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.
Highlights
Motivation for electric storage ring “traps” for electrons or protons.—The U.S particle physics community has recently updated its vision of the future and strategy for the decade in a Particle Physics Project Prioritization Panel (P5) Report
Issues to be studied with ETEAPOT include: (i) radial B-field: since the torque due to any residual radial B-field acting on the magnetic dipole moment (MDM) mimics the electric dipole moments (EDM) effect, this is expected to be the dominant systematic error; (ii) geometric phase: some EDM-mimicking precessions would average to zero except for the noncommutativity of 3D rotations; (iii) nonradial E-field, vertical quad misalignment, rf cavity misalignment etc.: these cause the closed orbit to deviate from design
The present paper describes our “resurrection” of Alternating Gradient Synchrotron (AGS) analog ring from historic BNL documentation, and simulates its performance with codes intended for the proton EDM experiment
Summary
Motivation for electric storage ring “traps” for electrons or protons.—The U.S particle physics community has recently updated its vision of the future and strategy for the decade in a Particle Physics Project Prioritization Panel (P5) Report. The electric dipole moment (EDM) of the proton is known to be so small that, in order to reduce systematic errors enough to measure it in a storage ring requires measuring differences between counter-circulating beams. Issues to be studied with ETEAPOT include: (i) radial B-field: since the torque due to any residual radial B-field acting on the magnetic dipole moment (MDM) mimics the EDM effect, this is expected to be the dominant systematic error; (ii) geometric phase: some EDM-mimicking precessions would average to zero except for the noncommutativity of 3D rotations; (iii) nonradial E-field, vertical quad misalignment, rf cavity misalignment etc.: these cause the closed orbit to deviate from design.
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