EDM planning using ETEAPOT with a resurrected AGS Electron Analogue ring

TL;DR

This paper demonstrates the use of the ETEAPOT simulation code to model the historic Electron Analogue ring for electron EDM measurement and predicts spin evolution, aiding future electric storage ring experiments.

Contribution

It introduces the ETEAPOT code for simulating electric storage rings and applies it to reconstitute and analyze the Electron Analogue ring's performance.

Findings

ETEAPOT accurately reproduces historical lattice optics.

Simulations predict electron spin evolution consistent with past observations.

Proton spin tracking confirms code's symplecticity and suitability for EDM experiments.

Abstract

There has been much recent interest in directly measuring the electric dipole moments (EDM) of the proton and the electron. Such a measurement will require storing a polarized beam of "frozen spin" particles in an all-electric storage ring. Only one such relativistic electric accelerator has ever been built---the "Electron Analogue" ring at Brookhaven National Laboratory in 1954. By chance this electron ring, long since dismantled, would have been appropriate both for measuring the electron EDM and to serve as an inexpensive prototype for the arguably more promising, but ten times more expensive, proton EDM measurement. Today it is cheaper yet to "resurrect" the Electron Analogue ring by simulating its performance computationally. This is one purpose for the present paper. To set up these calculations has required a kind of "archeological physics" to reconstitute the detailed Electron Analogue lattice design. The new UAL/ETEAPOT code, described in detail in an accompanying paper, has been developed for modeling storage ring performance, including (exact BMT) spin evolution, in electric rings. Illustrating its use, comparing its predictions with the old observations, and describing new expectations concerning spin evolution and code performance, are other goals of the paper. This paper describes the practical application of the ETEAPOT code and provides sample results, with emphasis on emulating lattice optics in the AGS Analogue ring for comparison with the historical maching studies and to predict the electron spin evolution they would have measured. To exhibit the ETEAPOT code performance and confirm its symplecticity, results are also given for 30 million turn proton spin tracking in an all-electric lattice that would be appropriate for a present day measurement of the proton EDM.