螺旋波是在有界磁化等离子体中存在的一种哨声波，其频率介于电子回旋频率和离子回旋频率之间。螺旋波在等离子体中传播时与等离子体发生耦合而高效的产生高密度的等离子体。该等离子体在材料处理、表面改性和空间电推进等产业中具有广阔的应用前景。随着射频功率的增加，螺旋波放电系统中至少存在容性耦合（E模态）,感应耦合（H模态）和螺旋波耦合（W模态）三种放电模态。不同模态之间的等离子体参数（如电子温度、电子密度、光谱分布）、供电系统参数（如输入电流、电路阻抗）等存在跳变，而模态转变机制不明，影响因素认识不清，限制了螺旋波等离子体的应用。因此，本文从实验入手，开展了氩气放电的模态转变及滞回特性与放电气压、气体流量、磁场强度、磁场方向、磁场位型以及放电功率之间依赖关系的研究。

为进行研究，研发了最大功率2 kW，最大轴向磁场400 G的线性螺旋波放电系统，实现了从容性耦合到螺旋波耦合的放电。为实现对含有强射频干扰的等离子体参数的诊断，新研发了一套采用宽频射频补偿技术和工频噪声抑制技术相结合的射频补偿探针；基于发射光谱自吸收特性，利用谱线分支比法获得了亚稳态粒子的绝对数密度。

基于上述实验系统及诊断技术首先开展了磁场强度和放电气压对E-H模态转变和滞回特性影响的研究。得到了不同磁场和气压下的等离子体密度和电子能量分布函数（EEDF）随功率变化的曲线。结果显示，无磁场时，气压小于2Pa工况，以及170G时，气压小于6Pa工况，等离子体密度出现E→H和H→E跳变，并伴随明显的反常滞回；更高的气压下，等离子体密度随功率的变化速率呈现慢-快-慢的形式，既在E和H模态直接出现混合模态，但无滞回。其中模态转变功率随放电气压的升高而减小，而轴向磁场的加入限制了等离子体径向输运，形成沿轴向的自建电场，因此有磁场时E→H模态转变功率升高。电子能量分布函数测量结果表明，无论有无磁场，E模态的EEDF主要呈现Druyvesteyn分布特性，H模态的EEDF为近似Maxwellian分布，导致不同模态同一化学反应的速率系数改变，因而不同模态的能量利用率存在显著差异。由此认为，EEDF在E→H过程中发生转变的阈值小于H→E过程中发生转变的阈值，是产生反常滞回的重要原因之一。

其次，研究了低气压高磁场时H模态产生的机理。利用750.43 nm谱线和811.49 nm/750.43 nm谱线比得到了表征直接电离的高能电子和多步电离的亚稳态相对密度随磁场的演化特性。结果表明，只有当磁场强度达到某一阈值后，H模态特征显现，而该阈值以下无H模态特性。实验数据表明，高磁场导致亚稳态密度增加，抑制高能电子减弱直接电离，促使多步电离增加，从而减少碰撞损失。同时磁场导致电子的碰撞频率升高，且电子在磁场作用下产生多次加速-碰撞亚稳态电离的循环，进一步提高了能量利用率，最终促使高磁场时产生H模态特性。实验数据还表明，高磁场时E模态的亚稳态密度始终低于H模态的亚稳态密度，而低磁场时，存在E模态功率范围内的亚稳态数密度高于H模态功率的工况。

最后，基于发射光谱研究了左旋天线放电时，不同磁场强度、磁场位型和气体流量下感应耦合向螺旋波耦合的转变特性及亚稳态密度的演化特性。结果表明，正向磁场（沿磁场方向观察，天线顺时针旋转）和会切磁场放电时，随着功率的增加等离子密度发生跳变，即发生H→W的模态转变。磁场越强、气体流量越大模态转变功率越小；反向磁场时，等离子体密度随功率增加平滑增加，无模态转变特性。而亚稳态的演化特性如下：

1）正向磁场放电时，随着电离率升高，亚稳态激发速率减弱，损失速率增加，因此混合模态的亚稳态随功率的增加而下降。当放电从混合模式变为W模态时，电离率突增导致亚稳态生成速率突降，等离子体密度突增导致亚稳态消耗速率突增，最终亚稳态密度突降。反向磁场时电离率同样随功率升高持续增加，因此在高磁场时亚稳态密度随功率增速逐步降低。

2）会切磁场时，亚稳态密度随功率变化曲线出现极小值，且极小值随流量增加而减小。分析认为，随着功率的升高，等离子体中螺旋波模态放电增强，导致电离率升高，使得亚稳态随功率升高而减小。当放电进入螺旋波模态后，天线两端产生的螺旋波向中间传播，在天线中间抵消，导致天线中间等离子体主要由天线产生的感应场维持，因而亚稳态密度逐渐升高。

In the bounded magnetic plasma, there is exist the whistle wave witch frequency is between electron cyclotron frequency and ion cyclotron frequency, and it is named helicon wave. Helicon wave will coupled with plasma when it is spread in the plasma and produce high efficiency high density plasma. It has broad application prospect in material handing, surface modification and space thruster. In helicon plasma system it is at least excist three discharge mode: capacitive coupling (E mode), inductive coupling (H mode) and helicon wave coupling (W mode). The plasma parameter (such as electron density, electron temperature and spectrum distribution) and the power system parameter (such as the input current, the circuit impedence) have the jump character when radio-frequency (RF) power achive the mode transition threshold. However, the mode transition mechanism is unclear and the influencing factors are unclear, which limits the application of helical wave plasma. Therefore, this paper studies the dependence of the modal transition and hysteresis characteristics of argon discharge on the discharge pressure, gas flow, magnetic field strength, magnetic field direction, magnetic field potential and discharge power.

The 2000 W maximum RF power and 400 G maximum axial magnetic intensity linear helicon discharge system is designed. In order to realize the diagnosis of plasma parameters with strong radio frequency interference, a new set of radio frequency compensation probes has been developed that uses a combination of broadband radio frequency compensation technology and power frequency noise suppression technology. Based on the self-absorption properties of emission spectra, the absolute number density of metastable particles was obtained by the spectral line branching ratio method.

At first, the influence of E-H mode transition and hysteresis by magnetic intensity and discharge pressure is studied. The plasma density, electron energy distribution function (EEDF) variation with RF power in different magnetic intensity and discharge pressure are acquired. The results show that when there is no magnetic field, when the pressure is less than 2Pa, and when the pressure is less than 6Pa at 170G, the plasma density appears E→H and H→E jumps, accompanied by obvious anti-hysteresis; At higher gas pressures, the rate of change of plasma density with power exhibits a slow-fast-slow pattern, with direct mixed modes in the E and H modes, but no hysteresis. The mode transition power decreases with the increase of the discharge pressure, and the addition of the axial magnetic field limits the radial transport of the plasma and forms a self-built electric field along the axial direction. Therefore, the E→H mode transition power is present when there is a magnetic field rise. The measurement results of the electron energy distribution function show that, with or without a magnetic field, the EEDF of the E mode mainly exhibits the Druyvesteyn distribution characteristics, and the EEDF of the H mode is an approximate Maxwellian distribution, which leads to the change of the rate coefficient of the same chemical reaction in different modes. There are significant differences in energy utilization. Therefore, it is considered that the transition threshold of EEDF in the process of E→H is smaller than the threshold value of transition in the process of H→E, which is one of the important reasons for the anti-hysteresis.

Secondly, the mechanism of H mode generation under low pressure and high magnetic field is studied. Using the 750.43 nm spectral line and the 811.49 nm/750.43 nm spectral line ratio, the evolution characteristics of the metastable relative density of the direct ionization high-energy electrons and multi-step ionization with the magnetic field are obtained. The results show that only when the magnetic field strength reaches a certain threshold, the H-mode characteristic appears, and there is no H-mode characteristic below the threshold. The experimental data show that the high magnetic field leads to an increase in the metastable density, which inhibits the weakening of direct ionization of high-energy electrons, and promotes an increase in multi-step ionization, thereby reducing collision losses. At the same time, the magnetic field leads to an increase in the collision frequency of electrons, and the electrons generate multiple acceleration-collision metastable ionization cycles under the action of the magnetic field, which further improves the energy utilization rate, and finally promotes the H-mode characteristics at high magnetic fields. The experimental data also show that the metastable density of the E mode is always lower than that of the H mode at high magnetic fields, while at low magnetic fields, the metastable number density in the power range of the E mode is higher than that of the H mode. state power conditions.

Finally, the transition characteristics of inductive coupling to helical wave coupling and the evolution characteristics of metastable density under different magnetic field strengths, magnetic field potential types and gas flow rates were studied based on emission spectra. The results show that when the forward magnetic field (viewed in the direction of the magnetic field, the antenna rotates clockwise) is discharged, the plasma density jumps with the increase of power, that is, the modal transition from inductive coupling to helical wave coupling occurs. The stronger the magnetic field and the larger the gas flow, the smaller the mode transition power. When the magnetic field is reversed, the plasma density increases smoothly with the increase of power, and there is no mode transition characteristic. The evolution characteristics of the metastable state are as follows:

1) The ionization rate increases, resulting in a weakening of the metastable excitation rate and an increase in the metastable loss rate. Therefore, in the mixed mode of forward magnetic discharge, the metastable state decreases with increasing power. When the discharge changes from mixed mode to W mode, a sudden increase in ionization rate leads to a sudden drop in metastable generation rate and a sudden increase in metastable consumption, resulting in a sudden drop in metastable density. In the opposite magnetic field, the ionization rate also continued to increase with the increase of power, so the metastable density gradually decreased with the increase of power in high magnetic field.

2) When the magnetic field is cut, the curve of metastable density with power shows a minimum value, and the minimum value decreases with the increase of flow rate. The analysis shows that with the increase of power, the discharge of the helical wave mode in the plasma is enhanced, which leads to an increase in the ionization rate, so that the metastable state decreases with the increase of power. When the discharge enters the helical wave mode, the two ends of the antenna are The generated helical wave propagates to the middle and cancels out in the middle of the antenna, so that the plasma in the middle of the antenna is mainly maintained by the induction field generated by the antenna, so the metastable density gradually increases.