Conversion of a beam of negative hydrogen ions to atomic hydrogen in a plasma target at energies between 0.5 and 1 MeV
Conversion of a beam of negative hydrogen ions to atomic hydrogen in a plasma target at energies between 0.5 and 1 MeV
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在等离子靶中以 0.5 至 1 MeV 的能量将负氢离子束转换为原子氢
DOI：
10.1088/0029-5515/15/3/021
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发表时间：
1975
期刊：
影响因子：
3.3
通讯作者：
G. V. Roslyakov
中科院分区：
文献类型：
--
作者：
G. Dimov;G. V. Roslyakov
当前平台期的前 50 ms，然后缓慢下降至 0.87 keV。图 1c 中还显示了从电荷交换中性粒子的能谱导出的离子温度。实线代表从 6 次发射中获得的 48 个时间分辨测量值的平均值（时间分辨率 10 毫秒）。在当前平台期间，离子温度从 0.75 keV 降至 0.67 keV。 Ne、Te 和 Ti 获得的结果表明，在当前平台期的一开始就达到了准稳态等离子体状态。 X 射线信号和 UV 区域发射线的时间行为进一步强调了这一结论。在图1d中给出了X射线信号的示例（任意单位；40jum Al）。在当前的平台期，该信号下降了 15%。还显示了典型放电中 O VI 1032 A 线的强度。该线在 t = 6.5 ms 时具有 1.5 X10 光子 cm' • s' • sr" 的最大强度，并且在当前平台期间保持恒定在 ± 5% 以内。这也可以通过其他杂质离子（例如 Fe XV 284 A 和 Mo XIII 341 A）的线观察到。在磁环信号上观察到准稳态等离子体状态的另一个说明。场扰动 (m = 2，n = 1）在当前平台期间检测到振幅（极向磁场的 s l%o）和旋转频率（f/ms 7 kHz）的显着稳定性当前平台期间的能量限制时间（如参考文献 [2] 中计算）为 15 毫秒；等离子体离子的有效电荷是根据观察到的电导率与 Te(r) A 值得出的预期电导率进行比较计算得出的。 Z eff = 6 ±0.7 是在 100 < t < 500 ms 内获得的，并且没有随时间的推移而增加。从绝对 X 射线通量中得出类似的结果。总之，我们可以得出结论，准稳态等离子体状态保持了 350 ms 以上（这一结果通过此处未明确讨论的诊断技术（即微波和 HCN 激光干涉测量以及电子同步加速器发射的强度和谐波谱的测量）得到了证实。这种准稳态等离子体状态的一个方面是，尽管等离子体环面周围介质 Z 的杂质离子密度很大，但 Zeff 在 t > 100 ms 内保持恒定。例如，O VI 1032 A 线的强度表明几厘米厚的壳中的 O 密度为 s 10 cm"。新古典理论预测，由于氘离子的密度梯度，氧离子的向内扩散速度在 10 至 100 cm/s 之间 [3]。下限可以解释在当前平台期间观察到的恒定 Zeff；只有在存在轻微向外扩散机制的情况下，上限才与该观察结果兼容。
first 50 ms of the current plateau and then decreases slowly to 0.87 keV. Also shown in Fig.lc is the ion temperature derived from the energy spectra of charge-exchange neutrals. The solid line represents the mean of 48 time-resolved measurements obtained from 6 shots (time resolution 10 ms). During the current plateau the ion temperature decreases from 0.75 to 0.67 keV. The results obtained on Ne, Te and Ti suggest that a quasi-stationary plasma state is reached at the very beginning of the current plateau. This conclusion is further underlined by the time behaviour of the X-ray signals and of emission lines in the UV region. In Fig.Id an example of a X-ray signal is given (arbitrary units; 40 jum Al). This signal decreases by 15% during the current plateau. Also shown is the intensity of the O VI 1032 A line in a typical discharge. This line has a maximum intensity of 1.5 X10 photons cm' • s' • sr" at t = 6.5 ms and remains constant to within ± 5% during the current plateau. This was also observed with lines from other impurity ions, for example, Fe XV 284 A and Mo XIII 341 A. Another illustration of the quasi-stationary plasma state is observed on the magnetic loop signals. A field perturbation (m = 2, n= 1) of remarkable stability in both amplitude (s l%o of the poloidal magnetic field) and rotation frequency (f/ms 7 kHz) is detected during the current plateau. The energy confinement time (calculated as in Ref.[2]) is 15 ms during the current plateau; the poloidal beta is « 0.41. The effective charge of the plasma ions was calculated from the observed conductivity compared to the expected conductivity derived from Te(r) profiles. A value of Z eff = 6 ±0.7 is obtained for 100 < t < 500 ms without detectable increase with time. A similar result is derived from the absolute X-ray flux. In conclusion, we can summarize that a quasi stationary plasma state is maintained over 350 ms (this result is confirmed by the diagnostic techniques not explicitly discussed here, i.e. microwave and HCN-laser interferometry and the measurements of the intensity and harmonic spectrum of electron synchrotron emission). The most striking aspect of this quasi-stationary plasma state is the fact that Zeff remains constant for t > 100 ms in spite of a large density of impurity ions of medium Z at the periphery of the plasma torus. For instance, the intensity of the O VI 1032 A line indicates an O density of s 10 cm" in a shell a few centimetres thick. Neoclassical theory predicts an inward diffusion of the oxygen ions due to the density gradient of the deuterium ions with a velocity between 10 and 100 cm/s [3]. The lower limit would explain the observation of a constant Zeff during the current plateau; the upper limit would be compatible with this observation only in the presence of a slight outward diffusion mechanism.