Linear servomotor probe drive system with real-time self-adaptive position control for the Alcator C-Mod tokamak

Area of Science:

• Plasma Physics
• Fusion Energy Research
• Instrumentation and Control Systems

Background:

• The Alcator C-Mod tokamak requires advanced diagnostic tools for plasma characterization.
• Horizontal reciprocating probes are crucial for in-situ measurements but face challenges with thermal management.
• Existing probe control systems lack self-adaptive capabilities to optimize insertion depth based on real-time conditions.

Purpose of the Study:

• To develop and implement a new servomotor drive system for a horizontal reciprocating probe on the Alcator C-Mod tokamak.
• To enable self-adaptive position control of the probe using real-time plasma data.
• To establish a universal trigger threshold for probe retraction based on surface temperature dynamics.

Main Methods:

• Integration of a commercial linear servomotor and controller with a mirror Langmuir probe bias system.
• Real-time computation of probe surface temperature and its rate of change.
• Development of a self-adaptive control algorithm for probe insertion depth and retraction.

Main Results:

• The developed system achieves self-adaptive position control of the reciprocating probe.
• A universal trigger threshold was defined using probe surface temperature and its rate of change.
• Probe retraction at the trigger threshold resulted in a consistent ultimate surface temperature, independent of operational parameters.

Conclusions:

• The new servomotor drive system effectively manages probe insertion depth and thermal load.
• The self-adaptive control strategy enhances diagnostic reliability and data acquisition in tokamak environments.
• This approach offers a robust method for controlling probe-based diagnostics under varying plasma conditions.