The C-Fusion code has been developed to model the plasma physics of the Inertial Electrostatic Confinement1 Cylindrical (IEC-C) fusion device and to predict the local volumetric and total neutron generation rates. The IEC-C neutron source uses purely electrostatic fields to confine circulating ion beams in a hollow cathode-type deuterium discharge geometry. The objective is to obtain a line-like source of neutrons in the dense beam interaction region within and near the cathode. This configuration is ideally suited to certain neutron activation analysis applications where a distributed source is desired. C-Fusion predictions are used to help support the design and testing of experimental IEC-C devices for such applications.

C-Fusion is a semi-analytical model that employs several simplifying approximations. The plasma is assumed to be locally quasi-neutral; there is a spatially one-dimensional variation of plasma properties; the plasma potential profile is linear. Electrons and ions are assumed to have a monoenergetic distribution, originating at the cathode and anodes respectively. The plasma current is axial and constant throughout the device and assumed equal to the electrode current. Local ion and electron velocities are evaluated based upon the local plasma potential. The effects of ion-ion and ion-neutral collisions, as well as charge exchange, are included in the model via a recirculation parameter (h), which relates the plasma particle current to the electric current measured.

C-Fusion calculations have been performed and compared against experimental results. Input parameters included deuterium gas pressure (0.5 - 10 mTorr), neutral gas temperature (300-500 K), electrode current (20 - 40 mA), anode voltage (20 - 40 kV), reflector to anode length (23 cm), anode to cathode length (36 cm), anode length (5 cm), cathode length (15 cm), and plasma diameter (10 cm). C-Fusion predicts that, for the test parameters used, the majority of fusion neutrons are created within the region of the cathode by beam-background reactions. The comparison of C-Fusion predictions with experiments shows that the magnitude formed by the recirculation parameter times the pressure (h p) behaves linearly with both the cathode voltage and the chamber pressure, and (h p) ~ 1 mTorr. Hence, for current pressure operation conditions, the number of ion recirculations in the chamber is approximately one, which is consistent with the theoretical prediction of h (estimated as the ratio between the ion mean free path to IEC C-device chamber length). This agreement sets C-Fusion as a valid description of the IEC C-device physics, and as a valid tool for its scaling.

Further parametric studies to predict future device operation (including pulsing) show a linear variation of the neutron generation rate above a certain voltage, reaching 108 D-D n/s for voltages and currents of 80-100 kV and 1 A, respectively.

1. Y. Gu, J.B. Javedani, and G.H. Miley, "A Portable Cylindrical Electrostatic-Fusion Device for Neutron Tomography", Fusion Technol., 26, 3, Part 2, 929-932 (1994).

** Work partly supported under Contract CC-S-622904-003-C