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HT-7 上的 MHD 行为及 动力学致稳的实验研究

HT-7. HT-7 上的 MHD 行为及 动力学致稳的实验研究. 自然科学基金项目 No. 19675041, No. 10275068 毛剑珊 2003/5. HT-7. OUTLINE. 研究动机与背景 托卡马克磁流体不稳定性基本概念及分类 HT-7 上典型的 MHD 行为的实验观察及分类 新经典撕裂模 （ NTM ） 及 DIII-D 、 JET 、 ASDEX-U 上有关的研究简介 DIII-D 上用 ECCD 完全抑制 NTM 实验简介 HT-7 上 动力学致稳的实验研究. HT-7. 研究动机与背景.

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HT-7 上的 MHD 行为及 动力学致稳的实验研究

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  1. HT-7 HT-7上的MHD行为及 动力学致稳的实验研究 自然科学基金项目 No. 19675041, No. 10275068 毛剑珊 2003/5

  2. HT-7 OUTLINE • 研究动机与背景 • 托卡马克磁流体不稳定性基本概念及分类 • HT-7上典型的MHD行为的实验观察及分类 • 新经典撕裂模（NTM）及DIII-D、JET、 ASDEX-U上有关的研究简介 • DIII-D上用ECCD完全抑制NTM实验简介 • HT-7上动力学致稳的实验研究

  3. HT-7 研究动机与背景 获得稳态、高参数聚变等离子体（高）一直是聚变界追求的目标。输运垒（内部、边界、双垒）的形成是实现托卡马克等离子体高约束的重要途径，MHD 不稳定性制约了 limit. 托卡马克等离子体 MHD 稳定性是目前世界聚变研究热点和前沿性课题之一。(最近有关的参考文献很多） HT-7实验研究取得重大进展.高参数、长脉冲放电出现 MHD 不稳定性，从而导致破裂是目前困扰HT-7向更高参数、更长脉冲冲击的主要障碍之一。 认识和抑制和控制撕裂模不稳定性是一个重要课题。

  4. HT-7 Magnetohydrodynamic (MHD) Instabilities 宏观不稳定性微观不稳定性 1. 米尔诺夫振荡(Mirnov Oscillation)磁场的周期性振荡 撕裂模不稳定性 (tearing modes instabilities) 2. 锯齿振荡(Sawteeth Oscillation) 等离子体芯部 m =1的不稳定 3. 破裂不稳定性(Disruption) 破裂的特征是等离子体的热能和磁能在毫秒量级内迅速流失，等离子体快速熄灭。例如JET，他们统计了各种破裂起因并将其分类为18种破裂。还有一些大、中型装置如TFTR、ASDEX-U和JT-60U等，则着重研究了高密度破裂、高β破裂和低q破裂，并对与破裂共生的VDE和HaLo电流进行了较深入系统地实验研究 托卡马克等离子体的磁流体行为

  5. HT-7 X-pt O-pt R R Tearing Modes The tearing instability in a tokamak is driven by the radial gradient of the equilibrium toroidal current density. The name derives from tearing and rejoining of magnetic field lines,which occur during the instability as a consequence of finite resistivity. (J.Wesson “TOKAMAK” 1997) q(ra) = m / n (m -极向模数，n -环向模数) 当等离子体出现非线性撕裂模时,磁场拓扑发生变化,嵌套整齐的轴对称磁面被撕裂，磁力线重联形成磁岛 (a) flux surfaces of m = 3 islands of full width w. (b) flux surfaces of m = 2 n = 1 islands of full width w.

  6. top view D A C B MTI-MT8 在HT-7真空室内安装了两套Mirnov探针阵列，分别在A段和C段，每套有12个切向探针和12个法向探针，固定在真空室半径为34cm的小圆截面上 LHCD

  7. 在HT-7真空室内安装了两套Mirnov探针阵列，分别在A段和C段，每套有12个切向探针和12个法向探针。在HT-7真空室内安装了两套Mirnov探针阵列，分别在A段和C段，每套有12个切向探针和12个法向探针。

  8. HT-7 MHD的观察 ( from B.Shen)

  9. MHD 的模数： m=2 f= 7 kHz (Shot 52586) from B.Shen

  10. HT-7 托卡马克等离子体的磁流体行为 from G. S. Xu.

  11. ~ 1 - 2 cm HT-7 Island Width Calculation m=2 White, R.B., et al., Phys. Fluids 20 (1977) 800

  12. For a large aspect-ratio circular plasma(J.Y.Zhao) P. H. Rutherford, Physics of Fluids16, 1903 (1973) The generalized Rutherford equation describes the dynamics of the island width Ip=130KA, It=3899A

  13. HT-7 . . HT-7 MHD行为 98年前

  14. HT-7 HT-7 运行区 1998 年

  15. HT-7 HT-7 MHD行为 初始等离子体过快的建立，dI/dt,dne/dt过大，引起MHD Shot No.52290 dIp/dt=66KA/16ms=4.1MA/s(这样的炮很多）

  16. dI/dt, 过大

  17. HT-7 慢 过快 no MHD

  18. HT-7 MHD induced disruption with LHCD in the Ne range 1.3~1.8

  19. HT-7 在低阶有理面附近过陡的压力梯度

  20. W ~ - 30% 低模数MHD不断增长，导致内能的迅速损失，引起电流通道收缩，最终导致破裂

  21. LHCD+IBW at high Ne (2e19m-3)放电一开始就有MHD，整个放电不稳定 高密度是保证聚变堆功率密度所必须的重要指标，但在高密度下，辐射损失过大（总辐射功率Ne2 )，当总辐射功率接近总加热功率，使边界区迅速冷却，导致低模数MHD不断增长，并最终导致破裂。但不同装置上表现的模式各有差异，JET主要是2/1,3/2模，D-III主要是3/2模,TFTR主要是1/1模，而ASDEX-U上2/1模和3/1模均存在，并观测到强烈的MARFE效应。此类破裂在全面破裂中所占比例最大，JET达25% HT-7主要是2/1模

  22. 高密度欧姆放电:充气过快，引起密度、温度的快变化，引起MHD。平衡条件的快速变化，而控制位移的响应跟不上，引起等离子体向器壁靠近，加大了与器壁的相互作用。高密度欧姆放电:充气过快，引起密度、温度的快变化，引起MHD。平衡条件的快速变化，而控制位移的响应跟不上，引起等离子体向器壁靠近，加大了与器壁的相互作用。 6.3 5.6 Ne(0)=3.0 97年13748#密度5.0e13cm-3

  23. 高参数高约束运行

  24. 大电流、高参数高约束运行 典型炮号 No.53291 Ip~200 kA, Ne~3.96，LHW~463kW；IBW~189kW qa=2.78 q=1面向外移（r from 10 to 13cm)， 电流极限破裂，即总电流超过磁流体稳定极限时产生的破裂，进入磁流体扭曲模不稳定参数区。MHD 使杂质流的突然增加导致电流通道的收缩。 2000年 39714# IP=255.2KA qa=2.26

  25. HT-7 初始位移快变引起MHD （硼化后）

  26. HT-7 No.52586 全波驱动实验 放电后期MHD引发破裂

  27. HT-7 长脉冲放电的后期，高温等离子体与限制器和真空室器壁长时间作用，引起杂质辐射,引起MHD，导至破裂

  28. HT-7 Neoclassical Tearing Mode (NTM) • A crucial issue for the extension of advanced tokamak scenarios to long pulse operation is to avoid these MHD instabilities. • In configurations with transport barriers the improved edge and core confinement leads to large pressure gradient and large edge bootstrap current density which often drive magnetohydrodynamic (MHD) instabilities neoclassical tearing mode (NTM)，terminating the discharge or reducing the discharge performance. The edge and the core transport barriers deteriorate or are completely lost.

  29. The papers about neoclassical tearing mode (NTM) * S. Günter, et al. “ Neoclassical tearing modes on ASDEX Upgrade: improved scaling laws, high confinement at high N and new stabilization experiments” NF/2003/Vol.43/No.3 161 (2003.3.10) * S. Saarelma, et al , “MHD stability analysis of type II ELMs in ASDEX Upgrade” NF/2003/Vol.43/No.3 262 * M.F.F. Nave, et al. “Triggering of neo-classical tearing modes by mode coupling” NF/2003/Vol.43/No.3 179 * R.J. Buttery, et al “Onset of neoclassical tearing modes on JET” NF/2003/Vol.43/No.3 69 * A. Gude, et al, “Temporal evolution of neoclassical tearing modes and its effect on confinement reduction in ASDEX Upgrade” NF/2003/Vol.43/No.3 833 * F. Salzedas, et al “The effect of ECRH on the stability of the radiation induced m = 2 mode and on the current quench of a major disruption” NF/2003/Vol.43/No.3 881

  30. HT-7 J || bs~ε1/2 p / Bθ The growth (or decay) of tearing mode islands is given by the Rutherford equation modified for the perturbed neoclassical bootstrap current [General Atomics Report GA–A23156] local resistive diffusion time for local plasma resistivity Lq ≡ q / (dq / dr) > 0 Lp ≡- p / (dp / dr) > 0 is the poloidal beta, i.e., the plasma pressure relative to poloidal magnetic field pressure B2 /20

  31. HT-7

  32. No.52586 Ip~120 kA, Ne:1.2e19m-3 NH89 ~ 2 LHW~465kW；IBW~220kW 高参数，高约束运行状态下，放电后期 M=2锁模引起破裂

  33. 高参数高约束运行下，放电后期 M=2锁模引起破裂 典型炮号 No.52586 Ip~120 kA, Ne:1.2e19m-3 LHW~465kW；IBW~220kW NH89 ~ 2

  34. MHD developing sequence m=2 (7KHZ) was stimulated at 600ms, m=3 (15KHZ) at 650ms, mode locked at 750ms, major disruption at 770ms

  35. No.59017 Ip=125KA Ne=2.4 X 1013cm-3 Bt (3768A) LHW=290KW IBW=200KW SX with lager sawteeth, no impurity increacing before MHD

  36. Examples of q = 1 Sawteeth Inducing m/n = 3/2 NTMs for DIII-D

  37. Examples of q = 1 Sawteeth Inducing m/n = 3/2 NTMs This mode can cause beta (at fixed input power) to drop by 10% ~ 30%.

  38. Examples of q = 1 Sawteeth Inducing m/n = 3/2 NTMs for JET

  39. No.59017 Ip=125KA Ne=1.4 X 1013cm-3 Bt 1.75T(3768A) LHW=290KW IBW=200KW A large MHD ( m=2) induced major disruption

  40. IBW LHCD W ~ - 30% SX with lager shouteeth, no impurity increacing before MHD A large q = 1 sawtooth instability can produce a perturbation at q = 2 The presence of a “seed” island [J.L. Luxon, et al., Plasma Phys. and Control. Fusion Research, Vol. 1 (1987) p. 159]

  41. No.53182 Ip=250KA Ne=1.6 X 1013cm-3 Bt ~1.97T(4229A) LHW=500KW IBW=250KW

  42. HT-7 No MHD on HT-7 high performance Bt~1.8T, H89*N >3 (4) and H93>1 (1.5) for ~50E

  43. HT-7可能引发MHD的几种主要原因 • 初始等离子体过快的建立，dI/dt,dne/dt过大，引起MHD (解决办法：如，400ms前程序控制，400ms后投入加热场反馈,低环压起动，调节充气速率等） • 长脉冲放电的后期，高温等离子体与限制器和真空室器壁长时间作用，引起杂质辐射(解决办法：如注意水平位移的调节、水冷石墨限制器等） • 高参数，高约束运行状态下，在某一局部形成过陡的压力梯度，特别是在低阶有理面附近过陡的压力梯度 NTM（避免办法：如改变Ne,Bt,IBW共振层，ECCD，动力学致稳等) • 运行在极限条件下，如：高密度极限，大电流、低q放电等等 • 。。。。。。

  44. HT-7 GA- A23843 & GA- 23255 The improved edge and core confinement leads to large pressure gradient and large edge bootstrap current density JBS (trapped particles and pressure gradient p )which often drive MHD to limit performance at higher poloidal beta “missing” bootstrap current in O-point parallel heat flow along field lines dominates over cross-field transport and flattens the pressure in the island MHD Instabilities Occurring near/at the Transport Barrier on D-III Tokamak

  45. HT-7 ECCD SEARCH AND SUPPRESSION OF NTM *The development of techniques for neoclassical tearing mode (NTM) suppression or avoidance is crucial for successful high beta/high confinement tokamaks. *Localized off-axis co-current drive ECCD could replace the “missing” bootstrap current in the island O-point and stabilize the NTM [Phys. Plasmas4, 2940 (1997)] *This(DIII-D) was confirmed both in ASDEX- U[Phys. Rev. Lett. 85, 1242 (2000)], and in JT-60U[Plasmas Phys. Control. Fusion 42, L37 (2001)] with electron cyclotron current drive (ECCD).

  46. Ip~1.0-1.2MA, Bt=-1.52 to -1.64 T.The injected rf power Pec is up to 2.3 MW for four gyrotrons. The second harmonic resonance 2 fce for the 110 GHz gyrotron frequency  Real-time control of optimum position for shot-to-shot and time-to-time variation in the optimum position with the plasma control system(PCS), PCS makes small changes in toroidal field BT  Best results (i.e. complete 3/2 NTM suppression) βN increases by about 25% as the 3/2 NTM is suppressed and remains at this level even after the ECCD is turned off

  47.  For fixed Rsurf , the PCS can do a BT “blind search”. Here the step size is BT=0 .01 T, equivalent to R = 0.9 cm (BT/ B T ~0.6 %)  The q = 3/ 2 location is essentially unchanged.  Searches and optimum until the optimum BT is adjusted and complete suppression NTM obtained

  48. X-pt O-pt R R Modulate ECCD for suppression MHD on DIII-D

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