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，同时也试图了解更多关于宇宙的基本原理，如引力的本质。伽马射线不能穿透地球大气层，但我们仍然可以从地面探测到它们。当伽马射线进入大气层时，它会产生一系列高能粒子，进而产生被称为切伦科夫辐射的闪光。这是一种微弱的、短暂的蓝光/紫外光闪光，被称为成像大气切伦科夫望远镜（IACTs）的望远镜可以探测到。这项技术已经被证明很有效，并向我们展示了一个充满比大型强子对撞机强大得多的粒子加速器的天空。来自世界各地的科学家，包括英国，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个观测南部天空的望远镜，以及位于加那利群岛的大约20个研究北部天空的望远镜。为了研究最低、中等和最高能量的伽马射线，需要三种不同尺寸的望远镜，分别是大、中、小。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，那里可见的最高能量伽马射线源的数量很少。智利将有大约70个小型望远镜。英国的科学家们正在为这些望远镜设计一个双镜设计和原型，被称为伽马射线切伦科夫望远镜（GCT）。制作这台望远镜的反射镜很有挑战性。所有切伦科夫望远镜的镜面都是凹形的。对于迄今为止使用的单镜望远镜来说，它们的焦距很长，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作反射表面成为可能。然而，GCT反射镜将有更大的曲率，这使得它不可能形成正确形状的冷玻璃。因此，我们正在与北威尔士圣阿萨弗的一家公司合作，研究一种在高温下形成玻璃的新技术。我们已经做了一些令人鼓舞的初步研究，这项拨款申请要求资金进一步推进这一过程，包括创造我们需要的GCT的正确形状，并与贝辛斯托克的Thin Metal Films公司合作，研究涂覆镜面的最佳方法。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，而且为美国领导的双镜望远镜设计制造镜子，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.