Proposal for a new spectrometer at ESS: Njord and Remora

E. Fogh; G.S. Tucker; J. Voigt; M. Aouane; N.L. Amin; R. Georgii; R. Toft-Petersen

arxiv: 2604.11383 · v1 · submitted 2026-04-13 · ⚛️ physics.ins-det

Proposal for a new spectrometer at ESS: Njord and Remora

E. Fogh , N.L. Amin , G.S. Tucker , M. Aouane , R. Georgii , J. Voigt , R. Toft-Petersen This is my paper

Pith reviewed 2026-05-10 15:20 UTC · model grok-4.3

classification ⚛️ physics.ins-det

keywords neutron scatteringESS spectrometerbeam focusingcomplementary instrumentssmall sample studiesspallation source design

0 comments

The pith

Njord focuses ESS neutrons into a tight beam while Remora runs a parallel spectrometer on the same port.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper proposes Njord and Remora as a paired instrument concept at the European Spallation Source to tackle two practical limits in neutron scattering: weak signals from tiny samples or extreme environments, and the shortage of available beamtime. Njord pushes the source brightness into a small focused spot to make measurements on materials like quantum magnets or pressure cells feasible. Remora exploits the unused part of the neutron spectrum on the identical beamline to add complementary data collection without needing a separate port. A sympathetic reader would care because this arrangement directly targets experiments that currently hit flux or time walls before the science questions are answered.

Core claim

By concentrating available brightness into a tightly focused beam at Njord and capturing the remaining spectral window with Remora on the shared beamport, the design aims to deliver higher effective flux for small-sample studies and increase overall experimental throughput without additional beamlines.

What carries the argument

The paired Njord-Remora instrument concept, with Njord providing beam focusing for high-intensity small-spot measurements and Remora adding a complementary spectrometer that uses the unused spectral component on the same port.

If this is right

Studies of metal-organic frameworks and organic superconductors become possible on samples too small for current setups.
Experiments requiring extreme conditions like high magnetic fields gain from the concentrated flux without longer run times.
The same beamport supports two independent measurements, raising the total number of experiments per allocated slot.
Quantum magnet and pressure-tuned material investigations can shift from marginal to routine data collection.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

Similar dual-use beamport strategies could be adapted at other spallation sources to stretch limited neutron resources.
The approach might shift instrument proposal priorities toward shared-port designs rather than entirely new beamlines.
Long-term, it suggests testing whether spectral window sharing preserves resolution for both instruments in practice.

Load-bearing premise

The technical design for focusing the beam at Njord and separating the spectral window for Remora can be built and operated without major unexpected losses in performance or conflicts between the two instruments.

What would settle it

A side-by-side measurement of signal strength and background on a standard small sample in a pressure cell, comparing the proposed Njord focus against an existing ESS or other-facility instrument to check whether the projected intensity gain is realized.

Figures

Figures reproduced from arXiv: 2604.11383 by E. Fogh, G.S. Tucker, J. Voigt, M. Aouane, N.L. Amin, R. Georgii, R. Toft-Petersen.

**Figure 1.** Figure 1: The structure of the MIL-53 and UiO-67 MOFs [3]. One example is known as the breathing MOF [4], exemplified by what is known as the MIL-53 system ( [PITH_FULL_IMAGE:figures/full_fig_p002_1.png] view at source ↗

**Figure 2.** Figure 2: Pressure-temperature diagram of the organic 1D superconductors [24] Each material resides on this phase diagram and thus the pressure axis is not on an absolute scale. Superconductivity remains one of the most challenging and exciting areas of condensed matter physics. Traditional superconductors are well understood, where lattice vibrations (phonons) mediate electron pairing, as described in the Bardee… view at source ↗

**Figure 3.** Figure 3: Phase diagram of water as a function of temperature and pressure [32]. Water is one of the most abundant molecules in the universe and a prerequisite for life as we know it. Hexagonal ice, known as ice-Ih, is the most common form and is produced by bulk nucleation of liquid water at ambient pressure. There are surprisingly many other phases of ice in the temperature-versus-pressure phase diagram of water … view at source ↗

**Figure 4.** Figure 4: Methane trapped in a water cage [38]. Njord offers a unique opportunity to go beyond the mere density of states and gain detailed information about the phonon Qdependence in systems like water and clathrates. Barocalorics refer to materials that exhibit the barocaloric effect, a thermodynamic phenomenon in which a material undergoes a reversible structural change when hydrostatic pressure is applied or … view at source ↗

**Figure 5.** Figure 5: a Magnetisation curve of MnCr2S4 with its large plateau at 25 − 50 T [52]. Crystal structure is shown in the inset [54]. b Predicted phase diagram for the Kitaev honeycomb with the quantum spin liquid in dark blue and the ambient-pressure position of Na3Co2SbO6 marked with the red star [59]. Na3Co2SbO6 is a layered honeycomb cobaltate and a candidate platform for frustrated magnetism with Kitaev-type inte… view at source ↗

**Figure 6.** Figure 6: (Top) Overview of the instrument setup (not to scale). Upstream of the bandwidth chopper (BW) of Njord, a vertically-focusing monochromator feeds Remora. A parabolic trumpet with a slit creates a well-defined virtual source, mirrored by an NMO onto the sample position of Njord. (Bottom) ToF Diagram, where the 1.7 Å bandwidth reaching Njord is shaded yellow to purple, while the green rays represent the neut… view at source ↗

**Figure 7.** Figure 7: Comparison between simulated beam spots for BIFROST and Njord. The dashed red lines indicate the 3.5 × 3.5 mm2 beam area used for performance estimates. 8 [PITH_FULL_IMAGE:figures/full_fig_p008_7.png] view at source ↗

**Figure 8.** Figure 8: Illustration of the Njord secondary spectrometer (left) alongside energy-resolution curves for different PSC opening times (right). The secondary spectrometer configuration shows a single analyser array, spanning 17.3◦ out-of-plane coverage. The resolution curves show the resolution for 3 PSC opening times (fully parked PSC, 1 ms opening time, and 0.5 ms opening time) for the lowest and highest final energ… view at source ↗

**Figure 9.** Figure 9: Comparison of FWHM resolution ellipses between Njord (blue) and BIFROST (red) for 1 ms PSC opening time, at 0 meV energy transfer, at a 45◦ in-plane scattering angle, and for the 5 meV analyser in both cases. Left panel shows the resolution perpendicular to the incident beam in the plane, and right panel shows the resolution parallel to the incident beam in the plane. impact on illuminated spot size. 3.3 R… view at source ↗

**Figure 10.** Figure 10: (Top) Elastic energy resolution for 4.8 Å, and 7.1 meV energy resolution for 2.4 Å scattering processes on REMORA, for different Fermi chopper frequencies. (Bottom) Flux at the sample position for different Fermi chopper frequencies. 10 [PITH_FULL_IMAGE:figures/full_fig_p010_10.png] view at source ↗

read the original abstract

Many of the most interesting scientific subjects are also the hardest to study with neutrons. Metal-organic frameworks, organic superconductors, quantum magnets, pressure-tuned materials, are systems where the relevant signals are weak, the samples are tiny, or the experiments need extreme sample environments such as pressure cells and high-field cryomagnets. Existing instruments often run into practical limits before the science is exhausted. For some questions the samples are simply too small; for others, the signal is buried in background or the required measurement time becomes prohibitive. This is both a scientific opportunity and a challenge for the European neutron scattering community. We present Njord and Remora as a paired instrument concept for the European Spallation Source (ESS). The proposal focuses on two linked problems: important science cases are being limited by neutron flux and sample geometry, and the community also needs more beamtime. Njord addresses the first by pushing the available brightness into a tightly focused beam, while Remora uses the remaining spectral window to add a complementary spectrometer on the same beamport.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

This is a high-level conceptual proposal for paired neutron spectrometers at ESS with no simulations, flux estimates, or engineering details to support feasibility.

read the letter

The main point is that Njord and Remora are pitched as a way to split an ESS beamport: one instrument takes a tightly focused high-brightness beam for small or weak-signal samples, while the other uses the remaining spectral window to add capacity. The authors correctly flag real limits in current neutron work on things like quantum magnets, pressure cells, and tiny samples where flux and background kill the measurement time. The linked idea of solving both the signal problem and the beamtime shortage on one port is a concrete optimization step that has not been laid out exactly this way before. It gives credit to the practical constraints at a new source like ESS and ties the design directly to those science cases. That part is useful as a starting point for discussion among instrument people. The clear gap is the total absence of any supporting work. No ray-tracing, no brightness calculations, no resolution or flux numbers, no assessment of how the spectral split would actually be done or what losses it would introduce. The whole claim rests on the untested assumption that the hardware can deliver net gains without major conflicts or performance hits. A reader cannot tell whether the concept is viable or just optimistic. This is aimed squarely at neutron instrumentation groups and ESS planning teams who already know the facility constraints. A condensed-matter experimentalist looking for a new method with evidence will find little to use. It is worth a reading-group conversation as an idea, but it is too preliminary for peer review in its current form. The authors need to add at least basic optical and engineering estimates before it makes sense to send out for referee comments.

Referee Report

1 major / 0 minor

Summary. The manuscript proposes Njord and Remora as a paired instrument concept for the European Spallation Source (ESS). Njord is intended to deliver a tightly focused neutron beam to overcome flux and sample-geometry limitations for weak-signal studies (e.g., metal-organic frameworks, quantum magnets, pressure-tuned materials), while Remora exploits the remaining spectral window to operate a complementary spectrometer on the identical beamport, thereby increasing overall beamtime availability.

Significance. If the assumed optical performance and shared-beamport operation can be realized without substantial losses, the concept would address two recognized bottlenecks in neutron scattering—insufficient flux for small or extreme-environment samples and limited beamtime—potentially enabling new classes of experiments at ESS. The paired-instrument approach is a creative attempt to maximize the utility of a single beamport; however, the manuscript supplies no quantitative support for these gains, so the significance remains prospective rather than demonstrated.

major comments (1)

Abstract: The central claim that Njord can extract a tightly focused beam while Remora simultaneously uses the remaining spectral window on the same ESS beamport, delivering net gains in signal strength and beamtime, is unsupported by any optical layout, ray-tracing results, flux estimates, resolution figures, or engineering assessment of spectral splitting or time-sharing. Without such evidence it is impossible to verify whether the assumed performance is attainable or whether major unforeseen conflicts or losses would arise.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading and constructive feedback on our proposal manuscript. The referee correctly notes that the abstract advances a conceptual instrument pairing without quantitative optical or engineering support. We have revised the manuscript to clarify the prospective character of the claimed gains, to moderate the language in the abstract, and to add an outline of the planned validation steps.

read point-by-point responses

Referee: The central claim that Njord can extract a tightly focused beam while Remora simultaneously uses the remaining spectral window on the same ESS beamport, delivering net gains in signal strength and beamtime, is unsupported by any optical layout, ray-tracing results, flux estimates, resolution figures, or engineering assessment of spectral splitting or time-sharing. Without such evidence it is impossible to verify whether the assumed performance is attainable or whether major unforeseen conflicts or losses would arise.

Authors: We agree that the original abstract presented the performance advantages of the Njord-Remora pairing as if they were already demonstrated. The manuscript is a high-level scientific proposal whose primary purpose is to articulate the motivation for a new beamport-sharing concept and its potential scientific impact, not to deliver a completed instrument design. Detailed ray-tracing, flux calculations, and engineering studies of spectral splitting lie outside the scope of the present paper and are intended for subsequent technical design reports. To meet the referee's legitimate concern we have (i) rewritten the abstract to state that the gains are prospective and contingent on successful optical implementation, (ii) inserted a new section that sketches the proposed neutron-optical layout and the spectral-window partitioning scheme, and (iii) outlined the simulation strategy (McStas-based ray tracing, moderator-to-sample transport, and time-structure considerations) that will be used to quantify flux, resolution, and any cross-talk between the two instruments. These additions make the manuscript's claims commensurate with the evidence supplied while preserving its focus on the scientific case. revision: yes

Circularity Check

0 steps flagged

No circularity: conceptual proposal with no derivations or fitted quantities

full rationale

This is a forward-looking instrument proposal document rather than a derivation or modeling paper. The provided text and abstract contain no equations, no fitted parameters, no predictions derived from data subsets, and no self-citations used to justify uniqueness theorems or ansatzes. The central claims rest on qualitative descriptions of scientific needs and high-level instrument concepts; they do not reduce by construction to their own inputs. The absence of any load-bearing mathematical chain means the circularity patterns (self-definitional, fitted-input-called-prediction, etc.) are not applicable. The document is therefore self-contained against external benchmarks for the purpose of this analysis.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The proposal rests on standard domain assumptions about neutron source performance and instrument limits at ESS; no free parameters, new axioms, or invented entities are introduced in the abstract.

axioms (1)

domain assumption Neutron scattering experiments on certain materials are limited by available flux, sample geometry, and beamtime availability at current and planned facilities.
Explicitly stated in the opening paragraphs of the abstract as the core motivation.

pith-pipeline@v0.9.0 · 5507 in / 1365 out tokens · 71723 ms · 2026-05-10T15:20:55.141950+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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Pressure tuning of Kitaev spin liquid candidate Na3Co2SbO6

Kumar, G. Jose, S. Samanta, W. Bi, Y. Xiao, D. Popov, Y. Wu, J.-W. Kim, H. Zheng, J. Yan, J. F. Mitchell, R. J. Hemley, and D. Haskel, “Pressure tuning of Kitaev spin liquid candidate Na3Co2SbO6”, Commun. phys.8, 310 (2025). 64R. Bewley, “The mushroom neutron spectrometer”, Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spect...

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