Modeling and Technology Development for Sensitive Near-Solar Particle Measurements.

MEMS;Micromachining;Nanoimprint Lithography;Pickup Ions;DRIE;Adiabatic Cooling;Atmospheric;Oceanic and Space Sciences;Electrical Engineering;Engineering;Science;Atmospheric and Space Sciences

Mukherjee, Pran R.Herrero, Federico Antonio ;

University of Michigan

关键词: MEMS;    Micromachining;    Nanoimprint Lithography;    Pickup Ions;    DRIE;    Adiabatic Cooling;    Atmospheric;    Oceanic and Space Sciences;    Electrical Engineering;    Engineering;    Science;    Atmospheric and Space Sciences;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/61664/pran_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The focus of this dissertation is the advancement of near-solar in-situ particle measurement techniques. Populations of dust, neutral atoms, and pickup H+ ions from 1.4 to 305 solar radii (Rs) are numerically modeled and scaled to measured data at 1.35 AU, and a measurement-enabling ultraviolet suppression grating for near-solar sensors is designed, fabricated, and tested.Dust grains within heliocentric distances of 50 Rs absorb solar wind ions and reemit them as neutral atoms that are quickly ionized and picked up by the solar wind. A parameterized model demonstrates the importance of the grains’ azimuthal velocity and the high speed of near-solar Alfv´en waves on the dynamic evolution of these ions. Pickup ion density is calculated using the continuity equation and adiabatic cooling models. This analysis shows very clearly that these additional velocity components cause density peaks much sharper and closer to the Sun than previously assumed, definitely inside of 15 Rs and quite possibly within five Rs.An instrument for the Solar Probe Plus mission is designed and fluxes of neutral hydrogen and solar Lyman-alpha are calculated. This instrument design is used to develop constraints for a UV blocking filter which enables the needed measurements. The micromachining technologies used in CMOS and MEMS are applied to the fabrication of freestanding, self-supported silicon nanogratings to block solar UV while allowing particles through for subsequent measurement. Nanoimprint lithography patterns 120 nm half-pitch gratings which are then etched to aspect ratios of >20 by breakthrough deep-reactive ion etch techniques. A custom carrier allows double-sided etching to free the grating without damage while leaving a built-in support grid.The efficacy of a grating in blocking UV light depends upon the grating geometry, the material or materials it is built with, and the polarization of the light. Silicon is far stronger than the gold previously used for this purpose, and when complemented by conformal thin film coatings should be capable of meeting the design specification. The slit widths of the fabricated gratings are currently too wide for the target application, but the measured transmission of the grating between 190-250 nm is shown to be 10^-4.