Comparison of Pedestal Stability on the Power Scrape-Off Layer Width in NSTX

Recent analysis shows that the pedestal ballooning parameter, $\alpha_{MHD}$ [1] can be used as a dimensionless parameter to describe NSTX H-mode pedestals across a wide range of plasma current and power. Similar analysis has been performed on Alcator C-MOD [2] and DIII-D [3]. $\alpha_{MHD}$ can also be used to describe the pedestal changes that occur when varying amounts of pre-discharge lithium evaporation are used [4]. Varying amounts of lithium deposition has also been shown to directly effect the power scrape-off layer width, $\lambda_q$ on NSTX [5]. Preliminary results indicate a corresponding correlation between $\alpha_{MHD}$ and $\lambda_q$. This suggests that the H-mode pedestal plays a critical role in setting $\lambda_q$.