Accuracy of using metastable state measurements in laser-induced fluorescence diagnostics of xenon ion velocity in Hall thrusters

Abstract

Laser-induced fluorescence (LIF) measurements of singly-charged xenon ion velocities in Hall thrusters typically target metastable states due to lack of available laser technology for exciting the ground state. The measured velocity distribution of these metastable ions are assumed to reflect the ground state ion behavior. However, this assumption has not been experimentally verified. To investigate the accuracy of this assumption, a recently developed xenon ion (Xe II) collisional-radiative (CR) model is combined with a 1D fluid model for ions, using plasma parameters from higher fidelity simulations of each thruster, to calculate the metastable and ground state ion velocities as a function of position along the channel centerline. For the HERMeS and SPT-100 thruster channel centerlines, differences up to 0.2 km/s were observed between the metastable and ground state ion velocities. While both the ground state ions and metastable state ions experience the same acceleration by the electric field, these small velocity differences arise because ionization directly into these states from the slower neutral ground state can reduce their mean velocities by different amounts. Therefore, the velocity discrepancy may be larger for thrusters with lower propellant utilization efficiency and higher neutral density. For example, differences up to 1.5 km/s were calculated on the HET-P70 thruster channel centerline. Note that although the creation of slow ions can influence the mean velocity, the most probable velocity should be unaffected by these processes.

A novel state-resolved actinometry method to determine the nitrogen atom number density in the ground state and intra-shell excited states in low-pressure electron cyclotron resonance plasmas

“…They are calculated according to the cross sections and the assumed EEDF (a Maxwell distribution is taken in this work; see [35]). There are six kinds of reaction kinetics considered in the CR model for the investigation of the key reactions affecting the population of the excited states in tables 3 and 4: (1) electron-impact dissociation processes (R 1 -R 3 ); the total dissociation cross section was measured by Cosby [37], and the branching ratios for R 1 -R 3 are assumed to be 0.5, 0.3, and 0.2, based on the predictions by Zipf et al [38]; (2) electron-impact dissociative excitation processes (R 4 -R 6 ); the cross sections were measured by Filippelli et al [39]; (3) electron-impact excitation processes from the ground and metastable states (R 7 -R 17 ); the cross sections were calculated by Wang et al, using the B-spline R-matrix-with preudostates method [40]; (4) spontaneous radiation (R 18 -R 20 ); their Einstein coefficients are taken from NIST [41]; (5) diffusion processes (R 21 -R 23 ); the diffusion coefficient D n and the sticking coefficient γ can be found in [42][43][44][45].…”

“…A Maxwellian distribution is assumed in the model, as shown in equation ( 4) [35]. The radiation and absorption terms in the rate balance equation are written in equation (5), where the escape factor Γ used is shown in equation (6). The coefficients of the escape factor are found in [36].…”

“…From figures 3(a) and (c), it can be seen that the 4p 5 ( 2 P • 3/2 )5p 2 [1/2] 0 , 4p 5 ( 2 P • 1/2 )5p 2 [3/2] 2 , and 4p 5 ( 2 P • 1/2 )5p 2 [1/2] 0 states of the Kr atom are mainly excited from the ground state, while the 4p 5 ( 2 P • 3/2 )5p 2 [5/2] 3 state is not only generated by excitation from the ground state but also by excitation from metastable states. Because of this difference, the line-ratio γ 1 (811.3 nm/758.7 nm), has a strong n e dependence as shown in figure 3(b), while the γ 2 ratio (826.3 nm/768.5 nm) has a strong T e dependence seen in figure 3(d).…”

“…Measuring the number densities of active atoms and radicals has been of interest for a long time, due to their chemical selectivity and high energy. These atoms and radicals can induce changes in the reaction paths, such as promoting the rate of formatting film in plasma material processing, changing the ionization path in electron propulsion devices, and reducing the delay time of plasma ignition in plasma-assisted combustion systems [1][2][3][4][5][6][7].…”

Transformer fault diagnosis based on MPA-RF algorithm and LIF technology

“…With the advancement of spectral analysis technology, LIF spectroscopy has found successful applications and advancements across various domains [10][11][12][13][14]. For example, Roger [15] used LIF technology to directly obtain the concentration distribution of nitrogen atoms in high enthalpy air.…”