Hot-Slumped Glass Mirrors for the Cherenkov Telescope Array

伽马射线天文学研究来自许多不同天体的高能辐射，如超新星遗迹和黑洞，以及寻求更多地了解宇宙的基本原理，如引力的性质。伽马射线不会穿透地球的大气层，但我们仍然可以从地面上探测到它们。当伽马射线进入大气层时，它会产生一系列高能粒子，从而产生一种称为切伦科夫辐射的闪光。这是一个微弱的，短暂的蓝色/紫外线闪光，被称为成像大气切伦科夫望远镜（IACTs）的望远镜可以检测到。这项技术已经被证明效果很好，并向我们展示了一个充满粒子加速器的天空，这些粒子加速器比LHC强大得多。来自世界各地的科学家，包括英国，现在正在建立一个伽马射线天文学观测站，切伦科夫望远镜阵列，或CTA。这将包括位于智利的大约100台观测南部天空的望远镜和位于加那利群岛的大约20台研究北方天空的望远镜。需要三种不同尺寸的望远镜，大，中，小，分别用于研究最低，中等和最高能量的伽马射线。智利的站点将拥有所有三种类型的望远镜，而加那利群岛只需要大型和中型望远镜，因为那里的最高能量伽马射线的可见源数量很少。智利将有大约70台小型望远镜。英国的科学家们正在领导这些望远镜的双镜设计和原型设计，称为伽马射线切伦科夫望远镜（GCT）。这架望远镜的镜子很难制造。所有切伦科夫望远镜的反射镜都是凹面的。对于迄今为止使用的单镜望远镜来说，这些望远镜的焦距很长，因此镜子的曲率很小。这使得将冷玻璃拉到合适的模具上以制造反射表面成为可能。然而，GCT镜将具有更大的曲率，这使得不可能将冷玻璃形成为正确的形状。因此，我们正在与北威尔士圣亚萨的一家公司合作，研究一种在高温下形成玻璃的新技术。我们已经做了一些初步的研究，这是令人鼓舞的，这一赠款申请要求资金进一步采取这一进程，包括创造正确的形状，我们将需要为GCT和工作与薄金属薄膜在贝辛斯托克看看最好的方式涂层的镜面。如果该项目成功，那么英国公司将有很好的机会不仅为GCT制造镜子，而且还为美国领导的双镜望远镜设计提出作为CTA的中型望远镜。

Gamma ray astronomy studies very energetic radiation from many different astronomical objects, such as supernova remnants and black holes, as well as seeking to learn more about the fundamentals of the Universe, such as the nature of gravity. Gamma rays do not penetrate the Earth's atmosphere, but nonetheless we can detect them from the ground. It so happens that when a gamma-ray enters the atmosphere, it creates a cascade of highly energetic particles, which in turn produces a flash of light known as Cherenkov radiation. This consists of a faint, brief flash of blue/UV light, which telescopes known as Imaging Atmospheric Cherenkov Telescopes (IACTs) can detect. This technique has been shown to work well, and has revealed to us a sky full of particle accelerators far more powerful than the LHC. Scientists from around the world, including the UK, are now building an observatory for gamma ray astronomy, the Cherenkov Telescope Array, or CTA. This will consist of about 100 telescopes for observing the southern sky, located in Chile, and about 20 telescopes for studying the northern sky, sited in the Canary Islands. Three different sizes of telescope are needed, large, medium and small, for studying the lowest, intermediate and highest energy gamma rays, respectively. The site in Chile will have all three types of telescope, while only large and medium sized telescopes are needed in the Canary Islands, where the number of visible sources of the highest energy gamma rays is small.There will be about 70 small sized telescopes in Chile. Scientists in the UK are leading the design and prototyping of a two-mirror design for these telescopes, known as the Gamma-ray Cherenkov Telescope (GCT). The mirrors for this telescope are challenging to make. All Cherenkov telescopes mirrors are concave in form. For the single-mirror telescopes that have been used until now, these have a very long focal length and the curvature of the mirrors is therefore small. This makes it possible to pull cold glass down onto a suitable mould to make the reflective surface. However, the GCT mirrors will have much greater curvature, and this makes it impossible to form cold glass to the correct shape. So, we are working with a company in St. Asaph in North Wales on a new technique to form the glass at high temperature. We have made some preliminary studies, which have been encouraging, and this grant application requests funds to take this process further, including creating the correct shape that we will need for the GCT and working with Thin Metal Films in Basingstoke to look at the best way of coating the mirror surfaces. If the project is successful, then UK companies will have a good chance of making mirrors not only for the GCT but also for an American-led dual-mirror telescope design being put forward as a medium size telescope for CTA.