Jesse Schelfhout

Abstract:

The leading experimental determinations of the fine-structure constant 𝛼 currently rely on atomic photon-recoil measurements from Ramsey-Bordé atom interferometry with large-momentum transfer to provide an absolute mass measurement. We propose an experimental scheme for an intermediate-scale differential atom interferometer to measure the photon recoil of neutral atomic species with a single-photon optical clock transition. We calculate trajectories for our scheme that optimize the recoil phase while nullifying the undesired gravity-gradient phase by considering independently launching two clouds of ultracold atoms with the appropriate initial conditions. For Sr and Yb, we find an atom interferometer of height 3 m to be sufficient for an absolute mass measurement precision of 𝛥⁢𝑚/𝑚∼1×10−11 with current technology. Such a precise measurement would halve the current uncertainty in 𝛼 — an uncertainty that would no longer be limited by an absolute mass measurement. The removal of this limitation would allow the current uncertainty in 𝛼 to be reduced by a factor of 10 by corresponding improvements in relative mass measurements, thus paving the way for higher-precision tests of the standard model of particle physics.

Abstract:

A method to confine plasmas based on a new form of z-pinch was discovered and published in the late 1970s by two European physicists, Owen Storey and Laurent Cairó, building on a prior discovery by American astrophysicist Eugene Parker [1]. They proved that when supersonically flowing plasma is confined by a magnetic field parallel to the flow, there are circumstances in which a secondary magnetic field discovered by Parker emerges that reinforces the confinement, thereby reducing the requirement for the external magnetic field. The resulting overall confining field is concentrated in the thin static sheath-like boundary layer between the plasma and the external field, while the bulk plasma remains field-free and current-free. They suggested that this might be applicable to fusion and proposed a conceptual device exploiting this effect [2, 3]. The confinement in this device would be intrinsically MHD-stable, and more energetically efficient than that of most devices currently under investigation. Despite its promises, this method was not investigated further at the time and eventually faded from memories. Moreover, the effect discovered by Parker has not yet been observed in numerical simulation or experimentally, because it has never been sought. In collaboration with one of the original scientists, our independent research group is reviewing and continuing this work to bring it to a Technology Readiness Level of 3 [4]. This involves numerical simulations to observe the emergent effect and to characterise the proposed device concept, including its plasma confinement and stability characteristics, and means to maintain plasma density, temperature, and bulk flow velocity. In the success case, the proposed device has the potential to confine an isotropic plasma more efficiently and economically, with immunity to the major MHD instabilities, good accessibility due to a simple and modular design with high aspect ratio, and continuous operation. This short paper based on the poster presented at the 50th Conference of the European Plasma Society in Salamanca, Spain, in July 2024, aims to present briefly Parker’s Effect and how it can be used to confine a flowing plasma using a sheath pinch, how this possibility can be verified. We summarise recent work and present a high-level work plan. We are seeking collaborators for this venture.