Fusion materials research started in the early 1970s following the observation of the degradation of irradiated materials used in the first commercial fission reactors. The technological challenges of fusion energy are intimately linked with the availability of suitable materials capable of reliably withstanding the extremely severe operational conditions of fusion reactors. Although fission and fusion materials exhibit common features, fusion materials research is broader. The harder mono-energetic spectrum associated with the deuterium–tritium fusion neutrons (14.1 MeV compared to <2 MeV on average for fission neutrons) releases significant amounts of hydrogen and helium as transmutation products that might lead to a (at present undetermined) degradation of structural materials after a few years of operation. Overcoming the historical lack of a fusion-relevant neutron source for materials testing is an essential pending step in fusion roadmaps. Structural materials development, together with research on functional materials capable of sustaining unprecedented power densities during plasma operation in a fusion reactor, have been the subject of decades of worldwide research efforts underpinning the present maturity of the fusion materials research programme. For achieving proper safety and efficiency of future fusion power plants, low-activation materials able to withstand the extreme fusion conditions are needed. Here, the irradiation physics at play and fusion materials research is reviewed.

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Materials research for fusion

The high-current low-emittance microwave proton source introduced two years ago act the Chalk River Laboratories has been extensively redesigned. The 2.45 GHz microwave line was modified to incorporate a 50 kV dc break and a rectangular-to-ridged waveguide transition. The layered microwave window has been replaced by a single plate of aluminum nitride. The solenoids were electrically isolated from the plasma chamber. Only the plasma chamber remains at the extraction potential. The total beam current and the proton beam current have been measured as a function of the microwave power, the hydrogen mass flow and the solenoid positions and currents. More than 95 mA dc of hydrogen ions with a proton fraction in excess of 85% were extracted from a single 2.5 mm radius aperture with only 500 W of microwave power and 2.0 sccm (3 μg/s) of hydrogen mass flow. The perveance at minimum divergence and the minimum emittance have been determined for various extraction geometries. The variation of the perveance with the aspect ratio of the extraction system was found to be virtually identical for microwave and arc discharge ion sources. The normalized rms emittance was less than 0.13 p mm mrad whatever the extraction geometry.

An advanced high-current low-emittance dc microwave proton source

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Overview of the IFMIF/EVEDA project

A 110-mA, 75-keV dc proton injector is being developed at Los Alamos. We use a microwave proton source coupled to a two solenoid, space-charge neutralized, low-energy beam transport (LEBT) system. The ion source produces 110-mA proton current at 75 keV using 600 - 800 W of 2.45 GHz input discharge power. Typical proton fraction is 85-90% of the total extracted ion current, and the rms normalized beam emittance after transport through a prototype 2.1 m LEBT is 0.20 ({pi}mm-mrad). Beam space-charge neutralization is measured to be > 98% which enables the solenoid magnetic transport to successfully match the injector beam into a radio-frequency quadrupole (RFQ). Beam simulations indicate small emittance growth in the proposed 2.8 m low-energy demonstration accelerator (LEDA) LEBT. The LEBT also contains beam diagnostics, steering, and a beam deflector for variable duty factor and accelerator fast protect functions. The injector computer controls and reliability status are also discussed.

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Status report on a dc 130-mA, 75-keV proton injector

A 110 mA, 75 keV dc proton injector is being developed at Los Alamos A microwave proton source is coupled to a two solenoid, space-charge neutralized, low-energy beam transport (LEBT) system The ion source produces 110 mA proton current at 75 keV using 600–800 W of 245 GHz discharge power Typical proton fraction is 85%–90% of the total extracted ion current, and the rms normalized beam emittance after transport through a prototype 21 m LEBT is 020 (πmm mrad) Beam space-charge neutralization is measured to be >98% which enables the solenoid magnetic transport to successfully match the injector beam into a radio-frequency quadrupole Beam simulations indicate small emittance growth in the proposed 28 m low-energy demonstration accelerator LEBT The LEBT also contains beam diagnostics, steering, and a beam deflector for variable duty factor and accelerator fast protect functions The injector beam availability status is also discussed

Status report on a dc 130 mA, 75 keV proton injector (invited)

A simple high-current low-emittance dc ECR proton source has been developed for a cw RFQ accelerator injector. Proton fractions of up to 90% have been obtained at beam current densities as high as 350 mA/cm2. The normalized rms emittance of a 25 mA beam from a single 4.0 mm diameter extraction aperture was 0.07 π mm mrad corresponding to a brightness of 5 A/(π mm mrad)2. Similar results were obtained with multiple aperture extraction systems.

Terence Taylor

Papers

An advanced high-current low-emittance dc microwave proton source

A high-current low-emittance dc ECR proton source