By applying the asymmetric magnetic field to a discharge, the dc self-bias and asymmetric plasma response can be generated even in a geometrically and electrically symmetric system. This is called magnetical asymmetric effect (MAE), which can be a new method to control the ion energy and flux independently (Yang et al 2017 Plasma Process. Polym. 14 1700087). In the present work, the effects of magnetic field gradient, gas pressure and gap length on MAE are investigated by using a one-dimensional implicit particle-in-cell/Monte Carlo collision simulation. It found that by appropriately increasing the magnetic field gradient and the gap length, the range of the self-bias voltage will be enlarged, which can be used as the effective approach to control the ion bombarding energy at the electrodes since the ion energy is determined by the voltage drop across the sheath. It also found that the ion flux asymmetry will disappear at high pressure when the magnetic field gradient is relative low, due to the frequent electron-neutral collisions can disrupt electron gyromotion and thus the MAE is greatly reduced.

Magnetical asymmetric effect (MAE) in a geometrically and electrically symmetric capacitively coupled plasma is investigated by a one‐dimensional implicit Particle‐in‐cell/Monte Carlo collision simulation. We applied four types of asymmetric magnetic field parallel to the electrodes and the discharge operates at a single‐frequency rf source of 13.56 MHz and 150 V in argon with the pressure of 30 mTorr. The simulation results show that the asymmetric magnetic field can generate a significant dc self‐bias, which is the result of a particle‐flux balance applied to each electrode. The asymmetric magnetic field with variable gradient can produce controllable asymmetry in the plasma density and ion flux profiles to each electrode, together with a significant change on IEDF shape and width on the powered electrode. It has demonstrated that the MAE is a promising approach to increase the ion flux and still make the ion energy be adjusted in a certain range, that is, independent control of ion flux and energy to the electrode. The results suggest that the MAE can be an effective means to control the plasma properties as an augmentation to conventional measures.

A multiple-mirror DT reactor with injected power supplied by a fast neutral D beam is considered, and the power-balance equations for the hot and warm components are solved. For a fixed mirror ratio M1 and fixed Q = fusion power/injected power, the warm- and hot-deuterium fractions, the warm temperature, and the injection energy are determined so as to minimize the plasma pressure-reactor length product p1L. The equilibrium hot-ion distribution and the energy transfer factors are found analytically from the Fokker-Planck equation. For Q = 2.8 and M1 = 3.3, it is found that the additional hot-component fusion reactions produce a 26% reduction in p1L, to 4 × 105 bar·m. The seeding of the plasma with low-Z impurities so as to reduce the axial power loss has also been considered. Using a corona equilibrium model and optimizing the impurity fraction, an additional 10% reduction in p1L is obtained.

Geometrically symmetric and electrically asymmetric discharges operating at 13.56 MHz and 27.12 MHz with variable phase angle between the harmonics are simulated by a one-dimensional implicit particle-in-cell/Monte Carlo collision model in argon at a pressure of 30 mTorr. The amplitude of each of the harmonics is chosen to be 150 V. The magnetic fields, with strengths of 10 G and 100 G, are parallel to the electrodes and homogeneous throughout the entire electrode gap in a direction perpendicular to the electrodes. It is found that, with a weaker magnetic field at 10 G, the plasma density is nearly doubled and the self-bias is almost unaffected. However, with a stronger magnetic field at 100 G, the plasma density is significantly increased and nearly independent of the phase angle, but at the cost of decreasing the self-bias, which results in a smaller adjustable range of ion bombardment energy. In general, we have demonstrated that an external magnetic field will expand the operational parameter spaces and thus may promote some related applications in coupled plasma sources with electrical asymmetry effects.

The characteristics of magnetized capacitively coupled plasmas (CCPs) driven by combined dc/rf sources in argon have been investigated by a one-dimensional implicit Particle-in-cell/Monte Carlo collision model. Discharges operating at 13.56 MHz with a fixed rf voltage of 300 V are simulated at the pressure of 50 mTorr in argon. Four cases, i.e., CCP driven by rf source, rf + dc sources, rf source with magnetic field, and rf + dc sources with magnetic field, are presented and compared at the Vdc = −100 V, B = 50 Gs, and γi = 0.2. It is found that, with the influence of dc voltage and magnetic field, the plasma density has been greatly enhanced by over one order of magnitude over the rf-only case. This is due to the fact that the mean free path of electrons decreases by the cyclotron motion and the energetic secondary electrons are trapped by the magnetic field, leading to a significant increase in heating and ionization rates. Moreover, transition of the stochastic to Ohmic electron heating mechanism takes place as the magnetic field increases because electron kinetics can be strongly affected by the magnetic field. In general, we have demonstrated that such a configuration will enhance the discharge and thus enable CCPs work under extremely high energy density stably that can never be operated by any other configurations. We expect that such a configuration can promote many related applications, like etching, sputtering, and deposition.