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高参数下 LHCD 与 IBW 协同 改善约束的实验研究

HT-7. Proposal for HT-7 2004 spring experiment. 高参数下 LHCD 与 IBW 协同 改善约束的实验研究. 丁伯江 赵燕平 单家方 匡光力. HT-7.  Motivation Possibility Synergetic mechanism of LHCD and IBW Obtained results on HT-7 tokamak  Experiment arrangement. Outline. HT-7. Motivation

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高参数下 LHCD 与 IBW 协同 改善约束的实验研究

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  1. HT-7 Proposal for HT-7 2004 spring experiment 高参数下LHCD与 IBW协同改善约束的实验研究 丁伯江 赵燕平 单家方 匡光力

  2. HT-7 • Motivation • Possibility • Synergetic mechanism of LHCD and IBW • Obtained results on HT-7 tokamak •  Experiment arrangement Outline

  3. HT-7 Motivation To extend HT-7 high performance with LHCD&IBW 利用LHCD & IBW 协同优化等离子体密度、温度、电流密度等参数的分布，以形成ITB( 增加等离子体体积）,实现尽可能高的等离子体约束运行(能量约束和粒子约束) 。为此，我们有目的地改变低杂波功率谱，使得低杂波的功率尽可能沉积在IBW的共振层附近，这样就可以在该区域驱动更大的等离子体电流，有可能形成中空的电流分布，即通常所说的反剪切位形，改善等离子体约束。

  4. HT-7 Possibility 低杂波的驱动效率直接依赖与等离子体的温度， IBW可以加热局部的等离子体温度（27MHz, 4200A时，IBW共振层对应在13cm左右），而低杂波的功率谱在一定范围内可以调节，完全有可能使低杂波的功率沉积在IBW共振层附近，从而有可能负剪切位形，改善等离子体约束。

  5. It(A) fIBW 3600 3800 4000 4200 HT-7 30 -18 -12.5 -6.7 -0.9 27 -6.7 -0.3 6.1 12.5 24 7.7 15 22.1 29.3 IBW对低杂波功率沉积分布的影响 HT-7tokamak不同纵场(A)、频率(MHz)时的2D共振层位置(cm)

  6. HT-7 Synergetic mechanism of LHCD and IBW IBW can modify the distribution function of the electrons by extracting the thermal electrons from the bulk distribution and accelerate them to contribution to the LHCD  IBW can sustain driven current, dissipating its energy on the parallel velocity of the asymmetric electron tail

  7. HT-7 Obtained results on HT-7 tokamak ---electron heating by IBW Global electron heating (left, f=27MHz, Bt=1.85T, r~3.4cm) and local electron heating (right, f=27MHz, Bt=2.0T, r~15.8cm) by IBW Revolution of oscillating IBW n// during the wave propagation along the trajectory IBW off-axis heating can modify the electron pressure profile B.N. Wan et al., Nucl. Fusion 43(2003)1279

  8. HT-7 Obtained results on HT-7 tokamak ---synergy of IBW and LHCD f=27MHz, Bt=2.0T (Global IBW electron heating ), N//peak=2.35 B.N. Wan et al., Nucl. Fusion 43(2003)1279

  9. HT-7 Experiment arrangement 实验方法： 改变纵场、IBW频率，移动IBW共振层的位置；改变低杂波波谱，优化低杂波功率沉积分布。 实验条件及参数: Ip~200kA, Ne~1.5, Te(0)~1.5keV PIBW~300-400kW, PLHW~300-400kW fIBW=27MHz, 30MHz, 24MHz It~3600,3800, 4000, 4200A 低杂波功率谱  (N//peak)=0 (2.35), 30(2.5),60(2.7),90 (2.9), 120（3.1),150 (3.25) ,180 (3.45) 希望需要配合的诊断： Te(r,t), Ti(r,t), Ne(r,t), HX(r,t), SX(r,t), W(t), li(t), Ha,AXUV(r,t), LP

  10. HT-7 Proposal for HT-7 2004 spring experiment 等离子体形状对低杂波耦合的影响 Effect of plasma shape on wave-plasma coupling 丁伯江 揭银先 高翔 张晓东 单家方

  11. HT-7 OUTLINE •  实验目的 •  实验背景 • 实验方法 • 预期结果

  12. HT-7 MOTIVATION • To investigate the effect of mismatch of plasma shape and LHW antenna on lower hybrid wave coupling • Try to solve this problem by gas puffing near the LHW antenna • To analyze the plasma behavior under these two conditions NOTE THAT this experiment is a pre-performance for EAST

  13. HT-7 可耦合条件 • LH波的可耦合条件： 在天线发射面处应满足： wp≥w0 forf0=2.45GHz 要求：ne≥7.44x1010cm-3

  14. 实验背景 r (cm) 28.0 27.0 26.0 25.0 24.0 23.0 22.0 HT-7 d (cm) 2.0 2.046 2.094 2.146 2.202 2.226 2.328

  15. HT-7 实验背景 理论研究表明天线端口附近的等离子体密度及其梯度是影响耦合效率的决定性因素。如果等离子体形状（最外层封闭磁面）与低杂波天线端口的形状基本吻合（即具有同样的曲率半径），则整个低杂波天线端口处于同一个磁面上，各处的密度相等，即反射系数基本差不多。在偏滤器位形等离子体（EAST）放电时，很难等离子体形状会经常发生变化，以致于等离子体形状很难与低杂波天线的曲率半径保持一致。等离子体形状的改变，导致等离子体的曲率半径亦发生变化，使得不同位置的磁力线长度不同，导致天线端口密度的不均匀性，使得各子波导的反射系数不一样。这种不平衡的反射使得低杂波在天线端口形成多次反射，影响波与等离子体的耦合。况且，距离太大，可能会导致天线端口的密度低于截止密度，增加低杂波的反射。

  16. HT-7 实验背景---JET

  17. HT-7 实验背景---JET

  18. HT-7 实验背景-Tore Supra

  19. 实验背景---HT-7 1.1x1013cm-3, 105KA, 135KW,D//扫描 等离子体位置扫描对耦合稍有影响（反射系数由4%增加到6.5%）, 但全程仍处于良好耦合之下

  20. HT-7 解决途径 为了解决由于曲率半径不匹配而引起的多次反射，在低杂波天线端口处充入可电离的气体，尽可能在天线端口处得到尽可能均匀的等离子体密度，且使其满足ne,grill, > ne,cut-off, 以提高波与等离子体的耦合效率。

  21. HT-7 实验方法: （1）通过移动极向活动石墨限制器来改变等离子体半径，然后改变等离子体水平位置保持等离子体和低杂波天线在赤道水平面上的距离dcp不变； （2）观察改变等离子体半径时上、中、下三排的反射系数； （3）通过喷气结构对天线周围喷射（gas puffing）CD4气体，再重复（1）、（2）的实验. 希望需要配合的诊断： Te(r,t), Ti(r,t), Ne(r,t), HX(r,t), SX(r,t), W(t), li(t), AXUV(r,t), Ha ,LP

  22. HT-7 实验预期结果 通过对天线周围喷射CD4气体来改善天线附近的等离子体密度，从而改善等离子体形状与低杂波天线不匹配时波与等离子体耦合状况； 可能得到LHCD情形下改善等离子体约束的一种新的途径； 有望为解决将来偏滤器位形的EAST因改变等离子体形状而引起的波与等离子体耦合问题进行探索和积累经验。

  23. HT-7 Proposal for HT-7 2004 spring experiment LHCD实现H-mode等离子体的实验研究 丁伯江 单家方 匡光力 ASIPP

  24. HT-7 Outline • Motivation • Improved confinement by LHCD a. Improved core plasma with an ITB b. Improved edge plasma • What is elicited from the results • Experiments arrangement ASIPP

  25. HT-7 Motivation 在HT-7上实现LHCD作用下的H-mode等离子体，分析形成H-mode等离子体的功率阈值。 HT-7实验结果(#46693)表明在LHCD的作用下，在等离子体芯部形成了ITB，能量约束时间从14.6ms（OH phase）增加到24.5ms （LHCD phase），相应的能量约束改善因子由0.78增加到1.42。在同样参数的情况下，Langmuir探针的测量结果也表明边缘等离子体约束得到了一定程度的改善，LHCD使得边缘的径向电场发生了变化。以上这些结果表明在HT-7上似乎有形成了H-mode、甚至Double Transport Barrier的迹象。但是，证据还不充分，尤其是缺乏边缘区域的等离子体参数。因此，进一步完善该部分工作是十分必要的。 ASIPP

  26. HT-7 A typical waveform of LHCD experiments (#46693)ne=1.51019m-3 , Ip=220kA, BT=2.0T, , N//peak=2.9 ,PLH =240kW. ASIPP

  27. HT-7 An ITB seems visible in the region around r/a ~ 0.55 Ion temperature profiles Electron temperature profiles ASIPP

  28. HT-7 Plasma density profile measured by the HCN laserThe electron density increases from 1.5 to 2.01019m-3 because of LHCD near the region of r/a~0.5. Also, the density profile broadens and the gradient becomes steeper in the outer region. ASIPP

  29. HT-7 Energy confinement time and H factor are improved by LHCDne=1.51019m-3 , Ip=220kA, BT=2.0T, N//peak=2.9 ,PLH =240kWphase I : E 14.6ms, EITER89P =18.7msphase II : E 24.5ms,EITER89P =17.2ms, EITER93ELM free=27ms The experimental energy confinement times during OH phase and during LHCD phase coincide with those predicated by EITER89P and EITER93ELM free, respectively. Phase I: H = 0.78 Phase II: H = 1.42 (H = E / EITER89P ) ASIPP

  30. HT-7 Power deposition and current density profile ASIPP

  31. HT-7 The magnetic shear modified by LHCD is thought to be an possible causality of confinement improvement a low magnetic shear is possibly formed because of the hollow current profile inside the surface of q=2 (r/a~0.8).Experiments described in early references show that a low magnetic shear inside the q=2 surface is favorable condition to form an ITB ASIPP

  32. HT-7 Signals of Langmuir probes (LCMS) before/after the onset of LHCD ASIPP Shot 46283 r = 27 cm Ne = 1.5 PLHCD= 240 kW

  33. HT-7 Edge fluctuations are suppressed by LHCD ASIPP

  34. HT-7 Edge fluctuations in the whole frequency region are suppressed by LHCD ASIPP

  35. HT-7 Particle and Heat Loss are greatly reduced after the onset of LHW Er and Vph are modified by LHCD ASIPP

  36. HT-7 Possible candidate for the improved edge plasma All of the above data indicate that turbulence and transport of edge plasma were suppressed, which suggests that edge plasma was improved due to LHW. WHY? Since the change of the poloidal propagation of the turbulence is nearly simultaneous with the evolution of the radial electric field, it may be regarded that the change of poloidal phase velocity of the turbulence is mainly resulted from the effect of ErxB. The electric radial electric is changed by LHW because of the energetic electrons loss. Due to the change of radial electric field, it is possible to form a sheared flow in the edge region. Therefore, the transport of the edge plasma might be reduced and the plasma confinement might be improved because of the poloidal sheared flow resulted from the varied radial electric field. ASIPP

  37. HT-7 What is elicited from the results 已有的实验数据表明： 由于LHCD的作用，很有可能在等离子体边缘存在pedestal结构, 即通常所说的H-mode. 甚至，可能存在Double-Transport Barrier （ITB and ETB)。但是，我们还缺乏足够的证据。 为此，我们打算测量LHCD情形下的边界等离子体参数的分布，包括温度分布、密度分布、和径向电场的分布等。 ASIPP

  38. HT-7 Experiment arrangement • 参照以前的放电条件（#46693, #46283），改变低杂波功率，观察边界等离子体参数分布的变化，以及等离子体芯部密度、温度分布的变化（ITB强度的变化）； • 改变低杂波功率谱，让低杂波主要沉积在边缘；同时改变功率，观察ITB位置和边界等离子体参数分布的变化 分析不同功率大小、不同功率谱时的 ITB的情形以及形成H-mode等离子体的功率阈值 ASIPP

  39. HT-7 Experiment condition and expected results 实验条件： Ip~220kA, Bt=2.0T, Ne~1.5,Te(0)~1.5keV, Plhw~150~400kW 低杂波功率谱  (N//peak)=60(2.7),90 (2.9), 120（3.1),150 (3.25) 预期结果： 在HT-7上实现LHCD作用下的H-mode等离子体，得到形成H-mode等离子体的功率阈值。 • 希望需要配合的诊断： • Te(r,t), Ti(r,t), Ne(r,t), HX(r,t), SX(r,t), W(t), li(t), Ha,AXUV(r,t), LP ASIPP

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