Space-resolved measurement of internal magnetic field in a bumpy torus by Li0-beam probe spectroscopy

Abstract

A new method combining Li0-beam probing and spectroscopic techniques has been developed to measure local magnetic fields in a bumpy torus. A collimated thermal Li0 beam is injected into the plasma. The Zeeman pattern of the lithium resonance radiation (22S–22P, 6708 Å) is observed with a Fabry–Perot interferometer. The strength of the local magnetic field is determined from the splitting between two π components of the 22S1/2–22P1/2 transition with the spatial resolution of about 7 mm. The magnetic fields from 2 to 4 kG were measured with accuracy of ±2%. This method is applicable to plasmas of a line-integrated electron density below 5×1012 cm−2.

Lithium Polarization Spectroscopy: Making Precision Plasma Current Measurements in the DIII-D National Fusion Facility

“…There are a number of ways to utilize these atomic properties to infer the local magnetic field components, and hence j, from the fluorescence emission. Prior analysis techniques have included linear polarization analysis of the collisional fluorescence [11,12] enhancement and polarization-dependent pumping using a resonant laser to induce fluorescence [13], line scanning and modulation of the circular polarization to identify parallel field components [14], and precision line profile intensity measurements to take advantage of the known sigma/pi variation with field direction [15,16]. In each case, the goal is to identify ratios of the various terms in Eq.…”

Diagnostics for current density and radial electric field measurements: overview and recent trends

“…For the measurement of the poloidal magnetic field and, hence, the current density one can make use of active Zeeman polarimetry, employing a diagnostic neutral lithium beam [122][123][124]. Such a system dedicated to current density measurements at the plasma edge is in preparation for the DIII-D plasma (see figure 13) [125].…”

Bumpy torus plasma confinement (NBT)

“…(d) The beta value of the hot-electron ring ranges from 3 to 6% at the present ECH power level. This value is smaller than the critical value needed to establish an MHD-stable configuration [8,[10][11][12][13]. The main factor limiting beta is considered to be the high-frequency oscillations due to the unstable hot-electron interchange mode, which are enhanced when the hotelectron density nh reaches the value 0.1-0.2 times n c , where n c is the background cold-electron density [8].…”