Separation of β̄_pand ℓ_iin tokamaks of non-circular cross-section

Abstract

Integral relations for the average poloidal beta J3 p and the plasma internal inductance 8j are derived from the magnetohydrodynamic (MHD) equilibrium equation for an axisymmetric torus. The volumedependent parameters that appear depend only weakly on the actual current density distribution inside the plasma and can be evaluated approximately, given the plasma shape and boundary poloidal magnetic field. In practice, these can be accurately and efficiently obtained for both diverted and limited plasmas from measured external poloidal magnetic field and flux values by approximating the plasma current distribution using a few filaments or distributed sources. For a tokamak plasma with a non-circular cross-section of sufficient elongation, J3 p and 8j can then be approximately determined separately. This is demonstrated for analytic equilibria of known shape as well as for actual Doublet III (D-III) plasmas for which /3 p and Z{ have been determined by using other methods. Results of a sensitivity study are described.

Optimization of the active MHD spectroscopy system on JET for the excitation of individual intermediate and high-n Alfvén eigenmodes

“…We note here the sensitive dependence of the antenna coupling to the n = 4 mode on the plasma profiles in these otherwise very stable plasma conditions: by comparing the successive scans of the n = 4 resonance at Here, k is the elongation and q is the safety factor, T e is the electron temperature and n e is the electron density, with the suffixes '0' and '95' indicating core and edge values respectively. The value of q 0 comes from standard EFIT [20] equilibrium reconstruction and its value has been adjusted by 11% to match the MSE-constrained equilibrium reconstruction at t = 6 s and the time of the appearance of sawteeth on the ECE temperature measurements in the plasma core at t = 4.9 s. t = 8.25, 8.75 and 9.55 s in figure 5, one observes a gradual increase both in in the mode amplitude and the number of time points that are resolved into a n = 4 mode. Damping rate measurements of lower-n AEs are also shown, namely with n = ±2 and n = 0.…”

Progress towards steady state at low aspect ratio on the National Spherical Torus Experiment (NSTX)

“…This capability has been used to make a quantitative comparison between the measured and expected plasma current profiles using a method first described in [22]. Shown in figure 6 are the total plasma current profile as determined by the MSE measurement and reconstructed by the EFIT [23] equilibrium reconstruction code. Also plotted in the figure is (1) the neutral beam driven current as calculated by the TRANSP code [24], (2) the neoclassical pressure driven currents according to a recent calculation that includes corrections important at low aspect ratio [25] and (3) the inductively driven current calculated according to the inferred time varying toroidal electric field as calculated by taking the time derivative of the flux from the equilibrium reconstructions multiplied by the calculated neoclassical resistivity.…”

Use of a twisted 3D Cauchy condition surface to reconstruct the last closed magnetic surface in a non-axisymmetric fusion plasma

“…This idea enables one to obtain accurate solutions of the boundary shape with a smaller amount of data than in the parameterization. One of such methods [3,4] uses a small number of current "filaments" assumed at fixed positions within the plasma. The currents in these filaments are then computed in such a way that one obtains the best fit to the measured magnetic fluxes and fields.…”