Disclosed are a method and a corresponding apparatus for converting a biomass reactant into synthesis gas. Releasable engagement of the first member with the spindle axially compresses the first gripping ring whilst urging the outer shaft against the second member thereby axially compressing the second gripping ring. On a time serial or sequential basis, several times for each line of firing, the contents of the per element memory buffer are read into the beamformer with different focusing values for each buffer reading cycle.