The Digital Mirror Langmuir Probe: FPGA Implementation of Real-Time Langmuir Probe Biasing

The Digital Mirror Langmuir Probe: FPGA Implementation of Real-Time Langmuir Probe Biasing

The Digital Mirror Langmuir Probe: FPGA Implementation of Real-Time Langmuir Probe Biasing 150 150 UKAEA Opendata
UKAEA-CCFE-PR(19)47

The Digital Mirror Langmuir Probe: FPGA Implementation of Real-Time Langmuir Probe Biasing

High bandwidth, high spatial resolution measurements of electron temperature, density and plasma potential are valuable for resolving turbulence in the boundary plasma of tokamaks. While conventional Langmuir probes can provide such measurements either their temporal or spatial resolution is limited: the former by the sweep rate necessary for obtaining I-V characteristics and the latter by the need to use multiple electrodes, as is the case in triple and double probe configurations. The Mirror Langmuir Probe (MLP) bias technique overcomes these limitations by rapidly switching the voltage on a single electrode cycling between three bias states, each dynamically optimised for the local plasma conditions. The MLP system on Alcator C-Mod used analog circuitry to perform this function, measuring T e , V F , and I sat at 1.1 MSPS. Recently, a new prototype digital MLP controller has been implemented on a Red Pitaya Field Programmable Gate Array (FPGA) board which reproduces the functionality of the original controller and performs all data acquisition. There is also the potential to provide the plasma parameters externally for use with feedback control systems. The use of FPGA technology means the system is readily customisable at a fraction of the development time and implementation cost. A second Red Pitaya was used to test the MLP by simulating the current response of a physical probe using C-Mod experimental measurements. This project is available as a git repository to facilitate extensibility (e.g. real-time control outputs, more voltage states) and scalability through collaboration.

Collection:
Journals
Journal:
Review of Scientific Instruments
Publisher:
AIP (American Institute of Physics)
Published date:
19/09/2019