Observation of m/n=2/1 magnetic island on the foot point of electron internal transport barrier using soft x-ray CCD camera in the Large Helical Device

Abstract

The existence of m/n=2/1 magnetic islands in the plasma with an electron internal transport barrier (ITB) is identified in tangential soft x-ray emission images measured with a soft x-ray CCD camera using the Fourier-Bessel expansion reconstruction technique in the Large Helical Device. A clear m/n=2/1 magnetic island is observed in the discharge with ECRH and NBI in the direction antiparallel to the equivalent plasma current (counter-NBI), where the magnetic shear is expected to become small enough to cause the formation of a magnetic island. On the other hand, no magnetic island is observed in the ECRH and NBI in the direction parallel to the equivalent plasma current (co-NBI), where the magnetic shear is expected to be sufficiently high. © 2008 IOP Publishing Ltd.