Construction of a linear plasma device for studying helicon plasmas relevant to plasma-wakefield accelerators

Abstract

The magnetized anisotropic ion apparatus (MARIA) was constructed to study the density buildup and particle balance in helicon plasmas. This device will help address key questions surrounding the dynamics of the neutral argon population and the role it plays in defining the ultimate density achieved. Insights gained from this research are particularly important for meeting the demanding high density and high uniformity requirements of plasma based wakefield accelerator concepts. A key feature of the MARIA device is it is fully transparent borosilicate glass chamber which enables the flexible use and development of optical techniques for measuring plasma parameters like electron temperature and density. Whistler-mode behavior featuring very high on-axis ionization fraction and a linear relationship between electron density and magnetic field strength up to 5 × 1018 m−3 has been measured with an RF compensated Langmuir probe in argon with 700 W RF power, 650 G at the antenna, and 2 mTorr neutral pressure. Laser induced fluorescence measurements, which build on the Langmuir probe measurements, are able to fully constrain the 2D particle balance by enabling ion and neutral sources and sinks to be spatially resolved. Initial flow velocity measurements in the axial direction are presented.