Dark Energy Spectrographic Instrument development

DESI is a ground-based dark energy experiment to study the cosmological expansion rate and the growth of structure with a wide-angle spectroscopic galaxy and quasar redshift survey. In order to undertake the proposed survey, a US-Europe-China collaboration has come together with the aim of constructing a 5000-fibre spectrograph that will be deployed on the Mayall 4m telescope at the Kitt Peak Observatory in the US. A wide range of additional science is possible using the 5000 fibre multi-object spectrograph required for this experiment, including studying galaxy formation and evolution, galaxy cluster surveys, the structure of the Milky-Way galaxy and Galactic archaeology.

The UK has internationally regarded expertise in several key areas of the proposed instrument, in particular being involved in the the optical corrector (consisting of six nearly metre sized optics), and the fibre system that takes the light from the focal plane to the spectrograph. The proposed research enables the UK to be involved in the optical and mechanical design and development work leading to the full instrument specification.

Skill development: The DESI project will develop the skills of ~10 PhD students and ~4 technical staff. The PhD students will be mostly in the data processing and data analysis areas. The technical staff will mostly be in the instrumentation area.

Fibre system: The massively multiplexed fibre system of DESI provides a significant technical challenge in developing an efficient coupling to the DESI spectrographs. Techniques to be investigated in this study could have wide applicability to spectral image reformatters based on optical fibres and applied in fields as diverse as process inspection and remote diagnostics, where access to the target area is restricted.

Optical system: The DESI optical system comprises of lenses of 0.8-1.25m in diameter which need to be aligned to within tolerances of approximately 100 micrometers. This poses a major challenge to the mounting and alignment of the lenses along with the testing of the complete system. Advances in mounting and alignment of large lenses coupled with large optics production developments at OpTiC, North Wales, give the UK the potential to produce large optical systems for use, for example, in proposed high power laser facilities such as the High Power laser Energy Research facility (HYPER).