Sensitivity to error fields in NSTX high β plasmas

It was found that error field threshold decreases for high beta in NSTX, although the density correlation in conventional threshold scaling implies the threshold would increase since higher beta plasmas in our study have higher plasma density. This greater sensitivity to error field in higher beta plasmas is due to error field amplification by plasmas. When the effect of amplification is included with ideal plasma response calculations, the conventional density correlation can be restored and threshold scaling becomes more consistent with low beta plasmas. However, it was also found that the threshold can be significantly changed depending on plasma rotation. When plasma rotation was reduced by non-resonant magnetic braking, the further increase in sensitivity to error field was observed.