Turbulence and transport measurements with cold and emissive probes in ISTTOK

Abstract

A probe array consisting of three emissive probes and one cold cylindrical probe was developed for edge plasma measurements in ISTTOK. Emissive probes are particularly suitable for turbulence studies as they are able to deliver a more accurate measure of the plasma potential by reducing the effect of temperature fluctuations. The probe array has the advantage of recording the density, the electric field and their fluctuations simultaneously. Radial plasma profiles were recorded with and without negative edge biasing by an emissive electrode. The statistical properties of the poloidal electric field and of the turbulent particle flux, measured with cold and emissive probes, were compared. Both the root mean square of the poloidal electric field and the fluctuation-induced particle flux were found to be significantly larger when measured with the emissive probes, indicating that temperature fluctuations are important for the measurement of the particle flux. The probability distribution of the particle flux was also found to be more peaked and asymmetric when measured with the emissive probes.

The Use of Emissive Probes in Laboratory and Tokamak Plasmas

“…1). It has turned out that in particular the fluctuations of T e and their phase have a strong influence on V fl [3].…”

“…[1,2]), while fluctuating electric fields are the main cause of radial transport phenomena in magnetized plasmas of tokamaks (see e.g. [3,4]). …”

“…This is often justified, except there are strong temperature fluctuations, which is frequently the case in the edge region of toroidal plasmas. Then this assumption is very questionable [3].…”

Ball‐Pen Probe Measurements in L‐Mode and H‐Mode on ASDEX Upgrade

“…The same theoretical assumption is also used in the case of the emissive probe [6]. In the midsize tokamak ASDEX Upgrade an array of BPPs was used for the first time.…”

Simulation of a Planar Emissive Probe in a Mid‐Sized Tokamak Plasma

“…The latter can also be affected by a strong oblique magnetic field always present in such devices. However, some successful experiments were finally carried out [6]. In our research we addressed the issue of the feasibility of use of emissive probes in plasmas similar to plasma of smaller tokamaks such as ASDEX-UPGRADE, COMPASS-D, CASTOR.…”