The microstructural change and aging behavior of Cu-1.8mass%Be-0.2mass%Co and Cu-3mass%Ti alloys severely deformed by high-pressure torsion (HPT) at room temperature were investigated on two-step aging condition; natural aging and subsequent arti cial aging. Application of HPT processing under an applied pressure of 5 GPa for 10 revolutions at 1 rpm to the alloys produced ultra-ne grained structures. The hardnesses of the Cu-Be-Co and Cu-Ti alloys increased with equivalent strain up to 7, and then saturated to constant values of 400 and 330 Hv, respectively. Aging the HPT-processed alloys at 293 K gradually decreased the resistivities of the alloys; however, even after the longest natural aging period of 2.59 Ms (1 month), the hardnesses of the alloys remained essentially unchanged. The attained peak hardness of the Cu-Be-Co alloy on subsequent arti cial aging at 593 K decreased with increasing natural aging time, while the age-hardening behavior of the Cu-Ti alloy during aging at 623 K was practically unaffected by natural aging at 293 K up to 2.59 Ms.

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Solution-treated Cu-1.8 mass%Be-0.2 mass%Co and Cu-3 mass%Ti alloys were subjected to severe plastic deformation using high-pressure torsion (HPT) process to examine the change in densities of grain boundary, dislocation and vacancy during natural aging of the two alloys at 293 K after HPT-straining, and the in uence of the natural aging on the age-hardening behavior of the alloys on subsequent articial aging. Application of HPT processing under an applied pressure of 5 GPa for 10 revolutions at 1 rpm to each alloy produced an ultrafine-grained structure. Aging the HPT-processed alloys at 293 K for the longest period of 2.59 Ms (1 month) did not essentially change the dislocation densities and grain sizes of the alloys; however, the vacancy concentrations of the alloys gradually decreased with increasing natural aging time. The attained peak hardness of the CuBe Co alloy on subsequent arti cial aging at 593 K decreased as natural aging time increased, while the natural aging at 293 K for 2.59 Ms had no in uence on the age-hardening behavior of the Cu-Ti alloy during arti cial aging at 623 K. This result is ascribed to the difference in formation mechanisms of strengthening precipitates between two alloys; G.P. zones are directly formed in CuBe Co alloy while β-Cu 4 Ti phase is formed via spinodal decomposition without nucleation events in Cu-Ti alloy.

A circular waveguide polarizer for 2.45 GHz microwaves has been designed and produced for electron Bernstein (EB) wave heating and current drive experiments on the low aspect ratio Torus experiment (LATE) device. In the experiments the microwaves are injected obliquely to the toroidal field to drive current carrying fast electrons. In the LATE case of the oblique injection of long free space wavelength waves onto a small plasma the coupling to the EB waves from the injected electromagnetic waves is improved when the injected waves have appropriate elliptical polarizations depending on the injection angle and the density gradient at the upper hybrid resonance layer (Igami et al 2006 Plasma Phys. Control. Fusion 48 573). Any elliptically polarized mode can be generated from a circular TE 11 mode by the combination of a half wave section and a quarter wave section of circular waveguide. The transformation of polarization arises from the difference in axial wave numbers between an orthogonal pair of modified circular TE 11 modes, which is realized by the insertion of a Teflon plate in a circular waveguide made of aluminum. Such a polarized wave is launched from the open end of a circular waveguide toward the plasma. An elliptically polarized mode adjusted to a steep density gradient and injected obliquely to the toroidal field has been found to be effective to sustain a highly over-dense plasma.