China
Africa
Explore chapters and articles related to this topic
Plasma Created in High-Frequency Electromagnetic Fields
Published in Alexander Fridman, Lawrence A. Kennedy, Plasma Physics and Engineering, 2021
Alexander Fridman, Lawrence A. Kennedy
Consider the low-pressure, wave-heated plasmas and focus on three discharge systems: the electron cyclotron resonance (ECR) discharges, the helicon discharges, and the surface wave discharges. In ECR-discharges, a right circularly polarized wave (usually at microwave frequencies, e.g. 2.45 GHz) propagates along the DC-magnetic field (usually quite strong, 850 G at resonance) under the conditions of the electron cyclotron resonance, which provides the wave absorption through a collisionless heating mechanism. In the helicon discharges, an antenna radiates the whistler wave, which is subsequently absorbed in plasma by collisional or collisionless mechanisms. The helicon wave-heated discharges are usually excited at RF-frequencies (typically –13.56 MHz), and a weak magnetic field of about 20–200 G is required for the wave propagation and absorption. In the case of surface wave discharges, a wave propagates along the surface of the plasma and is absorbed by collisional heating of the plasma electrons near the surface. The heated electrons then diffuse from the surface into the bulk plasma. Surface wave discharges can be excited by either RF or microwave sources and they do not require a DC-magnetic field. The plasma potential with respect to all wall surfaces for wave-heated discharges is relatively low (about 5 electron temperatures, 5Te) similar to the case of ICP-discharges. This results in the effective generation of high-density plasmas at reasonable absorbed power levels.
Dry Etch Damage in Widegap Semiconductor Materials
Published in Kazumi Wada, Stella W. Pang, Defects in Optoelectronic Materials, 2021
A number of different dry etch methods involving a chemical component to the etching in addition to physical sputtering. Figure 2 shows schematics of three different reactors [8–10]. In simple capacitively-coupled Reactive Ion Etching (RIE) the plasma is generated by application of rf power to the sample electrode via a coupling capacitor. The sample position sustains a negative potential with respect to the body of the plasma, and thus produces ion bombardment of the sample in addition to the impingement of neutral gas atoms and molecules. Increasing the applied rf power increases both the ion density and energy. Two different high density plasma systems are shown in the lower part of Figure 2. In both configurations, ion density is controlled by the rf chuck power. Decoupling these two parameters allows one to have a large ion flux, but a low ion energy and thus etch rate can be enhanced without creation of excessive lattice damage. In the system at center an Electron Cyclotron Resonance (ECR) source operating at microwave frequency couples power into the chamber and magnetic confinement of the plasma induces a high ion density through efficient electron-gas molecule collisions. Similar high ion densities (~ 5 × 1011 cm−3) can be achieved using an Inductively Coupled Plasma (ICP) source (lower part of Figure 2) that has the advantage of more mature automatic tuning technology and superior uniformity over large areas. Some of the typical characteristics of these three sources (and another variation, the Helicon wave source) are shown in Table I.
AlGaAs/GaAs Heterojunction Bipolar Transistors with InGaAs Etch-Stop Layer
Published in Jong-Chun Woo, Yoon Soo Park, Compound Semiconductors 1995, 2020
Yosuke Miyoshi, Shin'ichi Tanaka, Norio Goto, Kazuhiko Honjo
Prior to fabricating HBTs, we carried out preliminary experiments to determine the optimum In mole fraction for the InGaAs etch-stop layer. The dry-etching system used in this study (ANELVA ECR-6001) takes advantage of electron cyclotron resonance (ECR) plasma source for low damage, high yield GaAs etching. Main and sub-magnetic coils are combined for adjusting collimated magnetic field in ECR chamber. In contrast to conventional reactive ion beam etching (RIBE), no DC bias is applied to extract reactive ions from the plasma source, but samples are located near ECR plasma position to avoid surface damage caused by accelerated ions. In order to assist desorption of chlorides formed on etched surface, the ion energy is controlled by 13.56 MHz rf power which is supplied to the substrate. Throughout the experiment, low gas pressure of 0.4mTorr was used to ensure anisotropic etching profile of emitter mesa.
Plasma Wall Interaction of New Type of Divertor Heat Removal Component in LHD Fabricated by Advanced Multi-Step Brazing (AMSB)
Published in Fusion Science and Technology, 2023
Masayuki Tokitani, Yukinori Hamaji, Yutaka Hiraoka, Yuki Hayashi, Suguru Masuzaki, Hitoshi Tamura, Hiroyuki Noto, Teruya Tanaka, Tatsuya Tsuneyoshi, Yoshiyuki Tsuji, Gen Motojima, Hiromi Hayashi, Takanori Murase, Takeo Muroga, Akio Sagara, Tomohiro Morisaki
Three flat bar–type components composed of the AMSB joint structure of W/GlidCop/SUS, the so-called new type of divertor heat removal component, were placed in a horizontal row, as shown in Fig. 1, and then inserted into the divertor strike position of the LHD through a retractable material probe system, schematically shown in Fig. 2. The probe system was designed so that the W surface and the magnetic field lines of the divertor leg crossed at 45 deg. The magnetic field line direction, as drawn in Fig. 2, is the clockwise (CW) direction of the LHD helical magnetic field. The three components were completely the same design, and were distinguished as components A, B, and C. The size of the W plates was 20 × 20 × 5 mm3, and the numbers of each W array were named as positions 1 to 7, as shown in Figs. 1 and 2. The components were exposed to 1180 shots (~8000 s in total) of NBI-heated plasma discharges in the 2020FY plasma campaign. Electron cyclotron resonance heating (ECH) was sometimes used as an auxiliary heating.
Energy Confinement Dynamics and Some Properties of Plasma Self-Organization in ECRH Regime in the L-2M Stellarator
Published in Fusion Science and Technology, 2023
Aleksei Meshcheryakov, Irina Grishina
The experiments were performed at the L-2M stellarator, which is a classical two-turn stellarator (the number of helical windings is l = 2, and the number of field periods around the torus is N = 7) with major radius R = 1 m, plasma radius a = 0.115 m, and toroidal magnetic field B0 = 1.34 T (Ref. 20). The rotational transformation angle created by the magnetic system varies from ι = 0.18 at the magnetic axis of the system to ι = 0.78 at the plasma boundary. In the experiments, hydrogen is used as working gas. The facility can operate both in the regimes of ohmic (OH) and electron cyclotron resonance (ECR) plasma heating. In experiments on ECR plasma heating, the MIG-3 gyrotron complex, consisting of two gyrotrons with a total power of up to 1000 kW, is used to create and heat plasma.21 Usually, the duration of the heating pulse is 12 ms. Plasma is heated by microwave radiation with a frequency corresponding to the second harmonic of the electron gyrofrequency (75 GHz). The resonance magnetic surface B = Всe is located at the magnetic axis of the facility. In the quasi-stationary discharge stage, the plasma energy can reach 0.8 kJ at the mean plasma density of 2.5 × 1019 m–3.
Terahertz waves propagation in an inhomogeneous plasma layer using the improved scattering-matrix method
Published in Waves in Random and Complex Media, 2021
Youyi Zhang, Guanjun Xu, Zhengqi Zheng
Focusing on the subfigures in the second row, the higher electron density makes the absorption bandwidth of left-handed polarized waves wider, compared Figure 7(e) with Figure 7(a). Besides, a strong external magnetic field shifts the absorption peak to a lower frequency. Of particular note, Figure 7(g) demonstrates when , there are two obvious absorption peaks of right-handed polarized waves. The first peak caused by the electron cyclotron resonance is not only broadened and enhanced with external magnetic field increases but also be moved to a higher frequency. Another peak appears due to the incident frequency resonates with the plasma frequency, which increases absorbance. In addition, a strong external magnetic field reduces the depth of the absorption valley. Compared with the results obtained in some other studies, these phenomena are in accordance with [15,16], which further confirms the applicability of the ISMM method.