A method to determine the onset voltage of single and arrays of electrospray emitters

This paper reports on an accurate and rapid method to compute the onset voltage for a single or for an array of electrospray emitters with complex geometries and on the correlation of the simulation with experimental data. This method permits the exact determination of the onset voltage based only on the surface tension of the sprayed liquid and of the emitter geometry. The approach starts by determining the voltage at which electrostatic forces and surface tension forces are equal for a sharpening conic surface at the tip of a capillary as a function of the apex radius of the liquid. By tracing the curve of this computed equilibrium voltage as a function of apex radius, the onset voltage for a liquid surface with the Taylor half-angle of 49.3{degree sign} or larger can be determined. For smaller cone half-angles the method is only applicable to ionic sprays as an approximate knowledge of the critical field for ion emission is necessary. The combination of analytical models and finite element tools used to compute the necessary parameters are described. The method is validated on a complex MEMS emitter geometry as well as on a linear array of electrospray emitters. Finally an empirical model of the behavior of the electric field near the apex of a conic surface with asymptotes at a fixed half-angle is proposed which allows establishing a simple method for onset voltage determination

Microfabricated out-of-plane arrays of integrated capillary nano-electrospray emitters

This paper presents the fabrication and operation of an integrated nano-electrospray thruster consisting of an array of microfabricated silicon capillary emitters and microfabricated silicon extractor electrodes. Based on previous work in which we showed operation of single microfabricated capillaries, the improved thruster presented here allows simultaneously operation of arrays of emitters. In addition, we control the hydraulic impedance of the capillaries by filling them with silica beads, thus tailoring the flow rate in order to spray either in droplet regime or in ionic regime for two ionic liquids. Operation in both modes is confirmed by mass spectrometry and retarding potential analysis. In ion regime, a specific impulse of 3500 s is obtained at 1.2 kV for the ionic liquid EMI-BF4

Microfabrication and test of an integrated colloid thruster

This paper reports on the design, fabrication and test of an integrated colloid micropropulsion system for spacecraft attitude control using the ionic liquid EMI-BF4 as fuel. The principle of operation of the thruster is identical to electrospray ionization. The objective of the project was to demonstrate the feasibility and operability of arrays of microfabricated capillary emitters with individual extractor electrodes. This design approach results in an identical electric field distribution from one capillary to the other, avoids crosstalk and therefore allows for a more finely modulated thrust control. Spraying tests with different thruster configurations were conducted under vacuum conditions. Tests were performed with different thruster configurations and starting voltages around 700V were observed

Performance of a micro-fabricated Colloid thruster system

In order to fully characterize the performance of the colloid thruster system the electrospray (ES) beam must itself be fully characterized. This may be achieved by measuring various properties such as flow rate, current, droplet/ion charge to mass ratio and current profile. Beam properties of both standard electrospray mass spectrometry (ESMS) emitters and arrays of custom made micro-fabricated emitters have been determined. By varying the geometries of the micro-fabricated emitters two basic modes of thruster operation have been identified a high Isp with lower thrust density and a lower Isp with higher thrust density. The versatility of this system allows for a thruster design that has a thrust range spanning two orders of magnitude from ~ 5 to 500μN with highly competitive power requirements ~ 0.05W/μN. The proposed thruster system is designed to meet the needs of future formation flying missions

Design and fabrication of an integrated MEMS-based colloid micropropulsion system

The design, microfabrication and initial performance results of a prototype electrospray thruster with integrated individual extractor electrodes are reported in this paper. The aim was to demonstrate increased thrust with an array of emitters spraying simultaneously. Micromachining technologies were employed to achieve large emitter density per surface area, simple integration and good structural repeatability. The novelty of this work lies in the combination of high aspect ratio capillary emitters (height of 70 microns, inner diameter of 20 microns) with individual extractor electrodes having diameters from 80 microns upwards and a spacing as low as 25 microns from the capillary tips. The individual integrated electrodes, as opposed to the standard approach of one common electrode, allow for greater uniformity in critical voltages between capillaries and more finely modulated thrust control. Tests with the newly developed thrusters using the ionic liquid EMI-BF4 show that starting voltages below 700V and currents around 300nA per emitter can be achieved

Fabrication and operation of a two-dimensional ion-trap lattice on a high-voltage microchip

Microfabricated ion traps are a major advancement towards scalable quantum computing with trapped ions. The development of more versatile ion-trap designs, in which tailored arrays of ions are positioned in two dimensions above a microfabricated surface, will lead to applications in fields as varied as quantum simulation, metrology and atom–ion interactions. Current surface ion traps often have low trap depths and high heating rates, because of the size of the voltages that can be applied to them, limiting the fidelity of quantum gates. Here we report on a fabrication process that allows for the application of very high voltages to microfabricated devices in general and use this advance to fabricate a two-dimensional ion-trap lattice on a microchip. Our microfabricated architecture allows for reliable trapping of two-dimensional ion lattices, long ion lifetimes, rudimentary shuttling between lattice sites and the ability to deterministically introduce defects into the ion lattice

Micromachined electric propulsion using ionic liquids as fuel

MEMS-based electric propulsion (EP) presents several advantages over conventional EP approaches, including scalability, redundancy, fine thrust control, low thrust noise, and reduced operation voltage. Small spacecraft (1- 100 kg) in particular stand to benefit from MEMS-based propulsion. The design, microfabrication and performance of an electrospray thruster with integrated individual extractor electrodes are reported. Micro-machining technologies were employed to achieve large emitter density, simple integration and high structural repeatability