Temporally resolved plasma composition measurements by collective Thomson scattering in TEXTOR (invited)

Abstract

Fusion plasma composition measurements by collective Thomson scattering (CTS) were demonstrated in recent proof-of-principle measurements in TEXTOR [S. B. Korsholm et al., Phys. Rev. Lett. 106, 165004 (2011)]. Such measurements rely on the ability to resolve and interpret ion cyclotron structure in CTS spectra. Here, we extend these techniques to enable temporally resolved plasma composition measurements by CTS in TEXTOR, and we discuss the prospect for such measurements with newly installed hardware upgrades for the CTS system on ASDEX Upgrade.

Recent development of collective Thomson scattering for magnetically confined fusion plasmas

“…A systematic study of the possibility for such a diagnostic on ITER has been performed [14] and the technique is an obvious candidate for a diagnostic on ITER. …”

“…These measurements are particularly relevant for stellarator devices due to the general difficulty in diagnosing ion temperatures at high electron densities. In tokamas such measurements have been demonstrated on the TEXTOR and the ASDEX Upgrade devices [14,15]. Presently, bulk ion CTS measurements are also being made at the stellarator LHD [16] and the tokamak FTU [17].…”

Resolving the bulk ion region of millimeter-wave collective Thomson scattering spectra at ASDEX Upgrade

“…The shape and relative size of peaks in the ion cyclotron structures are highly sensitive to the density ratios of the corresponding ion species. Measurements of ion cyclotron structures were demonstrated as a plasma composition and ion temperature diagnostic on TEXTOR [30][31][32][33] and have been suggested as a possible fuel ion ratio diagnostic for ITER 35,42 . Resolving these features in the CTS spectra is therefore an important goal for the fast receiver system on AUG. Figure 14 compares CTS spectra from discharges with different plasma compositions.…”

“…Detailed interpretation of the measured spectra to infer the actual plasma temperature and composition requires fitting with a theoretical model for the CTS spectrum 30,32,33 , which is beyond the scope of the work presented here.…”

“…Signatures of the ion cyclotron motion and ion Bernstein waves are of particular interest for their sensitivity to ion density ratios. This has been used for measurements of the isotopic composition [30][31][32][33][34] , and it could potentially be exploited for measurements of the fuel ion ratio in burning DT-plasmas 35,36 . However, accessing the detailed information contained in the bulk ion region of CTS spectra requires a frequency resolution beyond what is generally achieved with the cavity filters commonly used for fast-ion measurements.…”