1 LHCD Properties with a New Lower Hybrid Wave Antenna on HT-7 Tokamak Wei Wei,Guangli Kuang,Bojiang Ding,Weici Shen and HT-7 Team Institute of Plasma Physics, Chinese Academy of Sciences, Hefei , China HT-7 ASIPP

2 Abstract HT-7 ASIPP The structure and the characteristic power spectrum of a new lower hybrid wave antenna on HT-7 tokamak are briefly described in this paper. The main experimental properties with the new LHW antenna have been demonstrated by showing the dependences of drive efficiency and particle confinement time on the wave phase difference and plasma density: (1) The current drive efficiency shows a strong relation with ΔΦ, which is as follows (2)In density range of 1.0~1.5(×10 19 m -3 ), the driven efficiency increases with increasing n e. When n e =2.0×10 19 m -3, the driven efficiency in ΔΦ =0 0 case keeps on increasing while in 60 0 、 、 cases decreases. (3)Particle confinement is obviously improved by LHCD andτ p during the LHCD phase depends on ΔΦ, A relationship of betweenτ p and ΔΦ is achieved. (4) At the case of n e =1.0×10 19 m -3 、 1.5×10 19 m -3 、 2.0×10 19 m -3, τ p in n e =1.0×10 19 m -3 is the largest.

3 Introduction HT-7. Plenty of experimental results on HT-7 show that LHCD is an important auxiliary mean to achieve steady state operation of the tokamak and to obtain plasmas with improved confinements in the machine.. The power spectrum of the launched LHW plays a dominant role in the coupling of the wave into the plasma, such as, the propagation traces of the LHW, the LHW power deposition and the driven current profile, as well as the current drive efficiency and the plasma confinement.. The LHW antenna determines the power spectrum,so it is very important for the LHCD experiments.

4 Description of the new LHW antenna The new LHW antenna is a phase-controlled multi- junction grill coupler with 3 (row) 4(column) 4 sub-waveguides. Frequency: 2.45GHz Power: up to 1.2MW HT-7

5 The prominent advantage of the new antenna :. The uni-directionality of the power spectrum is enhanced.. It keeps the flexibility to adjust wave phase difference just as the traditional antenna.. It reduces the excessive dependence of power spectrum on the LHW phase-shift system because of the fixed phase difference between the sub-waveguides. The power spectrum of the new LHW antenna HT-7 ASIPP

6 Experiment Intention: In order to study the effect of phase difference and plasma density on current drive efficiency and plasma confinement, thereby increase the current drive efficiency and improve the plasma confinement. Main parameters: R=1.22m,a=0.27m,I p ≈150KA,B t ≈1.9T,P LH ≈320KW n e =1.0×10 19 m -3,1.5×10 19 m -3, 2.0×10 19 m -3 ΔΦ =0 0,60 0,120 0,180 0 i.e. N // =2.3, 2.7, 3.1, 3.5 HT-7

7 Current drive efficiency HT-7 Estimation : Experimental results: (1) (2) When n e = 1.0~1.5(×10 19 m -3 ), increases with the growth of n e ; When n e = 1.5~ 2.0 (×10 19 m -3 ), in ΔΦ =0 0 case keeps on increasing while in ΔΦ = 60 0 、 、 cases decreases.

8 The analysis of the experimental results (1)The dependence of on ΔΦ.With the increase of ΔΦ, more and more LHW beam interact with electrons near to the boundary plasma, Since the density and the temperature in the core plasma are higher than that in the edge region, the drive efficiency in ΔΦ =0 0 case is the largest and it decreases with the increasing ΔΦ..The higher temperature in ΔΦ =180 0 may be the possible factor leading to the higher drive efficiency in ΔΦ =180 0 than that in ΔΦ = HT-7

9 (2) The dependence of on n e LHW can propagate in the plasma only when it satisfies the accessibility condition : More edge electrons interact with the wave beams with large and more LHW power deposit outside the plasma when the plasma density is large,which leads to the decrease of driven current,so current drive efficiency in ΔΦ = 60 0 、 、 cases reduces when n e = 2.0 ×10 19 m -3. The wave beams with small mostly interact with the core electrons.Even if the plasma density increase, LHW power still deposit inside the plasma,so when n e = 2.0 ×10 19 m -3,current drive efficiency in ΔΦ = 0 0 case dose not reduce. HT-7 The analysis of the experimental results

10.The particle confinement is improved After the onset of LHW..τ p depends on ΔΦ during LHCD phase:.The variation of edge radial electric field due to the loss of fast electrons in LHCD phase, which leads to the suppression of the fluctuation of edge plasma. Particle confinement time HT-7

11 Summary. The current drive efficiency shows a strong relation with ΔΦ, which is as follows.. When n e = 1.0~1.5(×10 19 m -3 ), increases with the growth of n e ; When n e = 1.5~ 2.0×10 19 m -3, in ΔΦ =0 0 case keeps on increasing while in ΔΦ = 60 0 、 、 cases decreases.. Particle confinement is obviously improved by LHCD and τ p during the LHCD phase depends on ΔΦ. A relationship of betweenτ p and ΔΦ is achieved.. At the case of n e =1.0×10 19 m -3 、 1.5×10 19 m -3 、 2.0×10 19 m -3, τ p in n e =1.0×10 19 m -3 is the largest. HT-7 Some experimental properties with the new LHW antenna have been demonstrated by showing the dependences of drive efficiency and particle confinement time on ΔΦ and n e :

12 References HT-7 ASIPP [1]Kuang G.L. et al 1999 Nucl.Fusion [2]Xie J.K. et al 2001 Nucl.Fusion [3]Ding B.J. et al 2003 Nucl.Fusion [4]Song M. et al 2003 Chin.Phys.Lett [5]Wang M. et al 2003 Nucl.Fusion and Plasma.Phys [6]Ding B.J. Ph.D Thesis (Institute of Plasma Physics, Chinese Academy of Sciences, 2001). [7] Shi B.R. 《 Magnetic Confinement Fusion Principles and Practice 》 Nuclear Publishing House 1999 [8] Liu Y. et al 1998 Nucl.Fusion and Plasma.Phys