Using bremsstrahlung for electron density estimation and correction in EAST tokamak

• The visible bremsstrahlung diagnostic provides a simple and effective tool for electron density estimation in steady state discharges.
• This method can make up some disadvantages of present FIR and TS diagnostics in EAST tokamak.
• Line averaged electron density has been deduced from central VB signal. The results can also be used for FIR ne correction.
• Typical ne profiles have been obtained with Te and reconstructed bremsstrahlung profiles.

In EAST electron density (ne) is measured by the multi-channel far-infrared (FIR) hydrogen cyanide (HCN) interferometer and Thomson scattering (TS) diagnostics. However, it is difficult to obtain accurate ne profile for that there are many problems existing in current electron density diagnostics. Since the visible bremsstrahlung (VB) emission coefficient has a strong dependence on electron density, the visible bremsstrahlung measurement system developed to determine the ion effective charge (Zeff) may also be used for ne estimation via inverse operations. With assumption that Zeff has a flat profile and does not change significantly in steady state discharges, line averaged electron density (n¯e) has been deduced from VB signals in L-mode and H-mode discharges in EAST. The results are in good coincidence with n¯e from FIR, which proves that VB measurement is an effective tool for ne estimation. VB diagnostic is also applied to n¯e correction when FIR n¯e is wrong for the laser phase shift reversal together with noise causes errors when electron density changed rapidly in the H-mode discharges. Typical ne profiles in L-mode and H-mode phase are also deduced with reconstructed bremsstrahlung profiles.