论文标题

深层或不深:监督的学习方法来建模基座密度

Deep or Not Deep: Supervised Learning Approaches to Modeling the Pedestal Density

论文作者

Kit, Adam, Jaervinen, Aaro, Frassinetti, Lorenzo, Wiesen, Sven, Contributors, JET

论文摘要

基座是Tokamaks中传统高性能等离子体场景的关键。但是,由于Tokamak基座所包含的多个物理过程和尺度,因此基座等离子体的高保真模拟极具挑战性。预测基座最高压力的主要范例由EPED样模型包含。但是,EPED不能预测基座顶密度,$ n_ \ text {e,ped} $,但要求它作为输入。 Europed采用简化的模型,例如日志线性回归,以在类似Eped的模型中使用Tokamak Machine Control参数约束$ n_ \ text {e,ped} $。但是,这些用于$ n_ \ text {e,ped} $的简化模型通常与实验观察结果表示分歧,并且不使用所有可用的数值和分类机器控制信息。在这项工作中,可以观察到,使用相同的输入参数,决策树的合奏和深度学习模型将$ n_ \ text {e,ped} $的预测质量提高了约23%,相对于用对数均值平方误差测量的对数线性缩放定律获得的预测质量。包括数值和分类的所有可用Tokamak机器控制参数,可进一步提高约13%。最后,在包括全局归一化等离子压力和有效电荷状态作为输入时,测试了预测质量,因为已知这些参数会影响基座。令人惊讶的是,这些参数只会导致预测质量的进一步提高。

Pedestal is the key to conventional high performance plasma scenarios in tokamaks. However, high fidelity simulations of pedestal plasmas are extremely challenging due to the multiple physical processes and scales that are encompassed by tokamak pedestals. The leading paradigm for predicting the pedestal top pressure is encompassed by EPED-like models. However, EPED does not predict the pedestal top density, $n_\text{e,ped}$, but requires it as an input. EUROPED employs simplified models, such as log-linear regression, to constrain $n_\text{e,ped}$ with tokamak machine control parameters in an EPED-like model. However, these simplified models for $n_\text{e,ped}$ often show disagreements with experimental observations and do not use all of the available numerical and categorical machine control information. In this work it is observed that using the same input parameters, decision tree ensembles and deep learning models improve the predictive quality of $n_\text{e,ped}$ by about 23% relative to that obtained with log-linear scaling laws, measured by root mean square error. Including all of the available tokamak machine control parameters, both numerical and categorical, leads to further improvement of about 13%. Finally, predictive quality was tested when including global normalized plasma pressure and effective charge state as inputs, as these parameters are known to impact pedestals. Surprisingly, these parameters lead to only a few percent further improvement of the predictive quality.

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