PASTIS: An insert for polarization analysis studies on a thermal inelastic spectrometer

Polarisation analysis on the LET time-of-flight spectrometer

“…Solutions to both of these issues will be detailed in Section 3. 2 The polarised beam is to be transported to the sample by a set of permanent magnet guide fields followed by a set of coils oriented perpendicular to the beam direction; in other words, the magnetic field throughout the instrument will point in the z (up) direction, meaning that nonadiabatic rotation of the neutron polarisation is less of a concern for the present implementation, as compared to cases where full three-direction polarisation analysis is attempted. The coils will also generate a homogenous holding field across the volume of the 3 He spin filter analyser cell, as demonstrated in Section 3.4.…”

“…While the technique has been applied successfully on a wide range of instruments at both reactor and spallation sources, its extension to wide-angle time-of-flight spectrometers has proved challenging. Indeed, despite 10 years passing since the first proof of principle [2], the technique is still not in routine use. The reasons for this are manifold.…”

Polarization analysis for the thermal chopper spectrometer TOPAS

“…Due to the high incident neutron energies E ≤ 150 meV corresponding to λ ≥ 0.74Å and the convergent focused incoming beam and large area detector array, TOPAS will use 3 He spin filter cells for both polarization [10] and analysis [11]. The incident beam polarizer will be placed on a guide changer before the final Fermi chopper as shown in Fig.…”

“…For the wide angle polarization analysis of the scattered neutrons we refine the original PASTIS design [11]. The present coil layout consists of a pair of Helmholtz coils coupled to horizontal µ-metal sheets, which work as a magnetic capacitor of sorts, and generate a field in the Z direction.…”

Considerations on Quality Factors from Super Mirrors and3He Spin Filters for Polarization Analyzers on Wide Q-Range Instrumentation

“…While typically MEOP can produce more polarized 3 He, up to 1-2 bar liters per hour [1], current methods with SEOP such as frequency narrowed diode array bars and Hybrid SEOP [2] have lead to increased performance and speed for this method such that cell containing 1-2 bar liters of gas can be highly polarized in 1 day time scales [3,4]. The amount of gas produced per day with either SEOP or MEOP would be enough to perform wide angle polarization analysis with the PASTIS method [5], if other technical constraints, to be discussed later, are met. For some applications 3 He could be polarized in-situ to provide higher time averaged performance and lower potential maintenance time.…”