Parametric Wave Coupling and Non-Linear Mixing in Plasma

等离子体是一种物质状态，当能级或温度变得如此之高时，电子不再与原子结合。这至少产生了两种电荷相反、质量不同的物种(负电子和正离子)(电子质量和离子质量)。这两种类型的粒子的电荷使它们各自对电磁场(如光、微波和无线电波)做出反应，但方向相反，速度也截然不同。它们尤其对频率接近自然等离子体振荡的波做出反应，这是由任何静态磁场的大小和方向、粒子的数密度和质量的复杂组合决定的。它们能以被称为“共振”的频率吸收波能，并以被称为“截止”的频率反射波能。在重要的实验室实验和应用中，这些效应经常被用来加热或测量等离子体，例如通过聚变反应(磁限制)和工业加工产生能量的新技术以及地球磁层和电离层中的天然等离子体。天然电离层和磁层等离子体对现代通信和导航系统都很重要。在工业加工中，等离子体物理是半导体加工的基础，因此也是现代数字技术的基础。在聚变能源研究中，影响潜力是实现几乎无限的能源供应，解决围绕化石燃料使用的严重环境问题，没有长期的放射性副产品。参数耦合指的是两个或更多波相互作用，当它们的频率与自然等离子体振荡频率相关时，交换能量。最近发现，这种过程在惯性约束聚变的激光-等离子体相互作用中造成了困难，同时为向惯性约束和磁约束聚变等离子体输送能量的新的、更灵活的方法提供了令人兴奋的潜力。有迹象表明，随着此类研究从基础实验转向应用规模的设备，这种新技术将变得越来越重要。因此，我们建议开展基础研究，在微波频率范围内研究这些相互作用。微波范围对这类研究特别有吸引力，因为为各种应用开发的强大源和放大器随时可用，可以非常精确地控制，增强了研究等离子体物理动力学的能力，而开创性的研究指向实现非常高水平的归一化强度(波的有效强度的测量，受波长影响的波的有效强度，这意味着与光学强度相比，微波强度有效地“提升”)。因此，这表明在不久的将来，在微波频率范围内有可能探索波-等离子体相互作用的极端范围的动力学。该项目将设在斯特拉斯克莱德大学，在那里它将受益于一个卓越的微波源研究实验室的共址。利用微波研究波耦合效应的另一个动机是它在工业处理和磁约束聚变等离子体物理中的直接应用。在(弱到强)磁化的螺旋形等离子体中，两个精确控制的微波束(~10 cm到3 cm波长)与电子和离子中的等离子体(类声学)振荡、电子和离子的回旋振荡以及包括准声和回旋运动的混合振荡的耦合将被研究，以及随机加热的影响，其中粒子在高振幅波中的准随机运动产生非常快的有效温度增加。

Plasma is a state of matter that exists when the energy level or temperature become so high that electrons are no longer bound to atoms. This produces at least two species (negative electrons and positive ions) with opposite charge and very different masses (electron mass << ion mass). The charge of both types of particle make them each respond to electromagnetic fields (such as light, microwave and radio waves), but in opposite directions, and at very different rates. They particularly respond to waves at frequencies close those of natural plasma oscillations, determined by complicated combinations of the magnitude and direction of any static magnetic field, the number density and mass of the particles. They can absorb wave energy at frequencies called 'resonances', and reflect wave energy at frequencies called 'cut-offs'. These effects are often used to heat or measure plasmas in important laboratory experiments and applications, such as new techniques for energy production through fusion reactions (magnetically confined) and industrial processing as well as natural plasmas in the Earth's magnetosphere and ionosphere. Both natural ionospheric and magnetospheric plasmas are important to modern communication and navigation systems. In industrial processing, plasma physics underpins semiconductor processing and hence modern digital technology. In fusion energy research the impact potential is to enable an almost unlimited supply of energy, addressing serious environmental concerns surrounding the use of fossil fuel, with no long term radioactive byproducts.Parametric coupling refers to a multi-wave interaction where two or more waves exchange energy when their frequencies are related by a natural plasma oscillation frequency. Such processes have recently been found to cause difficulties in laser-plasma interactions for inertial confinement fusion, whilst at the same time offering exciting potential for new and more flexible ways of delivering energy into both inertially and magnetically confined fusion plasmas. Indications exist that suggest such new techniques will be increasingly important as such research moves from fundamental experiments to application scale equipment. We therefore propose to undertake fundamental research investigating these interactions in the microwave frequency range. The microwave range is particularly appealing for such research since powerful sources and amplifiers, developed for a range of applications, are readily available, can be very precisely controlled, enhancing the ability to investigate the plasma physics dynamics, whilst groundbreaking research points towards microwave generators achieving very high levels of normalised intensity (a measure of the effective intensity of the wave, affected by the wavelength, meaning that microwave intensities are effectively 'uplifted' compared to optical intensities). This therefore indicates potential in the microwave frequency range to explore the dynamics of extreme ranges of wave-plasma interaction in the near future. The project will be based at the University of Strathclyde where it benefits from co-location within a pre-eminent microwave source research laboratory. A further motivation for investigating the effect of wave coupling using microwaves is its direct application relevance to industrial processing and magnetic confinement fusion plasma physics.The coupling of two precisely controlled microwave beams (~10cm to 3cm wavelength) in a (weakly to strongly) magnetised helicon plasma by plasma (acoustic-like) oscillations in the electrons and ions, cyclotron oscillation of the electrons and ions and hybrid oscillations including both quasi-acoustic and cyclotron motion will be investigated, as will the effects of stochastic heating where 'quasi-random' motion of particles in high amplitude waves gives very rapid increase in effective temperature.