A multi-channel capacitive probe for electrostatic fluctuation measurement in the Madison Symmetric Torus reversed field pinch

Journal Article · Wed Feb 08 00:00:00 EST 2017 · Review of Scientific Instruments

DOI:https://doi.org/10.1063/1.4975095· OSTI ID:1466044

Tan, Mingsheng ^[1]; Stone, Douglas R. ^[2]; Triana, Joseph C. ^[2]; Almagri, Abdulgader F. ^[2]; Fiksel, Gennady ^[3]; Ding, Weixing ^[4]; Sarff, John S. ^[2]; McCollam, Karsten J. ^[2]; Li, Hong ^[1]; Liu, Wandong  ^[1]

---

1. Univ. of Science and Technology of China, Hefei (People's Republic of China)
2. Univ. of Wisconsin, Madison, WI (United States)
3. Univ. of Michigan, Ann Arbor, MI (United States)
4. Univ. of Science and Technology of China, Hefei (People's Republic of China); Univ. of California, Los Angeles, CA (United States)

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. Furthermore, 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.

• Research Organization: Univ. of Wisconsin, Madison, WI (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES)
• Grant/Contract Number: FC02-05ER54814
• OSTI ID: 1466044
• Alternate ID(s): OSTI ID: 1349337
• Journal Information: Review of Scientific Instruments, Vol. 88, Issue 2; ISSN 0034-6748
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

Related Subjects

47 OTHER INSTRUMENTATION