Compressional Alfven and ion-ion hybrid waves in tokamak plasmas with two ion species

• Compressional Alfven and ion-ion hybrid waves excited by energetic beam ions are studied in plasmas with two ion species. In our experiment, a hydrogen-deuterium (H-D) plasma is used to produce instabilities similar to those likely to be present in the burning deuterium-tritium plasmas of future tokamaks. Modes are suppressed in the deuterium cyclotron frequency range with increasing hydrogen gas puffing. In plasmas with H/D concentrations of 2.57 or higher, short-lived modes with small and predominantly negative toroidal mode numbers are observed at frequencies omega/omega(beta D0) approximate to 2.25, where omega(beta D0) = omega(beta D0)(R-0) is the on-axis deuterium cyclotron frequency. These are the highest mode frequencies yet detected in the ion cyclotron range in a spherical tokamak. Modeling of the transparency regions and plasma resonances using the cold plasma dispersion relation explains the observed features. Mode conversion at ion-ion hybrid resonances and subsequent kinetic damping is believed to be responsible for mode suppression. The high frequency modes are present due to excitation by wave-particle resonances within the transparency region for high hydrogen concentrations. The absence of other wave-particle resonances explains significant features of our experiment. This technique has possible applications in plasma heating, current drive and real-time diagnosis of relative ion concentration in the plasma core.

Subject headings

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Keyword

alfven waves

tokamaks

multi-component and negative-ion waves

Publication and Content Type

ref (subject category)

art (subject category)