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The digital mirror Langmuir probe : field programmable gate array implementation of real-time Langmuir probe biasing.

Vincent, C. and McCarthy, W. and Golfinopoulos, T. and LaBombard, B. and Sharples, R. and Lovell, J. and Naylor, G. and Hall, S. and Harrison, J. and Kuang, A. Q. (2019) 'The digital mirror Langmuir probe : field programmable gate array implementation of real-time Langmuir probe biasing.', Review of scientific instruments., 90 (8). 083504.

Abstract

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 optimized for the local plasma conditions. The MLP system on Alcator C-Mod used analog circuitry to perform this function, measuring Te, VF, and Isat 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 customizable 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 and more voltage states) and scalability through collaboration.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.1063/1.5109834
Publisher statement:© 2019 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Vincent, C., McCarthy, W., Golfinopoulos, T., LaBombard, B., Sharples, R., Lovell, J., Naylor, G., Hall, S., Harrison, J. & Kuang, A. Q. (2019). The digital mirror Langmuir probe: Field programmable gate array implementation of real-time Langmuir probe biasing. Review of Scientific Instruments 90(8): 083504 and may be found at https://doi.org/10.1063/1.5109834
Date accepted:26 July 2019
Date deposited:04 September 2019
Date of first online publication:19 August 2019
Date first made open access:19 August 2020

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