The high power helicon (HPH) is capable of producing a high density plasma (1017−1018 m−3) and directed ion energies greater than 20 eV that continue to increase tens of centimeters downstream of the thruster. In order to understand the coupling mechanism between the helicon antenna and the plasma outside the immediate source region, measurements were made in the plasma plume downstream from the thruster of the propagating wave magnetic field and the perturbation of the axial bulk field using a type ‘R’ helicon antenna. This magnetic field perturbation (ΔB) peaks at more than 15 G in strength downstream of the plasma source, and is 3–5 times larger than those previously reported from HPH. Taking the curl of this measured magnetic perturbation and assuming azimuthal symmetry suggests that this magnetic field is generated by a (predominantly) azimuthal current ring with a current density on the order of tens of kA m−2. At this current density the diamagnetic field is intense enough to cancel out the B0 axial magnetic field near the source region. The presence of the diamagnetic current is important as it demonstrates modification of the vacuum fields well beyond the source region and signifies the presence of a high density, collimated plasma stream. This diamagnetic current also modifies the propagation of the helicon wave, which facilitates a better understanding of coupling between the helicon wave and the resultant plasma acceleration.
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May 2011
Research Article|
May 27 2011
Enhanced diamagnetic perturbations and electric currents observed downstream of the high power helicon
B. Race Roberson;
B. Race Roberson
a)
Department of Earth and Space Sciences,
University of Washington
, Johnson Hall 070, Box 351310, 4000 15th Avenue NE, Seattle, Washington 98195-1310, USA
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Robert Winglee;
Robert Winglee
Department of Earth and Space Sciences,
University of Washington
, Johnson Hall 070, Box 351310, 4000 15th Avenue NE, Seattle, Washington 98195-1310, USA
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James Prager
James Prager
Department of Earth and Space Sciences,
University of Washington
, Johnson Hall 070, Box 351310, 4000 15th Avenue NE, Seattle, Washington 98195-1310, USA
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a)
Author to whom correspondence should be addressed. Electronic mail: [email protected].
Phys. Plasmas 18, 053505 (2011)
Article history
Received:
October 01 2010
Accepted:
March 17 2011
Citation
B. Race Roberson, Robert Winglee, James Prager; Enhanced diamagnetic perturbations and electric currents observed downstream of the high power helicon. Phys. Plasmas 1 May 2011; 18 (5): 053505. https://doi.org/10.1063/1.3574753
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