HFM/EXED

High Magnetic Field Facility for Neutron Scattering

The HFM/EXED neutron scattering facility is not accepting any new proposals.

Modes of operation available in this call

-          TOF Diffraction

-          TOF Low-Q

-          Direct TOF Spectroscopy

(for details, see the instrument section below and Refs. [2-3])

Writing a proposal

-          All the proposals have to be discussed with the local contact and contain supplementary information on bulk sample characterization in high fields, previous neutron measurements, evidences of Q-range accessibility using EXEQ-calculator and detailed measurement plan  (for details, see a short Presentation).

 Experiment planning with EXEQ/InEXEQ: *** Final release of EXEQ and InEXEQ: 28th of April 2020 ***

A paper on the EXEQ and InEXEQ software is now available online. You are welcome to cite it if you used the software when preparing for your experiment.

The web interface of EXEQ/InEXEQ is no longer available. Source code of EXEQ and InEXEQ is still available for download. Additionally, single-file executables (built with PyInstaller) of the software are available for download. The source code bundles contain example input files, in order to illustrate the functionality of the code. Additionally, the InEXEQ user guide is available in the download section on the right.

EXEQ still needs to create multiple .PAR files in the working directory. Therefore, the first startup will take significantly longer that the subsequent startups. The startup time of the pre-built executables may also differ between platforms.

The Linux executables can be found here for EXEQ and InEXEQ.

The Windows executables can be found here for EXEQ and InEXEQ.

The links to the source code are located in the download box, to the right from here.

Preparing your experiment

-        Please, check with your local contact which cryostat (³He, ⁴He or dilution) will be used for your experiment. The ³He and dilution cryostats have no sample rotation capabilities, i.e. the sample has to be properly oriented and fixed on a sample holder prior to the experiment. The ⁴He cryostat is equipped with a sample rotation stage around one (vertical) axis. Information about the sample space geometry and dimensions are available in the download area. Limited capabilities for checking the sample orientation can be provided on E4 2-axis diffractometer.

-        Always check the news stream below to have the latest updates.

News:

-      April, 2019 - a new cryostat is now available on the HFM/EXED. Equipped with a dilution refigerator, it can cool down the sample to temperatures as low as 100 mK in zero-field conditions.

-      December 4, 2017 - major update of InEXEQ. Release 2 (version 0.18) is now available for download, and is the recommended one for inelastic experiment planning.

-      May 12, 2017 - both inEXEQ and Mantid DGS Planner are available for calculating the E,Q coverage for EXED in direct spectrometer mode

-      March 27, 2017 - a new release of EXEQ is available for download. Version 0.16 reflects the geometry of the instrument after the installation of the new detectors, chopper and vacuum chamber. Please use the new version from now on, as the accessible scattering angles on EXED have changed.

 -     March 27, 2017 - 26 T is back! The new resistive-coil has been installed and successfully tested.

 -     March 2017 - First inelastic measurements of standard samples.

 -     Oct 2016 - Installation of the inelastic components is complete

Facility description

High Magnetic Field Facility for Neutron Scattering consists of two main components: the High Field Magnet (HFM) and the Extreme Environment Diffractometer (EXED). The former is a dedicated 26 T hybrid magnet, built by the HZB in collaboration with the National High Magnetic Field Laboratory (Florida, US). The latter is a time-of-flight instrument optimized for neutron scattering in restricted angular geometry of the magnet.

The High Field Magnet

The HFM is a "first of its kind" hybrid magnet system reaching fields as high as 26 T, making it by far the strongest continuous field available for neutron scattering experiments worldwide (see Fig. 1 below) [1]. The HFM utilizes Series Connected Hybrid System Technology where water cooled resistive insert coils are mounted in the room temperature bore of a superconducting cable-in-conduit solenoid. Operation of the magnet system requires a dedicated technical infrastructure consisting of high-pressure water cooling for the resistive coil, 4 K Helium refrigerator for cooling of the superconducting coil and 20 kA DC power supply. More information on the magnet can be found in [1] and references therein and under the following link: HFM.

As the field is horizontal, a special feature of the HFM is 30° degrees conical openings at both ends of the resistive insert envisaged for neutron-scattering access. Rotating the magnet by a maximum of 12° with respect to the incoming beam results in 2θ_max≈27° in forward scattering.

Sample Environment

A dedicated ³He horizontal cryostat allows high-field experiments to be combined with temperatures down to about 0.6 K for samples with cross section <1.5x1.5 cm².

Another cryostat enables sample rotation around vertical axis by +/- 90 deg and temperatures down to about 1.5 K (⁴He) for samples with cross section <1.5x1.5 cm².

A special dilution fridge (0.1 K) has been constructed in collaboration with Uni. Birmingham. The geometry of the cryostat is the same as that of the ³He cryostat.

The instrument

Time-of-flight instrument EXED (Fig. 2) is equipped with a multispectral extraction system as a part of about 70 m long supermirror guide [2]. As a result, neutrons from both thermal and cold moderators with a wavelength range from 0.7 to 15 Å are available for experiments. The lower wavelength limit is given by the kink in the guide that blocks the direct view of the source and provides a sharp cut-off. Apart from the kink, the guide is essentially straight (100x60 mm² (HxW)) and ends with a two-channel focusing section that compresses the beam spatially in both directions. For applications requiring low beam divergence, the focusing end can be replaced by a 6 m long pin-hole collimation section with variable apertures.

Flexibility of the instrument is ensured by three alternative systems that are available to create neutron pulses: a curved Fermi chopper for very high resolution (Δt ~ 6 μs), a straight Fermi chopper for high resolution (Δt ~ 15 μs) and a double disc chopper for medium to low resolution (from 115 μs up to >5000 μs). A number of single disc choppers located downstream prevents frame overlap and defines the bandwidth of interest. Due to the chopper system one can operate the instrument from narrow (~ 0.6 Å) to wide (~ 14.4 Å) wavelength band mode centered at the region of interest, and easily trade resolution for intensity. For inelastic applications there is a double disc chopper (Δt ~ 15 μs) in front of the sample. When running, it picks up a single wavelength out of the wavelength spectrum.

The secondary instrument is equipped with position-sensitive ³He detector tubes combined in 6 detector panels and positioned in forward (FWD) and backward (BWD) scattering to reflect the geometry of the magnet (Fig. 2). The backscattering panels are stationary, while the forward ones rotate together with the magnet.

Operation Modes of HFM/EXED

In order to enable a broad range of scientific applications using a unique combination of neutron scattering and high magnetic fields, EXED combines several scattering techniques in one instrument. The operation modes of the instrument are described below.

Diffraction mode is used for studying single crystalline and powder samples in high magnetic fields [2]. The accessible Q-range is from 0.1 up to 3 Å^-1 in FWD (mainly in direction perpendicular to the field) and from 1 up to 12 Å^-1 in BWD (mainly along the field). The precise Q-maps can be obtained by means of EXEQ-software.

Low-Q mode enables studies of mesoscopic entities in high magnetic fields such as e.g. vortex state in type-two superconductors [2]. Its momentum transfer range extends down to 10^-2 Å achieved by a 6m-long collimation section which replaces the focusing guide.

Spectroscopy mode has been built to study magnetic fluctuations and excitations as function of high magnetic field, and is best  suited for non-dispersive modes along the field (e.g. 1D- and 2D-sytems, isotropic systems with respect to the field, etc). EXED enables energy-resolved measurements over a limited Q-range < 3.25/λ (Å^-1) for the incoming energies below 25 meV (>1.8 Å) and energy resolution of a few percent [3]. The precise (Q,E)-maps can be obtained by means of inEXEQ software for inelastic mode. Mantid users can benefit from DGS Planner from nightly built Mantid.

Experiment planning

The web-based interface for calculating the instrument Q-range has been deactivated.

The source code of EXEQ and InEXEQ is available for download, licensed under GNU GPL v3. The last released version 1.0 uses Python 3.

Applications

• Quantum magnets and quantum phase transitions
• Superconductivity
• Correlated electrons in 3d, 4f and 5f metal compounds
• Spin, charge and lattice degrees of freedom in transition metal
  oxides
• Frustrated magnets
• Novel states of matter