Improved confinement in the TPE-RX RFP by means of the PPCD

Abstract

Pulsed poloidal current drive (PPCD) (Sarff J S et al 1994 Phys. Rev. Lett. 72 3670) is conducted in a reversed-field pinch (RFP) machine, TPE-RX. The PPCD yields a twofold improvement of poloidal beta and energy confinement time. A quiescent phase is observed in the magnetic fluctuations, δb, during the PPCD. The result is discussed in terms of the change of the equilibrium configuration along the F -trajectory (F and are the reversal and pinch parameters, respectively). Representative mode amplitude is numerically simulated. The result indicates that a transient nature of the PPCD, where τ PPCD (characteristic time of the PPCD operation) τ D (0) (resistive diffusion time of the core) holds, allows a trajectory with a deeper F which yields a less turbulent configuration than shot-by-shot F -scans. It is shown that the improvement ratio of τ E approximately scales as δb −2 for five cases of the PPCD experiments in three RFP machines, including the present work in TPE-RX.

Current profile modification experiments in EXTRAP T2R

“…The time evolution of the central ion temperature in PPCD discharges is quite different from that of reference discharges. The ion temperature does not change during PPCD (as also observed in [1,4,6]), and it is around 130 eV as shown in figure 3(b). However, at the end of the PPCD phase the ion temperature increases quite rapidly up to 240 eV and then decays to the pre-PPCD value on the same timescale required for the restoration of the equilibrium.…”

“…During PPCD, the fluctuation level decreased and the energy confinement time increased. This technique has been gradually improved in later experiments in MST [2][3][4] and has also been successfully applied in the RFX [5] and TPE-RX [6] RFP experiments.…”

Microwave Imaging Reflectometry Experiment in TPE-RX

“…TPE-RX has the following operation modes [3]: standard RFP plasma, high-Θ plasma, PPCD plasma [13,14], and quasi-single helicity (QSH) plasma [15]. Here, F and Θ are the toroidal and poloidal fields, respectively, normalized by the average toroidal field at the plasma boundary, and are defined as…”

A novel feedback algorithm for simulating controlled dynamics and confinement in the advanced reversed-field pinch

“…[7][8][9][10][11] There are several schemes in the literature describing how to design the regulator. [7][8][9][10][11] There are several schemes in the literature describing how to design the regulator.…”