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

Abstract

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 D 2 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 I 1.7 for cathode grid current in the range I = 0.1 − 1 mA. This approaches the ideal ∝ I 2 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 I 1.7 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 temperaturedependent deuteron absorption by the grid cathode.

Preliminary results of a miniature cylindrical inertial electrostatic confinement fusion device equipped with inductively coupled plasma generator

“…Figures 5 to figure 7 represent the various measured neutron production rate (NPR) at different operational voltages of 30 kV, 35 kV and 40 kV which are depicted as a function of cathode current at different pressure and radio frequency (RF) power. It is deduced that by increment of cathode current the NPR increases almost as linear function for each data set at a fixed pressure while the RF power was changeable, (figure 5 to figure 7), and these linearity is in agreement with other similar IEC neutron yield results performed by K. Masuda and co-workers Also J. Kipritidis and J. Khachan [10][11][12]15]. Furthermore, in pulsed mode of operation which the IEC current increased of the order Ampere range, the NPR still have linear relation with the cathode current [2].…”

“…Apparently the slope of NPR increment grows by increment of cathode current. Volumetric NPR (in unit of m 3 per second) in a beam-target fusion machine could be written as: N PR volumetric = n i n t σv (ion-beam) [10] in which n i is the incident ion density n t is target ion density that here is proportinal with the gas presure, v ion-beam is ion-beam velocity and σ is the nuclear fusion cross section which is a function of ion beam velocity (or energy). The cathode gride current is proportinal to n i as: I = 4πer 2 n i v(r) [16] where I is the total ion recirculating current and v(r) is the ion velocity and σ is a function of cathode voltage.…”

“…of the cathode grid. Coulomb interactions reduce the beam-beam reactions, moreover, chargeexchange reactions which have the dominant cross sections in the usual operational pressure of the IEC device, reduce the beam-background reactions [10]. The operational pressure of the IEC device to sustain the glow discharge regime is around 1 Pa, at this pressure the charge-exchange (C-X) cross section reactions are much more than that of fusion reactions and the mean free path of ions for charge-C-X is around 10 cm which is lower than the usual distance between the electrodes.…”

Modeling the time variation of beam–grid fusion reaction rates in an Inertial Electrostatic Confinement device driven by a ring-shaped magnetron ion source

“…As such the gas presents a limitation to ion lifetimes and deuteron confinement. A new experimental IEC at Kyoto University aims to maximize the mean-free path λ CX of ion-gas charge exchange by operating at units of mPa gas pressures with the aid of an internal ring-shaped magnetron ion source (RS-MIS) [2].…”

“…In section 3 we present a model relating σ D2 (t) and the surface temperature T (t) to the simulated flux. In section 4 we calculate the beam-grid contribution to NPR for the experimental conditions of [2], and consider the role of beam-grid reactions in explaining the observations of time-varying NPR in that work.…”