Determination of Transverse Distributions of Ion Plasmas Confined in a Linear Paul Trap by Imaging Diagnostics

概要

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This paper presents a diagnostic method to measure the transverse distribution of an ion plasma confined in a linear Paul trap with a relatively large number of ions (${\sim}10^{7}$). The distribution of the plasma extracted from the trap is converted to a luminosity distribution using a microchannel plate (MCP) with a phosphor screen, and it is recorded with a charge-coupled device (CCD) camera. The linearity of the imaging system, which is the basis of the quantitative analyses, is ensured by correcting the saturation of MCP gain over a wide range of ion number. The correspondence between the density profile of an ion plasma in the trap and that at the MCP surface is examined by numerical simulation. The density profile in the trap can be reconstructed accurately from the observed luminosity distribution based on the linearity and the correspondence. Moreover, the transverse temperature and the tune depression can also be determined from the observed transverse density profile. The detailed measurement of the transverse plasma distribution is essential for the experimental study of various collective effects in space-charge-dominated beams using the ion trap. As an example of observations by the imaging diagnostic system, we also demonstrate the shrinking of the transverse plasma distribution by buffer-gas cooling.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2008-10-25