Speaker
Anshu Verma
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4008.pdf
Possibility of Ion Acceleration in ECR Produced Expanding Plasma
A. Verma, A. Ganguli, D. Sahu, R. Narayanan and R. D. Tarey
Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi, India 110016
Of the different mechanisms that have been used for ion acceleration for thruster application,
helicon wave thrusters have gained considerable attention [1]. It is well known that in helicon
thrusters, the main acceleration is given by a double layer that forms near the junction of the
source chamber and an expansion chamber, in an axially converging-diverging magnetic
field. It is noteworthy however, that in spite of their high efficiency in producing high density
plasmas, ECR based ion thrusters have not received significant attention [2]. This may be due
to the fact in the few studies conducted till now on ECR based thrusters it has not been
possible to observe double layer formation. This paper revisits this problem using a
somewhat different magnetic field configuration.
The experimental system is very similar to that used for helicon thrusters. It consists of a long
cylindrical vessel (dia. 85 mm, length 356 mm) that opens into another much larger diameter
(~ 50 cm) expansion chamber. Permanent ring magnets have been employed for producing
the magnetic field in the source chamber, and in the expansion chamber as well. Within the
source chamber an ECR zone is formed, immediately followed by an on-axis magnetic null,
beyond which the magnetic field exhibits converging-diverging behavior [3]. Argon plasma
is produced using 300 Watts of microwave power (2.45 GHz) ≤ 0.1 mTorr.
Typical measurements at 0.1mTorr, reveal evidence for strong bulk electron heating (Te ~ 40
eV) along with fairly high plasma density (n ~ 3.8×1011 cm-3). This is accompanied by very
high plasma potentials (Vp ~ 250 V). Both, the high electron temperature and the plasma
potential are quite unusual for ECR plasmas that are generated in similar configurations. The
significance of the role of the magnetic field geometry in the present experiments can be
gauged from the fact that n, Te, and Vp all peak in the vicinity of magnetic null, before
decreasing smoothly along the axis (n ~ 3×1010 cm-3, Te ~ 10 eV and Vp ~ 100V typically ~
35 cm away from null). These results indicate that the high axial plasma potentials in the
present configuration can be exploited suitably for efficient ion acceleration. Further work
along these lines is already underway.
References:
1. C. Charles, J. Phys. D: Appl. Phys. 42, 163001 (2009).
2. Cannat et al. Phys. Plasmas 22, 053503 (2015).
3. A.Ganguli et al. Plasma Sources Sci. Technol. 25, 025026 (2016).
