Kinetics of electrons and neutral particles in radio-frequency transformer coupled plasma H⁻ion source at Seoul National University

Abstract

In volume production H − ion sources, control of electron temperature is essential due to its close correlation with the generation of vibrationally-excited hydrogen molecules in the driver region as well as the generation of H − ions by dissociative attachment in the extraction region. In the ion source group at Seoul National University (SNU) in Korea, a lot of research effort has been made to the development of a volume production H − ion source based on radio-frequency (RF) transformercoupled plasma (TCP) for long lifetime continuous wave (CW) operation. It has a spiral RF antenna located outside the discharge chamber to generate a plasma with high electron temperature in the driver region and employs a magnetic filter field to prevent high energy electrons from being transported to the extraction region. In this paper, we present the recent progress on understanding of the underlying physics of the RF TCP H − ion source at SNU. Special attention is paid to the characterization of electron kinetics regime for controlling electron energy distribution and the influence of relaxation of neutral particles during the transport across the magnetic filter region. Effect of the degree of dissociation on the production of H − ions is also discussed.Hence, the E-V reaction is more efficient than the e-V reaction to excite hydrogen molecules to higher vibrational states in spite of its higher threshold energy. For example, the rate of E-V reactions is 4-5 orders of magnitude higher than that of e-V reaction for an excitation reaction from u = 0 to u = 7, as depicted in figure 1(a). The second step is a production of H − ions by DA reaction of the highly vibrationally-excited molecules generated from the previous step with low energy electrons. In this step, the electron temperature must be kept low because the cross section for DA reaction depends greatly on the energy of electrons interacting with vibrationally-excited molecules (see figure 1(b)). Also, low electron temperature has a benefit in minimizing the destruction of H − ions by collisional detachment by electrons.

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

“…From another point of view, our results indicate that it is possible to control the eepf within the magnetically expanding plasma generated by the ECR or helicon sources by changing the bounce region of confined electrons according to the magnetic field conditions. It is meaningful that these characteristics can play a leading role in the generation of specific radical and ion species in the plasma processing, in which the spatial distribution of eepf is a decisive factor [45,46].…”

Direct measurements of electronic ground state ro-vibrationally excited D2 molecules produced on ECR plasma-facing materials by means of VUV-FT absorption spectroscopy

“…Gabriel et al mentioned rotational temperature in the 3000-4000 K range 95 while Briefi et al indicated a two-temperature Boltzmann distribution with a low (564 K) and a high (5440 K) component 56 and Wagner et al 66 showed up lower rotational temperature, 380 K. In our reactor, in plasma-OFF condition it appears slightly above the temperature of the temperature-regulated walls of the reactor (283 K). In plasma-ON condition, it is surprisingly low even if at low pressure (8 µbar) and low electron density (∼3×10 15 m −3 ) energy transfer between electrons and neutrals through inelastic collisions is weak 96 . Péalat et al 67 measured similar rotational temperature in a plasma of analogous density and highlighted the effect of passive gas surrounding the plasma, mentioned in 4.1, on the rotational temperature of the low ro-vibrational levels (v = 0, J 3) attributed to the plasma volume.…”

Magnetic confinement and instability in partially magnetized plasma

“…From semiconductor processes to electric propulsion in space, most plasma sources are operated with an external magnetic field to achieve high plasma density [1][2][3][4][5][6]. The magnetic field applied to plasma devices is in the range of tens to hundreds of gauss, so that light electrons are fully magnetized while the Larmor radius of heavy ions often exceeds the source dimensions.…”