Influence of antenna aiming on ECE in MAST

Abstract

The effect of the direction of the detected beam on the intensity of ECE is studied. It is found that the combined effects of the strong dependence of the conversion efficiencey of O mode at the plasma resonance on the direction of the incident wave and the partial screening of the beam waist by the MAST vessel wall, can be responsible for the weakening of ECE emission for some frequencies. The theoretical model for ECE data interpretation on MAST has been significantly improved. New features of the model are as follows: the quasioptical treatment of the receiving antenna, interference, polarization and screening effects of the vacuum window and collisional damping of EBWs in the peripheral plasma.

EBW simulation for MAST and NSTX experiments

“…This model is then used to interpret the experimental results from MAST and NSTX. EBW for ELM free H-modes in MAST suggests that the magnetic equilibrium determined by the EFIT code does not adequately represent the Bfield within the transport barrier [1]. Using the EBW signal for the reconstruction of the radial profile of the magnetic field, we determine a new equilibrium and see that the EBW simulation now yields better agreement with experimental results.…”

“…Thus only electron Bernstein waves (EBW), (modes not subject to a density limit), which mode convert into electromagnetic waves in the upper hybrid resonance region, can be responsible for the measured radiation [3]. The 3D plasma and antenna model was described in [1,4,5].…”

Chapter 3: Microwave Diagnostics

“…EBE radiometry via B-X-O and B-X conversion has also been studied on the Mega Amp Spherical Torus 97,98 MAST! between 16 and 60 GHz.…”

T e ( R , t ) measurements using electron Bernstein wave thermal emission on NSTX

“…6͒ is not EBW emission, but pickup from a nearby reflectometer source. Detailed three-dimensional ͑3D͒ EBW ray tracing and EBW emission simulations 4 will be employed to determine the B-X-O mode conversion efficiency, allowing the T e ͑R , t͒ profile to be measured from the evolution of the measured EBW emission spectrum. Experiments to study B-X-O mode conversion efficiency in H-mode plasmas in NSTX are planned for the near future.…”