Investigation of a Cluster of High-Power Helicon Thrusters for Advanced In-Space Electric Propulsion Applications
Vereen, Keon L
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The High-Power Helicon (HPH) cluster experiment aimed to investigate whether clustered helicon thrusters could outperform a single monolithic thruster in terms of beam collimation and exit velocities. The clustered HPH experiment operated at power levels ≥100 kW and could produce high energy, collimated plasma beams for in-space propulsion and beamed momentum applications. For this dissertation research, three magnetic flux conserving configurations were housed within a compact structural chassis in a space simulation facility. For variant 1 and 2 configurations, the thruster units were oriented at 12.7 degree off-parallel yaw angle and 15.8-degree pitch angle for single and double HPH operations. Magnetic nozzles were repositioned to measure the effect on downstream plume properties. For variant 3 configuration, the thruster units were oriented at 12.7 degree off-parallel yaw angle and 0.0-degree pitch angle for double HPH operations and slight axial adjustments of the magnetic nozzles. Variant 3 configuration was implemented to minimize potential plume asymmetries present in the initial architectural design. Measurements were gathered using the double Langmuir probe, RF-compensated double Langmuir probe, time-of-flight probe, and nude Faraday probe at axial locations downstream of the Z = 0 source region. In the variant 1 configuration, the double HPH plasma density was measured as 50% larger than the sum of the left and right HPH thruster densities. In the variant 2 configuration, the single HPH operation yielded ion velocity and peak ion flux of 11 km/s and 1.29x〖10〗^22 m^(-2) s^(-1) respectively. The double HPH operation yielded ion velocity and peak ion flux of 18.3 km/s and 9.15x〖10〗^22 m^(-2) s^(-1) respectively. For variant 2 configuration, the double HPH peak ion flux was estimated as 256% (3.56-fold) larger than the sum of the left and right helicon thrusters. The radial profiles of plasma density and ion current density exhibited wide beam profiles, full width at half maximum (FWHM) of 35 cm and 37.5 cm respectively. In the variant 3 configuration, the double HPH operation yielded ion velocity and peak ion flux of 21.1 km/s and 1.56x〖10〗^23 m^(-2) s^(-1) respectively. The double HPH peak ion flux was approximately 71% larger than the variant 2 configuration. Narrow beam profiles, FWHM of ~16 cm, were obtained from the radial plasma density and ion current density profiles. A narrower beam profile combined with an increase in peak ion flux could suggest an improvement in coupling mechanism. The results from this dissertation can be considered a 1st pass investigation into the clustering effects of helicon thrusters. Additional work is needed to develop two-dimensional mapping of the downstream clustered plume properties.