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Spectroscopic investigations of the ion source at BATMAN upgrade

2018; American Institute of Physics; Linguagem: Inglês

10.1063/1.5083739

1935-0465

Plasma Diagnostics and Applications

The steady improvement of the analysis of atomic and molecular hydrogen emissivities together with the possibility to apply a high-resolution spectrometer motivated repeating at BATMAN Upgrade the detailed optical emission spectroscopy investigations performed at the BATMAN test facility in 2006. Although the test facility as a whole was upgraded, the RF-driven prototype source for the ITER NBI systems basically remained the same. The measurements were carried out in the first operation phase of BATMAN Upgrade i.e. in hydrogen in the volume operation mode of the negative ion source. The previously measured gas temperature of 1000 K in the driver, increasing to about 1200 K towards the grid is now determined to be 630 K in the whole source. Moreover, by evaluating now 12 rotational lines of the molecular Fulcher-α radiation instead of five, the presence of a two-temperature rotational distribution is demonstrated, revealing a hot ensemble with a temperature of about 4300 K. For the line of sight through the driver and the one parallel to the grid, the evaluation of the electron density and temperature showed similar values and trends as in the campaign of 2006. The third line of sight observes the expansion region and gives access, for the first time, to the plasma parameters in this region. Dependencies on the variation of the magnetic filter field strength and its topology are observed. The density ratio of atomic to molecular hydrogen is about 0.3 in all source regions, revealing no pronounced dependence on the filter field; however, due to the complex analysis procedure, the uncertainties are quite high for this parameter.