Cathode grid current dependence of D(d, n)3He reaction rates in an inertial electrostatic confinement device driven by a ring-shaped magnetron ion source

We present D(d, n)3 He reaction rates for a new inertial electrostatic confinement (IEC) device which aims to overcome neutralization (charge exchange) of accelerating ions by operating at D2 gas pressures of just 5–10 mPa with the aid of an internal ring-shaped magnetron ion source. Initial experiments with a voltage of −60 kV applied to a central spherical cathode grid yield neutron production rates (NPR) proportional to I1.7 for cathode grid current in the range I = 0.1 − 1 mA. This approaches the ideal ∝ I2 dependence for a system dominated by energetically preferred, 'beam–beam' reactions between converging nuclei. However, later measurements show NPR ∝ I and also indicate changes in the pressure dependence. In fact the I1.7 dependence was recovered by increasing the cathode grid voltage to −80 kV, though this too was only temporary. We suggest that time variation of NPR may be partially explained by a significant contribution of beam–grid reactions and temperature-dependent deuteron absorption by the grid cathode.