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The TAMUTRAP facility: A Penning trap facility at Texas A&M University for weak interaction studies

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Highlights

  • Commissioning of world's largest Penning trap facility for weak interaction studies.

  • Novel design of TAMUTRAP Penning trap differs from typical designs in two key aspects: The electrode structure has an 180 mm inner diameter and an overall length of 334.89 mm leading to a uniquely small length/radius ratio l/r=3.72; and we do not use the long end cap approximation, instead our short endcap electrodes are closed and capable of being placed at an arbitrary potential (Which means the end cap can be diskshaped charged particle detectors).

  • The Penning trap geometry is suited for intrap and posttrap precision decay experiments.

  • The facility is suitable for the precision betadecay experiment as well as a wide range of nuclear physics experiments.

  • It has been demonstrated that one can use a single Penning trap system to both purify the trapped ion bunch and perform a mass measurement. The design of Penning trap allows the detection of decay products such as beta's and protons with nearly 4π collection (in-trap decay experiments).

Abstract

The Texas A&M University Penning Trap (TAMUTRAP) facility aims to test the standard model of the electroweak interaction by measuring the β-ν correlation parameter, aβν, for β-delayed proton emitters in the atomic mass range 20 < A < 40. Precision measurements of this correlation parameter and, inextricably, the Fierz interference parameter, are a sensitive probe of physics beyond the standard model. Using off-line ion sources, the TAMUTRAP facility has been commissioned by demonstrating the ability to manipulate the trapped-ion motions as well as to perform precision mass measurements. Our novel cylindrical Penning trap – the world's largest – differs from typical designs in two key aspects: the electrode structure has an 180-mm inner diameter and an overall length of 334.89 mm leading to a uniquely small length/radius ratio l/r = 3.72; and we do not use the long end cap approximation, instead our short endcap electrodes are closed and capable of being placed at an arbitrary potential. This geometry is optimized for observing β-delayed proton decays, but is also well suited for other in-trap and post-trap precision decay experiments. In addition to presenting an overview of the TAMUTRAP facility, we demonstrate that our unique Penning trap is able to measure masses with a precision similar to typical trap designs.

Graphical abstract

The World's largest Penning trap with an inner diameter of 180 mm with a unique length/radius ratio of l/r0=3.72. The facility allow to perform in-trap and post-trap decay experiments. It has been demonstrated that one can use a single Penning trap system to purify the trapped ion bunch and perform mass measurements. Mass measurement precision of 10-8 has been reached for stable isotopes 23Na, 85,87Rb and 133Cs. Ion motions were manipulated by implementing different excitation schemes.

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Introduction

Low-energy, high-precision measurements of the β-ν angular correlation and ft values in nuclear β-decay have been used extensively to form our understanding of the fundamental symmetries of the weak interactions [[1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]]. Measurement of the β-ν angular correlation, aβν, in nuclear β-decay is a direct tool to search for possible scalar (S) and tensor (T) contributions to the charged weak interaction [2,7] which would indicate physics beyond the standard model (BSM). More generally, precision β-decay experiments have proven to be an excellent complement to high-energy searches for new physics since the dependencies on the BSM parameters are different, see Ref. [1] and references therein. The advent of ion-trapping technologies has made it possible to observe nuclear decay in a very clean environment. They are ideal sources for nuclear decay studies [12,13] due to the fact that the backing-free environment allows the daughter particles to escape the shallow-trap potential with negligible distortions to their momenta. In addition, an open ion trap design makes efficient detection of the decay products possible. In recent years, there were few measurements of the β-ν angular correlation coefficient performed with Paul and Penning traps [2,14]. Several experiments with a goal of reaching 0.1% precision are currently being proposed [[15], [16], [17]], including the program being pursued at the TAMUTRAP facility [10,18].

Section snippets

Scientific motivation

The primary focus of the TAMUTRAP research program is to perform precision measurements in nuclear β-decay as a test of the fundamental symmetries of the standard model (SM) in the charged electroweak sector. In particular, we aim to measure aβν for T = 2 and T = 3/2 β transitions to a precision at or below the 0.1% level and thus search for contributions beyond the currently accepted time-reversal-invariant V − A interaction. The nuclei of interest are β-delayed proton emitters in the 20 to 40

Production of radioactive ion beams for TAMUTRAP

The radioactive ion beam (RIB) for the planned research program will be produced using the light-ion guide (LIG) technique [[24], [25], [26]] and delivered to the TAMUTRAP facility at 50 − 75 keV. In this technique, the reaction products from a nuclear reaction are thermalized in high-purity helium gas where they remain mainly as singly charged ions due to the high ionization potential of the stopping gas. Ions are flushed out of the gas cell to a differential pumping section where they are

The TAMUTRAP facility

A singly-charged, low-energy (50–75 keV) radioactive ion beam from the exit of the isobar separator will be directed vertically up through the shielding concrete blocks to the TAMUTRAP facility. Alternatively, aluminosilicate ion sources can be used to produce ion beams of stable isotopes. Two such ion sources are installed at two different locations upstream of the cooler/buncher as depicted in Fig. 2.

The TAMUTRAP beamline shown in Fig. 2 includes all elements necessary for transporting ions

Performance of the RFQ

The transmission efficiency of the RFQ was studied in continuous mode as function of gas pressure, drag potential, and initial injection ion energy. The transmission efficiency in continuous mode was defined as the ratio of the extracted and injected ion currents, as measured by Faraday cups placed after and before the RFQ. During this measurement, the pulsing drift tube on the extraction side was grounded and the extracted ion beam had 10 keV of kinetic energy. Fig. 6 shows the design of the

The Penning trap system

In nuclear physics, Penning traps are widely used as a reliable tool to precisely measure the atomic masses of both stable and unstable nuclides [46,47]. The mass of an atom or a nucleus is one of its most fundamental properties and are required to study nuclear shell structure, nuclear astrophysics, determination of β-decay Q-values and to test the theory of weak interaction. Today, quite a number of Penning traps are in operation at accelerator based nuclear physics research facilities [[48],

Conclusion

The initial research program at the TAMUTRAP facility of measuring β-ν angular correlation parameter for T = 2 and T = 3/2 β-delayed proton emitters will investigate symmetries of the weak interaction. The TAMUTRAP facility has been successfully commissioned (offline) by demonstrating that we can bunch and cool a continuous beam of stable ions using the RFQ and successfully trap them for an extended period of time in the Penning trap, which are critical steps needed before a measurement of β − ν

Author statement

D. McClain: Investigation; A. Ozmetin: Investigation; B. Schoreder: Investigation; K.S. Marble: Investigation, Validation; E.Gilg: Investigation; L.Cooper: Investigation; G. Duran: Investigation; R. McAfee: Investigation; M.McDonough: Investigation; C. Gonzalez-Ortiz: Investigation, software; M.Soulard: Investigation; M. Nasser: Investigation, software, Data Curation, Validation Formal analysis; V.E.Iacob: Investigation, software; G. Chubarian: Conceptualization; G. Tabacaru: Conceptualization;

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors would like to thank R. Ringle (NSCL), T. Eronen (JYFL), J. Clark (ANL) and A. Kwiatkowski (TRIUMF) for fruitful discussions and advice. This work was supported by the U.S. Department of Energy, Office of Science, under Award No. DEFG02-93ER40773, by the Department of Energy Early Career Award DE-SC0006936, and by the Department of Energy, National Nuclear Security Administration through the Center for Excellence in Nuclear Training And University-based Research (CENTAUR) under Award

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