Neutron production from feedback controlled thermal cycling of a pyroelectric crystal

Abstract

The LLNL Crystal Driven Neutron Source is operational and has produced record ion currents of approximately 10 nA and neutron output of 1.9(+/-0.3)x10(5) per thermal cycle using a crystal heating rate of 0.2 degrees C/s from 10 to 110 degrees C. A 3 cm diameter by 1 cm thick LiTaO(3) crystal with a socket secured field emitter tip is thermally cycled with feedback control for ionization and acceleration of deuterons onto a deuterated target to produce D-D fusion neutrons. The entire crystal and temperature system is mounted on a bellows which allows movement of the crystal along the beam axis and is completely contained on a single small vacuum flange. The modular crystal assembly permitted experimental flexibility. Operationally, flashover breakdowns along the side of the crystal and poor emitter tip characteristics can limit the neutron source. The experimental neutron results extend earlier published work by increasing the ion current and pulse length significantly to achieve a factor-of-two higher neutron output per thermal cycle. These findings are reviewed along with details of the instrument.

Intense pulsed neutron emission from a compact pyroelectric driven accelerator

“…The rear of the crystal is grounded. The crystal is heated and cooled using a feedback controlled TE cooler as described in [4]. The spark ion source provides the ion beam for the accelerator and is operated with input pulse lengths of ~50 ns and voltages of ~4 kV, resulting in peak plasma spark currents of ~65 A shown in Figure 2.…”

“…The pressure in the system is kept below 10 -8 Torr. For diagnostics, a 14 tube 3 He array similar to the one in ref [4] is used; the total efficiency is 3(±0.45) x 10 -3 detected neutrons per source neutron. For this study, the electronics render detected neutrons for a total 524 µs after they are triggered Concerning the bremsstrahlung spectra and crystal voltages, in addition to data from neutron experiments, runs with the spark source replaced by a thin tungsten foil to increase bremsstrahlung signal and with the NaI detector at various angles to the foil were performed to deduce voltages for different temperature cycles.…”

“…To achieve pulse operation in a proof-of-principle experiment, we have re-configured the LLNL CDNS experiment [4]. Specifically, by incorporating a compact independently controlled spark plasma ion source with a negative high voltage pyroelectric crystal, we are able to produce intense, user-controlled, pulsed D-D neutron emission with rates greater than ~10 10 n/s during the pulse, pulse widths on the order of ~100's ns, and neutron yields greater than 10 k per pulse in the experiment.…”

“…Simple and compact pyroelectric based accelerators [1][2][3][4] for neutron generation are of interest for various applications, including as a source for active interrogation of unknown threats containing explosives or nuclear materials [5]. For these applications, the ability to produce high intensity user-requested pulses of neutrons with very short pulse widths is highly desirable.…”

D-D nuclear fusion using different size pyroelectric crystals

“…Currently, neutron production from D-D fusion using pyroelectric crystals is orders of magnitude below the theoretical limit. Typical neutron yields are 10 3 neutrons per thermal cycle with some isolated events reaching 10 4 to 10 5 neutrons per thermal cycle [5]- [7]. A possible reason for low neutron production may be due to the effects of electrons accelerated from the target crystal to the tip crystal.…”