Multi-dipolar microwave plasmas and their application to negative ion production

Abstract

During the past decade multi-dipolar plasmas have been employed for various purposes such as surface treatments in biomedicine, physical and chemical vapour deposition for hydrogen storage, and applications in mechanical engineering. On the other hand, due to the design and operational mode of these plasma sources (i.e., strong permanent magnets for the electron cyclotron resonance coupling, low working pressure, and high electron density achieved) they are suitable for studying fundamental mechanisms involved in negative ion sources used in magnetically confined fusion and particle accelerators. Thus, this study presents an overview of fundamental results obtained with: (i) a single dipolar source, (ii) a network of seven dipolar plasma sources inserted into a magnetic multipolar chamber (Camembert III), and (iii) four dipolar sources housed in a smaller metallic cylinder (ROSAE III). Investigations with Langmuir probes of electron energy probability functions revealed the variation of the plasma properties versus the radial distance from the axis of a dipolar source in its mid plane and allowed the determination of the proportion between hot and cold electron populations in both chambers. These results are compared with the density of hydrogen negative ions, measured using the photodetachment technique. Electron energy probability functions obtained in these different configurations show the possibility of both hot and cold electron production. The former is a prerequisite for increasing the vibrational level of molecules and the dissociation degree and the latter for producing negative ions via dissociative attachment of the cold electrons or via surface production induced by H atoms. V C 2013 AIP Publishing LLC. [http://dx.

Negative hydrogen ion production mechanisms

“…Copyright 2002 AIP Publishing LLC. 264 Camembert III was presented by B echu et al 159 Aleiferis et al 160 described the magnetic field of the network of five dipolar sources forming the source Prometheus and present the photo of the produced plasma.…”

Alternative solutions to caesium in negative-ion sources: a study of negative-ion surface production on diamond in H2/D2 plasmas

“…Negative-ion production on surfaces in low-pressure plasmas rely on two distinct mechanisms. Depending on where the ions are formed, one distinguishes volume production [1][2][3][4][5] associated with dissociative attachment of electrons on molecules and surface production associated with the capture of one or two electrons by neutral atoms or ions impinging on the surface. Depending on the targeted application, either surface or volume production can be the most favourable process.…”

Negative-ion surface production in hydrogen plasmas: Determination of the negative-ion energy and angle distribution function using mass spectrometry

“…Negative-ion (NI) production in low-pressure plasma has many applications and is studied in various areas, such as microelectronics 1,2,3,4,5,6 , magnetically confined fusion 7,8 , space propulsion 9,10,11 and sources for particle accelerators 12,13,14 . NI in low pressure plasmas are usually created by dissociative attachment of electrons on molecules (volume production) 15,16,17 , but they can also be created on surfaces by the bombardment of positive ions or hyperthermal neutrals 18,19,20,21,22,23,24 . Volume-produced NI sources are mainly used in microelectronic 1,2,3,4,5,6 and space propulsion applications 9,10,11 while surface production of NI is employed in magnetically confined fusion devices 7,8 and sources for particle accelerators 12,13,14 .…”