A portable waveguide microwave discharge (WMD) is used for the development of advanced optical diagnostics relevant for the study of aerospace plasma flows. Several configurations of the torch can be realized, which makes it possible to operate with different plasma flow regimes in low pressure environments.
Advanced numerical modelling capability is also available to assist in designing experiments, to extract more information from test results, and for relating test conditions to flight.
Inductively-coupled "Plasmatron“ wind-tunnel produces high-enthalpy plasma flows representative of atmospheric entry flows for fundamental studies and material characterization.
The high purity plasma is generated by electrical induction heating (400kHz, 2kV, 8kA solid-state generator) in a 200mm diameter quartz tube in the absence of electrodes. Test objects are mounted 300-500mm behind the typically subsonic torch exit of 160mm diameter. Supersonic nozzles of various exit diameters reaching Ma = 3.5 high-temperature flows can be attached to the torch exit, including a semielliptical nozzle for flat plate measurements.
The plasma temperature around the test object can exceed 10,000K, at typically low-speed (incompressible) flows to reproduce the aerothermochemical environment of an atmospheric entry object (typically spacecraft, meteor, or debris). This is done following the Local Heat Transfer Simulation (LHTS) methodology reproducing enthalpy, pressure, and Damköhler number.
The facility is computer controlled using a 719 I/O lines PLC, and two PC’s for controlling and monitoring the Plasmatron operation. Available instrumentation includes intrusive pitot pressure and heat flux probes, emission spectrometers with ICCD camera, several broad, double, and single-band radiometers, as well as scientific observation cameras. In addition, a dedicated laser-spectroscopy laboratory is currently being developed for plasma diagnostics.
Advanced numerical modelling capability is also available to assist in designing experiments, to extract more information from test results, and for relating test conditions to flight.
Main applications are
The "DRAG-ON" facility (Dual-chamber for RArefied Gases and ON-ground testing) is used to simulate the high speed, low density flow that a spacecraft would encounter in (Very) Low Earth Orbit, (V)LEO, at an altitude of approximately 200 km - intermediate between the "Kármán line" (100 km) and the orbit of the International Space Station (400 km).
The facility supports the investigation of a new concept of electric propulsion called Air-Breathing Electric Propulsion. This new technology would make it possible to use the atmosphere as a propellant.
Another application includes the exposure of satellite material samples to the atomic oxygen beam. Some materials may suffer from oxygen erosion and may cause critical damage to the satellite. Different material samples or representative satellite geometries can be tested in DRAG-ON to evaluate their effectiveness for VLEO space applications. The orbital flow conditions are created through a Particle Flow Generator (PFG) that can operate continuously in vacuum conditions with both argon and molecular oxygen feed gases. The working gas is ionized from an inductively coupled plasma source. The charged particles are then accelerated to orbital speed (8 km/s) using an electric field. A sealed chamber and a high vacuum pumping system are necessary to maintain the pressure around 0.001 Pa (1/100th of a millionths of an atmosphere) during operation. Plasma diagnostics include electrostatic probes (Faraday probe to measure plasma current density and Retarding Potential Analyzer to measure velocity distributions) and non-invasive techniques (Optical Spectroscopy).
The Minitorch is a high enthalpy facility generating a vertical jet of plasma in a 0.5 m diameter, 1.2 m long test chamber, where pressure can be varied from 30 mbar to atmospheric. The plasma is generated by electrical induction inside a 4 cm diameter water cooled quartz tube. The four-turn inductor is supplied by a high frequency power generator (13.56 MHz, 15 kW) coupled with an automatic impedance matching network. A recirculating water system is used to protect the test chamber from plasma heating, as well as to cool the gas extracted from the test chamber by a 190 m3/h vacuum pump. The facility operates normally in the subsonic regime. Argon, nitrogen, carbon dioxide, air or other gas mixtures can be used to generate the plasma. The gas is supplied through a single-flow annular injection system.
Available instrumentation includes cooled pressure and heat flux probes, Langmuir probes, and a laser Doppler velocimeter that uses a special seeder for plasma velocity measurements. Also the Plasmatron instrumentation (emission spectrometer and two-color pyrometer) can be used in the Minitorch.
The facility is used for instrumentation studies and training, for inductively coupled plasma torch optimization studies, and for comparisons with numerical simulations of inductively coupled plasma flows. Finally, thermal protection material testing, including catalycity determination, can be performed in the Minitorch at lower heat flux levels than in the Plasmatron.
