Experimental study of density fluctuations in the STOR-M tokamak by small-angle microwave scattering

Density fluctuations in high temperature fusion plasmas have been a central challenge to the development of fusion power. They are the cause of excessive anomalous losses from the plasma and are still not fully understood. A microwave scattering experiment is performed on the Saskatchewan Torus-Modified (STOR-M) tokamak for the first time to study these density fluctuations with wave-numbers in the range |k| = 5 /cm to 10 /cm. The fluctuations are found to follow k⊥ρₛ scaling consistent with ion drift waves; signatures of the electron temperature gradient (ETG) mode connected with anomalous electron losses are not detected. The fluctuation level in the STOR-M is measured to be ñ/n ≈ 0.1 at a mean perpendicular wave-number of k⊥≈ 7 /cm and is reported for the first time. The fluctuation levels are inversely proportional to the energy confinement time suggesting that these fluctuations are driving anomalous particle and energy losses from the STOR-M. The system is now fully operational and this work paves the way for future experiments with this equipment.