Abstract
The output and target lifetime of a conventional electrostatic neutron generator are limited by the voltage stand-off capability and the acceleration of molecular species from the ion source. As an alternative, we suggest that the deuterium beam achievable from a compact high intensity ECR source can be injected directly into a compact RFQ to produce a more efficient compact neutron production system. Only the d+ ions are accelerated by the RFQ, which can also produce much higher output energies than electrostatic systems, resulting in a higher neutron output with a longer target lifetime. The direct injection of the beam makes the system more compact than the multielement, electrostatic systems typically used for extraction of the beam and subsequent transport and matching into the RFQ. We have designed and optimized a combined extraction/matching system for a compact high current deuterium ECR ion source injected into a high frequency RFQ structure, allowing a beam of about 12 mA of d+ ions to be injected at a modest ion source voltage of 25 kV. The end wall of the RFQ resonator serves as the ground electrode for the ion source, resembling DPI (direct plasma injection). For this design, we used the features of the code IGUN to take into account the electrostatic field between the ion source and the RFQ end wall, the stray magnetic field of the ECR source, the defocusing space charge of the low energy deuteron beam, and the rf focusing in the fringe field between the RFQ vanes and the RFQ flange.
Highlights
The radiofrequency quadrupole (RFQ) accelerator has a number of advantages as a neutron generator over other accelerator-based devices such as sealed tubes, electrostatic accelerators, and cyclotrons
We suggest that the deuterium beam achievable from a compact high intensity ECR source can be injected directly into a compact RFQ to produce a more efficient compact neutron production system
We used the features of the code IGUN to take into account the electrostatic field between the ion source and the RFQ end wall, the stray magnetic field of the ECR source, the defocusing space charge of the low energy deuteron beam, and the rf focusing in the fringe field between the RFQ vanes and the RFQ flange
Summary
The radiofrequency quadrupole (RFQ) accelerator has a number of advantages as a neutron generator over other accelerator-based devices such as sealed tubes, electrostatic accelerators, and cyclotrons. A revolutionary new extraction system is used to inject the deuterons directly from the ion source into the RFQ structure without the standard matching lens used in conventional RFQ linacs This small 425 MHz RFQ produces a 500 keV deuteron beam in less than 0.5 m and can be powered by a very compact solid-state rf power system. The high current ion beam exits the RFQ linac with a low divergence in both planes, which makes it possible to transport the beam in a short drift tube from the accelerator to a remote target, resulting in smaller shielding and neutron moderator requirements. This makes it ideal for generating thermal neutrons. The new technology used for this system can be extended to higher energy RFQs to produce larger systems capable of neutron outputs of two orders of magnitude more, but these are not compact systems packaged into a single unit
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