The ultra-soft x-ray multilayer mirror-based duochromator for the reverse field experiment reversed field pinch experiment

The transport of injected impurities is investigated in the multiple helicity (MH) and improved confinement quasi single helicity (QSH) magnetic regimes of RFX-mod reversedfield pinch. Impurities are introduced through injections of room temperature pellets of carbon (in MH and QSH) and lithium (in MH). Simulation of experimental spectroscopic measurements, including line and soft x-rays emission, electron density and radiated power is carried out with a 1D collisional-radiative impurity transport code, allowing to determine the transport parameters: diffusion coefficient and convective velocity. The transport coefficients were found close to those deduced in previous experiments through the introduction of Ni and Ne, confirming the existence of an external velocity barrier also for light impurities.

“…The total radiated power is measured by a multichord bolometer [17]. Brightness of C VI 33.7 Å and O VII 21.7 Å lines is measured by a multi-layer mirror spectrometer [18].…”

Section: Experimental Set-upmentioning

confidence: 99%

Light impurity transport studies with solid pellet injections in the RFX-mod reversed-field pinch

Barbui¹,

Carraro²,

Franz³

et al. 2014

“…The line emissivities of He-like and H-like states of carbon are routinely measured by an XUV extreme grazing incidence spectrometer [17] absolutely calibrated via the branching ratio technique [18]. The emission of the O He-like resonance line is observed by means of a multi-layer mirror (MLM) system [19] absolutely calibrated via the branching ratio.…”

Section: Experimental Set-up and Simulation Modelmentioning

confidence: 99%

Impurity transport during pulsed poloidal current drive experiment in the reversed field pinch experiment RFX

Carraro¹,

Puiatti²,

Sattin³

et al. 2002

The characteristics of the impurity transport in the RFX reversed field pinch experiment during enhanced confinement regimes, such as those obtained performing pulsed poloidal current drive and oscillating poloidal current drive, have been investigated. It is found that during the enhanced confinement period, the ratio between the Ly α line of C VI and the resonance line of C V increases systematically well beyond the expected enhancement due to the temperature improvement.Experimental data have been reproduced by means of a one-dimensional, time dependent, collisional-radiative impurity transport code, which simulates several C and O lines, continuum emission and radiated power. In standard RFX plasmas the typical diffusion coefficient is ∼20 m 2 s −1 at the plasma centre decreasing to ∼1 m 2 s −1 at the edge. Best simulations of the spectroscopic data during the enhancement confinement phases are obtained by expanding the low diffusion region at the edge from r/a = 0.9 to r/a = 0.8 ± 0.05 and shrinking the neutral density profile at the edge.

“…The emission of the O He-like resonance line is evaluated by means of a multi-layer mirror (MLM) system [7] absolutely calibrated via the branching ratio. A survey between 100 and 1110 Å is routinely provided by a 71 • grazing incidence flat field spectrometer (SPRED) [8] with the purpose of monitoring the impurities in RFX; an example of the collected spectrum is shown in figure 2.…”

Section: Experimental Set-upmentioning

confidence: 99%

Reconstruction of the radiation emitted by the intrinsic impurities in the RFX reversed field pinch

Carraro¹,

Costa²,

Puiatti³

et al. 2000

Experimental data concerning line, continuum radiation and total radiated power emitted by the intrinsic impurities (carbon and oxygen) in the RFX reversed field pinch have been reproduced with a one-dimensional time-dependent collisional radiative impurity diffusion model. The reconstruction has been performed both in discharges with fixed current at different densities and with different currents at fixed density. The results of the model confirm the relatively low Z eff values measured in RFX at all current levels, despite the high power flow to the wall.A diffusion coefficient of 20 m 2 s −1 at the centre of the plasma, decreasing to 1 m 2 s −1 at the edge, and a pinch velocity which is outwardly directed in the central region and inward at the edge have to be used to simulate the experimental data. The diffusion coefficient behaviour deduced for light impurities is coherent with the transport properties deduced for the main plasma species and is consistent with a plasma in which the confinement region is localized at the edge, where strong density gradients have been observed; the pinch velocity profile characteristics agree with the plasma radial flow resulting from three-dimensional nonlinear MHD codes.