  In the R&D of the CSNS Drift Tube Linac (DTL), the first unit tank with 28
drift tubes has been developed. The axial accelerating field is ramped from
2.2MV/m to 3.1MV/m in this tank. The required field flatness is less than 2 %
with the standard deviation of 1 % for the beam dynamics. And the field
stability should be less than 1% for machine stable operation. After the
successful alignment, the RF tuning was carried out focusing on the field
profile measurement. Four slug tuners and 11 post couplers were applied in this
procedure. The ramped filed and required stability had been achieved by fine
adjustment of the slug tuners and post couplers. In this paper, the preliminary
tuning results are presented and discussed.
