The impact of magnetic flux expansion on heat flux width estimation in NSTX

The heat flux width has been well investigated with poloidal flux expansion (f _exp) from 10 to 40 in NSTX [1]. The filamentary structure on the divertor heat flux was observed with edge MHD or high edge fluctuation level, which will broaden heat flux width by 2-3 times [2]. Here we extend previous studies [1] to low f _exp ~2 and without filamentary divertor heat flux. When the f _exp changed from ~2 to ~12, it was found that the integral power decay width (λ_int) decreased from 16mm to 5mm, while the λ_int didn’t change much when the f _exp >~12. With the f _exp~12, the SOL power decay length (λ_q) estimated from the divertor heat flux profile indicate the λ_q is 2 times smaller than the prediction based on multi-machine database.