A large-orbit model of fast ion slowing down during ICRH: Comparison with JET data
A large-orbit model of fast ion slowing down during ICRH: Comparison with JET data
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DOI：
10.1088/0029-5515/31/1/006
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发表时间：
1991
期刊：
影响因子：
3.3
通讯作者：
G. Cottrell;D. Start
中科院分区：
文献类型：
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作者：
G. Cottrell;D. Start
在欧洲联合环（JET）托卡马克产生的等离子体中的H和3 He少数离子的局部和强烈的离子回旋共振加热（ICRH）产生平均能量在多MeV范围内的快离子分布，类似于反应堆中预期的3.5 MeV聚变α粒子。对于JET极向磁场的典型值，粒子轨道的半径可以显著超过RF沉积的尺寸。此外，在快速离子减速时间中存在陡峭的径向梯度的情况下，加热离子的大的径向偏移将它们带入外等离子体区域，其中摩擦阻力大于热等离子体核心。因此，在用ICRH模拟快离子分布时，重要的是要包括对有限轨道尺寸的校正，因为这会导致少数组分的计算能量含量显著降低。本文描述了一个ICRH的大轨道宽度模型，它已被用来预测在JET托卡马克ICRH期间H和3 He少数离子的全局快离子能量。该模型是能够解释某些差异，以前已经观察到的JET之间的测量快离子的能量含量和那些已经使用零轨道宽度模型计算。对于低电流H少数放电，快离子的总能量含量的最大修正被发现是1.56%，其中离子-电子慢化时间很长（在磁轴处为1.6s）。在实验散射范围内，我们可以对任何额外的非经典能量损失过程的快离子扩散系数设置Dfast < 0.18 m2·s−1的上限。
Localized and intense ion cyclotron resonance heating (ICRH) of H and 3He minority ions in plasmas produced in the Joint European Torus (JET) tokamak create fast ion distributions having average energies in the multi-MeV range, similar to 3.5 MeV fusion alpha particles expected in a reactor. For typical values of the JET poloidal magnetic field, the radii of the particle orbits can significantly exceed the size of the RF deposition. Moreover, in the presence of a steep radial gradient in the fast ion slowing-down time, the large radial excursions of the heated ions take them into the outer plasma region where the frictional drag is larger than in the hot plasma core. In modelling the fast ion distribution with ICRH, therefore, it is important to include a correction for the finite orbital size since this gives rise to a significant reduction in the calculated energy content of the minority component. A large orbit width model for ICRH is described which has been used to predict the global fast ion energies of both H and 3He minority ions during ICRH in the JET tokamak. The model is capable of explaining certain discrepancies which have previously been observed on JET between the measured fast ion energy contents and those which have been calculated using a zero orbit width model. The largest corrections to the global energy content of the fast ions are found to be ≈56% for low current H minority discharges in which the ion-electron slowing-down time is long (≈ 1.6 s at the magnetic axis). Within experimental scatter, we can place an upper limit of Dfast < 0.18 m2·s−1 on the fast ion diffusion coefficient for any additional non-classical energy loss processes.