Optical Measurements of High-Density Helicon Plasma by Using a High-Speed Camera and Monochromators

Abstract

Electric propulsion is an established high-efficiency method in deep space explorers. However, most of the applied methods feature electrodes in direct contact with the plasma, thus its lifetime is limited by the electrodes' erosion. We developed electrodeless electric propulsion systems in order to overcome this problem, and performed optical measurements to estimate the high-density helicon plasma performance of the systems. The electron and neutral particle density profiles were measured by a high-speed camera, and the velocity of the singly-charged Ar ions was determined by a high-resolution monochromator. Additionally, a preliminary experiment of a spectroscopic method using an intensity ratio based on a collisional radiative model with a CCD monochromator was performed. The plasma parameters were in good agreement with the results obtained by an electrostatic probe, and the non-invasive optical measurements presented here can constitute an effective tool for evaluating an electric propulsion system.

Optical Emission Spectroscopic (OES) analysis for diagnostics of electron density and temperature in non-equilibrium argon plasma based on collisional-radiative model

“…Therefore, the atomic data like cross sections should be updated frequently. Various schemes for the determination of T e and N e with the OES data have been proposed with this methodology, one of which is shown in Figure 6 [76,77]. Similar research reports have been published [78][79][80].…”

“…Parameter survey is carried out for the density ratio of excited states under the following discharge condition: the plasma diameter D = 20 mm, the gas temperature T g = 500 K, and the discharge pressure P = 7 mTorr, over the parameter range 2 ≤ T e [eV] ≤ 8 and 10 10 ≤ N e [cm -3 ] ≤ 10 13 . As a result, some level-pairs are found to be strongly dependent on either one of the plasma parameters, T e or N e [76,77], an example of which is shown in Figure 5 as a contour of density ratio. Even if the ratio depends on both parameters, provided that two level-pairs with opposite dependences are found, T e and N e can be determined as an intersection of two curves in the density ratio contours.…”

“…Thus, in principle, if two densitypairs are found to have different dependences on the set of T e and N e , i.e. the density contour lines do not show parallel traces, they can determine the parameters T e and N e as an intersection of the contour lines of the density ratio of level-pairs [76,77]. This scheme applies only two line-pairs to determine the parameters, and consequently, statistical improvement with many line intensities cannot be expected for precision.…”

High-Density Helicon Plasma Thrusters Using Electrodeless Acceleration Schemes

“…Since various plasma parameters can be derived in this device, we can estimate generation and acceleration schemes in detail. 1,8,9) 2. Generation and Acceleration Method 2.1.…”

Space micropropulsion systems for Cubesats and small satellites: From proximate targets to furthermost frontiers

“…Furthermore, spectroscopic measurements were conducted to use a collisional radiative (CR) model to estimate n e and T e by a visible monochromator. 110,111 The latter two optical methods are powerful means for the measurement of small sized plasmas. This is because the optical measurements are not restricted by the plasma size, whereas it is difficult to insert conventional electrostatic probes into a small diameter plasma due to a geometrical restriction and a strong perturbation of the plasma.…”