Deli Tang

Interaction of electromagnetic waves with a magnetized nonuniform plasma slab

The absorption, reflection, and transmission of electromagnetic waves by a nonuniform plasma slab immersed in an ambient uniform magnetic field of various strengths are studied in this paper. The effects of the plasma parameters and magnetic field strength on the absorbed, reflected, and transmitted power are discussed. The magnetized nonuniform plasma slab is modeled by a series of magnetized uniform plasma subslabs. The calculation results show that the effects of the magnetic field strength and density gradient on the absorbed power, as well as the frequency band of resonant absorption, are significant. A complete analysis utilizing the scattering matrix method is also used to compare the above calculation results which neglect multiple reflections between subslab interfaces. Broadband absorption of electromagnetic waves can be achieved by changing the magnetic field strength and plasma density. More than 90% of the electromagnetic wave power can be absorbed in a magnetized nonuniform plasma slab with width of 12 cm and the absorption bandwidth can range from 1 to 20 GHz with different plasma parameters and external magnetic field strengths.

Current control for magnetized plasma in direct-current plasma-immersion ion implantation

A method to control the ion current in direct-current plasma-immersion ion implantation (PIII) is reported for low-pressure magnetized inductively coupled plasma. The ion current can be conveniently adjusted by applying bias voltage to the conducting grid that separates plasma formation and implantation (ion acceleration) zones without the need to alter the rf input power, gas flux, or other operating conditions. The ion current that diminishes with an increase in grid bias in magnetized plasmas can be varied from 48 to 1 mA by increasing the grid voltage from 0 to 70 V at −50 kV sample bias and 0.5 mTorr hydrogen pressure. High implantation voltage and monoenergetic immersion implantation can now be achieved by controlling the ion current without varying the macroscopic plasma parameters. The experimental results and interpretation of the effects are presented in this letter. This technique is very attractive for PIII of planar samples that require on-the-fly adjustment of the implantation current at hig...

Effects of external magnetic field on propagation of electromagnetic wave in uniform magnetized plasma slabs

A simple method is proposed to describe the propagation of electromagnetic waves in magnetized uniform plasma slabs. Using this method, the reflection, absorption and transmission coefficients of such plasmas for right-hand circularly waves are studied and the effects of the continuously changing external magnetic field on the power of the electromagnetic waves propagated in magnetized plasma slabs with fixed parameters are presented. Our method enables more detailed numerical analyses which are useful in practical applications pertaining to the control of the reflection or absorption coefficients of electromagnetic wave through a uniform magnetized plasma slab by adjusting the external magnetic field.

Improved planar radio frequency inductively coupled plasma configuration in plasma immersion ion implantation

Plasmas with higher density and better uniformity are produced using an improved planar radio frequency (rf) inductively coupled plasma configuration in plasma immersion ion implantation (PIII). An axial magnetic field is produced by external electromagnetic coils outside the discharge chamber. The rf power can be effectively absorbed by the plasma in the vicinity of the electron gyrofrequency due to the enhanced resonant absorption of electromagnetic waves in the whistler wave range, which can propagate nearly along the magnetic field lines thus greatly increases the plasma density. The plasma is confined by a longitudinal multipolar cusp magnetic field made of permanent magnets outside the process chamber. It can improve the plasma uniformity without significantly affecting the ion density. The plasma density can be increased from 3×109 to 1×1010 cm−3 employing an axial magnetic field of several Gauss at 1000 W rf power and 5×10−4 Torr gas pressure. The nonuniformity of the plasma density is less than 1...

Effects of magnetic field gradient on ion beam current in cylindrical Hall ion source

The effects of the magnetic gradient on the ion beam current in an end Hall-type ion source with a magnetic mirror field are investigated. In a cylindrical Hall ion source in which a cylindrical magnetic ring other than a regular magnetic pole is shortened and centrally inserted, a mirror magnetic field profile can be formed around the annular anode. A positive-negative variable magnetic gradient is shown experimentally to enhance ionization; the ionization efficiency is substantially affected by the different magnetic gradient. The high ionization results in 60% efficiency in the conversion of discharge current to ion beam current. The experimental results and interpretation of the effects are presented in this paper.

Effects of assistant anode on planar inductively coupled magnetized argon plasma in plasma immersion ion implantation

The enhancement of planar radio frequency (RF) inductively coupled argon plasma is studied in the presence of an assistant anode and an external magnetic field at low pressure. The influence of the assistant anode and magnetic field on the efficiency of RF power absorption and plasma parameters is investigated. An external axial magnetic field is coupled into the plasma discharge region by an external electromagnetic coil outside the discharge chamber and an assistant cylindrical anode is inserted into the discharge chamber to enhance the plasma discharge. The plasma parameters and density profile are measured by an electrostatic Langmuir probe at different magnetic fields and anode voltages. The RF power absorption by the plasma can be effectively enhanced by the external magnetic field compared with the nonmagnetized discharge. The plasma density can be further increased by the application of a voltage to the assistant anode. Owing to the effective power absorption and enhanced plasma discharge by the a...

Linear ion source with magnetron hollow cathode discharge

A linear ion source with magnetron hollow cathode discharge is described in this paper. The linear ion source is based on an anode layer thruster with closed-drift electrons that move in a closed path in the E×B fields. An open slit configuration is designed at the end of the ion source for the extraction of the linear ion beam produced by the magnetron hollow cathode discharge. The special configurations enable uninterrupted and expanded operation with oxygen as well as other reactive gases because of the absence of an electron source in the ion source. The ion current density and uniformity were experimentally evaluated. Using the ion source, surface modification was conducted on polyethylene terephthalate polymer films to improve the adhesion strength with ZnS coatings.

Anode double layer in magnetized radio frequency inductively coupled hydrogen plasma

The formation of the double layer created around the anode in magnetized radio frequency inductively coupled plasma, which is visually apparent because of enhanced light emission from the neutrals excited by energetic electrons, is investigated in detail in this work. The effects of the external magnetic field and anode voltage on the evolution of a cylindrical luminous anode double layer from the anode glow are evaluated in magnetized hydrogen plasmas. The anode glow is initially produced by the additional dc discharge which forms when a cylindrical anode inserted into the plasma diffusion region is positively biased. If the anode voltage is sufficiently high, the anode glow is transformed into an elongated luminous anode double layer in the plasma diffusion region, to which a diverging magnetic field generated by external magnetic coils is coupled. A weakly magnetized plasma is needed for the formation of the anode double layer in our experiments, and there is a magnetic field strength ceiling beyond wh...

Three-dimensional numerical investigation of electron transport with rotating spoke in a cylindrical anode layer Hall plasma accelerator

The effects of increased magnetic field and pressure on electron transport with a rotating spoke in a cylindrical anode layer Hall plasma accelerator are investigated by three-dimensional particle-in-cell numerical simulation. The azimuthal rotation of electron transport with the spoke has a frequency of 12.5 MHz. It propagates in the direction of the E × B drift at a speed of ∼1.0 × 106 m/s (about 37% of the E × B drift speed). Local charge separation occurs because the azimuthal local electron density concentration is accompanied by an almost uniform azimuthal ion distribution. The non-axisymmetrical electron density concentration and axisymmetrical ion distribution introduce two azimuthal electric fields with opposite directions in the plasma discharge region. The axial electron shear flow is excited under the additional Eθ × B field. The anomalous electron transport with the rotating spoke may be attributed to the axial electron shear flow induced by the two azimuthal electric fields with opposite dir...

Three-dimensional particle-in-cell simulation of discharge characteristics in cylindrical anode layer hall plasma accelerator

A current drop is found when the discharge voltage is increased in the cylindrical anode layer hall plasma accelerator and three-dimensional particle-in-cell simulation is performed to investigate the phenomenon. The simulation results which agree with experiments show that the ion density in the discharge region does not always rise when the discharge voltage is increased and the ion density reaches a maximum value at the appropriate voltage. This phenomenon is considered to be the macroscopic ramification of the change in the ionization cross section as the electron energy varies. With regard to Ar+, the largest ionization cross section appears when the electron energy is 45–110 eV. In the hall plasma accelerator, the electron drift speed is governed by E/B and controls the electron energy. Finally, the cross section of producing Ar+ is determined by E/B. Our analysis reveals that the proper E/B value in the ionization region is 2.81 × 106 m/s to 4.40 × 106 m/s for argon.