The far-field plasma characterization in a 600 W Hall thruster plume by laser-induced fluorescence

Abstract

Non-intrusive characterization of the singly ionized xenon velocity in Hall thruster plume using laser induced fluorescence (LIF) is critical for constructing a complete picture of plume plasma, deeply understanding the ion dynamics in the plume, and providing validation data for numerical simulation. This work presents LIF measurements of singly ionized xenon axial velocity on a grid ranging from 100 to 300 mm in axial direction and from 0 to 50 mm in radial direction for a 600 W Hall thruster operating at the nominal condition of discharge voltage 300 V and discharge current 2 A, the influence of discharge voltage is investigated as well. The ion velocity distribution function (IVDF) results in the far-field plume demonstrate a profile of bimodal IVDFs, especially prominent at radial distances greater than channel inner radius of 22 mm at axial position of 100 mm, which is quite different from that of the near-field plume where bimodal IVDFs occur in the central core region for the same power Hall thruster when compared to previous LIF measurements of BHT-600 by Hargus (2010 J. Propulsion Power 26 135). Beyond 100 mm, only single-peak IVDFs are measured. The two-dimensional ion velocity vector field indicates the bimodal axial IVDF is merely a geometry effect for the annular discharge channel in the far-field plume. Results about the IVDF, the most probable velocity and the accelerating potential profile along the centerline all indicate that ions are still accelerating at axial distances greater than 100 mm, and the maximum most probable velocity measured at 300 mm downstream of the exit plane is about 19 km s −1 . In addition, the most probable velocity of ions along radial direction changes a little except the lower velocity ion populations in the bimodal IVDF cases. The ion temperature at axial distances of 10 and 300 mm oscillates along the radial direction, while the ion temperature first increases, and then decreases for the 200 mm case. Finally, the axial position for the ion peak axial velocity on the thruster centerline is shifted upstream for higher discharge voltages, and the velocity curve is becoming steeper with the discharge voltage before reaching the maximum. This observation can be used as a criterion to optimize the thruster performance.

On a force balance and role of cathode plasma in Hall effect thrusters

“…Multimodal iVDF is not a novelty and is often mentioned in the literature. For example, in [85] using the LIF method, it was found that a multi-peaked iVDF is present at the outer radius of the plume even at a great distance from the thruster. In [86][87][88], LIF measurements of the iVDF were carried out near the channel, depending on the time.…”

Laser induced fluorescence diagnostic for velocity distribution functions: applications, physics, methods and developments

“…One way to accurately determine the zero-Doppler shift excitation wavelength is to send a laser in both forward and backward directions of the diagnosed volume and compare the resultant fluorescence spectrum, this eliminates potential particle drift within the diagnosed volume [61,63]. Alternatively, optogalvanic cells are also used to obtain absolute wavelength calibration, and they are often better than iodine in the sense that an optogalvanic cell can give the exact same line as the target fluorescence line if one chose the same gas as the one being probed [16,17,64,65]. However, by nature of the optogalvanic cell being a plasma source, there is also no guarantee that the ion VDF in the cell is free of any drift velocity, particularly when they are generally very small device without any form of confinement to ensure plasma uniformity.…”

“…LIF technique had been used to measure the IVDFs of Xe + ions in the plasma of several Hall thrusters and in Hall thruster plumes [16][17][18][19][20][21]. For instance, the far-field plasma characteristics of ion VDF and plasma ion temperature in 600 W magnetic shield and unshielded Hall thrusters are studied in [65,150]. An LIF optical bench along with the methodology is extensively described in [21].…”

Experimental and numerical studies of low power Hall thruster performance

“…Matthew Baird et al obtained a quiescent sinusoidal discharge current in only the low flow and voltage operation condition [12]. Duan X Y et al investigated the far-field plasma characterization in a 600W Hall thruster [13]. Ding Y J et al found the point of intersection of the characteristic magnetic field line with the channel wall affected the performance and lifetime of the low power cylindrical Hall thruster [14].…”