Generation of cold electrons in the downstream region of a microwave plasma source with near boundary resonances for production of negative ions |
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Authors: | D Sahu S Bhattacharjee M Bandyopadhyay and A K Chakraborty |
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Abstract: | A microwave driven multicusp plasma based volume negative ion source equipped with a magnetic filter is developed. Instead
of employing any electrodes or current carrying filaments, microwaves of frequency 2.45 GHz is used to generate plasma by
resonance heating mechanisms namely the electron cyclotron resonance (ECR) and upper hybrid resonances (UHR), occurring near
the boundary plasma layers. The principal process of negative ion production in hydrogen is dissociative attachment of low
energy (0.5–1.0 eV) electrons to vibrationally excited neutral molecules generated from high energy (15–20 eV) electron impact.
The source therefore necessitates two distinct spatial regions (a) production and (b) attachment chambers; which would contain
electrons with optimum cross section for the aforementioned processes. A biased grid after the magnetic filter further helps
to lower down the electron temperature to ≤1 eV which is favorable for the dissociative attachment process. |
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