Neutral density profiles are measured on the outboard midplane of the National Spherical Torus Experiment Upgrade (NSTX-U) using a two dimensional camera (ENDD, edge neutral density diagnostic) filtered for deuterium Balmer α (Dα) emission interpreted via simulations using the Monte Carlo neutral transport code DEGAS 2. Deuterium atomic densities nD are calculated by inverting the line-integrated Dα brightness and using local measurements of electron density ne and temperature Te to determine atomic rate coefficients. The assumptions used in the derivation of nD from Dα emissivity are validated using DEGAS 2 to estimate contributions to emissivity due to electron impact excitation and molecular processes. Experimental measurements and DEGAS 2 simulations are compared over a database of L- and H-mode discharges, showing good agreement in Dα emissivity profiles. Residual disagreement between experiment and simulations is suggestive of the possible role of intermittent transport and uncertainties in the molecular data. DEGAS 2 simulations are further used to complement the ENDD diagnostic, extracting neutral (atomic and molecular) densities at locations where the ENDD measurement are not made or where the assumptions used in the ENDD analysis are not valid. Deuterium atomic densities and ionization profiles on the outer midplane are compared for L-mode and H-mode discharges in NSTX-U. One-way coupling of DEGAS 2 to UEDGE multi-fluid simulations constrained by experimental data is used to study edge fueling and neutral penetration in NSTX-U discharges.
中性密度分布是在国家球形环实验升级装置（NSTX-U）的外中平面处，使用二维相机（ENDD，边缘中性密度诊断）测量的，该相机针对氘的巴耳末α（Dα）发射进行了滤波，并通过蒙特卡洛中性输运代码DEGAS 2进行模拟来解释。氘原子密度nD是通过反演线积分Dα亮度，并利用电子密度ne和温度Te的局地测量来确定原子速率系数而计算得到的。从Dα发射率推导nD所依据的假设，通过使用DEGAS 2估计电子碰撞激发和分子过程对发射率的贡献而得到验证。在L模和H模放电的数据库上，将实验测量与DEGAS 2模拟进行了比较，结果显示Dα发射率分布具有良好的一致性。实验与模拟之间的残余差异表明，间歇输运和分子数据的不确定性可能起到作用。DEGAS 2模拟进一步用于补充ENDD诊断，在未进行ENDD测量或ENDD分析中所用假设不成立的位置，提取中性（原子和分子）密度。在NSTX-U中，针对L模和H模放电，比较了外中平面处的氘原子密度和电离分布。将DEGAS 2与受实验数据约束的UEDGE多流体模拟进行单向耦合，用于研究NSTX-U放电中的边缘加料和中性粒子穿透。