Ultracold plasma expansion in a magnetic field.
We measure the expansion of an ultracold plasma across the field lines of a uniform magnetic field. We image the ion distribution by extracting the ions with a high-voltage pulse onto a position-sensitive detector. Early in the lifetime of the plasma (<20 micros), the size of the image is dominated by the time-of-flight Coulomb explosion of the dense ion cloud. For later times, we measure the 2D Gaussian width of the ion image, obtaining the transverse expansion velocity as a function of the magnetic field (up to 70 G). We observe that the expansion velocity scales as B(-1/2), explained by a nonlinear ambipolar diffusion model with anisotropic diffusion in two different directions.
Zhang
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XL
Joint Quantum Institute, Department of Physics, University of Maryland, College Park, MD 20742, USA.
Fletcher
R S
RS
Rolston
S L
SL
Guzdar
P N
PN
Swisdak
M
M