  Absolute value measurements of turbulence amplitude in magnetically confined
high-temperature plasmas can effectively explain turbulence-driven transport
characteristics and their role in plasma confinements. Two-dimensional phase
contrast imaging (2D-PCI) is a technique to evaluate the space-time spectrum of
ion-scale electron density fluctuation. However, absolute value measurement of
turbulence amplitude has not been conducted owing to the nonlinearity of the
detector. In this study, the absolute measurement method proposed in the
previous study is applied to turbulence measurement results in the large
helical device. As a result, the localized turbulence amplitude at
$n_e=1.5\times 10^{19}$m$^{-3}$ is approximately $3.5\times 10^{15}$m$^{-3}$,
which is 0.02\% of the electron density. In addition, the evaluated poloidal
wavenumber spectrum is almost consistent, within a certain error range, the
spectrum being calculated using a nonlinear gyrokinetic simulation. This result
is the first to the best of our knowledge to quantitatively evaluate turbulence
amplitudes measured by 2D-PCI and compare with simulations.
