Plasma Facilities

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1200 KW Induction Plasmatron

The Plasmatron is a high enthalpy facility in which a jet of plasma is generated in a test chamber kept at sub-atmospheric pressure (between 5 and 350 mbar).  The plasma is generated by heating a gas (argon, N2 ,CO2 ,air or any other gas mixture) to temperatures up to about 10000 K, using electrical current loops induced inside a plasma discharge.  Electrodeless inductively-coupled plasma generators of this type offer much better plasma purity compared to classical arcjets, as there is no pollution from any vaporized electrode material.

The facility, which is the most powerful induction-coupled plasma wind tunnel in the world, uses a high frequency, high power, high voltage (400 kHz, 1.2 MW, 2 kV) solid state (MOS technology) generator, feeding the single-turn inductor of an 80mm or 160mm diameter plasma torch.  The torch is mounted on a 1.4m diameter, 2.5m long, water-cooled test chamber, fitted with nine 500mm diameter portholes that allow unrestricted optical access to the horizontally oriented plasma jet.  Hot gas from the test chamber exits trough a 700 kW heat exchanger to a group of three rotary-vane vacuum pumps and a Roots pump, which are capable of extracting 9000 m3/h, with a terminal vacuum capability of 0.005 mbar.

A 1050 kW cooling system using a closed loop deionized water circuit (2090 litres/min) and fan-driven air coolers provide cooling to all facility components.  The facility is computer controlled using a 719 I/O lines PLC, and two PC’s for controlling and monitoring the Plasmatron operation.  A dedicated 96-channel data acquisition system using a 12-bit A/D converter at 100 kHz is also available. The facility is used for space re-entry materials testing at heat fluxes up to 15 MW/m2, including catalycity determination, as well as for general studies of plasma flows. The Plasmatron facility is equiped with a sonic nozzle, two supersonic nozzles (Mach: 2,6 and 3,2) and a semi-eliptic nozzle for supersonic testing. Available instrumentation includes intrusive cooled pressure and heat flux probes, a one-meter emission spectrometer with CCD camera and a two-color pyrometer.  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.

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Dual-chamber for RArefied Gases and ON-ground testing (DRAG-ON)

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 Earth Orbit, 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.

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).

Among several applications, the facility is used to measure the «collection efficiency » of an intake-collector component for Air-Breathing Electric Propulsion system. The dual chamber configuration serves this purpose, with collection efficiency being directly related to the pressure difference between the two chambers.

The experimental activity is supported by plasma and rarefied gas modeling and simulation. The Particle-in-Cell/Direct Simulation Monte Carlo method, is used, where the plasma is described statistically at the molecular level. The combination of simulations and detailed experiments makes it possible to study how gas molecules interact with the surfaces of different materials.

Vacuum environment

• Roughing pumps
• Turbomolecular pumps
• Pumping speed (N2): 3050 l/s + 2150 l/s
• Ultimate pressure < 1 x 10^-7 mbar
• Operating pressure < 8 x 10-5 mbar

LTA-100 plasma source

• Output beam current 10 mA
• Ion energy 5 - 50 eV
• Exit beam diameter 90 mm
• Operating gas: Ar, O₂

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15 KW Induction-Coupled Plasma Minitorch

The Minitorch is a high enthalpy facility generating a vertical jet of plasma in a 0.3 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 3 cm diameter uncooled quartz tube. The two-turn inductor is supplied by a high frequency, high voltage, vacuum tube generator (27.12 MHz, 15 kW, 6kV) via a capacitive 4x voltage multiplier and impedance match. 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, but by addition of a cooled Laval nozzle a supersonic plasma jet at Mach 2.2 can be obtained. Argon, nitrogen, carbon dioxide, air or other gas mixtures can be used to generate the plasma.

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.

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