Spatial retarding field energy analyzer measurements downstream of a helicon double layer plasma

Abstract

Spatial ion energy measurements using a retarding field energy analyzer are performed in the exhaust of a 0.30mTorr, 250W helicon double layer plasma to investigate the divergence of the argon ion beam formed by acceleration in the double layer. Various divergence angles are computed by considering the radial distribution of beam density; the average beam ion diverging by 9°. The efficiency at which momentum is imparted parallel to the longitudinal axis of the thruster is calculated to be 98%. The results show that a few centimeters downstream of the source, the beam ions do not follow the magnetic field lines.

Transport of energetic electrons in a magnetically expanding helicon double layer plasma

“…3͑b͒ shows the parabolic profile as previously reported; 3,18 while both the total current I total and electron density n e are found to have peaks at around r = 8 cm, confirming the presence of the local maximum of bulk ions and electrons. 19 Although the particle transport across the magnetic field lines is complex, it is likely that the local maximum in the measured electron density ͑with the CP͒ and ion density ͑with the RFEA͒ would result from a local increase of ionization from the 9 eV population.…”

“…8 Experiments have previously characterized the beam and bulk ions two dimensionally using retarding field energy analyzers ͑RFEAs͒ and Langmuir probes. 3,[16][17][18][19][20] Ions accelerated by DLs in low-pressure expanding plasmas are weakly divergent and magnetically detached about 10 cm downstream of the double layer. [16][17][18] The physical mechanisms leading to the dense ring of bulk plasma observed in Langmuir probe measurements downstream of the double layer has been unclear.…”

“…Spatial measurements of the ion energy distribution function and ion density are performed in the diffusion chamber with a similarly rotating RFEA. 18 Figure 2͑a͒ shows the EEPF at ͑z , r͒ = ͑17 cm, 4 cm͒, the region where magnetic field lines terminate in the source tube walls and do not extend into the diffusion chamber. Previous measurements in this region have reportedly exhibited depletion from a Maxwellian distribution at a break energy of break = 45 eV, 21 indicated as an arrow in Fig.…”

Operation of a permanent-magnets- expanding plasma source connected to a large-volume diffusion chamber

“…One of the key issues for the application to the thruster is an ion detachment phenomenon from the magnetic nozzle downstream of the DL. The previously reported simulation and two-dimensional experimental results have already shown that the accelerated ions are detached from the field lines at about ten centimeters downstream of the DL [22,24].…”

“…For the development of the electrodeless thruster, the experiments in laboratory plasmas have recently been extended into two-or three-dimensional measurements [21][22][23]. One of the key issues for the application to the thruster is an ion detachment phenomenon from the magnetic nozzle downstream of the DL.…”