute has developed a novel cryogenic system that will facilitate future study of hypervelocity impacts into ice and icy regolith. The target consists of a copper block, cooled by liquid nitrogen, upon which layers of vapor-deposited ice, pre-frozen ice, or icy regolith can be built in a controlled and quantifiable environment. This ice can be grown from a variety of materials, including H2O, CH3OH, NH3, and slurries containing nanophase iron. Ice temperatures can be varied between 96 K and 150 K and ice thickness greater than 150 nm can be accurately measured. Importantly, the composition of ion plumes created during micrometeoroid impacts onto these icy layers can be measured even in trace amounts by in situ time-of-flight mass spectroscopy. In this paper, we present the fundamental design components of the cryogenic target chamber at IMPACT and proof-of-concept results from target development and from first impacts into thick layers of water ice.

Polyvinylidene fluoride (PVDF) films have been utilized as interplanetary dust detectors for many years in a variety of space environments. PVDF serves as a dust detector by producing a ‘depolarization’ charge upon hypervelocity impact. Previous instruments have relied on empirical calibrations to establish the relationship between the mass and velocity of the impacting dust particle and the generated charge. Here, we present a new theoretical derivation of PVDF response to non-penetrating hypervelocity particle impacts. We compare our simulation results to experimental calibration data from the Cosmic Dust Experiment on the Aeronomy of Ice in the Mesosphere satellite and the Student Dust Counter on the New Horizons mission. The simulation results agree well with the experimental data, yet suggest a modified crater diameter scaling law for non-penetrating hypervelocity impacts into PVDF.