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Radially scanning magnetic probes to study local helicity injection dynamics
N J Richner1, M W Bongard1, R J Fonck1
1Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
The Review of Scientific Instruments
|November 8, 2018
Summary
Two new magnetic probes were developed for the Pegasus spherical tokamak to investigate plasma dynamics during startup and current drive. These probes enhance the study of local helicity injection and plasma behavior.
Area of Science:
- Plasma physics
- Fusion energy research
- Magnetic confinement fusion
Background:
- Spherical tokamaks are crucial for fusion energy research.
- Understanding plasma dynamics is key to achieving controlled fusion.
- Local helicity injection is a promising method for non-solenoidal plasma startup and current drive.
Purpose of the Study:
- To introduce and characterize two novel magnetic probes for the Pegasus spherical tokamak.
- To study the dynamics of local helicity injection (LHI) during non-solenoidal plasma startup and current drive.
- To provide advanced diagnostic capabilities for plasma equilibrium and current dynamics.
Main Methods:
- Deployment of a magnetic radial array probe with 15 printed circuit board pickup coils (measuring dB/dt).
- Deployment of a magnetic radial scanning probe with 8 Hall effect sensors (measuring magnetic field strength and direction).
- Calibration using Helmholtz coils to determine bandwidths (up to ~2 MHz) and sensitivities (0.18-0.96 mV T^-1 s).
Main Results:
- The magnetic radial array probe offers balanced frequency response and sensitivity for dB/dt measurements.
- The magnetic radial scanning probe accurately measures magnetic field strength (up to ~100 mT) and direction at 8 spatial points.
- Both probes are electrostatically shielded and designed for insertion into the tokamak vacuum vessel.
Conclusions:
- The new magnetic probes provide essential diagnostic tools for studying LHI in spherical tokamaks.
- These diagnostics will advance the understanding of plasma startup and current drive mechanisms.
- The successful deployment and calibration pave the way for detailed plasma dynamics research on Pegasus.
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