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文物体的非常高能量的辐射，如超新星遗迹和黑洞，并试图了解更多关于宇宙的基本原理，如引力的性质。伽马射线不会穿透地球大气层，但我们仍然可以从地面探测到它们。碰巧的是，当伽马射线进入大气层时，它会产生高能粒子的级联，进而产生一种称为切伦科夫辐射的闪光。这是由微弱的、短暂的蓝色/紫外光组成的，被称为成像大气切伦科夫望远镜(IACT)的望远镜可以探测到。这项技术已经被证明是有效的，并向我们展示了一片充斥着比大型强子对撞机强大得多的粒子加速器的天空。包括英国在内的世界各地的科学家现在正在建造一个伽马射线天文学天文台--切伦科夫望远镜阵列，简称CTA。这将包括位于智利的大约100个用于观测南方天空的望远镜，以及位于加那利群岛的大约20个用于研究北方天空的望远镜。研究最低能量、中等能量和最高能量的伽马射线分别需要三种不同尺寸的望远镜，大、中、小型。智利的地点将拥有所有三种类型的望远镜，而加那利群岛只需要大中型望远镜，那里最高能量伽马射线的可见光来源很少。智利将有大约70台小型望远镜。英国科学家正在领导这些望远镜的双镜设计和原型设计，被称为伽马射线切伦科夫望远镜(GCT)。这架望远镜的镜面很难做。所有切伦科夫望远镜的镜面都是凹面的。对于目前使用的单镜望远镜来说，它们的焦距很长，因此镜面的曲率很小。这使得将冷玻璃拉到合适的模具上以制作反射面成为可能。然而，GCT反射镜的曲率要大得多，这使得不可能将冷玻璃形成正确的形状。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研究，这是令人鼓舞的，这项拨款申请要求资金进一步推动这一进程，包括创建我们将需要的正确形状的GCT，并与贝辛斯托克的金属薄膜公司合作，寻找在镜面上镀膜的最佳方法。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，而且还为美国主导的双镜望远镜设计制造镜子，该设计被提出为CTA的中等尺寸望远镜。

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.