EXPANSION EFFECTS OF HIGH TEMPERATURE FIELD OF INDUCTION THERMAL PLASMA BY SUPERIMPOSING LOW FREQUENCY MAGNETIC FIELD

感应热等离子体提供了一种温度超过一万开尔文的高反应性等离子体源，正在成为新型功能材料等离子体加工的重要技术。然而，由于工作频率的限制，磁场的尺寸仅限制在约50毫米直径内，其工作频率为MHz的高阶。该项目涉及一种等离子炬，可产生宽高温区域，可用于高容量和高速率等离子体处理。该火炬由一个高频（射频）和一个低频感应等离子体部分组成。频率较低的几十千赫磁场以其较长的表皮深度穿透射频等离子体内部，并以叠加效应使射频等离子体半径变宽。结果总结如下：1。首先设计并测试了感应耦合射频（13.56MHz）等离子体部分。在300 ~ 750 torr的压力条件下，在直径为30mm的圆柱形石英管内稳定地建立了功率为15kW的等离子体。由此产生的等离子体温度经光谱观测测得超过10,000K。射频放电部分的温度和电导率足以与低频磁场耦合。新开发的计算机程序分析了从发电机到等离子体负载的功率流，结果表明，使用直径为85毫米、长度为72毫米的3匝线圈作为第二低频线圈，可以吸收10000安培的高线圈电流产生的60 kHz磁能，从而扩大等离子体场。实验方法是采用单脉冲电流波形，峰值电流为5700a，持续时间为100微秒，并提供LC振荡电路。通过低频磁场的叠加，等离子体的发射光强度有微弱的增强。为了更清晰、更定量地验证耦合效应，应该进行进一步的实验，将脉冲电流的幅度或持续时间加倍。少

The induction thermal plasma provides a high reactivity plasma source with a high temperature beyond a ten of thousand Kelvin, and is becoming an important technique for plasma processing of new functional materials. The dimension of the field is, however, restricted only within about 50-mm diameter by a limit of the operating frequency with a high order of MHz. This project concerns with a plasma torch producing a widened high temperature region which can be used for high capacity and high rate plasma processing. This torch consists of a high(radio frequency) and a low frequency induction plasma parts. The magnetic field with a lower frequency of several tens of KHz penetrates inside the r.f. plasma with its long skin depth and widens the radius of the r.f. plasma as a superimposing effect. The results are summarized as follows.1. The inductively coupled r.f.(13.56MHz) plasma part was first designed and tested. The plasma was established in stable with a power of 15kW within a cylindr … More ical quarz tube of 30-mm diameter under the pressure condition of 300 to 750 torr. The temperature of the plasma thus produced was measured as more than 10,000K from the spectral observation. The temperature and thus the electrical conductivity of the r.f. discharge part is quite enough for being coupled with the low-frequency magnetic field.2. A newly developed computer program for analyzing the power flow from the generator to the plasma load reveals that with using a 3-turn coil of 85-mm diameter and 72-mm length as the second low frequency coil, the plasma field can be expanded by absorbing the 60 kHz magnetic energy generated by a high coil current of 10,000 amperes.3. Experimental approach was carried out by using single pulse current waveform with a peak current of 5,700A and a duration of 100 micro second which is provided an LC oscillating circuit. The emission light strength from the plasma was observed to be enhanced weakly by superimposing the low frequency magnetic field. A further experiment should be performed to verify the coupling effect more clearly and quantitatively, with doubling the amplitude or duration of the pulse current. Less