Fast dynamics of radiofrequency emission in FTU plasmas with runaway electrons

Abstract

Radiofrequency emission in the 0.4-3 GHz range from FTU tokamak in presence of runaway electrons (REs) has been measured in various plasma regimes. Rapid emission bursts associated with enhanced RE pitch-angle scattering reveal kinetic instabilities affecting evolution of the RE population from the buildup phase. Such measurements also provide a sensitive monitor for instabilities during early RE formation. The leading edge of radio bursts is much shorter than interleaving periods of low emission; spectral broadening during growth indicates nonlinear wave coupling as an explanation for the observed intermittency. Both broadband and coherent spectra have been observed. Radio emission disappears at the beginning of post-disruption RE plateaus, and subsequently reappears in the shape of very intense bursts accompanied by macroscopic magnetic perturbations.

Results on quiescent and post-disruption runaway electrons studies at Frascati Tokamak Upgrade: RE mitigation via solid deuterium pellets and anomalous Doppler instability

“…To further support the increase of background temperature following ADI, we show the analysis of SPRED spectrometer [42] in the UV range (100-1700 Å) revealing that the series of ADI in the shot #42648, between 0.5 s and 0.6 s, have increased the background temperature over 200 eV in order to ionize the iron injected at 0.9 s and whose line intensity is shown in figure 14. Although Thomson-scattering data are corrupted with consistent RE population, a temperature above 1 keV is measured at 0.85 s when NE123 is below 8 × 10 11 , a value that is associated to a modest RE population.…”

Колебания В Промежуточном Диапазоне Частот В Омическом Разряде Токамака Фт-2

“…Эти электроны являются источником синхротронного излучения при частотах от 30 GHz и выше, они же дают свой вклад в частотные спектры при самой малой плотности (рис. 6, a) [9]. Описываемые здесь колебания лежат в области более низких, так называемых нижнегибридных (НГ) частот, < 1 GHz.…”

“…Возможно, это излучение может приводить к раскачке цепочки параметрических распадных неустойчивостей, существенно понижающих частоты излучения [15]. К подобному объяснению склоняются авторы работ [8,9].…”

“…В настоящей работе описываются интенсивные радиочастотные колебания, обнаруженные в промежуточном диапазоне частот (100−1000) MHz в чисто омическом разряде в отсутствие ВЧ мощности. Подобное излучение, но в диапазоне (0.6−1.5) GHz, наблюдалось в режимах с низкой плотностью и убегающими электронами в токамаке FTU (Фраскатти) [8,9].…”

Overview of the COMPASS results *

“…During the last dedicated RE campaign (Nov-Dec 2020) various types of instabilities that can be excited or driven by REs [36,55] with certain energy were studied with a set of four antennas, jointly with similar experiments performed at the Frascati Tokamak Upgrade (FTU) [56]. Two loop antennas (11 × 11 cm) placed in the midplane radial ports opposite to each other and two external antennas (twin loop and a logarithmic antenna) localized in front of the vacuum windows of ports with in-vessel antennas were acquiring signal with tunable sampling frequency from several hundreds of MHz up to 12.5 GHz.…”