Proposal of LHCD & fast electron behaviors study on HT -7 Exp2005

1. ASIPP Proposal of LHCD & fast electron behaviors study on HT -7 Exp2005 PHA team Email: czy1003@ipp.ac.cn

2. Motivation • 低杂波电流驱动（LHCD）实验是托卡马克非感应电流驱动的重要手段，也是调节电流密度剖面，实现先进位形（如反剪切）和实现长脉冲稳态运行的重要工具，实验中还发现了其改善约束，抑制sawtooth，m＝1模的现象。 • HT－7上已经开展了多轮LHCD实验，并获得了丰富的物理结果。在HT－7上深入研究LHCD下的快电子行为是为EAST的稳态先进运行模式打下基础,也是LHCD反馈控制电流密度和q profile的基础。 • 低杂波电流驱动的驱动效率，功率沉积剖面，以及快电子与剩余环电压之间的作用有丰富的物理内容，对其进行深入研究有利于我们理解低杂波和等离子体之间的物理过程，以及为LHCD反馈控制实验奠定基础。

3. Diagnostics and functions • FEB Camera The energy range of fast electrons build up by the LHW, and DC field Fast electrons distribution function，LH wave power deposition profile Propagation, absorption of the LH waves Details of momentum dynamics and the relativistic angular anisotropy slow down，confinement, relaxation and oscillation behaviors of fast electron • Runaway electron spectrometer The energy range of runaway electrons，generation，evolution provide confidence for FEB signals • SX_PHA (S.Y.LIN) Te profile and metallic impurities content • li（B.Shen, X.Q.Zhang）

4. Upgrade of FEB camera(vertical array) Improved one-way CdTe detection system Lay out of sight lines Old detector with T039 house Vertical 15-channel Measuring range: + 27 cm Spatial resolution : 5 cm

5. Upgrade of FEB camera(toroidal array) • 正向 14道，分辨率：5cm 测量范围：－25～+30cm • 反向 5道，分辨率：10cm 测量范围： －16～+24cm 电流方向 切向硬X射线诊断示意图

6. HT－7上逃逸电子诊断 NaI探测器(40*40),测量范围：0.3～10MeV • 正向 2道，一道正对真空室内壁，一道对等离子体中心 • 反向 1道，分辨率：10cm 测量范围： －16～+24cm 正向一道CdTe探测器(65mm3)

7. Exp2005 related with FEB • Fast electron dynamics • Slow down time, confinement time, • Oscillation behavior in sawtooth activity plasma • 2. LHCD efficiency with IBW heating plasma • Comparison of experimental data in current ramp-up/down with Karney-Fisch curves • Runaway electron dynamics • Searching LHEP mode on HT-7

8. 快电子的辐射分布 HT－7上低杂波与等离子体作用（ELD）产生的快电子能量在30keV～100keV，如果存在电场，能量可以达几十MeV。高能快电子辐射的硬X射线具有空间不均匀性，辐射主要集中于电子运动方向。已有的极向硬X射线诊断对环向这种不均匀辐射不敏感，只有沿电子运动方向进行观测才可以得到准确的硬X射线能谱。通过FEB Camera测量其发射的硬X射线，我们得到快电子的信息。

9. 快电子分布模型 三温分布可调节的参数： T , T//F, T//B,, pc, 分别是垂直光温，前向光温，反向光温，截止动量 对LHCD，通常有 T//F>>T//B, T ;T～ T//B， Pc由低杂波的波谱n//决定，但是存在环电压的时候Pc可以更高 • 三温分布模型 三温模型一维平行动量分布图

10. FEB sawtooth Possible explains for FEB inverted sawtooth: • During internal disruption, runaway electrons travel from q=1 surface to the limiter, producing thick-target bremsstralung emissions. • Internal disruption give rise to perturbation, fast electrons were redistributed during internal disruption. • Resulting from changes in the current profile that shift the drift orbit displacement of the runaway electrons at the edge of the plasma

11. Relation of current profile with HXR profile • , If collisional slowing down time prevails on radial diffusion, transport of parallel momentum across field lines is small, and the radial LH current profile matches that of the LH power deposition, with a possible minor broadening due to radial transport. And fast electron confinement time is approximately given by average of over the plasma volume, . Or else, the HXR profile cann’t be used to estimated the current profile. • , parallel momentum is transported radially before its destruction be Coulomb collisions, leading to a decoupling between the power deposition and LH current profile. , and the CD efficiency value is smaller than theory prediction. It is important to determine the LHW power deposition profile in HT-7. Last experiment on this point has failed due to the generated runaway electrons in LHW turn off phase. Slow down time and power profile.

12. FEB spectrum • Fast electron dynamics during OH free • Fast electron dynamics with partial current drive by LHW( different loop voltage) • Fast electron dynamics during pellet injection

13. Exp2005 related with FEB • Fast electron dynamics • LHCD efficiency with IBW heating plasma • Comparison of experimental data in current ramp-up/down with Karney-Fisch curves • Runaway electron dynamics • Searching LHEP mode on HT-7

14. LHCD实验结果 快电子的约束与能量损失 JT-60

15. CD efficiency with non-zero loop voltage (v) can be well derived when the 0 and 1 have been obtained. Hot conductivity theory Ip=126kA ne=1.45*1019m-3

16. Parameter dependence of CD efficiency Dependence of the current drive efficiency with plasma density. LH wave with phase of 0º, there exist a density range for higher current drive efficiency Dependence of the current drive efficiency on LH wave n//

17. The fast electron hot conductivity can be determined as a by-product from the 1. From the defining of , the hot conductivity can be determined: This need the Rsp to be determined accurately. One of ways to determine it is to obtain the current decay time, 测量方法：当电流到达平顶端时，关断OH场，让电流自由衰减，其复合指数函数衰减，根据衰减时间，和等离子体电感，我们可以得到等离子体电阻，大约是几个微欧。

18. Synergy effect of LHCD and IBW has been observed in HT-7. Such as high performance, H mode… Global CD efficiency may be improved in combination of LHCD with IBW heating. Local CD efficiency has be improved combination of IBW heating. Investigating the CD efficiency with IBW heating plasma, which may give valuable information on the volume averaged temperature dependence for HT-7 plasma Scan IBW Power(kW): 100, 200, 300, 400 … HT-7 data

19. Exp2005 related with FEB • Fast electron distribution function(Three temperature model) • LHCD efficiency with IBW heating plasma • Comparison of experimental data in current ramp-up/down with Karney-Fisch curves • Runaway electron dynamics • Searching LHEP mode on HT-7

20. LI2/2 Pext Bulk V2/Rsp PH Pel Hot electron Pabs=Prf (1- )Prf Prf Model (2)－K-F curve Power flow in LHCD experiments Karney-Fisch curve vs Pel=VloopIrf , Pabs=aPinjected , nabs=bn//0 VR is the run away velocity These inefficiency arise for some reasons: a fraction for the rf energy may be launched in the wrong direction, may be scattered off various plasma inhomogeneity, or for other reasons, may not be absorbed by the intended electrons Fisch’s theory:

21. Experiment results from 2004Exp (1) • HT-7 data with various values of density, current, LH phase velocity, and LH power, were plotted in terms of Pel/Pabs and Vph/VR in Karney-Fisch Curve. • For Vph/VR>0, it corresponds to current ramp-up, or OH transformer recharging, RF power flows into the field energy. • For Vph/VR<0, it indicates that RF power is insufficient to sustain the constant current and the power flows from the poloidal field energy into the kinetic energy of resonant electrons. • For Vph/VR=0, it corresponds full driven current operation. HT-7 data with 180shots The two free parameters  and  are related through the wave damping mechanism. =0.75, =1.9, 1.7, 1.5, 2.6 for LH phase velocity 0, 90, 180, 270 respectively are choose to fit the experiment data well. It correspond to the absorbed n// at the value of about 5. The efficiency of recharging OH transformer during LHCD is about 7%

22. CD efficiency can be well determined according the theory form: Upshift of LH waves n// in plasma

23. Optimizing Current ramp-up region The remarkable fitting results for the experiment data to theory curves provide us a guidance to achieve high conversion efficiency in current ramp up experiments. It seems that large u is in favor of high efficiency, but this depends on the role of runaway electrons. Since the theory curves have ignored the role of runaway electrons, if the number of runaway electrons is not negligible, or the runaway electrons are confined well, the theory will not hold. Runaways are very important in the conversion efficiency because runaways gain energy at the expense of the poloidal magnetic field. For u>2, almost all resonant electrons will run away. Unless they are not confined, even a small number of runaway electrons can greatly reduce the efficiency. Runaway probability R(u) For HT-7 machine, the highest ramp-up efficiency may be achieved by operating ramp-up experiments in the region of 1.5<u<2.

24. Ramp-up experiment • Aim at: • High ramp-up efficiency • Fast ramp-up • Reverse shear physics • Effect of runaway electron on • ramp-up experiment • Maximum ramp-up velocity • No transformer ramp-up 我们用2倍的全波驱动功率进行ramp-up实验,期望其在优化的区域运行

25. Exp2005 related with FEB • Fast electron dynamics • CD efficiency with different volume averaged temperature • Comparison of experimental data in current ramp-up with Karney-Fisch curves • Runaway electron dynamics • Searching LHEP mode on HT-7

26. For fast electrons, them endure both the electric filed force due to the residual loop voltage and the damp force due to collisions. The critical kinetic energy of fast electron to be runaways is =2.21*(2+Zeff)*ne/E (keV)

30. Runaway electron dynamics Aim at: OH pulse, MHD activity, disruption

31. Exp2005 related with FEB • Fast electron dynamics • CD efficiency with different volume averaged temperature • Comparison of experimental data in current ramp-up with Karney-Fisch curves • Runaway electron dynamics • Searching LHEP mode on HT-7

32. Searching LHEP mode on HT-7(1) LHEP－LH enhanced performance Suppress sawtooth and the m=1mode by high power LHW, may be 500kW LHW is enough for HT-7 plasma. The suppress effect is related with the peaked n// ASDEX

33. Searching LHEP mode on HT-7(2) LH enhanced performance during OH free pulse. The current will be ramp-up again if the LHEP mode is triggered. OH free Ip LHEP phase LH Traim-1M

34. Synergy effect with LHW+IBW

35. LHW power deposition on axis during IBW heating

37. Long pulse operation alternation LHW power HT-7实现长脉冲的可选方案： 低杂波引起的杂质，以及限制器温度上升在长脉冲放电中影响较大。由于等离子体的电流的衰减时间在几百毫秒左右，我们可以采取低杂波调制运行方式， Ip Ip=50~60kA OH free PLH 300kW, 5~10Hz >10 minutes ?

38. Thank you for your attention!