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@INPROCEEDINGS{Eisenhut:867785,
author = {Eisenhut, S. and Klaus, M. and Baggemann, J. and Rücker,
U. and Beßler, Y. and Haberstroh, C. and Cronert, T. and
Gutberlet, T. and Brückel, T. and Lange, C.},
title = {{C}ryostat for the provision of liquid hydrogen with
variable ortho-para-ratio for a low-dimensional cold neutron
moderator},
reportid = {FZJ-2019-06395},
year = {2019},
abstract = {A significant contribution to the enhancement of the
neutron brilliance achievable with Compact
Accelerator-driven Neutron Sources (CANS) can be made by an
optimized cold moderator design. When using liquid para-H2
as the moderating medium, the concept of low-dimensional
cold moderators can be employed to increase the neutron
brightness (as currently foreseen at the European Spallation
Source ESS). Para-H2 shows a drop in the scattering cross
section by about one order of magnitude around 15 meV,
resulting in large deviation between the mean free paths of
thermal and cold neutrons. Taking advantage of this effect,
the cold moderator geometry can be optimized to allow the
intake of thermal neutrons through a relatively large
envelope surface and then extracting them in an efficient
way towards the neutron guides. One drawback of this
solution is the lack of thermalization of the cold neutrons.
In the context of the HBS (High Brilliance Source) project,
efforts are made to overcome this problem by increasing the
scattering cross section of the H2 in a defined way. The
idea is to admix small amounts of ortho-H2, which maintains
its large scattering cross section in the region below 15
meV. Like this, the neutron spectrum can be shifted towards
lower energies and adjusted for the needs of the respective
instrument. In a cooperation between TU Dresden and FZ
Jülich, an experimental setup has been created to proof the
feasibility of this concept. The main component of the
experimental setup is a LHe-cooled flow cryostat that
enables the separate condensation of a para-H2 and a
normal-H2 flow and a subsequent mixing of the two in precise
proportions. The resulting LH2 mixture at 17 – 20 K is fed
into a small cold moderator vessel (approx. 200 ml). In this
work, the current status of the setup is presented. The
construction and commissioning of the mixing cryostat have
been completed and extensive test runs show that different,
stable ortho-para-H2 mixtures can be produced and monitored.
Currently, preparations for first measurements of the
resulting neutron spectra are being prepared at
Forschungszentrum Jülich.},
month = {Dec},
date = {2019-12-16},
organization = {Workshop SCANS – A Compact
Accelerator-Driven Neutron Source for
Scandinavia?, Institute for Energy
Technology, Kjeller (Norway), 16 Dec
2019 - 17 Dec 2019},
subtyp = {Invited},
cin = {JCNS-2 / PGI-4 / JARA-FIT / JCNS-HBS / ZEA-1},
cid = {I:(DE-Juel1)JCNS-2-20110106 / I:(DE-Juel1)PGI-4-20110106 /
$I:(DE-82)080009_20140620$ / I:(DE-Juel1)JCNS-HBS-20180709 /
I:(DE-Juel1)ZEA-1-20090406},
pnm = {144 - Controlling Collective States (POF3-144) / 524 -
Controlling Collective States (POF3-524) / 6212 - Quantum
Condensed Matter: Magnetism, Superconductivity (POF3-621) /
6213 - Materials and Processes for Energy and Transport
Technologies (POF3-621) / 6G4 - Jülich Centre for Neutron
Research (JCNS) (POF3-623)},
pid = {G:(DE-HGF)POF3-144 / G:(DE-HGF)POF3-524 /
G:(DE-HGF)POF3-6212 / G:(DE-HGF)POF3-6213 /
G:(DE-HGF)POF3-6G4},
typ = {PUB:(DE-HGF)6},
url = {https://juser.fz-juelich.de/record/867785},
}