The Dark Energy Spectroscopic Instrument (DESI) Fibre Systems - interim funding

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. 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 archeology.

In order to undertake the proposed survey, a US-Europe-China collaboration led by the US Department of Energy has come together with the aim of constructing a 5000-fibre spectrograph that will deploy on the Kitt Peak Mayall 4m-telescope. The key science goals represent a field in which the UK has world leadership and strong scientific interest, built up through STFC support for participation in the 2-degree Field Galaxy Redshift Survey and the Dark Energy Survey.

The conceptual design review is scheduled for 28-30 Jan 2014 (CD1). Formal construction starts Oct 2014 (CD-2) contingent on passing CD-1. Installation should start in 2018 followed by start of observations later the same year. The project will be funded by a mixture of DoE money and institutional buy-ins including contributions in-kind. Durham will be requesting support from STFC to provide the fibre system for DESI as part of an in-kind UK buy-in.

Continued development funding up to the conceptual design review is sought for two key areas of hardware development where the UK has internationally regarded expertise - the optical corrector, and the fibre system, and will retain UK involvement in this project.

This request is for interim funding for Durham to continue the development of the fibre systems begun (as BigBOSS) under STFC grant ST/J004642/1 and an earlier grant from Lawrence Berkeley National Laboratory

DESI will deploy 5000 fibres simultaneously over the wavelength range 0.4-1 um with a spectral resolving power ~4000. Durham CfAI has internationally-recognised expertise in the production of highly-multiplexed fibre systems. This includes the fibre termination and encapsulation together with the fibre-management system designed to minimise stress which would otherwise degrade performance.

Manpower for R&D: 4 staff-months to support our chief fibre specialist Graham Murray. His participation is critical. Some mechanical design support (David Bramall) for e.g. cable design. Senior academic support, including theoretical development, will be provided by Durham University (Jeremy Allington-Smith) with management support from Gordon Talbot.

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 0.9-1.25m in diameter which need to be aligned to within tolerances of approximately 100 micrometers. This poses a major challange 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).