Estia

A focusing reflectometer for small samples at ESS

Estia is one of the two initial reflectometers for the European Spallation Source ESS. It will have a horizontal scattering plane and is optimised for a small sample area and polarized measurements. Estia was developed by the Swiss-Danish Instrumentation Consortium under the lead of J. Stahn. Starting from summer 2015, after the acceptance of the instrument proposal as one of the initial 16 instrument of the ESS, the project is lead by PSI as Swiss in-kind contribution. The design effort is lead by the Estia lead scientist A. Glavic and lead engineer S. Schütz at PSI.

contents

contacts

Artur Glavic, lead instrument scientist
Sven Schütz, lead engineer
Jochen Stahn, scientist responsible for the Estia concept
Dieter Graf, engineer

Estia description

brennglas lr.jpg Estia will be the reflectometer at the ESS optimized for magnetic samples and in-situ or in-operando studies. The complementary instrument Freia is optimized for studies on liquid/liquid or liquid/gas interfaces.

The special feature of Estia is the focusing of the neutron beam to the sample in both the scattering and the surface plane with a high divergence of 1.5 deg x 1.5 deg. This allows to choose between various operation modes, e.g. for high-intensity specular reflectivity, extended q_-range high-resolution, or _almost conventional measurements with a well collimated beam at a fix angle. In all modes the beam footprint and the divergence can be controlled independently by apertures far from the sample. This is realized using a so called Selene neutron guide optics.

The main characteristics of Estia are:
  • horizontal scattering geometry
  • polarization and polarization-analysis
  • wavelength-range 3 Å to 25 Å with 7 Å bandwidth (optional pulse skipping for 14 Å and 21 Å bandwidth)
  • divergence 1.5 deg x 1.5 deg
  • scattering angles from -10 deg to 145 deg
  • minimal beam size < 60 µm x 1 mm
  • maximum beam size ~ 1 mm x 10 mm
  • natural resolution 2-7%
  • high resolution options ~1%
  • main band average intensity ~7·109 n/s/cm² (21 Å bandwidth for 2.5·109 n/s/cm²)
  • option for simultaneous measurement of either spin-up/spin-down or full 4 state polarization analysis
  • fast sample changes and quick alignment
Estia is the Greek goddess of the hearth (Latin focus), the family, and architecture. In modern Greek the word means point of interest or importance and is used for example when adjusting a telescope or a camera lens.



Selene neutron guide

selene carlsberg.jpg The centrepiece of Estia is its truly focusing neutron guide, based on the Selene concept. A Selene guide transports only the useful neutrons and enables beam manipulation similar to a photographic lens. In conventional optics, point-to-point focusing allows to define the image size with an illumination field diaphragm located at the initial focal point (here called virtual source). The divergence of the beam is controlled by an aperture behind the optical lens, far from the image.

For neutrons the lens has to be replaced by a reflecting device, here a planar-elliptic mirror. Like all focusing optical devices this suffers from aberrations, which are largest in this case for reflections close to the focal points. Avoidance of these regions and compensation of the coma aberration by a second, identical reflector results in the optical path as illustrated in the 3D graphics on the right (red: reflectors, yellow: beam).

selene guide red yellow.jpg The Selene guide is truly focusing in a sense that the phase space density is zero outside a volume defined by the virtual source and the aperture. Thus the beam footprint on the sample can be tuned and over-illumination can be avoided. This is in contrast to all other elliptic guides discussed nowadays, which suffer from strong coma aberration effects leading to multiple reflections and thus to poor focusing. In addition, compared to these conventional neutron optics, the total beam intensity within the Selene guide (including neutrons not reaching the sample) is drastically reduced, which results in a lower background.

The special guide geometry allows for efficient optics to polarize and filter the beam or to implement constant resolution without using pulse shaping choppers. The convergent beam can be used efficiently on sample surfaces from 1 x 1 mm2 to 50 x 10 mm2. To allow for high detector angles and to reduce the influence of gravity, the scattering plane of Estia is horizontal.

A prototype of the Selene guide with a total length of 4 m was built and tested sucessfully at PSI. It is now used to reduce the measuring time on tiny samples (width below 2 mm) by up to two orders of magnitude. It out-performs the predicted focusing capability and confirms that it is possible to build and align such a high-precision guide.
Selene is the titan-goddess of the moon in Greek mythology. The relation to the neutron guide is the light-to-shadow border on the moon, which forms half an ellipse as seen from the earth.

Preliminary design

Currently the project is in the preliminary engineering and design phase, that will be finished in September 2016 and conclude with a design review process at ESS. As one of the shorter instruments at ESS, Estia will be build within the east hall of the ESS target building.

The image below shows an overview of the Estia instrument within the ESS experimental hall:
estia overview.jpg
The central components of the design are the two elliptical guides for the Selene optics, which require µm adjustment precision. To achieve this technically challenging accuracy, all of the 50 cm long elliptical neutron supermirrors are positioned by individual motorized adjusters. All these axes are directly mounted on a single, 7 m long block of granite, as can be seen in the artistic rendering below.
estia selene guide.jpg
Experiments will be performed within a closed cave structure that houses a sample positioning stage and a rotatable detector arm running with air-pads on a "dance Floor". Instrument specific sample environment for magnetic fields and low temperatures will be present at the instrument as well as a laser supported alignment system. The detector arm also houses a resonant spin-flipper and the polarization analyzer, that separates the scattered beam into the individual polarization components, which both can be detected with the two large position sensitive detectors.
estia experimental cave.jpg

documentation

2014

"Estia, A Truly Focusing Reflectometer"
Article-series presenting the instruements planned at the ESS (10. 2014)


"Estia, a focusing reflectometer for small samples using the Selene guide concept"
Proposal for a focusing reflectometer for the ESS (03. 2014)

" Estia , a focusing reflectometer for small samples using the Selene guide concept"
Reflectometry proposal review meeting, 15. 01. 2014, Lund, Sweden

2013

"Estia, a focusing reflectometer for small samples using the Selene guide concept"
Draft of the proposal for a focusing reflectometer for the ESS

"Status report on the WP2 of the Swiss-Danish instrumentation work packages for the European Spallation Source, ESS: Estia, a focusing reflectometer for small samples using the Selene guide concept" 2013/2


"Status report on the WP2 of the Swiss-Danish instrumentation work packages for the European Spallation Source, ESS: Estia, a focusing reflectometer for small samples using the Selene guide concept" 2013/1

2012

"Status report on the WP2 of the Swiss-Danish instrumentation work packages for the European Spallation Source, ESS: focusing reflectometer (Selene)" 2012/4


"Status report on the WP2 of the Swiss-Danish instrumentation work packages for the European Spallation Source, ESS: focusing reflectometer (Selene)" 2012/3


"Status report on the WP2 of the Swiss-Danish instrumentation work packages for the European Spallation Source, ESS: focusing reflectometer (Selene)" 2012/2


"Status report on the WP2 of the Swiss-Danish instrumentation work packages for the European Spallation Source, ESS: focusing reflectometer (Selene)" 2012/1

2011

"Selene -- guide concept for a reflectometer for the ESS"
Meeting of the Danish-Swiss working group with ESS instrumentation group on reflectometers (WP2)

presentations

2015

"the Selene neutron guide"
Seminar at ISIS, Rutherford Appleton Laboratory, 11. 2015, Great Britain

"Estia"
ECNS 2015: Vi European Conference on Neutron Scattering, 30. 08. - 04. 09. 2015, Zaragoza, Spain (poster)

"Focusing Reflectometry for In-situ Studies
workshop: Current trends and future perspectives in neutron reflectometry, 08.-09. 06. 2015, Lillestr{\o}m, Norway

"Estia"
STAP and IKON8, 02.-05. 02. 2015, Oxford, Great Britain

2014

"Estia"
one-slide presentation of Estia to the ESS Steering Committee, 10. 2014, Lund, Sweden

"Estia - focusing reflectometer: lay-out, beam extraction, shielding and optics"
ESS workshop on neutron optics and shielding, 03.-04. 09. 2014, Lund, Sweden

"focusing optical elements and guides for neutron reflectometry: experiences, projects and ideas"
ESS Science Symposium Surface and Interface Reconstruction: A Challenge for Neutron Reflectometry, 24.-26. 09. 2014, Bernried, Germany

"Estia, a focusing reflectometer for small samples based on the Selene guide concept"
Presentation of Estia to the ESS Scientific Advisory Committee, 21. 05. 2014, Lund, Sweden

2013

"benefits, prospects and limitations of a truly focusing neutron guide"
ESS seminar, 01. 10. 2013, Lund, Sweden

"Estia - a focusing reflectometer for small samples, based on the Selene guide concept"
IKON5, 25.-26. 09. 2013, Lund, Sweden


"Focusing on small samples"
ICNS 2013, 09.-12. 07. 2013, Edinburgh, Great Britain


"Selene a truly focusing neutron guide"
NOP&D 2013, International Workshop on Neutron Optics and Detectors 02.-05. 07. 2013, Munich (Ismaning), Germany


"first tests with a model Selene-type neutron guide"
IKON 4 - working meeting for the in-kind contributors to the ESS instruments, neutron technologies and science support facilities, 13.-14. 02. 2013, Lund, Sweden

2012

"Selene guide concept - recent developments & MCNPX calculations"
ESS guide workshop, 27. 09. 2012, Lund, Sweden


"progress report of the Swiss-Danish instrument initiative for the ESS / WP2 / focusing reflectometer"
IKON 3 - third in-kind contributions meeting for neutron science for the ESS, 19.-20. 09. 2012, Lund, Sweden


"concept for a reflectometer using focusing guides"
TUM & FRM II seminar, 12. 03. 2012, München, Germany


"progress report of the Swiss-Danish instrument initiative for the ESS, WP2: focusing reflectometer"
09.-10. 02. 2012, Malmoe, Sweden


"Concept for a reflectometer for the ESS with focusing in the sample plane and in the scattering plane"
Workshop on off-specular neutron scattering, 09.-10. 01. 2012, Bruxelles, Belgium

2011

"TOF reflectometry at PSI: from an optical bench set-up to a new instrument concept with a focus on small samples"
JCNS instrumentation workshop, 04. -07. 10. 2011, Tutzing, Germany


"concept for a reflectometer for the ESS with focusing in the sample plane, and a convergent beam in the scattering plane"
meeting of the ESS reflectometry TAP, 15. 09. 2011, Lund


"concept, design and first results: convergent-beam reflectometry using a focusing elliptic guide"
IKON-1, First In-Kind Contributions Meeting for Neutron Science for the ESS, 8. 9. 2011, Lund, Sweden


"Selene: high-intensity specular reflectometry"
5th European Conference on Neutron Scattering, ECNS 2011 July 17.-22. 2011, Prague, Czech Republic

2010

"specular reflectomety on small samples using a convergent beam"
reflectometer seminar, Oslo, 17. 06. 2010


"study on a focusing, low-background neutron delivery system"
JCNS seminar, Garching, 04. 05. 2010


"study on a focusing, low-background neutron delivery system"
neutron optics workshop NOP2010, Alpe d'Huez, 17.-19. 03. 2010
Contact:
J. Stahn