Page 80 - ILL Annual Report 2019

MODERNISATION PROGRAMME AND INSTRUMENT UPGRADES
Jacques Ollivier. French
The ILL
‘As the person responsible for IN5, I have led several projects aimed at improving the performance of the instrument. My present scientific interests are frustrated magnetism, molecular magnetism, quantum liquids and solids, and water clathrates.’
The Endurance project IN5+: enhancing the potential
of the IN5 spectrometer
Two important projects have been completed over the past 12 months around the IN5 instrument. On the one hand, as part of the Endurance upgrade programme the guide delivering neutrons to the instrument has been almost entirely refurbished, increasing the flux at the sample by an average factor of three. On the other, a 10-Tesla vertical field magnet has been commissioned and is now in use for regular experiments.
Figure 1
Roland Gandelli and Julien Bonnevaux installing and aligning the last guide pieces between the choppers and the sample chamber.
AUTHORS
J. Ollivier, B. Giroud and M.M. Koza (ILL)) REFERENCES
[1] J. Ollivier, M. Plazanet, H. Schober and J.C. Cook, Physica B 350 (2004) 173
[2] J. Ollivier and H. Mutka, J. Phys. Soc. Jpn. 80 (2011) SB003
[3] J.Ollivier,B.Giroud,M.Kreuz,E.Farhi,J.BeaucourandC.Dewhurst,
J. Neutr. Res. 20 (2018) 123
The IN5 instrument has undergone regular improvements over the years, approximately once every ten years. However, the neutron guide that transports neutrons to the instrument has never been completely renewed in any of these upgrades.
The focus of the various projects has always been downstream, on the instrument itself: sample environment, choppers and instrument focusing guide, detectors and flight chamber [1, 2].
Amongst these projects, a refurbishment of the last straight 15 m guide was undertaken in 2000-2002, within the framework of the Upgrade of Five Instruments projects, together with the introduction of a new chopper system for monochromatising the beam. It was decided at that time to benefit from the full upstream (width x height) 30 x 200 mm2 guide cross section and focus
on a 15 x 50 mm2 area at the sample position, using a tapered, supermirror-coated guide with coatings ranging from M = 1 to M = 3 in the high-focus section. At the time they were installed, the guide and its coatings
were at the cutting-edge of technology. Since then, however, only the first section of the guide—close to
the reactor core and in the light water pool—has been upgraded, with an M = 2 coating, performed during the ten-yearly beam tube refurbishment operation in 2006. The resulting gain in neutron transport was annihilated, however, because the curved guide section situated between the new section and the instrument guide was left unchanged.
New guide
More recently it was decided, within the framework of the Endurance programme, to take the opportunity presented
by the next ten-year refurbishment of the H1 beam tube to replace this heterogeneous guide with a homogeneous, state-of-the-art, ballistic guide. The challenge was to renew the guide while retaining most of the components of the existing IN5 instrument, particularly the chopper system, and without moving the time-of-flight chamber. The aim, apart from limiting costs, was to get the guide installed early in the life of the Endurance programme and minimise downtime for the in-high-demand IN5 (figure 1).
Despite the constraints, refurbishment of the guide has brought a substantial although finite gain in neutron flux;
in particular, it now favours warmer neutrons, which were previously disadvantaged by the natural nickel, curved guide (figure 2). Computed optimisation resulted in an M = 2
to M = 6 supermirror-coated elliptic guide with reduced height (150 mm) in the straight section following the curved guide section [3]. As the aim was to focus on sample heights of below 30 mm, such a highly focusing guide
ANNUAL REPORT 2019