{"id":3630,"date":"2011-07-08T19:53:01","date_gmt":"2011-07-08T19:53:01","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/?p=3630"},"modified":"2011-07-19T20:49:10","modified_gmt":"2011-07-19T20:49:10","slug":"batch-micromachined-rpas-for-plasma-and-ion-measurements","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2011\/batch-micromachined-rpas-for-plasma-and-ion-measurements\/","title":{"rendered":"Batch-micromachined RPAs for Plasma and Ion Measurements"},"content":{"rendered":"

Retarding potential analyzers (RPAs) were first developed in the 1960’s.\u00a0 RPAs find widespread application including characterization of near-spacecraft environments and assessment of the propulsion efficiency of plasma-based space thrusters.\u00a0 In this project we are exploring the multiplexing and scaling-down limits of RPAs using micro and nanotechnology.\u00a0 Miniaturized RPAs will weigh visibly less, which will reduce the cost of a nanosatellite-based mission.\u00a0 Also, miniaturized RPAs will provide better diagnostics of spacecraft plasma plumes as smaller projected area will be less disruptive to plasma under observation.\u00a0 In addition, batch-fabricated miniaturized RPAs can be used as part of a spacecraft \u201csensorial skin\u201d that provides detailed local information of the plasma surrounding the spacecraft, particularly during re-entry, when monitoring exterior conditions is essential to ensuring safety during the mission.<\/p>\n

An improvement of our work from the state-of-the-art RPAs is the introduction of enforced aperture alignment<\/em>.\u00a0 When the apertures of each successive grid are aligned, the optical transparency of the sensor increases, which should result in improved signal strength.\u00a0 We recently developed a first-generation prototype of a hybrid microRPA (Figure 1).\u00a0 The hybrid microRPA has micromachined electrodes and a stainless steel housing.\u00a0 Internal dynamics of this type of energy analyzer, however, are more complex than simple transmission or reflection of the various ion species [1<\/a>] <\/sup> [2<\/a>] <\/sup>. This fact is made evident by the experimental characterization of the microRPA using a commercial thermionic ion source for mass spectrometry.\u00a0 Figure 2 shows that the measured data reveal a peak in the energy distribution function around 5.4 V of retarding potential when the ionization region is at 10 V.\u00a0 Therefore, the observed ion energy distribution (dotted) deviates from the expected (continuous line) by approximately 4.6 V, a shift that is constant for a wide range of ionization region potentials.\u00a0 We speculate that changes in the internal dynamics due to enforced aperture alignment, sources of error in the applied voltages due to the materials selected, or a combination thereof are cause for this anomaly.\u00a0 Exploration of these potential sources of error continues, as well as the manufacturing of a fully batch-microfabricated RPA sensor with housing based on 3D HV packaging technology [3<\/a>] <\/sup> [4<\/a>] <\/sup>.<\/p>\n\n\t\t