Cryogenic pellets with controlled length for pellet ablation studies

A prototype of a pneumatic injector of hydrogen cryogenic pellets with controlled length is under development at Kyushu University. The major element of the prototype is a remote cylindrical freezing cavity with controllable length which allows the length of a frozen hydrogen pellet formed in situ to be adjusted precisely and continuously from sub-millimeter to a few millimeters. The design and operation of the prototype are described. The initial results of experimental adjustment of the pellet length are also reported. The length of 1.4 mm diameter hydrogen ice pellets has been varied continuously from 0.5 to 3.0 mm at a temperature range of 6-9 K. The prototype has launched single solid pellet with controlled length through room temperature helium gas at a pressure of 0.5-2 MPa.