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利用硬X射线探测系统监测HT-7托卡马克装置中逃逸电子轰击到装置第一壁材料时所产生的高能硬X射线,研究了在放电平顶阶段提高等离子体密度对逃逸电子行为的影响。实验结果表明,通过提高放电平顶阶段等离子体密度,HXR强度迅速降到很低的水平,这意味着能有效减少这个阶段形成的逃逸电子的数目及能量。     

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用NaI闪烁体探测器组成的逃逸电子诊断系统和CdTe半导体探测阵列组成的快电子轫致辐射诊断系统,研究了一定等离子体密度条件下低杂波功率和等离子体电流对逃逸产生的影响以及一定低杂波功率下等离子体密度对逃逸电子产生的不同作用效果。根据实验数据计算了HT-7装置等离子体中电子逃逸的阈值电场和一定放电条件下电子逃逸的阈值能量。     

AC operation and runaway electron behaviour in HT-7 tokamak

Operation of HT-7 tokamak in a multicycle alternating square wave plasma current regime is reported. A set of AC operation experiments, including LHW heating to enhance plasma ionization during the current transition and current sustainment, is described. The behaviour of runaway electrons is analysed by four HXR detectors tangentially viewing the plasma in the equatorial plane, within energy ranges 0.3--1.2~MeV and 0.3--7~MeV, separately. High energy runaway electrons (\sim MeV) are found to circulate predominantly in the opposite direction to the plasma current, while the number of low energy runaway electrons (\sim tens to hundreds of keV) circulating along the plasma current is comparable to that in the direction opposite to the plasma current. AC operation with lower hybrid current drive (LHCD) is observed to have an additional benefit of suppressing the runaway electrons if the drop of the loop voltage is large enough.     

Experimental observation of interaction of runaway electrons with lower hybrid waves in slide-away regime in the HT-7 tokamak

The characters of slide-away regime in the HT-7 tokamak have been investigated, and evidences that lower hybrid waves (LHW) are excited in slide-away regime are presented based on local fast electron bremsstrahlung (FEB) emission profile and FEB emission spectrum. The interaction of high energy runaway electrons with those excited LHW via anomalous Doppler resonance is analyzed and the resonance energy is derived with which the behavior of those relevant signals in the experiment can be explained very well. It is shown that this interaction can provide an effective way to reduce the damage to the machine caused by runaway electrons.     

EAST 装置等离子体逃逸电子同步辐射行为的实验研究

通过红外可见内窥镜诊断系统对EAST 等离子体芯部逃逸电子的同步辐射功率谱进行了分析,得出低能段逃逸电子同步辐射主要在红外波段,随着逃逸电子能量的增加,同步辐射向短波方向移动进入可见光波段。在欧姆放电条件下,对逃逸电子同步辐射所产生的的红外可见光进行了成像分析,同时研究了EAST 等离子体在低杂波和中性束注入加热条件下的逃逸电子行为。实验结果显示,低杂波和NBI 的投入总体抑制电子的逃逸,但低杂波投入初期产生的快电子对逃逸电子的产生具有促进作用。     

HL-1M装置逃逸电子的定标律

使用一维数值模型, 推断了逃逸能量ε_r与逃逸约束时间τ_r的关系。模拟结果给出能量ε_r 和放电参数的定标律。在HL- 1M 装置中不同实验条件下测量了硬X 射线谱, 研究了逃逸电子能量 ε_r模拟的定标律, 并推导出HL- 1M 装置放电的逃逸电子的约束时间与逃逸电子扩散系数。     

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通过红外可见内窥镜诊断系统对EAST等离子体芯部逃逸电子的同步辐射功率谱进行了分析,得出低能段逃逸电子同步辐射主要在红外波段,随着逃逸电子能量的增加,同步辐射向短波方向移动进入可见光波段。在欧姆放电条件下,对逃逸电子同步辐射所产生的的红外可见光进行了成像分析,同时研究了EAST等离子体在低杂波和中性束注入加热条件下的逃逸电子行为。实验结果显示,低杂波和 NBI 的投入总体抑制电子的逃逸,但低杂波投入初期产生的快电子对逃逸电子的产生具有促进作用。     

Positron creation and annihilation in tokamak plasmas with runaway electrons

It is shown that electron-positron pair production is expected to occur in post-disruption plasmas in large tokamaks, including JET and JT-60U, where up to about 10(14) positrons may be created in collisions between multi-MeV runaway electrons and thermal particles. If the loop voltage is large enough, they are accelerated and form a beam of long-lived runaway positrons in the direction opposite to that of the electrons; if the loop voltage is smaller, the positrons have a lifetime of a few hundred ms, in which they are slowed down to energies comparable to that of the cool ( less, similar 10 eV) background plasma before being annihilated.     

Energy confinement and high-k turbulence on HT-7 tokamak

A CO₂ collective scattering system has been developed to measure medium and high-k density fluctuation on HT-7 tokamak. Energy confinement and high-k density fluctuation are studied in ohmic discharges. The saturation of confinement was observed at approximately . For kθ=23 cm⁻¹ turbulence, it is found that fluctuation levels have great increase for , and simultaneously a high frequency turbulence feature appear in the frequency spectra. For kθ=14 cm⁻¹ turbulence, it is observed that fluctuation levels have no changes in uncertainties and the spectra are similar at all discharges in this experiment.     

Synchrotron radiation intensity and energy of runaway electrons in EAST tokamak

A detailed analysis of the synchrotron radiation intensity and energy of runaway electrons is presented for the Experimental Advanced Superconducting Tokamak(EAST). In order to make the energy of the calculated runaway electrons more accurate, we take the Shafranov shift into account. The results of the analysis show that the synchrotron radiation intensity and energy of runaway electrons did not reach the maximum at the same time. The energy of the runaway electrons reached the maximum first, and then the synchrotron radiation intensity of the runaway electrons reached the maximum.We also analyze the runaway electrons density, and find that the density of runaway electrons continuously increased. For this reason, although the energy of the runaway electrons dropped but the synchrotron radiation intensity of the runaway electrons would continue rising for a while.     

Investigation of fast pitch angle scattering of runaway electrons in the EAST tokamak

This paper reports that an experimental investigation of fast pitch angle scattering(FPAS) of runaway electrons in the EAST tokamak has been performed.From the newly developed infrared detector(HgCdTe) diagnostic system,the infrared synchrotron radiation emitted by relativistic electrons can be obtained as a function of time.The FPAS is analysed by means of the infrared detector diagnostic system and the other correlative diagnostic systems(including electron-cyclotron emission,hard x-ray,neutrons).It is found that the intensity of infrared synchrotron radiation and the electron-cyclotron emission signal increase rapidly at the time of FPAS because of the fast increase of pitch angle and the perpendicular velocity of the energetic runaway electrons.The Parail and Pogutse instability is a possible mechanism for the FPAS.     

Investigation of fast of runaway electrons pitch angle scattering in the EAST tokamak

This paper reports that an experimental investigation of fast pitch angle scattering （FPAS） of runaway electrons in the EAST tokamak has been performed. From the newly developed infrared detector （HgCdTe） diagnostic system, the infrared synchrotron radiation emitted by relativistic electrons can be obtained as a function of time. The FPAS is analysed by means of the infrared detector diagnostic system and the other correlative diagnostic systems （including electron-cyclotron emission, hard x-ray, neutrons）. It is found that the intensity of infrared synchrotron radiation and the electron-cyclotron emission signal increase rapidly at the time of FPAS because of the fast increase of pitch angle and the perpendicular velocity of the energetic runaway electrons. The Parail and Pogutse instability is a possible mechanism for the FPAS.     

HT-7托卡马克等离子体slide-away放电研究

在HT-7托卡马克上,只在等离子体放电击穿阶段充气,击穿后关闭充气阀门,让装置内真空室器壁的出气维持放电的进行,通过密度衰减实现了slide-away放电.实验分析了不同等离子体电流平台下的slide-away放电模式的密度阈值,以及相同充气量的条件下放电等离子体电流对实现slide-away放电的影响.研究了slide-away放电模式下密度提升对等离子体放电状态的影响.结果发现,slide-away放电模式下的密度提升使得H_a线辐射强度增强,等离子体中超热电子的约束性能变差,等离子体芯部的超热电子减少,高能逃逸电子厚靶轫致辐射增加. 关键词： slide-away放电 托卡马克 等离子体 逃逸电子     

Observation of trapped and passing runaway electrons by infrared camera in the EAST tokamak

In EAST, synchrotron radiation is emitted by runaway electrons in the infrared band, which can be observed by infrared cameras. This synchrotron radiation is mainly emitted by passing runaway electrons with tens of Me V energy. A common feature of radiation dominated by passing runaway electrons is that it is strongest on the high field side. However,the deeply trapped runaway electrons cannot reach the high field side in principle. Therefore, in this case, the high field side radiation is expected to be weak. This paper reports for the first time that the synchrotron radiation from trapped runaway electrons dominates that from passing runaway electrons and is identifiable in an image. Although the synchrotron radiation dominated by trapped runaway electrons can be observed in experiment, the proportion of trapped runaway electrons is very low.     

相干结构Blob在HT-7托卡马克边界的传播

相干结构Blob的间歇爆发清晰地反映在HT-7托卡马克边界探针的离子饱和流信号中,Blob 的径向传播在近刮削层堆积出一个温度和密度的平台区,使密度和温度分布偏离了指数分布.条件平均方法提示了间歇脉冲结构空间分布的均匀性,Blob内部等离子体参数远高于背景等离子体参数,并且呈现出涡旋的形态.最后闭合磁面附近的数据显示,...     

Study of particle behaviour at the edge in HT-7 tokamak

The cross-field diffusion coefficient (D_⊥) at the edge in the HT-7 tokamak is close to the Bohm value when the line average electron density ranges from 1.5×10^{19} to 3.0×10^{19}m^{-3}. The energy profile of the particles is derived directly from the H_α(D_α) line shape; the dissociative excitation of molecules is dominating when the local electron temperature is above 10eV. By means of the Monte Carlo method the D_α line shape is also simulated. We find that the molecular dissociation contributes to 57% of neutral atoms and 53% of emission intensity in front of the limiter, and 85% of neutral atoms and 82% of emission intensity in front of the wall. The influence of atomic and molecular processes on the energy balance is discussed for the scrape-off layer (SOL), and the power loss from molecular dissociation is found to be 6×10^4kW at the SOL. The ion Bernstein wave (IBW) can effectively suppress the magnetohydrodynamic behaviour, the fluctuation levels and the turbulence; the D_⊥ in front of the limiter declines from 0.84 to 0.2m^2·s^{-1} and the particle confinement time rises from 9 to 12ms.     

HT-7 装置回旋质谱探测器边界离子诊断

介绍了回旋质谱探测器的原理和设计及其在HT-7 装置欧姆放电下对边缘等离子体中离子的诊断实验。探测器安装在限制器附近, 通过一小孔引进等离子体; 设置的前置偏压使电子和离子分离, 并使离子减速; 进入腔体内部的离子在射频电场和平行磁场的作用下发生回旋共振; 通过考察收集的离子电流信号中的共振峰可得到离子的荷质比、回旋频率等参数。实验中观察到荷质比为1、0. 5、0. 3333、0 . 1819 的离子共振峰。     

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为了检测到散射信号且有较高的信噪比,使用硅雪崩二极管(APD)探测器探测汤姆逊散射光,采用电荷敏感运算放大器减小电子噪声。同时,设计了放大电路,并采取了一些抗干扰措施。在实验中,此激光汤姆逊散射系统成功地测量出HT-7等离子体的电子温度。