Improvement of the Laser Beam Pointing Stability for EAST Thomson Scattering Diagnostic

摘要

Thomson scattering diagnostic, measuring the spatial profiles of the electron temperature and density in fusion plasma, is one of the most important diagnostic on tokomaks. The accuracy of its results could be strongly impacted by the stability of the laser beam passing plasma. However, the stability of the laser beam pointing is influenced by many factors. On experimental advanced superconducting tokamak (EAST), the laser beam of Thomson scattering diagnostic (1,064 nm wavelength, 10 ns pulses, 10-50 Hz repetition rate) traverses a network of 7 mirrors approximately 35 m before enters the vacuum chamber. To ensure that the laser beam transports stably and accurately, vibration isolation platforms and a remote supervisory and control system for laser alignment are built. The vibration isolation platforms could mitigate the impact of external vibrations in the beam path. And by using the remote supervisory and control system, misalignments will be found and corrected in time. With these renovations, the beam pointing stability of EAST Thomson scattering diagnostic can be improved from about 120 to 10 urad successfully.