摘要:

Experiments and analytical methods for determining electron‐ion recombination and attachment coefficients in highly collisional, cylindrically symmetric plasmas are presented. Photoionization by sparkboard light sources of tetrakisdimethylaminoethylene (TMAE) seeded in atmospheric‐pressure helium is used to produce the plasma. The electron density is probed by microwave transmission techniques. The effective recombination coefficient for electrons recombining with TMAE ions in atmospheric pressure helium is found to be (9.0±1.1)×10−6cm3 s−1forTe=300 K.

ISSN:0021-8979    

DOI:10.1063/1.352269

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A formalism is developed for numerically calculating reflection and absorption of right‐hand polarized waves and reflection of left‐hand polarized waves propagating into a cyclotron resonance zone in a medium in which both magnetic field and plasma density are varying. The results are shown to agree with previous analytic calculations in the limit of constant density, weak collisionality, and linearly varying magnetic field, where the analytic calculation applies. The formalism is then applied to a plasma with general field and density variations, and arbitrary collisionality. The absorption and reflections are calculated for various boundary conditions along the propagation path, showing that there is an optimum density for power absorption. The collisionless absorption in the resonance zone, calculated from the single particle heating averaged over the flux is shown to be consistent with the linear wave absorption at low absorption and collisionality. At high absorption a prescription for bringing the two calculation methods into agreement is advanced. The results are used to qualitatively explain some previously puzzling experimental observations.

ISSN:0021-8979    

DOI:10.1063/1.352244

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Collisionless orbit theory is used to model isolated particles in low‐pressure discharges with and without the presence of negative ions. The key results are as follows: (1) Debye–Hu¨ckel theory works well for approximating the potential profile around the particle, and (2) the size of the sheath around the particle is determined by a Debye length that results from linearizing the Poisson–Vlasov equation. These results are valid as long as the ratio of particle radius to Debye length is small and the ratio of Debye length to mean free path is small.

ISSN:0021-8979    

DOI:10.1063/1.352245

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A description is given of characteristics of a plasma produced by electron cyclotron resonance (ECR) in a linear hexadecapole device. The field configuration generated by eight straight current rods circumferentially located in a glass chamber has a wide magnetic field‐free region inside the rods and a strong peripheral field region between the rods and the chamber wall. Plasma was produced by ECR in the strong peripheral field using 2.45 GHz of radio frequency (rf) power and was effectively transferred into the field‐free central region along radial field lines. Radial distribution of the ion saturation currentIswas measured by a Langmuir probe, being remarkably flat in the field‐free region and showing extremely low fluctuations ofIs. The electron density at the chamber center increased in proportion to the rf power and significantly exceeded the cutoff density determined by the rf frequency. The production mechanism for the overdense plasma, the influence of the rf electric field direction upon the electron density profile, and the effect of ion drift motion due to the field line curvature are also discussed.

ISSN:0021-8979    

DOI:10.1063/1.352246

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

dc voltage holding characteristics were investigated to obtain a data base for designing high‐energy and high‐power ion sources of neutral beam injectors. We confirmed that the voltage holding characteristics almost obey the clump theory in the experimental gap length of up to 50 mm. The magnetic field in the gap lowered the breakdown voltage in a gas discharge region higher than a pressure of 10−3Torr. The breakdown voltage of 30% was reduced by seeding cesium on the electrode with one order higher density than that of actual ion source at the pressure region of lower than several mTorr.

ISSN:0021-8979    

DOI:10.1063/1.352247

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The numerical calculations of the transition phase of a streamer to an arc in nitrogen is reported. The proposed model includes an extensive set of collisional processes leading to gas heating. Radial variations of the species concentration and temperature are included in the calculation. Starting with the streamer parameters as an initial condition, the calculations are carried out until ‘‘quasisteady’’ state arc conditions are reached. The time evolution of the species concentration, the discharge voltage, and the current are discussed. The steady‐state arc temperatures, radii, currents, and voltages are compared with available experimental data.

ISSN:0021-8979    

DOI:10.1063/1.352248

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Pulsed laser vaporization of graphite is rapidly emerging as an effective technique for the preparation of high quality diamond‐like carbon films. However, the dynamics of the process and mechanisms by which diamond‐like properties are obtained have not been well understood. The characteristics of the vapor plume generated by 248 nm KrF excimer laser irradiation of a graphite target are investigated using laser induced fluorescence and a Langmuir probe. It is found that the kinetic energy of the C2molecule increases with laser fluence, reaching a value in excess of 12 eV in the moderate fluence range (3–5 J/cm2) employed for deposition. The Cn+ions are 5–10 times more energetic and comprise ∼10% of the vapor flux. A notable finding is that irradiation of the surface at an angle of 70° with respect to the target normal increases the ion velocity when compared with 0° laser incidence at the same surface fluence. Analysis of the films prepared under such conditions supports the theory that diamond‐like film character is directly related to the kinetic energy of the depositing species.

ISSN:0021-8979    

DOI:10.1063/1.352249

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A self‐consistent continuum (fluid) model for a radio‐frequency discharge is presented. The model is one dimensional, incorporates an electron energy balance, and is valid for both electropositive and electronegative discharges. A connection of the fluid model with the underlying physics is presented: issues such as the derivation of the fluid equations from moments of the Boltzmann equation, the closure of the set of moments, and the fundamental assumptions behind the fluid equations are discussed. A detailed set of results for an electropositive and an electronegative discharge is presented, and contrasted. The sustaining mechanisms and the electrical characteristics of the two discharges are also discussed. Comparison with experimental data of spatially and temporally resolved plasma induced emission is successfully done.

ISSN:0021-8979    

DOI:10.1063/1.352250

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A plasma simulator which employs efficient numerical methods is used to do parametric studies on an electropositive (Ar), and an electronegative (SF6) discharge. The effects of pressure and current amplitude variation are studied; the phenomena associated with the transition of the discharge into different operating regimes at low currents, and at high currents, are demonstrated and discussed. Comparison of the model results with experimental data is good. The effect of ion mobility variation with electric field is also studied, and is shown to be important in improving the comparison with experimental data. Finally, a sensitivity analysis on the values of the transport and kinetic parameters is done. The sensitivity analysis and the agreement with experimental data demonstrate the validity of the continuum modeling approach, as long as reasonably accurate experimental data for the model parameters are available.

ISSN:0021-8979    

DOI:10.1063/1.352251

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

80–100 keV Ar+, 200 keV Xe+, and 200 keV Hg+were implanted into Si3N4films under angles of 0°, 45°, 60°, and 75°. Both normal and oblique incidence Rutherford backscattering of 2.1 MeV He ions have been used to study tilted angle implantation, i.e., the lateral spread of Ar, Xe, and Hg ions in the Si3N4films. The results extracted are compared with the simulation of transport of ions in matter (TRIM’89 code). The experimental lateral spread seems to be in good agreement with the TRIM’89 prediction.  

ISSN:0021-8979    

DOI:10.1063/1.352252

出版商:AIP    

年代:1992

数据来源: AIP