Recent Posters by the MIT ICR Group
Transparencies of Recent Talks
[J2.007] Towards an order of magnitude improvement in high-precision
atomic mass measurements
Simon Rainville, James K. Thompson, David E. Pritchard (Massachusetts Institute of Technology)
The use of single ions in Penning traps has made possible the measurement
of some atomic and molecular masses with a precision of about a part in
10^10. This is achieved by measuring the cyclotron frequency of an ion
trapped in a strong magnetic field, and comparing it to the cyclotron frequency
of a reference ion trapped in the same field several minutes later. The
precision of these measurements is limited by fluctuations of the magnetic
field. Recent improvements on the MIT mass spectrometer have opened the
way to higher precision by allowing us to simultaneously confine and detect
two different ions in the same trap. A direct measurement of the difference
in the cyclotron frequencies of the two ions can then be completely insensitive
to magnetic field fluctuations! The Coulomb interaction between the two
ions introduces perturbations which can potentially cause systematic errors
and are under study. Statistical uncertainties below a part in 10^11 are
possible after only a few hours of measurement. The beauty and challenges
of this technique will be presented as well as recent experimental results.
(transparencies in pdf,
1.2 MB)
[Q2.002] Electronic Refrigeration and Single Ion Mass Spectrometry
James K. Thompson, Simon Rainville, David E. Pritchard (Massachusetts Institute of Technology)
The MIT Ion Cyclotron Resonance Lab has determined the atomic mass of
13 neutral atoms with accuracies of \sim 10^-10 by comparing the cyclotron
frequencies of single ions stored in a Penning trap. During the past year,
we have developed an electronic refrigeration technique which uses feedback
to reduce the effective temperature of the superconducting transformer
used to detect the ion. Because our S/N is only limited by the broadband
thermal noise of the transformer, our ability to measure the axial frequency,
phase, and amplitude has been improved by \sim 4, 2, and 2 respectively.
The ion's temperature is also lowered because it comes to equilibrium with
the subthermal transformer. The reduction of the ion's temperature is especially
important since thermal fluctuation of the ion's cyclotron amplitude coupled
with special relativity leads to shot-to-shot cyclotron frequency measurement
noise. These shot-to-shot fluctuations should be the dominant source of
noise (especially for lighter species) once the effect of magnetic field
noise is eliminated.
(transparencies in pdf,
188 kB)