Study of impurity transport in HL-2A ECRH L-mode plasmas with radially different ECRH power depositions

• Published in: Nuclear fusion 2018-05, Vol.58 (5), p.56012
• Main Authors: Cui, Z.Y., Zhang, K., Morita, S., Ji, X.Q., Ding, X.T., Xu, Y., Sun, P., Gao, J.M., Dong, C.F., Zheng, D.L., Li, Y.G., Jiang, M., Li, D., Zhong, W.L., Liu, Yi, Dong, Y.B., Song, S.D., Yu, L.M., Shi, Z.B., Fu, B.Z., Lu, P., Huang, M., Yuan, B.S., Yang, Q.W., Duan, X.R.
• Format: Article
• Language: English
• Subjects: ECRH; impurity transport; LBO; MHD instability; numerical simulation
• ISSN: 0029-5515; 1741-4326
• DOI: 10.1088/1741-4326/aab166

In HL-2A, an inverse sawtooth oscillation is observed with a long-lasting m/n  =  1/1 mode during ECRH phase with power deposition inside sawtooth inversion radius (inner-deposited ECRH), while a normal sawtooth instead appears when the ECRH power is deposited outside sawtooth inversion radius (outer-deposited ECRH). Aluminum is then injected as a trace impurity with laser blow-off (LBO) method into the inner- and outer-deposited ECRH phases of HL-2A discharges to investigate the effect of ECRH on impurity transport. Temporal behavior of soft x-ray (SXR) array signals is analyzed with a 1D impurity transport code, and radial structures of impurity transport coefficients are obtained. The result shows that the radial transport of Al ions is strongly enhanced during the inner-deposited ECRH phase. In particular, an outward convection velocity is developed with positive values of 0     V(ρ)     3.8 m s−1 in ρ     0.5, while the convection velocity is inward in ρ     0.6. In the outer-deposited ECRH discharge, on the other hand, the convection velocity takes a big negative value in ρ     0.4 and close to zero at ρ ~ 0.6. In ohmic discharges, an inward V(ρ) always appears in the whole plasma radii and gradually increases toward the plasma edge (−3.2 m s−1 at ρ  =  1). The simulation result also indicates that centrally-peaked Al ion density profiles presented in the outer-deposited ECRH discharge can be flattened by the inner-deposited ECRH. Modification of impurity transport is discussed in the presence of long-lasting m/n  =  1/1 MHD mode.