(FT/P2-23) Alternate Concepts for Generating High Speed DT Pellets for Fueling ITER

R.W. Callis1), L.R. Baylor2), P.B. Parks1), N.B. Alexander1), C.P. Moeller1)
1) General Atomics, P.O. Box 85608, San Diego, California 92186-5608, USA
2) Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA

Abstract.  There is a growing concern that the velocity of the DT-ice pellets being proposed to fuel ITER will not have the velocity to effectively penetrate through the pedestal of the plasma edge. For ITER, the present pellet-fueling concept has DT-ice pellets traversing through a guide tube to reach the high field side (HFS) launch location. The forces on the ice pellet as it goes around bends causes the pellets to disintegrate at velocities above 300 m/s. Thus, in order to achieve deeper penetration the pellet velocity has to be increased. To achieve this, either the pellet needs to have its velocity increased after the pellet has passed the last bend, or the pellet has to be made stronger to survive the increased forces higher velocities create. Previously Parks and Perkins have proposed a novel concept to acceleration DT-ice pellets using microwave power from MW gyrotrons to develop high-pressure gas, by absorbing the microwave in a composite “pusher” medium attached to the backside of the pellet. This gas boost is created in the last meter of the guide tube after the last bend. The basic concept of the microwave-based accelerator was validated in the lab by measuring the losses in a section of fundamental waveguide loaded with paraffin and various mixtures of 1 - 2 micron zinc powder. The length of the paraffin in the waveguide was adjusted to have all samples contain the same total amount of Zn powder. It was demonstrated that for constant number of particles in the waveguide the absorption is found to be constant. The next test is to actually heat a sample of naphthalene seeded with 1 - 2 micron Zn powder. For this test a 500 kW pulse from a 110 GHz gyrotron will be pulsed into a naphthalene slug 4 mm diameter, 25 mm long for 1 - 2 ms. The pressure and temperature of the generated gas will be measured and compared to theory. Results of these tests will be reported. Methods have also been evaluated to increase the strength of the ice pellets by either encapsulating the pellet inside a solid shell of either metal or plastic. Or, to stiffen the ice by integrating it into a plastic foam sphere. Analysis indicates a plastic shell with < 5% of the volume of the pellet will increase the strength of a DT Ice pellet by a factor of 100, tests will be performed to validate the modelling.

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