Determining the Ice Phase, Nucleation Process, and Electromagnetic Interaction Properties of the Ice Grains in an Ice Dusty Plasma

该奖项支持在弱电离等离子体环境中形成水冰粒的实验研究。等离子体是一种含有自由电子和离子的气体，它可以被弱电离，所以这种气体几乎都是中性的原子和分子，只有百万分之一的带电粒子。这个实验研究计划将研究弱电离等离子体，其中中性气体被安排在极冷的地方，如-300华氏度。当少量的水蒸气被注入到这样的等离子体中时，人们发现微小的冰粒会自发形成，变得带电，并悬浮在等离子体中。根据实验条件，冰粒的大小从纳米到数百微米不等。这项新研究将提供与自然界中发生的情况有关的信息，比如存在于太阳系演化早期的原行星盘、土星的扩散环，以及在极地地区50英里高度形成的陆地夜光云。该项目有两个主要目标。首先是确定冰粒红外吸收光谱随温度的变化规律。在许多天体物理环境中发现的极冷温度下，冰可以处于无定形阶段，因此具有与普通经验中的结晶冰不同的红外吸收光谱。第二个主要目标是确定冰为什么以及如何在等离子体中成核。在陆地大气条件下，冰核的形成需要一个非冰固体物质的核心，如碳或硅酸盐，冰在其上形成一层涂层。然而，实验室等离子体实验不包含任何非冰物质，初步证据是弱电离等离子体催化冰核。这项研究将探索弱电离等离子体环境如何使冰成核，并将以一个理论预测为指导，即高能等离子体电子（所有自由电子中的一小部分）可能在这一过程中发挥关键作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

The award supports an experimental study of water ice grain formation in a weakly ionized plasma environment. Plasma - a gas containing free electrons and ions - can be weakly ionized so that the gas is almost all neutral atoms and molecules with only one part in a million consisting of the electrically charged particles. This experimental research program will study a weakly-ionized plasma where the neutral gas is arranged to be extremely cold, such as -300F. When a small amount of water vapor is injected into such plasma, it is found that tiny grains of ice spontaneously form, become electrically charged, and are suspended in the plasma. The ice grains range in size from nanometers to hundreds of micrometers depending on experimental conditions. The new study will provide information relevant to situations that occur in nature such as the protoplanetary disk that existed in the early stage of solar system evolution, the diffuse rings of Saturn, and terrestrial noctilucent clouds that can form at 50-mile altitudes in polar regions.The project has two main goals. The first is to determine how the ice grain infrared absorption spectrum varies with temperature. At the extremely cold temperatures found in many astrophysical situations, ice can be in an amorphous phase and so have a different infrared absorption spectrum from the crystalline ice of ordinary experience. The second main goal is determining why and how ice nucleates in a plasma. For terrestrial atmospheric conditions it is well established that ice nucleation requires a core of non-ice solid material, such as carbon or silicate, on which ice forms as a coating. However, laboratory plasma experiments do not contain any non-ice material and preliminary evidence is that the weakly-ionized plasma catalyzes ice nucleation. The investigation will explore how the weakly-ionized plasma environment may enable ice nucleation and will be guided by a theoretical prediction that high-energy plasma electrons, a tiny minority of all free electrons, may play a key role in the process.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.