A series of experimental emission images for medium-density SMB. Distance between nozzle and skimmer is 10 mm, stagnation pressure 50 bar, and central density of SMB about 8.48× 10¹³ cm^–3, RF power 1000 W, initial central plasma density about 1.97× 10¹² cm^–3, at time (a) 0.3125 ms, (b) 1.2500 ms, (c) 2.1875 ms, and (d) 3.1250 ms after SMB has hit plasma column and exposure time of each image is 0.3125 ms.