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

功率在100kW以上的感应耦合射频热等离子体，无论是用于新型功能材料的加工，还是用于环境耗损物质的销毁，都逐渐成为一种高温、高反应性的重要来源。虽然等离子体的体积被频率限制在50~60 mm，但作为一种未来的技术，对于更高的处理速度，对大面积等离子体的需求非常强烈。在本项目中，试图通过在小面积的直流等离子体上叠加低频(50 KHz)磁场来扩展高温等离子体场。基于动态等离子体模型的数值模拟结果表明，在760托和76托压力下，激励等离子体膨胀的最小功率约为90 kW，维持直径100 mm的较宽等离子体的最小功率约为60 kW。计算还表明，达到新的稳态所需的时间约为几十毫秒，在此之后，广域等离子体即使在没有直流电源输入的情况下，也可以通过50 kHz场保持稳定。实验采用频率为50 kHz、最大功率为300 kW的电源。用单色仪观测到了794 nm和801 nm两个ArI光谱强度，定量地分析了这些瞬变现象。通过在60Torr软真空条件下进行的多次实验，发现功率为1kW的小尺寸直流等离子体在55~60kW的50 kHz功率指示器水平上如预期的那样膨胀，并在膨胀开始后20ms达到一个新的稳态。在直径10 cm以上的稳态模式下，成功地获得了8000~10000 K的均匀等离子体温度分布。

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.