  Systematic uncertainties in accelerator oscillation neutrino experiments
arise mostly from nuclear models describing neutrino-nucleus interactions. To
mitigate these uncertainties, we can study neutrino-nuclei interactions with
detectors possessing enhanced hadron detection capabilities at energies below
the nuclear Fermi level. Gaseous detectors not only lower the particle
detection threshold but also enable the investigation of nuclear effects on
various nuclei by allowing for changes in the gas composition. This approach
provides valuable insights into the modelling of neutrino-nucleus interactions
and significantly reduces associated uncertainties. Here, we discuss the design
and first operation of a gaseous argon time projection chamber optically read.
The detector operates at atmospheric pressure and features a single stage of
electron amplification based on a thick GEM. Here, photons are produced with
wavelengths in the vacuum ultraviolet regime. In an optical detector the
primary constraint is the light yield. This study explores the possibility of
increasing the light yield by applying a low electric field downstream of the
ThGEM. In this region, called the electroluminescence gap, electrons propagate
and excite the argon atoms, leading to the subsequent emission of photons. This
process occurs without any further electron amplification, and it is
demonstrated that the total light yield increases up to three times by applying
moderate electric fields of the order of 3~kV/cm. Finally, an indirect method
is discussed for determining the photon yield per charge gain of a ThGEM,
giving a value of 18.3 photons detected per secondary electron.
