R.S. Van Dyck

High-Resol Ution Spectroscopy of Stored Ions

Publisher Summary This chapter reviews the high-resolution experiments that have employed the stored ion technique. The main advantage of the stored ion techniques is that the ideal of an unperturbed species at rest in space is approached to a high degree. Four types of “traps” have been most commonly used for high-resolution work—namely, the Paul (or rf) trap, the Penning trap, the Kingdon (or electrostatic trap), and the magnetostatic trap (magnetic bottle). The Paul or rf trap has the advantage that the trapped ions are bound in a (pseudo) potential well in all directions and no magnetic fields are required for confinement. An important practical advantage of the Penning trap is that parasitic heating mechanisms (like rf heating in the Paul trap) are nearly absent. It can also be best suited for studies of magnetic field-dependent structure. The Kingdon trap has the advantage of being simpler than the Paul or Penning trap, requiring only a dc voltage for trapping. Because a potential minimum in free space cannot exist for purely electrostatic fields, the Kingdon trap relies on angular momentum of the ions about a central axis to provide dynamical stability. Certainly, the prevalent method for creating ions is from direct ionization of neutrals inside the trap by an externally injected electron beam. However, many times it is desirable to rid the trap of extraneous ions. In the rf trap this can be accomplished by operating the trap in the “mass-selective” mode.

Past Electron-Positron g − 2 Experiments Yielded Sharpest Bound on CPT Violation for Point Particles

In our past experiments on a single electron and positron we measured the cyclotron and spin-cyclotron difference frequencies omega_c and omega_a and the ratios a = omega_a/ omega_c at omega_c = 141 Ghz for e^- and e^+ and later, only for e^-, also at 164 Ghz. Here, we do extract from these data, as had not done before, a new and very different figure of merit for violation of CPT symmetry, one similar to the widely recognized impressive limit |m_Kaon - m_Antikaon|/m_Kaon < 10^-18 for the K-mesons composed of two quarks. That expression may be seen as comparing experimental relativistic masses of particle states before and after the C, P, T operations had transformed particle into antiparticle. Such a similar figure of merit for a non-composite and quite different lepton, found by us from our Delta a = a^- - a^+ data, was even smaller, h_bar |omega_a^- - omega_a^+|/2m_0 c^2 = |Delta a| h_bar omega_c/2m_0 c^2) < 3(12) 10^-22.

Trapping and thermalization of positrons for geonium spectroscopy

Abstract A static technique for continuously catching positrons in a Penning trap under ultra-high vacuum conditions has been demonstrated and a preliminary measurement of the positron/electron mass ratio was made yielding m(e+)/m(e)- = 1 ± 1.3 × 10−7.

High mass resolution with a new variable anharmonicity Penning trap

A modified Penning trap has been developed and shown to yield 100 times narrower axial resonance linewidths on electrons than that of a previous unmodified Penning trap. An extra pair of electrodes is inserted in the standard trap configuration, which effectively nulls the quartic term in the trapping potential. With existing signal‐to‐noise limitations, an axial frequency resolution of 0.02 ppm can be obtained. This device is particularly attractive to high‐resolution mass spectrometry.

New measurement of the proton-electron mass ratio

Abstract Using a compensated quadring Penning trap operated in a high magnetic field (5.05 T) at cryogenic temperatures (4.2 K), an r.f. resonance ion storage technique allows cyclotron resonances for both electrons and protons, alternately trapped in the same magnetic well, to be compared in order to yield the proton-electron mass ratio m p / m e = 1836.152470(76). The 41 p.p.b. uncertainty primarily reflects a systematic shift which arises from the two charge types not having the same average magnetron orbit.

Ultrastable superconducting magnet system for a penning trap mass spectrometer

A custom-designed magnet/cryostat system is described which has demonstrated remarkably improved field stability over previous designs. To shield from external magnetic noise, a custom-fabricated flux-gate device remotely senses the changes in magnetic field and cancels them out at the site of the magnet/cryostat via a 1.7-m-diam Helmholtz coil. To provide further shielding, the basic superconducting solenoid includes a passive flux-stabilizing coil. To stabilize internal field shifts, the temperature of the materials in the immediate vicinity of the solenoid (which have a temperature-dependent susceptibility) is stabilized via the new cryostat geometry and by controlling the pressure of the evaporating liquid helium to a few parts per million. As a result, the total system now has a composite shielding factor of approximately 104 and an overall temporal stability on the order of 17(2) parts in 1012 per hour. This instrument, the heart of our new Penning trap mass spectrometer, has recently been used to d...

A Compensated Penning Trap Mass Spectrometer and the 3

Abstract The use of a compensated Penning trap to measure an ions mass relative to some calibration ion is described along with the leading systematic effects which must be considered. In this respect, magnet stability should no longer be a major limitation. This particular spectrometer has recently been used to determine preliminary atomic masses of both 3H and 3He and can be combined to yield a preliminary endpoint energy for the tritium decay (relative to neutral ground states) of 18 588(10) eV.

Progress on the 3H-3He mass difference using the compensated Penning trap spectrometer

The use of the compensated Penning trap to measure an ions mass relative to some calibration ion is described along with the leading systematic effects which must be considered. In this respect, magnet stability should no longer be a major limitation. Sideband techniques are described that center ions in the trap and equilibrate the cyclotron motion. The spectrometers accuracy has been checked at the 1-ppb level by comparing the same atom with different charge states. The present application determines preliminary atomic masses of both 3H and 3He. These can be combined to yield an endpoint energy for the tritium decay (relative to neutral ground states) of 18 588(10)eV.

Variable magnetic bottle for precision geonium experiments

A novel technique has been developed which allows a quadratic magnetic field to be continuously varied (via a superconducting flux transformer) from the outside of an ultrahigh‐vacuum container placed within a superconducting solenoid. Enclosed within each of these vacuum vessels is a high‐precision (compensated) Penning trap which is used in a variety of geonium experiments at the University of Washington. By varying the dc current in an outer (normal) primary solenoid, the secondary current flowing within a shorted superconducting loop is varied accordingly. The superconducting loop need only be placed in a cylindrically symmetric position within the Penning trap in order to generate the B2 term, and with a clever choice of geometry, the zeroth‐order term can be totally eliminated. As an additional highlight, the uniform field from the main solenoid is drift stabilized to the same degree as the basic cancellation and further, an auxiliary trim coil can be used to fine trim the zeroth‐order null.

Physics accessible through ultrahigh resolution trapped ion mass spectroscopy

Abstract We describe how precision mass spectroscopy can test fundamental physics such as QED and CPT invariance. We also describe how mass spectroscopy can measure a variety of fundamental constants. This is followed by a brief description of the University of Washingtons compensated quadring Penning trap and a compilation of the current mass measurements it has taken.