The development of a 835-900-GHz biasable funda- mental balanced mixer using planar GaAs Schottky diodes is pre- sented. The monolithic microwave integrated circuit integrates two planar Schottky anodes in a balanced configuration, stripline fil- tering elements, and on-chip capacitor on a thin GaAs membrane. At 850 GHz, double side-band (DSB) mixer noise temperature of 2660 K and conversion loss of 9.25 dB are measured, respectively, at room temperature. When the mixer is cooled to 120 K, the DSB mixer noise temperature and conversion loss improve to 1910 K and 8.84 dB, respectively. Index Terms—Cryogenic test bench, fundamental balanced mixer (FBM), monolithic microwave integrated circuit (MMIC), passive cooling, planar Schottky diode, submillimeter wavelengths, vacuum chamber.

A Broadband 835-900-GHz Fundamental Balanced Mixer Based on Monolithic GaAs Membrane

The flowfield of a magnetoplasmadynamic thruster was simulated numerically using an advanced code specifically developed for this purpose, and the results were compared to experimental measurements, to validate the code and obtain insight into underlying physical processes. The thruster chosen was the full-scale benchmark thruster because it has been the subject of many experimental studies. The parallelized axisymmetric code featured detailed physical models and a finite volume formulation that allowed for nonorthogonal grids. Flowfield properties, such as electron density, velocity, current density, electron temperature, ionization fraction, and mass and momentum flux, as well as thrust, compared favorably with existing data. The simulation provided insight into some aspects of thruster operation, such as the weak role of the anode geometry in affecting the thrust, the predominantly electromagnetic nature of the thrust at nominal operating conditions, and the importance of the near-cathode region in energy dissipation. The simulated structure of the flow was found to embody a number of photographically recorded features of the actual discharge.

Comparison of Simulated Magnetoplasmadynamic Thruster Flowfields to Experimental Measurements

Numerical modeling of spacecraft electric propulsion thrusters

Since the early eighties the development of plasma thrusters has been an important research topic at the IRS, where a broad spectrum of stationary plasma thrusters has been investigated experimentally as well as theoretically. High power MPD thrusters (50 kW-1 MW) and a wide range of thermal arcjets (0.5–150 kW) are developed under contracts with ESA, NASA, USAF, USNAVY and with German funding. The IRS has excellent installations for continuous tests of high power accelerators. The high current power supply is a current regulated d.c. thyristor rectifier of 6 MW. The maximum current is 48 kA with a ripple less than 1%. The vacuum system is a roots pump system consisting of four stages with a total suction power of about 250,000 m 3 /h at 1 Pa. Eight vacuum tanks of different sizes are connected to this system; six of them are used for plasma thruster development and two serve as plasma wind tunnels. For low power arcjet development and basic cathode erosion experiments four additional independent test stands are available.

Plasma thruster development program at the IRS

Simulation of plasma flows in self-field Lorentz force accelerators

The plasma flow in magnetoplasmadynamic (MPD) self-field thrusters is described by conservation equations for heavy particles, turbulence, electrons, and the magnetic field for reaction and thermal nonequilibrium. The equations are discretized on unstructured adaptive meshes. The numerical results, which are verified by experimental data, show that the newly developed finite volume code predicts the thrust well. It is found that electron pressure diffusion drives the arc out of nozzle-type MPD thrusters. The drop of density in front of a water-cooled anode is the reason for the beginning of thruster instabilities at high electric currents.

Joerg Heiermann

Papers

Numerical and Experimental Investigation of the Current Distribution in Self-Field Magnetoplasmadynamic Thrusters

Numerical and experimental investigation of the current distribution in self-field MPD thrusters

Experimental and numerical investigation of a power augmented thermal arc jet

Investigations of the 1 kW Class Arcjet ARTUR-2 with Helium as Propellant

Numerical Investigation of the Electrodes in High Power Self-Field MPD Thrusters