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首页> 外文期刊>Plasma physics and controlled fusion >Modelling the Ohmic L-mode ramp-down phase of JET hybrid pulses using JETTO with Bohm-gyro-Bohm transport
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Modelling the Ohmic L-mode ramp-down phase of JET hybrid pulses using JETTO with Bohm-gyro-Bohm transport

机译：使用具有Bohm-gyro-Bohm传输的JETTO对JET混合脉冲的Ohmic L模式斜降相位建模

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摘要

The empirical Bohm-gyro-Bohm (BgB) transport model implemented in the JETTO code is used to predictively simulate the purely Ohmic (OH), L-mode current-ramp-down phase of three JET hybrid pulses, which combine two different ramp rates with two different electron densities (at the beginning of the ramp). The modelling is discussed, namely the strategy to reduce as much as possible the number of free parameters used to benchmark the model predictions against the experimental results. Hence, keeping the gas puffing rate as measured whilst controlling the line-averaged electron density via the recycling coefficient (which in the modelling is taken at the separatrix instead of the wall), one of the many possible ways to fix the total particle source, it is shown that the BgB model reproduces well the experimental data, as far as both average quantities (plasma internal inductance and volume-averaged electron temperature) and profiles (electron density and temperature) are concerned, with relative errors remaining mostly below 20%. The sensitivenesses with respect to the recycling coefficient, the ion effective charge, the energy of neutrals entering the plasma through the separatrix and the need to introduce a particle pinch are assessed; the necessity for a proper sawtooth model if experimental results are to be reproduced is also shown. The strong non-linear coupling in a OH plasma between density, temperature and current (essentially via interplay between the power-balance equation, Joule's heating with a temperature-dependent resistivity and the dependence of BgB transport coefficients on profile gradients) is put in evidence and analyzed in light of modelling results. It is still inferred from the modelling that the real value of the recycling coefficient at the separatrix (basically, the so-called fuelling efficiency times the actual recycling coefficient at the wall) must become close to one in the final stages of the discharges, when the gas puffing is switched off and so recycling comes to be the only source of particles. If the wall recycling remains close to one (as standard for tokamaks), this may indicate that the fuelling efficiency also approaches unity, apparently consistent with the observed fact that the plasma is pushed towards the machine wall at the end of the current ramps.
机译：JETTO代码中实现的经验性Bohm-gyro-Bohm（BgB）传输模型用于预测性地模拟三个JET混合脉冲的纯欧姆（OH）L模式电流下降阶段，该阶段结合了两种不同的斜坡率具有两个不同的电子密度（在斜坡开始时）。讨论了建模，即减少尽可能减少用于根据实验结果对模型预测进行基准测试的自由参数数量的策略。因此，在通过循环系数控制线平均电子密度的同时保持测出的抽气速率（在模型中，该系数是在分离线而不是壁上获得的），这是固定总粒子源的多种可能方法之一，结果表明，就平均量（等离子体内部电感和体积平均电子温度）和分布图（电子密度和温度）而言，BgB模型很好地再现了实验数据，相对误差大部分保持在20％以下。评估了对循环系数，离子有效电荷，通过皮下层进入等离子体的中性能量以及引入微粒夹挤的敏感性;如果要再现实验结果，还显示了正确的锯齿模型的必要性。证明了OH等离子体在密度，温度和电流之间的强非线性耦合（主要是通过功率平衡方程，焦耳热（与温度相关的电阻率）之间的相互作用以及BgB输运系数对轮廓梯度的依赖性）并根据建模结果进行分析。从模型中仍然可以推断出，在排污的最后阶段，分离线处的再循环系数的实际值（基本上，所谓的燃料效率乘以壁处的实际再循环系数）必须接近于一。停止排气，因此回收成为唯一的颗粒来源。如果壁回收率保持接近一个（作为托卡马克的标准），这可能表明加油效率也趋于统一，这显然与观察到的事实相一致，即等离子在电流斜坡结束时被推向机器壁。

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