Designing a Low-Noise Amplifier for a BES System
Beam emission spectroscopy (BES) systems are used to measure plasma density inside reactors by detecting the intesity of light given off by electrons excited by the neutral beam. The objective of this research project was to analyze the BES system used on NSTX-U, the tokamak at PPPL, to evaluate potential changes. If any such modifications were shown to be advantageous, they would be implemented in the BES system being designed for the W7-X stellarator in Griefswald, Germany.
Changes considered included:
- Introducing a photodiode array to replace a single photodiode and increase resolution.
- Eliminating a JFET-based gain stage and compensate by leveraging modern op-amp designs.
- Alterations to operating temperature
In addition to the above modifications, I performed a sensitivity analysis to determine which parasitic properties in the circuit had the greatest impact on circuit performance. My workflow was centered around using LTSpice to simulate the design, then using a C++ tool I created to filter and cross-compare data from multiple simulations. As a result, I was able to identify which compenents had the greatest impact on noise factor and detail how the JFET gain stage could be eliminated without substantially affecting performance.
I would like to thank the US Department of Energy’s Science Undergraduate Laboratory Internship (SULI) program for the opportunity to participate with this research.