Accelerator system and method of accelerating particles

An accelerator system and method that utilize dust as the primary mass flux for generating thrust are provided. The accelerator system can include an accelerator capable of operating in a self-neutralizing mode and having a discharge chamber and at least one ionizer capable of charging dust particles. The system can also include a dust particle feeder that is capable of introducing the dust particles into the accelerator. By applying a pulsed positive and negative charge voltage to the accelerator, the charged dust particles can be accelerated thereby generating thrust and neutralizing the accelerator system

Hollow Cathode and Low-Thrust Extraction Grid Analysis for a Miniature Ion Thruster

Miniature ion thrusters are well suited for future space missions that require high efficiency, precision thrust, and low contamination in the mN to sub-mN range. JPL’s miniature xenon Ion (MiXI) thruster has demonstrated an efficient discharge and ion extraction grid assembly using filament cathodes and the internal conduction (IC) cathode. JPL is currently preparing to incorporate a miniature hollow cathode for the MiXI discharge. Computational analyses anticipate that an axially upstream hollow cathode location provides the most favorable performance and beam profile; however, the hot surfaces of the hollow cathode must be sufficiently downstream to avoid demagnetization of the cathode magnet at the back of the chamber, which can significantly reduce discharge performance. MiXI’s ion extraction grids are designed to provide >3mN of thrust; however, previous to this effort, the low-thrust characteristics had not been investigated. Experimental results obtained with the MiXI-II thruster (a near replica or the original MiXI thruster) show that sparse average discharge plasma densities of ∼5×10^15–5×10^16 m^−3 allow the use of very low beamlet focusing extraction voltages of only ∼250–500 V, thus providing thrust levels as low as 0.03 mN for focused beamlet conditions. Consequently, the thrust range thus far demonstrated by MiXI in this and other tests is 0.03–1.54 mN

Cold plasma treatment for biomedical applications: using aluminum foam to reduce risk while increasing efficacy

Plasma medicine is an emerging and innovative interdisciplinary research field combining biology, chemistry, physics, engineering, and medicine. However, the safe clinical application of cold atmospheric plasma (CAP) technology is still a challenge. Here, we examine the use of aluminum (Al) foam with three pores-per-inch (PPI) ratings in clinical plasma applications. Al foams can filter sparks to avoid damage from high voltage discharge during surgery and efficiently deliver reactive species generated in CAP to the target. The sparks appear and plasma intensity increases at the foam/discharge interface, which just slightly increases the interface temperature without changing the interface microstructure during a 30-minute treatment. After CAP penetrated the Al foams, N2, N2+, *OH, O, and He emission peaks were characterized, and the highest values appeared using Al foams with 10 PPI. CAP with and without Al foam intermediating was used to treat deionized water, and the results indicate CAP in combination with 10 PPI Al foam led to much higher ROS concentration than CAP alone. For melanoma cell experiments, CAP with and without Al foam had a similar effect on cell viability after 30-second treatment, while CAP with the 10-PPI Al foam had much higher killing efficiency than CAP alone after 60-second treatment. In summary, 10-PPI Al foam can not only prevent damage to tissues resulting from high discharge voltage during clinical surgery but also increase the delivery efficiency of reactive species generated in plasma for biomedical applications

Simulation of Electrospray Emission Processes for Highly Conductive Liquids

An electrohydrodynamic numerical model is used to explore the electrospray emission behavior of both moderate and high electrical conductivity liquids under electrospray conditions. The Volume-of-Fluid method, incorporating a leaky-dielectric model with a charge relaxation consideration, is used to conserve charge to accurately model cone-jet formation and droplet breakup. The model is validated against experiments and agrees well with both droplet diameters and charge-to-mass ratio of emitted progeny droplets. The model examines operating conditions such as flow rate and voltage, with fluid properties also considered, such as surface tension, electrical conductivity, and viscosity for both moderate and high conductivity. For high conductivity and surface tension, the results show that high charge concentration along with the meniscus and convex cone shape results in a higher charge-to-mass ratio of the emitted droplets while lower conductivity and surface tension tend towards concave cone shapes and lower charge-to-mass droplets. Recirculation flows inside the bulk liquid are investigated across a range of non-dimensional flow rates, and electric Reynolds numbers. For high conductivity liquid emission at the minimum stable flow rate, additional recirculation cells develop near the cone tip suggesting the onset of the axisymmetric instability.Comment: submitted to Journal of Fluid Mechanic

Design of a pressurized lunar rover

A pressurized lunar rover is necessary for future long-term habitation of the moon. The rover must be able to safely perform many tasks, ranging from transportation and reconnaissance to exploration and rescue missions. Numerous designs were considered in an effort to maintain a low overall mass and good mobility characteristics. The configuration adopted consists of two cylindrical pressure hulls passively connected by a pressurized flexible passageway. The vehicle has an overall length of 11 meters and a total mass of seven metric tons. The rover is driven by eight independently powered two meter diameter wheels. The dual-cylinder concept allows a combination of articulated frame and double Ackermann steering for executing turns. In an emergency, the individual drive motors allow the option of skid steering as well. Two wheels are connected to either side of each cylinder through a pinned bar which allows constant ground contact. Together, these systems allow the rover to easily meet its mobility requirements. A dynamic isotope power system (DIPS), in conjunction with a closed Brayton cycle, supplied the rover with a continuous supply of 8.5 kW. The occupants are all protected from the DIPS system's radiation by a shield of tantalum. The large amount of heat produced by the DIPS and other rover systems is rejected by thermal radiators. The thermal radiators and solar collectors are located on the top of the rear cylinder. The solar collectors are used to recharge batteries for peak power periods. The rover's shell is made of graphite-epoxy coated with multi-layer insulation (MLI). The graphite-epoxy provides strength while the thermally resistant MLI gives protection from the lunar environment. An elastomer separates the two materials to compensate for the thermal mismatch. The communications system allows for communication with the lunar base with an option for direct communication with earth via a lunar satellite link. The various links are combined into one signal broadcast in the S-band at 2.3 GHz. The rover is fitted with a parabolic reflector disk for S-band transmission, and an omnidirectional antenna for local extravehicular activity (EVA) communication. The rover's guidance, navigation, and control subsystem consists of an inertial guidance system, an orbiting lunar satellite, and an obstacle avoidance system. In addition, the rover is equipped with a number of external fixtures including two telerobotic arms, lights, cameras, EVA storage, manlocks, a docking fixture, solar panels, thermal radiators, and a scientific airlock. In conclusion, this rover meets all of the design requirements and clearly surpasses them in the areas of mobility and maneuverability

Pulsed Operation of an Ion Accelerator

Electronic circuitry has been devised to enable operation of an ion accelerator in either a continuous mode or a highpeak power, low-average-power pulsed mode. In the original intended application, the ion accelerator would be used as a spacecraft thruster and the pulse mode would serve to generate small increments of impulse for precise control of trajectories and attitude. The present electronic drive circuitry generates the extraction voltage in pulses. Pulse-width modulation can affect rapid, fine control of time-averaged impulse or ion flux down to a minimum level much lower than that achievable in continuous operation

Increasing the Life of a Xenon-Ion Spacecraft Thruster

A short document summarizes the redesign of a xenon-ion spacecraft thruster to increase its operational lifetime beyond a limit heretofore imposed by nonuniform ion-impact erosion of an accelerator electrode grid. A peak in the ion current density on the centerline of the thruster causes increased erosion in the center of the grid. The ion-current density in the NSTAR thruster that was the subject of this investigation was characterized by peak-to-average ratio of 2:1 and a peak-to-edge ratio of greater than 10:1. The redesign was directed toward distributing the same beam current more evenly over the entire grid andinvolved several modifications of the magnetic- field topography in the thruster to obtain more nearly uniform ionization. The net result of the redesign was to reduce the peak ion current density by nearly a factor of two, thereby halving the peak erosion rate and doubling the life of the thruster

Magnetically Shielded Miniature Hall Thruster: Design Improvement and Performance Analysis

ABSTRACT: Magnetic shielding has been shown to dramatically reduce discharge channel wall erosion of high powered Hall thrusters, thereby increasing their useful lifetimes. However, unique challenges exist for developing a low power magnetically shielded Hall thruster. A previously tested 4 cm magnetically shielded miniature Hall thruster demonstrated low performance of its magnetic circuit, resulting in an asymmetric field topology, low thrust, and low efficiency. A 6 cm magnetically shielded Hall thruster was developed to improve upon the 4 cm design. The 6 cm device, which generated a symmetric and fully shielded field topology, was tested at 30 operating conditions ranging from 160 W to nearly 750 W. Visual observation of the plasma and discharge channel during and after operation was used to assess the level of magnetic shielding that was achieved. Hall2De plasma simulations were also used to offer further evidence of magnetic shielding. Thrust stand measurements provided thrust, anode specific impulse, and anode efficiency data at each operating condition. Pole face erosion, which is believed to be associated with the 6 cm thruster's non-optimized magnetic shielding field topology and strength, identify the near-term challenges to resolve before long lifetimes and high efficiencies can be achieved in low power Hall thrusters