Simulation of the VUV spectral emission from the JT-60SA divertor

A divertor survey dual-spectrometer is being designed by an EU-Japan team [1] to be installed on JT-60SA [2], the new fusion experiment expected to start operating in 2020. Positioned on an upper port, the primary role of the spectrometer is to analyse the radiation losses in the divertor region and to aid studying the physics of the divertor plasmas, including plasma detachment. Its spatial resolution capability is around 10 cm at the divertor and its two branches together cover the wavelength range from 10 to 130 nm, to satisfy the physics scope [3]. The spectrometer Lines Of Sight (LOS) are mapped onto a 2D SOLEDGE [4] simulations of the divertor region carried out for different density levels of the JT-60SA scenario #2 (Single Null – 5.5 MA, 2.25 T, 41 MW of input power [3]). The electron temperature, electron density and impurity profiles (intrinsic C and injected Ne or Ar) along the spectrometer LOS are turned into LOS-integrated emissivities of spectral lines using the ADAS atomic database [5]. In the simulations the inner divertor is easily detatched, even in absence of seeding impurities, while the outer divertor requires large amounts of extrinsic radiating species to reach the detachment conditions. The spectral features are to some extent the result of the transport assumed in the simulations. In the real experiment the emission spectra will viceversa provide constraints to the simulations to investigate the underlying plasma transport.