Temporal structure of blobs in NSTX

Abstract

The time dependence of the blob pulse shape and the waiting time between blobs was found using data from the gas puff imaging diagnostic in NSTX. The database used was of 103 shots from 2010 as described in a previous paper (Zweben et al., Phys. Plasmas 29, 012505 (2022).]. The blob pulse shape was well fit by an exponential rise and fall where the average rise time was τr = 9.0 ± 2.7  μs and the average fall time was τf = 16.6 ± 5.8  μs. The waiting times between blob pulses above a threshold of three times the mean had a broad distribution with an average of τw = 1.2 ± 0.85 ms over the database. The blob intermittency parameter γb = τd/τw, where the blob pulse duration was τd =  τr+ τf, ranged from γb∼1% to 5% for shots in this database and increased almost linearly with the blob fraction.