Engineering Papers⌕ Search

Engineering topics

Mueller, Juergen

Publications and source records attributed to Mueller, Juergen.

31 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Micromachined Ion Accelerators

Proposed ion accelerators made by micromachining techniques. Advantages include small size and weight, modularity, and compatibility with integrated circuits. Used as sources of ion beams for industrial processes. Ion accelerator of this type combined with integrated electronic control and power circuitry, plus similarly miniaturized valves and other mechanisms for regulating flow of gas used to generate ions - all micromachined on single chip. Provides flexibility for tailoring characteristics of ion sources for specific applications; for example, construct array of many such devices to obtain large ion source or position multiple devices to obtain desired ion-beam pattern in processing chamber.

Brophy, John↗
NASA NTRS1996

Ion-Accelerator Grids With Elongated Holes

Ion-accelerator grids designed and fabricated with elongated holes instead of circular holes. Although grids made of lightweight carbon/carbon composites and conceived for use in ion thrusters for spacecraft, also made of other materials and installed in industrial ion accelerators for material-processing applications. Elongated holes offer advantages of lower costs of fabrication and option to increase open-area fractions of grids, thereby increasing output ion currents extracted through grids.

Mueller, Juergen↗
NASA NTRS1995

Endurance Testing and Fabrication of Advanced 15-cm and 30-cm Carbon-Carbon Composite Grids

Two sets of carbon-carbon grids in a three-grid SAND configuration were endurance tested for 700 hours. Pre- and post test inspections employing electron microscope scans, x-ray fluorescence, grid mass loss measurements, and measurements of grid aperture diameters and thicknesses revealed an extraordinary low degree of erosion. No reduction in grid thicknesses was detectable within the margin of error of the measurements.

Carbon-Carbon↗
NASA NTRS1995

Pulsed-Microwave Electrothermal Thrustors

Pulsed-microwave electrothermal thrustors investigated as alternatives to continuous-microwave electrothermal thrustors. Intended for use in spacecraft propulsion systems, also prove useful on Earth in some material-processing and manufacturing applications.

Mueller, Juergen↗
NASA NTRS1994

Developments in Fullerene Ion Propulsion Research

Several reports of successful operation of DC discharges using fullerene vapor have been made. However, degradation of the propellant molecules in the vapor source and in contact with the filament cathode was observed in each case. Because disintegration of the fullerene cage could result in poor performance or thruster failure, we have developed an RF ion thruster for use with C 60 propellant to avoid the presence of electrodes inside the discharge chamber. Also, we conducted a series of experiments to ascertain the stability of fullerenes at high temperatures. We find that when C 60 and C 70 are maintained at temperatures above 1073 K, or are exposed to hot metal surfaces, significant degradation occurs. We find an activation energy of 261.5 kJ/mol for this process. At temperatures below 873 K, no breakdown of fullerenes can be detected, even after heating for 6 hours. The effect of these findings on C 60 ion thruster design is discussed.

fullerenes↗
NASA NTRS1994

Segmented Ion Engine Operation and Performance

The continuing trend toward smaller and smaller planetary spacecraft to enable the use of smaller, less expensive launch vehicles has motivated an examination of new approaches to reduce the size and mass of xenon ion propulsion systems for these new spacecraft. A system is proposed which is based on the use of a single 4x15-cm segmented ion thruster operated from a single internally redundant power processing unit. An engine input power throttling range of 380 to 4640 W is projected. The design and operation over a power range of 600 to 2400 W of a laboratory model segmented ion engine equipped with carbon-carbon grids is presented. There appear to be no problems associated with interactions with multiple ion sources operating from a single set of high voltage power supplies, neutralization of multiple ion sources from a single centrally located neutralizer, or operation of flat, thin carbon-carbon grids.

ion↗
NASA NTRS1994

Performance Characteristics of 15 cm Carbon-Carbon Composite Grids

Three 15 cm carbon-carbon grid sets in a three-grid SAND optics configuration have been fabricated and tested. Grid panels were made from unidirectional tape. The screen grid panels were roughly 0.5 mm thick whereas the accelerator and decelerator panels were 0.94 mm thick.

ion↗
NASA NTRS1994

Segmented Ion Engine Plume Characteristics

Preliminary evaluation of the segmented ion thruster (SIT) ion beam characteristics was performed by measuring the two dimensional ion current density distribution at four axial locations downstream from the thruster. Current density profiles were measured with the concurrent operation of multiple ion sources. Preliminary assessments regarding symmetry of the plume, characterization of plume development as a function of axial position, and the interactions of multiple simultaneously operating ion sources were conducted. A numerical integration scheme was applied to the acquired data to determine the total beam current. A qualitative analysis of the downstream development of the ion beam was conducted. Most of the data acquired so far has been on somewhat of a trial basis and extensive testing is scheduled to resume in August 1994.

ion↗
NASA NTRS1994

Effect of the Thermal Stability and Reactivity of Fullerenes on Ion Engine Propellant Applications

Because vapor phase fullerene molecules collide with high temperature surfaces at both the cathode in DC discharges and at the walls of vapor sources, knowledge of the thermal stability and material compatibility of fullerenes is important for ion thruster applications. Here, we present a study of the high temperature behavior of fullerenes. We find that when C 60 and C 7O are maintained at temperatures above 1073 K, or are wxposed to hot metal surfaces, significant degradation occurs. We find an activation energy of 261.5 kJ/mol for this process. At temperatures below 873 K, no breakdown of fullerenes can be detected, even after heating for 6 hours. The effect of these findings on C 60 ion thruster design is discussed. Our present C 60 ion thruster experiment is also described.

fullerenes↗
NASA NTRS1994

(abstract) Design and Testing of a Fullerene RF Ion Engine

Because of the large mass, low ionization potential and large electron impact ionization cross section, use of buckminsterfullerene (C 60 ) as a propellant might result in significant increases in ion engine efficiency over that obtained with xenon at low specific impulse. Consequently, an experimantal program to investigate the feasibility of using fullerenes as a propellant was initiated. To eliminate the possibility of hot cathode surfaces causing fragmentation, fabrication of a radio-frequency discharge chamber was pursued. Experimental results using the radio-frequency source will be presented.

fullerenes↗