Design Considerations for Neutron Activation and Neutron Source Strength Monitors for ITER

Abstract

The International Thermonuclear Experimental Reactor1 will require highly accurate measurements of fusion power production in time, space, and energy. Spectrometers in the neutron camera could do it all, but experience has taught us that multiple methods with redundancy and complementary uncertainties are needed. Previously, conceptual designs have been presented for time-integrated neutron activation2 and time-dependent neutron source strength monitors3, both of which will be important parts of the integrated suite of neutron diagnostics for this purpose.4 The primary goals of the neutron activation system are: to maintain a robust relative measure of fusion energy production with stability and wide dynamic range; to enable an accurate absolute calibration of fusion power using neutronic techniques as successfully demonstrated on JET5 and TFTR67; and to provide a flexible system for materials testing. The greatest difficulty is that the irradiation locations need to be close to plasma with a wide field of view. The routing of the pneumatic system is difficult because of minimum radius of curvature requirements and because of the careful need for containment of the tritium and activated air. The neutron source strength system needs to provide real-time source strength vs time with ∼1 ms resolution and wide dynamic range in a robust and reliable manner with the capability to be absolutely calibrated by in-situ neutron sources as done on TFTR8, JT-60U9, and JET10. In this paper a more detailed look at the expected neutron flux field around 1TER is folded into a more complete design of the fission chamber system. Overall issues of neutron calibration for ITER will be presented elsewhere11.