Use of coated silicon field emitters as neutralisers for fundamental physics space missions

Spacecraft neutralisers are required as part of the ion propulsion system for accurate station keeping in fundamental physics missions. This paper describes the use of thin layers of insulating materials as coatings for the gated silicon field emitter array structure used in a spacecraft neutraliser. These thin coatings are postulated to reduce power consumption and reduce overheating. The power consumption and lifetime of aluminium nitride and amorphous hydrogenated diamond-like carbon coatings have been tested by current–voltage and endurance tests. Diamond-like carbon coatings were promising, performing better in endurance tests than uncoated samples, but further work is required to characterise the coating’s physical properties and its effects on field emission. The thermal conductivity of the coating material had little effect on measured sample lifetimes. Aluminium nitride had reduced power consumption compared to diamond-like carbon coated and uncoated samples. A thin (∼5 nm) layer of aluminium nitride was found to be optimal, meeting European Space Agency specifications for the neutraliser engineering model.     

The dust content of clusters of galaxies

We have statistically investigated the infrared luminosity of clusters of galaxies in comparison with the known tracers of the cluster mass like the X-ray luminosity and the cluster richness (e.g. the number of member galaxies). Our results show that there is a clear positive correlation of the infrared luminosity with the cluster mass. Quantitatively speaking, the infrared luminosity is on average 20 times higher than the X-ray luminosity. Moreover, the infrared luminosity increases with the redshift. This probably shows that a major part of this infrared luminosity is due to star formation in the member galaxies. Another possible contribution would be the thermal emission from dust particles in the diffuse intracluster medium. However our method does not allow us to infer conclusions about this second hypothesis. Depending on their size and abundance, such particles would contribute to the infrared luminosity of galaxy cluster and have an impact on the cooling function of the baryons and thus on the formation of the large scale structures. This is an important cosmological question which still remains open.     

利用高空科学气球收集宇宙尘粒

本文叙述了高空科学气球上一种自行研制的宇宙尘收集器以及气球吊篮系统。利用该系统进行了五次高空字宙尘粒的收集飞行,简述了对所收集的尘粒进行系统研究的结果。     

Interplanetary medium – A dusty plasma

The average mass of dust per volume in space equals that of the solar wind so that the interplanetary medium should provide an obvious region to study dust plasma interactions. While dust collective behavior is typically not observed in the interplanetary medium, the dust component rather consists of isolated grains screened by and interacting with the plasma. Space measurements have revealed several phenomena possibly resulting from dust plasma interactions, but most of the dust plasma interactions are at present not quantified. Examples are the production of neutrals and pick-up ions from the dust, dust impact generated field variations at spacecraft and magnetic field variations possibly caused by solar wind interacting with dust trails. Since dust particles carry a surface charge, they are exposed to the Lorentz force in the interplanetary magnetic field and for grains of sub-micrometer sizes acceleration can be substantial.     

Characteristics of piezoelectric lead zirconate titanate multilayered detector bombarded with hypervelocity iron particles

A cosmic dust detector is currently being developed using a piezoelectric lead zirconate titanate (PZT) element. The characteristics of the multilayered detector (MD), which was composed of one hundred PZT disks, were investigated by bombarding it with hypervelocity iron particles supplied by a Van de Graaff accelerator. It was confirmed that there was a linear relationship between the signal amplitude observed from MD and the momentum of the particles. As compared with the single-layered detector (SD) that was composed of one PZT disk, it was found that the sensitivity of MD was ∼3 times higher than that of SD within the limits of the experimental conditions.     

Relativistic waves raised by explosions in space as sources of ultra-high-energy cosmic rays

The paper discusses the possibility of particle acceleration up to high energies in relativistic waves generated by various explosive processes in the interstellar medium. We propose to use the surfatron mechanism of acceleration (surfing) of charged particles trapped in the front of relativistic waves as a generator of high-energy cosmic rays (CRs). Conditions under which surfing in the waves under consideration can be made are studied thoroughly. Ultra-high-energy CRs (up to 10²⁰ eV) are shown to be obtained due to the surfing in relativistic plane and spherical waves. Surfing is supposed to take place in nonlinear Langmuir waves excited by powerful electromagnetic radiation or relativistic beams of charged particles, as well as in strong shock waves generated by relativistic jets or spherical formations that expand fast (fireballs).     

Relative ion Fe,C and O abundances in quiet time particle fluxes in the 23 SC

Using ACE and SOHO data the origin of quiet-time low-energy particle fluxes at 1 AU is studied in the 23rd solar cycle. One of the selection criteria of quiet-time periods is to demand that H/He < 10 provided that periods with noticeable contribution of remnants of gradual events have been excluded from consideration. Our results suggest different origin of 0.03–3 MeV/nucleon particles – different seed populations accelerated and different acceleration processes. During the ascending, maximum and descending phases of solar activity quiet-time ions consist of coronal particles accelerated to suprathermal energies in about a half of the quiet periods, the rest of quiet-time fluxes originates from particle acceleration in processes similar to those in small impulsive solar flares rich in Fe. At solar minimum the bulk solar wind particles serve as seed population.     

四极－十六极分区式线型阱中汞离子囚禁仿真研究

利用SIMION软件建立了四极-十六极分区式线型离子阱系统模型,在此基础上仿真模拟了汞离子在四极阱和十六极阱中被囚禁时的第一稳定区,并分析了离子在不同阱中的运动特性。研究了汞离子云在分区式阱中的囚禁体积和速度分布,以及在不同囚禁区域之间的穿梭过程。模拟得出了稳态情况下分区式阱中不同囚禁区域的粒子数密度分布,验证了分区式离子阱中离子云被连续囚禁、穿梭时粒子数衰减和补偿。同时,根据以上数据分析讨论了汞离子囚禁时的多普勒效应,估算了基于此分区式离子阱的汞离子微波钟的性能水平。     

Development and coupling test of active spacecraft potential control – Next generation (ASPOC-NG)

The active spacecraft potential control (ASPOC) system developed in the 1990s emits positive ions to neutralise the spacecraft potential, such as used in several missions like Geotail, Equator-S, Cluster, Doublestar and MMS. With the experience gained, the next generation of the active spacecraft potential control (ASPOC-NG) instrument has been developed over the last three years. Thereby, three emission technologies were tested including Liquid Metal Ion Source (LMIS), Liquid Metal Electron Source (LMES) and Solid Metal Electron Source (SMES). The development of the emitter module by FOTEC and the corresponding electronics control unit by IWF is presented. Optimisations were carried out with the focus on the reduction of mass and power consumption to comply with the requirements of future scientific missions. Coupling tests of the modules and the electronics control unit were performed including range, accuracy and lifetime tests. Both ASPOC-NG instruments for positive and negative charge compensation and their performance values show excellent results.     

Preliminary results from the second flight of CREAM

Launched from McMurdo (Antarctica) in December 2005, the balloon experiment CREAM (cosmic ray energetics and mass) collected about 15 million triggers during its second flight of 28 days. Redundant charge identification, by two pixelated silicon arrays and a time resolved pulse shaping technique from a scintillator system, allowed a clear signature of the primary nuclei. The energy was measured with a tungsten/SciFi calorimeter preceded by a graphite target. Preliminary results from the analysis of the data of the second flight are presented.