# Upgrades of a Small Electrostatic Dust Accelerator at the University of Stuttgart
## 1 Introduction  
Micron-sized particles acceleration can be achieved using plasma acceleration [1], light gas guns [2], laser pulses [3], as well as electrostatic acceleration. The latter method is the most promising solution to obtain a continuous and stable beam with individual high speed particles. The dust accelerator system normally consists of a dust source, an acceleration stage, dust monitors, a Particle Selection Unit (PSU) and an experiment chamber. The dust particles are charged in the dust source and they acquire kinetic energy when they pass a potential difference. The accelerated dust particles carry surface charges that can be characterized with dust detectors using charge induction methods. Individual dust particles are monitored, selected and recorded with the PSU.  
The first electrostatic dust accelerator was reported by [PERSON] [4] to study impact phenomena of single high speed particles. It consists of a dust source connected to a high voltage generator (100 kV), a dust detector and a test chamber. Similar systems were developed further with the 2 MV [PERSON] accelerator at the TRW Space Technology Laboratories [5], the 2 MV Van de Graaff accelerator at the University of Stuttgart [6], the 2 MV Van de Graaff accelerator at the University of Kent [7], the 3.75 MV Van de Graaff accelerator at the University of Tokyo [8] and the 3 MV Pelletron accelerator at the University of Colorado (Boulder) [9].  
For simplified operation of these large scale accelerator facilities, small dust accelerators with low potential differences are synchronously built to test dust sources and dust samples. The entire system of these small accelerators work without a tank filled with protection gas and without a special high voltage terminal. Hence, the volumes to be pumped down are small and can be quickly evacuated. The small dust accelerators arevery useful to determine the dust source function before mounting them in a big accelerator facility. Small dust accelerators usually work with acceleration voltages of up to 20 kV and they can launch micron-sized particles with speeds up to several km/s.  
The low velocity range of such accelerators allows us to study a variety of science cases that are relevant in planetary science. Laboratory research recently provided evidence that dust particles above an airless object can be charged under UV radiation and/or plasmas and levitated with local electric fields [10]. For example, the micron-sized dust particles covering the lunar surface are expected to be electrostatically charged by their interaction with the solar wind, UV and X-ray radiation and the local plasma environment [11]. The charged particles are proposed to be naturally lifted by near-surface electric fields [12]. The data gathered by the LDEX detector onboard NASA's LADEE mission show that there is a permanent, asymmetric dust cloud around the Moon [13]. The density of the dust grains in the cloud varies with annual meteoroid showers. Micron-sized secondary ejecta particles generated by these meteoroid showers and interplanetary dust are considered as the main source of the lunar dust cloud, which were launched from the lunar surface with speeds up to several km/s.  
Over the next decades, space agencies and private players have plans for missions (Lunar Gateway, Chang'e-6 and Luna 25, etc.) to send spacecrafts and astronauts to the surface of our nearest neighbour, the Moon. Dust is considered one of the highest-priority challenges for these future robotic or human explorations [14; 15], which should be studied in depth with in situ detectors to develop an environmental model for future lunar exploration. The velocities of dust particles launched by small accelerators are sufficient to calibrate the dust sensors used for the detection of secondary ejecta and levitated dust, which provides new application opportunities for small dust accelerators. In this article, we present our new upgrades of our 20 kV dust accelerator and related parameters of the accelerated dust particles.