Influence of transient behavior on the determination of the energy confinement time in a tokamak

Abstract

The disregard of fast processes (e.g., the L-H transition) in a tokamak plasma can lead to large errors in the determination of the energy confinement time τ_E. A major upgrade in the electromagnetic diagnostic system for the analysis of plasma parameters and in the collection system has made it possible to take into account the influence of the transient character of the radial profile and the value of the plasma current I _P as well as the stored energy W on the determination of τ_E from diamagnetic measurements and to investigate fast processes involved in the L-H transition. The energy confinement time τ_E is calculated from the equation τ _E=W/[U _PI_P-d/dt(LI ²_P /2)-dW/dt] where U _P is the plasma loop voltage (V), I _P is the plasma current (A), and L is the total internal inductance (H). The total inductance L of the plasma column has been determined from measurements of the quantity β _J+I _i/2, where β _J is the ratio between the gas-kinetic pressure and the pressure of the poloidal magnetic field, and I _i is the internal inductance. The inclusion of transient behavior in the determination of τ _E from diamagnetic measurements gives a correction of up to 50%.