Enhancement of negative hydrogen ion production at low pressure by controlling the electron kinetics property with transverse magnetic field

Kim, June Young; Cho, Won-Hwi; Dang, Jeong-Jeung; Kim, Seong-Cheol; Chung, Kyoung−Jae; Hwang, Y. S.

doi:10.1088/0963-0252/25/6/065019

Cited by 7 publications

(6 citation statements)

References 16 publications

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“…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].…”

Section: Discussionmentioning

confidence: 99%

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Kim

Ryu

et al. 2018

New J. Phys.

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Thermodynamics of a magnetically expanding plasma (magnetic nozzle (MN)) has been investigated considering the existence of confined electrons bouncing back and forth inside a potential well formed by a combination of external magnetic field and self-generating ambipolar electrostatic potential. The properties of confined electrons are distinguished from that of the adiabatically expanding electrons with γ e ≈5/3 by the separate measurement of each species using a double-sided planar Langmuir probe. Relationship between the electron pressure versus electron density averaged over electron energy probability functions (eepfs) clearly reveals that the confined electrons in MN have a nearly isothermal characteristic. Existence of isothermally behaving confined electrons together with adiabatically expanding electrons separates the MN system into two regions with different thermodynamic properties; one is a nearly adiabatic region located near the nozzle throat and the other is nearly isothermal region located far from the nozzle. A transition of electron thermodynamic property along a distance from the nozzle throat can be explained with conservation of magnetic moment of electrons bounced back by ambipolar electrostatic potential. Coexistence of the nearly adiabatic electrons with Maxwellian eepf and the nearly isothermal electrons with high energydepleted eepf makes the overall eepf shape low energy-populated eepf, indicating a need for careful analysis on the measured eepfs near the nozzle throat. In spite of significant contribution of confined electrons to eepf and overall electron thermodynamics, it is found that the confined electrons behaving isothermally do not contribute to the generation of ambipolar electrostatic potential which is important for ion acceleration in MN. The present study suggests that ion acceleration should not be directly inferred from the value of polytropic exponent γ e because thermodynamic property of a MN is influenced by isothermally behaving confined electrons as well as adiabatically expanding electrons.

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Section: Discussionmentioning

confidence: 99%

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Kim

Ryu

et al. 2018

New J. Phys.

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“…the frequency scale of the electron-electron collision greatly exceeds the inelastic collision between low energy electrons and neutral species. Recently, we observed that the magnetic filter field changes the bi-Maxwellian EEPF to the low-energy populated Maxwellian [39], which is similar to the effect of gas pressure on the EEPF. We are attempting to understand the mechanism of magnetic filter in the context of the enhanced electron-neutral collision by the electron confinement due to the filter field.…”

Section: Destruction Processmentioning

confidence: 56%

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

et al. 2016

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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.

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“…A systematic Boltzmann analysis is performed on the EEDF, to act as the support for the model of SiH 4 -containing plasmas. Due to the formant of vibrational excitation, the EEDF drops sharply in the energy range of 0.1-4 eV in low reduced electric field (E/N < 100 Td) [56]. The presence of the formant probably contributes to the electron energy loss in the vibrational excitation.…”

Section: Discussionmentioning

confidence: 99%

Electron energy distribution functions relevant for weakly ionized SiH₄–H₂plasma

Zhang

2020

J. Phys. D: Appl. Phys.

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In the existing fluid and global models for SiH4-containing plasmas, the Maxwellian distribution (MD) of the electron energy distribution function (EEDF) is assumed to determine the reaction coefficients and transport coefficients. However, the EEDFs can exhibit bi-Maxwellian or more complex distributions, which causes large deviations in simulation results. In this paper, the Boltzmann analysis of the EEDF for pure SiH4 and SiH4–H2 plasmas is presented. Calculation results suggest the clear impact of electric field on the behavior of the EEDF. In low reduced electric field (E/N = 5 Td), the shape of the calculated EEDF is close to MD. Due to the vibrational excitation of pure SiH4, the EEDF drops sharply within 4 eV at 100 Td. The difference of EEDF between AC and DC fields is analyzed by the diffusion coefficient of the distribution function. In high-frequency field, the EEDF is more prone to MD. In low-frequency field, the relationship between mean electron energy and E/N has no dependence on the field frequency. Unlike some monoatomic molecular plasmas, the influence of electron–electron collisions on the EEDF is prominent only when the ionization degree is higher than 10−3. Besides, in the SiH4–H2 mixture, it is found that increasing the H2 concentration enhances the electron energy tail. Negative differential conductivity of the drift velocity is observed, and it keeps decreasing with the H2 increasing and finally disappears. Remarkable synergism is observed in the SiH4–H2 mixture. The electron transport coefficients of the pure SiH4 and pure H2 are in satisfactory agreement with available measurements.

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Enhancement of negative hydrogen ion production at low pressure by controlling the electron kinetics property with transverse magnetic field

Cited by 7 publications

References 16 publications

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

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

Electron energy distribution functions relevant for weakly ionized SiH₄–H₂plasma

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Enhancement of negative hydrogen ion production at low pressure by controlling the electron kinetics property with transverse magnetic field

Cited by 7 publications

References 16 publications

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

Thermodynamics of a magnetically expanding plasma with isothermally behaving confined electrons

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

Electron energy distribution functions relevant for weakly ionized SiH4–H2plasma

Contact Info

Product

Resources

About

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

Electron energy distribution functions relevant for weakly ionized SiH₄–H₂plasma