title: A multi-channel capacitive probe for electrostatic fluctuation measurement in the Madison Symmetric Torus reversed field pinch.
abstract: A 40-channel capacitive probe has been developed to measure the electrostatic fluctuations associated with the tearing modes deep into Madison Symmetric Torus (MST) reversed field pinch plasma. The capacitive probe measures the ac component of the plasma potential via the voltage induced on stainless steel electrodes capacitively coupled with the plasma through a thin annular layer of boron nitride (BN) dielectric (also serves as the particle shield). When bombarded by the plasma electrons, BN provides a sufficiently large secondary electron emission for the induced voltage to be very close to the plasma potential. The probe consists of four stalks each with ten cylindrical capacitors that are radially separated by 1.5 cm. The four stalks are arranged on a 1.3 cm square grid so that at each radial position, there are four electrodes forming a square grid. Every two adjacent radial sets of four electrodes form a cube. The fluctuating electric field can be calculated by the gradient of the plasma potential fluctuations at the eight corners of the cube. The probe can be inserted up to 15 cm (r/a = 0.7) into the plasma. The capacitive probe has a frequency bandwidth from 13 Hz to 100 kHz, amplifier-circuit limit, sufficient for studying the tearing modes (5-30 kHz) in the MST reversed-field pinch.
authors.affiliation: CAS Key Laboratory of Geospace Environment and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China.
authors.forename: Mingsheng
authors.initials: M
authors.lastname: Tan
authors.affiliation: Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Douglas R
authors.initials: DR
authors.lastname: Stone
authors.affiliation: Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Joseph C
authors.initials: JC
authors.lastname: Triana
authors.affiliation: Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Abdulgader F
authors.initials: AF
authors.lastname: Almagri
authors.affiliation: Center for Ultrafast Optical Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Gennady
authors.initials: G
authors.lastname: Fiksel
authors.affiliation: CAS Key Laboratory of Geospace Environment and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China.
authors.forename: Weixing
authors.initials: W
authors.lastname: Ding
authors.affiliation: Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: John S
authors.initials: JS
authors.lastname: Sarff
authors.affiliation: Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA.
authors.forename: Karsten J
authors.initials: KJ
authors.lastname: McCollam
authors.affiliation: CAS Key Laboratory of Geospace Environment and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China.
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.affiliation: CAS Key Laboratory of Geospace Environment and Department of Modern Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China.
authors.forename: Wandong
authors.identifier: 0000000335265079
authors.initials: W
authors.lastname: Liu