Numerical simulation of self-field MPD thrusters

Langendorf

Review of Scientific Instruments

et al. 2015

With high-speed imaging, it is possible to directly observe the time-evolution of the macroscopic behavior of the discharge plasma in a magnetoplasmadynamic thruster (MPDT). By utilizing direct high-speed imaging capable of capturing many images over the course of a single discharge, the velocity of the cathode erosion particles can be measured, opening the possibility of a novel, noninvasive technique for discharge plasma flow field velocimetry. In this work, an 8 kA argon MPDT discharge is imaged at 26 173 fps utilizing a 0.9 neutral density filter. The camera is aligned with thruster centerline 4 m downstream of the thruster exit plane. By tracking visible particles appearing in the multiple images, the particle motion in the radial and azimuthal directions is directly imaged. Through the use of traditional techniques in digital particle image velocimetry, the cathode particles emanating from the discharge are measured to have a mean radial velocity of 44.6 ± 6.0 m/s with a 95% confidence interval and a statistically insignificant azimuthal velocity. The setup and analysis employed permits measurement of the particle velocity in orthogonal direction to the image sensor plane using a single camera. By combining a background removal subtraction technique and knowledge of the optical focal plane, the estimated mean axial velocity of the particles is 1.59 km/s. This investigation ends with a discussion of important factors to consider for future MPDT high-speed imaging particle velocimetry, such as frame-rate, image size, spatial resolution, optics, and data handling selections.

“…The system features a 678 in. 3 internal volume scuba tank rated to 3000 psi as a propellant plenum and an Omega SV251 3-way solenoid valve. A 0.0625-in.…”

Section: Pulsed Gas Feed Systemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Velocimetry of cathode particles in a magnetoplasmadynamic thruster discharge plasma

Langendorf

Review of Scientific Instruments

et al. 2015

“…LaPointe (19) developed a two-temperature code to simulate self-field MPD thrusters and tested this model against the experimental results of the Princeton University full-scale benchmark thruster operated It is obvious from this formula that the thrust coefficient is independent of current, mass flow rate, and propellant type. Therefore, this model always contradicts with experimental measurements.…”

Section: Lapointe Modelmentioning

confidence: 99%

Performance characterisation of MPD thrusters

Nada

2007

Aeronaut. j.

This paper introduces a characterisation of the performance indices and operating limits of the self field magnetoplasmadynamic thruster. The thrust, specific impulse, and efficiency are considered as the main performance indices, while the operating limits are the cathode lifetime, onset phenomenon, and the overfed state of the thruster. The effects of thruster parameters (current, mass flow rate, geometry, and propellant type) on the performance indices and operating limits are examined using one-dimensional model of cylindrical self-field thrusters. Design charts are presented to help the designers to choose the optimum and safe set of the thruster parameters that realise certain mission requirements.

Journal of Propulsion and Power

“…1 All calculations are performed here for a single value of E\lrn^i^ji n -0.022, mks, equivalent to a J 2 /(dm/dt) value of ~20 [kA 2 /(g/s)], a stable operating regime below the critical "onset" mode. 1 ' 23 Flow through the injection wall is assumed isentropic, with total temperature T 0 -1000 K, and the flow Mach number treated as a variable, with 1 < M < 3. The neutral particle velocity is assumed constant for X Q < x < x 1 and is given by u n = a 0 M/(l + M 2 /3) 1/2 with a 0 = (yRT 0 ) l/2 and y = f.…”

Section: Boundary Conditionsmentioning

confidence: 99%

Injected propellant ionization in MPD thrusters

Burton

Tiliakos

1993

A model is presented for the self-magnetized, weakly ionized preionization region at the entrance to a magnetoplasmadynamic (MPD) accelerator. The model is steady, one-dimensional and inviscid, and assumes supersonic flow of argon plasma with zero current in the region. Heavy particle temperature is constant, and electron temperature T e is determined by ambipolar diffusion and by photo-and electron-impact ionization processes. The plasma continuity, momentum, and energy equations are integrated numerically with appropriate boundary conditions, giving a region width AJC ranging from 3 to 17 mm, depending on density, and a degree of ionization a increasing from an initial value of a = 10 ~7 to a -4 ± 2 x 10 ~4 at the MPD accelerator inlet. The electron temperature rises monotonically from T e -1000 K to T e = 18,000 K, a level sufficient to sustain MPD accelerator operation. The total electrostatic potential across AJC is AV = 12.5 ± 0.6 V. Reducing the injected particle flux Q (} increases AJC, until a critical Q 0 is reached below which no solutions exist. Nomenclature B= magnetic field, T E X7 E y -laboratory electric field, V/m £4 = average excess energy of ionizing photoelectrons, eV /' = photon fraction with hv > E f G = electron temperature gradient, dTJdx h = Planck's constant, J-s j = current density, A/m 2 L = arc length in flow direction, m ROSS = Rosseland mean free path, m n = particle density, m~3 n n = neutral particle density, m~3 n 0 = total heavy particle density, m~3 p e = electron pressure, Pa Q ei = coulomb cross section, m 2 Qen = electron-neutral cross section, m 2 Qo = particle flux n 0 u, particles/m 2 -s q e = electron heat flux vector, W/m 2 r L = Larmor radius, m r, T e -heavy particle, electron temperature, K 7" ex = excitation temperature, K u, v -axial, transverse mass average velocity, laboratory reference frame, m/s V -electron/ion ambipolar diffusion velocity, m/s V n = neutral diffusion velocity, m/s AJC = preionization width, (x l -Jt 0 )> m a = degree of ionization F ex = excitation rate, excitations/m 3 -s F, = electron impact ionization rate, electrons/m 3 -s r r = recombination rate, atoms/m 3 -s T^ = photoionization rate, electrons/m 3 -s K e = electron thermal conductivity, W/m K v = collision frequency, s" 1 f\ = electron hall parameter Constants Ef = argon ionization potential, J e = electron charge, C k = Boltzman constant, J/K Associate Fellow AIAA. tGraduate Student. Student Member AIAA. M= ion mass, kg m = electron mass, kg S = slope of argon excitation cross section, m 2 /J