The ALPHATRAP experiment

Abstract

The Alphatrap experiment at the Max-Planck Institute for Nuclear Physics in Heidelberg aims at probing the validity of quantum electrodynamics in extremely strong electromagnetic fields. To this end, Alphatrap will determine the value of the magnetic moment, or the g-factor, of the electron bound in highly charged ions. Quantum electrodynamics predicts this value with extraordinary precision. As the bound electron in highly charged ions is exposed to the strongest fields available for high-precision spectroscopy in the laboratory, reaching up to 10 16 V/cm in hydrogenlike lead 208 Pb 81+ , a comparison of the theoretical prediction with a measured value can yield the most stringent test of the Standard Model in strong fields. The targeted precision of eleven digits or more can be achieved by storing single highly charged ions in a cryogenic Penning trap, where its eigenfrequencies can be determined with ultra-sensitive electronics to highest precision. Additionally, the spin state can be non-destructively determined using the continuous Stern-Gerlach effect, allowing spectroscopy of the Larmor precession. Alphatrap is constructed to enable the injection and the storage of externally produced ions. The coupling to the Heidelberg EBIT gives access to even the heaviest highly charged ions and thus extends the available field strength by more than two orders of magnitude compared to previous experiments. This article describes the technical architecture and the performance of Alphatrap and summarises the experimental measurement possibilities.This article comprises parts of the thesis work of I. 1426The European Physical Journal Special Topics and served as a blueprint for the development of the other theories. Accordingly, the experimental verification of this theory is of major importance and interest. Indeed, QED is today considered to be the best tested theory of the SM. The magnetic moment associated with the spin of the electron can be calculated within the framework of QED and has thus served for experimental tests of the theory. Probably the most intriguing of these experiments is the g − 2 experiment of the free electron [1], which has determined the gyromagnetic ratio, or g-factor, of the electron up to the 13th decimal. This unique agreement of the experiment with the prediction by the SM is a far-reaching confirmation of the validity of the theory. However, in this experiment, except for the weak magnetic trapping field, the electron couples only to the vacuum field, so that non-linear effects in the field strength might go unnoticed.In order to specifically address such interactions, for example a hypothetical photon self-interaction or any other strong-field deviation of the known interactions, tests at the strongest possible electromagnetic field are desirable. Externally applied static fields are limited in strength to about 50 T for static or 300 T for pulsed magnetic fields, or to about 1600 kV/cm in vacuum gaps [2] in case of electrostatic fields. These limitations can be overcome in intense laser ...

QED corrections to the g factor of Li- and B-like ions

“…Recently, the g factor of B-like 40 Ar 13+ was measured by the ALPHATRAP experiment [76] at the Max Planck Institute for Nuclear Physics [29]. The experiment constitutes the first high-precision measurement of the bound-electron g factor of a B-like ion, greatly improving the previous experimental value [77].…”

Towards a He-buffered laser ablation ion source for collinear laser spectroscopy

“…The drawback of this method is that the ions are produced in a plasma at very high temperatures, typically in the order of 10 5 K and the ions are released over a 2π solid angle into the ablation chamber [2]. Sometimes a low emittance is not needed because the ions do not have to be transported [3], only a few ions are sufficient [4,5], lower precision tests are performed [6] or other methods like highly time-resolved measurements are used to compensate the emittanceinduced effects afterwards [7].…”

g Factor of Boronlike Argon Ar4013+

“…A detailed description of Alphatrap can be found in Ref. [13]. A double Penning-trap system is inserted into the bore of a 4.02 T superconducting magnet.…”