On the energy transport in internal transport barriers of RFP plasmas

Abstract

Single helical axis (SHAx) states obtained in high current reversed field pinch (RFP) plasmas feature an internal transport barrier delimiting the hot helical core region. The electron temperature jump across this region, and the related temperature gradient, display a clear relationship with the normalized amplitude of the secondary MHD modes. A transport analysis performed with the ASTRA code, taking into account the helical geometry, yields values of the thermal conductivity in the barrier region as low as 5 m2 s−1. The thermal conductivity is also related to the secondary mode amplitude. Since such amplitude is reduced when plasma current is increased, it is expected that higher current plasmas will display even steeper thermal gradients and hotter helical cores.

RFX-mod: A multi-configuration fusion facility for three-dimensional physics studies

“…This role of the secondary modes is confirmed also by transport analyses done with the ASTRA code. 34 As speculated above, this is likely due edge cooling due to uncontrolled PWI.…”

What is a Reversed Field Pinch?

“…In contrast the pinch-stellarator equation shows that no current is necessary in the highly resistive edge of a RFP to provide the reversal. This indicates that the decrease of the experimental V loop in RFP's might be obtained by a mere decrease of the resistivity inside the internal transport barrier, which might result from operation at higher currents [90].…”

“…It spans a significantly bigger volume than in Double Axis states [89], and the maximum electron temperature gradient at the internal transport barrier is a decreasing function of the amplitude of secondary modes [90]. Since this amplitude is reduced when plasma current is increased, it is expected that higher current plasmas will display even steeper thermal gradients and hotter helical cores.…”

Thermal transport dynamics in the quasi-single helicity state

“…Experimentally, plots of S(t) normalized to the edge magnetic field versus I p show a negative trend. 18 Figure 2 shows the normalized secondary mode amplitude from the dynamical model as a function of . Since the model does not account for an edge magnetic field, the secondary mode is normalized to the dominant mode.…”

“…The behavior of the augmented model is tested by comparison to the measurements carried out on RFX-mod. These include scalings of quantities like persistence and secondary mode amplitude with the plasma current 18 which, given the changes to model parameters introduced to ensure energy-conserving mode coupling and positive definite energies, need to be reevaluated.…”