Hot-Slumped Glass Mirrors for the Cherenkov Telescope Array
Lead Research Organisation:
Durham University
Department Name: Physics
Abstract
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.
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.
Description | Successful development of cheap, easily reproduced glass mirrors for gamma-ray telescopes. |
Exploitation Route | Any other applications requiring similar mirrors to ground-based gamma-ray telescopes. |
Sectors | Manufacturing including Industrial Biotechology |
Description | Collaboration with Optical Laboratory, Olomouc, Czech Republic |
Organisation | Academy of Sciences of the Czech Republic |
Department | Institute of Physics |
Country | Czech Republic |
Sector | Learned Society |
PI Contribution | Working with colleagues in the Czech Republic to test mirror samples and train a PhD student. |
Collaborator Contribution | Use of facilities at their institute for mirror testing; travel an living costs for student. |
Impact | Agreement for PhD student to visit Durham for two 1-month period in March and July 2019. |
Start Year | 2019 |
Description | Collaboration with TMF |
Organisation | Thin Metal Fims Ltd |
Country | United Kingdom |
Sector | Private |
PI Contribution | Intellectual input regarding suitability of coatings for Cherenkov telescope mirrors and also for the window for the UK-designed CHEC camera. |
Collaborator Contribution | Coating design |
Impact | Coated mirrors, design for future coatings, grant application to look at diamond-like coatings, impact acceleration award for aluminium mirrors |
Start Year | 2016 |
Description | CTA & Ireland Workshop - CTA calibration talk |
Form Of Engagement Activity | Participation in an activity, workshop or similar |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Professional Practitioners |
Results and Impact | Talk to introduce colleagues in Northern Ireland to CTA in the UK. |
Year(s) Of Engagement Activity | 2017 |
Description | Talk at GCT Mirror Meeting |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Professional Practitioners |
Results and Impact | Talk about progress with glass mirrors (and other optical tests) for GCT telescope. |
Year(s) Of Engagement Activity | 2018 |
Description | Talk to TMF, Basingstoke |
Form Of Engagement Activity | A formal working group, expert panel or dialogue |
Part Of Official Scheme? | No |
Geographic Reach | Local |
Primary Audience | Industry/Business |
Results and Impact | Talk to TMF to introduce CTA to industrial partners |
Year(s) Of Engagement Activity | 2017 |