Characterization of a radio-frequency inductively coupled electrothermal plasma thruster

Abstract

A radio-frequency (RF) inductively coupled electrothermal plasma thruster operating with argon is experimentally characterized for different mass flow rates, RF powers, and propellant injection configurations. Depending on the propellant mass flow rate, significant neutral gas heating is observed with effective stagnation temperatures around 2000 K (giving a maximum estimated thrust and specific impulse of about 100 mN and 125 s, respectively) for absorbed powers between 300 and 500 W. A self-consistent theoretical discharge model is developed and used to study the basic physics and operation of RF electrothermal thrusters, and predictions of the gas temperature are in good agreement with experimental measurements. The model identifies primary power inefficiencies as electron-neutral excitation losses and neutral gas heat losses to the thruster walls. Both experimental and theoretical results indicate that a relatively high stagnation pressure (of the order of 100 Torr or higher) is critical for high performance. For pressures significantly below this the electron-neutral collisional power transfer is too low to effectively heat the neutral gas.

Bidirectional vortex stabilization of a supersonic inductively coupled plasma torch

“…The forward vortex plasma eventually extinguishes at a mass flow rate of 170 mg s −1 . Other conventional gas injection configurations, such as single or double flux axial injection at the upstream end of the torch, have been previously studied and found to produce similar stagnation temperatures as the forward vortex [53]. By contrast, the stagnation temperature with the reverse vortex continues to increase for mass flow rates above 80 mg s −1 , reaching approximately 3200 K at 155 mg s −1 before the plasma extinguishes.…”

“…Thus, the ratio of the hot-to-cold stagnation temperature is proportional to the square of the hot-to-cold pressure ratio. Thermocouple measurements give T s,cold of approximately 20 • C. Note that the gas stagnation temperature is an effective average temperature within the torch (and a more appropriate value to use when estimating some torch performance metrics), whereas the actual maximum gas temperature (which typically peaks on, or close to, the torch central axis) is expected to be about 3 times higher [53]. Once the stagnation temperature is determined from equation ( 2), the enthalpy flow and thermal efficiency of the plasma torch can be estimated from…”

Radial profile control of a magnetically expanding plasma and its impact on a plasma thruster

“…for plasma etching, sputtering, and chemical vapor deposition, [1][2][3][4][5] where a uniform density profile is required when processing a large diameter substrate. The RF plasma sources have also been vigorously investigated for the development of space electric propulsion devices such as an ICP plasma thruster, 6) a gridded ion thruster based on the RF plasma source, 7) and a magnetic nozzle (MN) RF plasma thruster (sometimes called a helicon thruster). [8][9][10][11] The MN RF plasma thruster typically consists of the RF plasma source and the MN; the plasma produced and energized in the source is transported along the magnetic field lines and expands along the MN.…”

Inductively-coupled plasma discharge for use in high-energy-density science experiments

“…Inductively-coupled plasma (ICP) discharges were first discovered more than a century ago [1][2][3][4], and the technology has been extensively-developed for a range of applications from light sources [5] to plasma propulsion [6], but in particular it is utilized within the semiconductor manufacturing industry for plasma-aided fabrication of integrated circuits [7,8]. In an ICP, large volume plasmas are generated as energy is coupled into an ionized gas from a radio-frequency (RF) power source using an inductive circuit element (such as helical coil) positioned near-to, or immersed in, a discharge region [9,10].…”

“…A transformer model of its operation was developed in the 1930s [19], and it has been characterized extensively experimentally over the past few decades [20][21][22]. The cylindrical ICP has been introduced to number of applications, including as a plasma torch in the 1960s [23], which has been applied in materials processing for decades; for plasma propulsion [6]; and is often applied as a remote plasma source in atomic layer deposition [24,25].…”