Bremsstrahlung measurements in the near infrared on ASDEX

In the ASDEX Thomson scattering system the scattered light of a Nd:YAG laser beam (λ=1064 nm) is measured to obtain electron density and temperature profiles every 16 ms. The same system is continuously used to measure bremsstrahlung in the near infrared, allowing determination of radial Zeff profiles. Some characteristic examples of radiation and Zeff profiles are given. The time resolution of the detection system (≤50 kHz) is sufficiently high to observe fast MHD phenomena such as sawtooth instabilities around the q=1 surface and density fluctuations in the plasma edge. Furthermore, the diagnostic can also be used for real time control of the electron density. This applies in particular in cases where large sawteeth and pellet injection generate counting errors in the interferometer signal. The relation between the line density n and the central chord bremsstrahlung signal Ub was investigated for different heating scenarios in a wide density range