Nugget on Multi-Species Cyclotron Modes
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Nugget on Multi-Species Cyclotron Modes
Cyclotron Modes in Multispecies mθ=2 + + fci + + fExB Driscoll /Dubin/O'Neil, UCSD Ion Plasmas Plasmas exhibit a variety of cyclotron modes, and electric fields shift the mode frequencies away from the “bare” cyclotron frequencies 2πfci =qiB/mi. Recent theory (Dubin 2013) gives precise predictions of these shifts, for the "regular" mθ=1 (center-of-mass) mode, and for the unusual mθ=2 (cartoon shown) and mθ=0 modes. For a species of fraction δi, the shift is given by fExB [ mθ-2 + δi (1-R ) ], where fExB is the ExB drift rotation frequency, and R represents image charge corrections from Rwall. 1950 A new laser-thermal cyclotron spectroscopy technique (Affolter 2013) gives the first quantitative measurement of these shifts. The figure shows mθ=0, 1, 2 modes for Mg isotopes 24, 25, 26. The novel mθ=0 mode has no radial electric field, and thus couples only at the ends. A theory fit to the data shown gives the three φχι to an accuracy of 2 parts in 104. These new results may be relevant to "space charge" and "amplitude" calibrations for cyclotron mass spectroscopy devices widely used in molecular chemistry and biology. Cyclotron frequencies [kHz] m =2 θ 1900 f m =1 Mg ci 24 θ 24 m =0 1850 θ m =2 f 1800 θ ci 25 m =1 Mg θ 25 1750 f m =0 θ m =2 θ m =1 Mg ci 26 θ 26 1700 m =0 θ 1650 0 5 10 15 20 25 30 Plasma ExB Rotation Frequency [kHz] M.Affolter et al, Phys. Plasma 22, 055701 (2015)