Charge measurement diagnostics with improved SNR and bit utilization for electron plasma confined in a partial toroidal trap

The SMall Aspect Ratio Toroidal EXperiment in a C-shaped torus recently reported an unprecedented electron plasma confinement, τconfine, of >100s. Understanding the plasma transport mechanism is essential to validate the observed long confinement. Measurement of the total charge Qtotal and its spatial and temporal evolution offers insight into the plasma transport mechanism. The existing charge collector for measuring Qtotal is affected by fast transients, resulting in a low signal-to-noise ratio (SNR) and insufficient bit resolution, which makes its measurement difficult, especially at long confinement times. This restricted the measurement of Qtotal only to about 20 ms. The upgraded charge collector has modified switching circuitry and has utilized components that are carefully considered to mitigate the effect of transients. The resulting increase in SNR and improvement in bit resolution have thereby allowed measurement of Qtotal for extended confinement periods of up to 30 s.