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Canadian Journal of Physics

A charged particle Stern–Gerlach experiment

Eric Enga, Myer Bloom

Published Nov 1, 1970• 4 citations
Publisher

Abstract

It is shown that a charged particle Stern–Gerlach experiment can be performed in a magnetic field geometry which is similar to that used in accelerators of the strong-focusing type. In particular, we analyze the helical quadrupole system. The analysis is based on an extension of the theory of the transverse Stern–Gerlach experiment to time-independent, inhomogeneous magnetic fields. The effect of the Lorentz force is reduced by using orthogonal inhomogeneous electric fields.

DOI
10.1139/p70-310

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Observation of the transverse Stern-Gerlach effect in neutral potassium and an analysis of a charged particle Stern-Gerlach experiment

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Two experiments are described. One is the successful observation of the resonant deflection of a beam of neutral potassium atoms at a frequency of 7.2 Mhz, in agreement with the predictions of the theory of the Transverse Stern-Gerlach (TGS) experiment. The other is a proposal for a charged particle Stern-Gerlach experiment, which is based on an extension of the TSG experiment to time independent, inhomogeneous magnetic fields having the form [formula omitted] If the field B₁(r) is well chosen, the charged particle trajectories are confined in a stable beam by the resulting Lorentz forces for motion generally along the z axis. This is, in fact, the principle of strong focusing which is now widely used in accelerator design. But in such a system it is also possible to satisfy the criterion for a TSG experiment, since in a frame of reference moving with a particle in the z direction, the field B₁(r) is rotating in time.

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It is shown that a charged particle Stern–Gerlach experiment can be performed in a magnetic field geometry which is similar to that used in accelerators of the strong-focusing type. In particular, we analyze the helical quadrupole system. The analysis is based on an extension of the theory of the transverse Stern–Gerlach experiment to time-independent, inhomogeneous magnetic fields. The effect of the Lorentz force is reduced by using orthogonal inhomogeneous electric fields.
Two experiments are described. One is the successful observation of the resonant deflection of a beam of neutral potassium atoms at a frequency of 7.2 Mhz, in agreement with the predictions of the theory of the Transverse Stern-Gerlach (TGS) experiment. The other is a proposal for a charged particle Stern-Gerlach experiment, which is based on an extension of the TSG experiment to time independent, inhomogeneous magnetic fields having the form [formula omitted] If the field B₁(r) is well chosen, the charged particle trajectories are confined in a stable beam by the resulting Lorentz forces for motion generally along the z axis. This is, in fact, the principle of strong focusing which is now widely used in accelerator design. But in such a system it is also possible to satisfy the criterion for a TSG experiment, since in a frame of reference moving with a particle in the z direction, the field B₁(r) is rotating in time.
It has been proposed by Enga and Bloom that combined electric and magnetic helical quadrupole fields may be used to perform a Stern–Gerlach experiment on charged particles. A detailed investigation shows that the longitudinal Lorentz force due to coupling of the transverse velocity of the particles to the transverse magnetic field produces an additional focusing effect which masks the Stern–Gerlach force in large regions of initial phase space. Consideration of uncompensated magnetic fields, produced by small random variations in conductor dimensions and location, shows that the tolerances required to preserve spin separation in the useful range of initial conditions are several orders of magnitude higher than can be achieved at this time.
A successful transverse Stern–Gerlach experiment has been performed, using a beam of neutral potassium atoms and an inhomogeneous time-dependent magnetic field of the form[Formula: see text]A classical analysis of the Stern–Gerlach experiment is given for a rotating inhomogeneous magnetic field. In general, when space quantization is achieved, the spins are quantized along the effective magnetic field in the reference frame rotating with angular velocity ω about the z axis. For ω = 0, the direction of quantization is the z axis (conventional Stern–Gerlach experiment), while at resonance (ω = −γH 0 ) the direction of quantization is the x axis in the rotating reference frame (transverse Stern–Gerlach experiment). The experiment, which was performed at 7.2 Mc, is described in detail.
Abstract We present a feasibility study with several magnetic field configurations for creating spin-dependent forces that can split a low-energy ion beam by the Stern–Gerlach (SG) effect. To the best of our knowledge, coherent spin-splittings of charged particles have yet to be realised. Our proposal is based on ion source parameters taken from a recent experiment that demonstrated single-ion implantation from a high-brightness ion source combined with a radio-frequency Paul trap. The inhomogeneous magnetic fields can be created by permanently magnetised microstructures or from current-carrying wires with sizes in the micron range, such as those recently used in a successful implementation of the SG effect with neutral atoms. All relevant forces (Lorentz force and image charges) are taken into account, and measurable splittings are found by analytical and numerical calculations.
Abstract The Stern–Gerlach (SG) experiment is a fundamental experiment for revealing the existence of “spin”. In this experiment, beams of silver atoms are sent through inhomogeneous magnetic fields to observe their deflection. Thus, the conventional SG experiment can be viewed as a magnetic-type spin effect. In this work, we successfully generalize the SG effect from magnetic-type to electric-type by solving Dirac’s equation with a potential barrier, revealing an extraordinary spin effect. Beams of Dirac particles can be regarded as matter waves. Based on Dirac’s equation, we obtain the explicit forms of the incident, reflected, and transmitted waves. The electric-type SG effect shows that the reflected and transmitted waves can exhibit notable spatial shifts, which depend on the spin direction and the incident angle of the wave. The electric-type SG effect has potential applications for separating Dirac particles with different spin directions and for estimating the spin direction of Dirac particles. Some discussions related to the interaction between spin and the electric field are also presented.
The motion of neutral particles with magnetic moments in an inhomogeneous magnetic field is described in a quantum mechanical framework. The validity of the semiclassical approximations which are generally used to describe these phenomena is discussed. Approximate expressions for the evolution operator are derived and compared to the exact calculations. Focusing and spin-flip phenomena are predicted. The reliability of Stern-Gerlach experiments to measure spin projections is assessed in this framework.