GENERATION OF LARGE AREA INDUCTION THERMAL PLASMA BY SUPERIMPOSING 50-KHz OSCILLATING FIELD

感应耦合射频热等离子体产生的功率超过100 kW，具有高温、高反应性，正逐渐成为新型功能材料加工和环境破坏物质销毁的重要来源。虽然等离子体的体积被MHz量级的发生器的施加频率限制在直径为50至60 mm，但是为了作为未来技术的更高处理速率，强烈需要大面积等离子体。在本计画中，我们尝试在一个小面积的直流等离子体上叠加一个低频（50 kHz）磁场来扩大高温等离子体场。基于等离子体动力学模型的数值模拟结果表明，在760和76 ℃下，激发等离子体膨胀并维持直径为100 mm的等离子体的最小功率分别为90和60 kW。计算还表明，达到一个新的稳定状态所需的时间是几十毫秒左右，在此之后，即使没有直流电源输入的广域等离子体保持稳定的50 kHz的字段。使用50 kHz频率和300 kW最大功率的电源进行实验。用单色仪观察到ArI在794和801 nm的两个光谱强度，定量分析了瞬态现象。通过在60 μ m软真空条件下进行的几次实验，发现功率为1 kW的小尺寸直流等离子体在50 kHz功率指示级55 ~ 60 kW处膨胀，如预期的那样，在膨胀开始后20 ms达到新的稳态。在10 cm直径范围内，以稳定模式成功地产生了8，000 ~ 10，000 K的等离子体温度分布。

The inductively-coupled radio frequency thermal plasma produced with a power over a hundred kW is now becoming gradually an important source with high-temperature and high-reactivity either for processing of new functional materials or for destruction of circumstance depleting substance. Although the volume of the plasma is restricted to 50 to 60 mm in diameter by the applied frequency of the generator of MHz order, a large area plasma is required strongly for higher rate of processing as a future technology. In this project, an attempt is made to expand the high temperature plasma field by superimposing a low-frequency (50kHz) magnetic field on a small area dc plasma. Because the penetration depth of such a low frequency field is as long as a few hundreds mm, a more wider plasma in diameter can be produced.Numerical simulations based on the dynamic plasma model showed that the minimum power to motivate the plasma expansion and sustain a wider plasma of 100 mm in diameter was found to be around 90 and 60kW for the pressure of 760 and 76 torr, respectively. The calculation also showed that the time necessary for reaching a new steady state is around a few tens of ms and after this the wide area plasma is kept stationary by 50-kHz field even without dc power input. Experiments were carried out with using a power supply of 50-kHz frequency and 300-kW maximum power. Two ArI spectral intensities of 794 and 801 nm were observed by using a monochromator to analyze the transient phenomena quantitatively. Through several shots of experiments carried out under 60 torr soft vacuum condition, the small size dc plasma with 1-kW power was found to expand at the 50-kHz power indicator level of 55 to 60 kW,as expected and a new steady state of the plasma was achieved 20 ms after the initiation of the expansion. A quite uniform profile of the plasma temperature of 8,000 to 10,000 K was produced successfully in steady mode over 10 cm diameter.