Gyrotrons are a high-power source of coherent microwave radiation 1 . Their oscillation mechanism is a cyclotron-resonance maser effect, in which a fraction of the rotational kinetic energy of a mildly relativistic magnetized electron beam is converted into electromagnetic energy. The most active area of gyrotron development is their potential use for heating magnetically confined fusion plasmas to the point of thermonuclear ignition. A major obstacle to this endeavour is that during high-power millimetre-wave operation 2-9 competing modes and mode shifts seriously degrade a gyrotron's stability and efficiency 10-13 . Here, we show that these problems can be overcome by active control of the electron-beam parameters during the oscillation. In doing so, we successfully demonstrate the robust steady-state operation of a 170 GHz gyrotron producing a continuous 1 MW output power with an unprecedented efficiency of over 55% in a hard-selfexcitation region. Moreover, we find that an adjacent resonant mode previously expected to compete with and adversely affect the principal operating mode does not in fact jeopardize but rather helps this mode as a result of nonlinear effects. The result improves the outlook for using these devices for heating and instability control in future experimental fusion reactors, such as ITER [14][15][16][17][18][19] .A basic configuration of the high-power gyrotron oscillator used in the experiment 7 is shown in Supplementary Information, Figs S1,S2. The nominal operation mode is TE 31,8 , in a cylindrical open resonator, whose radius is 17.9 mm. An annular electron beam of 9.13 mm in radius is injected into the resonator along the axial magnetic field to excite TE 31,8 . The oscillation millimetre-wave power P osci is converted to a gaussian-like beam using a quasi-optical launcher 20,21 attached to the resonator, and transmitted through an edge-cooled diamond window as P out . Here, P out ∼ 0.92P osci due to the ohmic loss and the diffraction loss P loss . The collector of the gyrotron is earthed. By applying a positive voltage V d.c. to the resonator section against the collector, the energy recovery of the spent electron beam is available to enhance the overall efficiency 22 .After a demonstration of 1 h oscillation at P out = 0.6 MW with fixed parameters, the operation parameters are actively controlled with a slow timescale to investigate the oscillation characteristics in the continuous-wave state. Figure 1a shows the dependence of the output power on the magnetic field in the resonator, B c . Here, V b ∼ −72.5 kV and V d.c. ∼ 25.5 kV. After the electron-beam I b had stabilized at ∼30 A completely, which takes ∼1 min, the B c scan started from 6.72 T. The frequency is ∼170 GHz. The power increases as the B c decreases, that is, the cyclotron resonance mismatch factor Δ = (1 − (f ce /γf )) increases. Here, f and f ce are oscillation and non-relativistic cyclotron frequencies, respectively, and γ is a relativistic factor of the initial electrons. The maximum power of 0.8 MW is obtained...

SUMMARYThis paper evaluates the potential of hydrogen (H2) and ammonia (NH3) as carbon‐free fuels. The combustion characteristics and NOx formation in the combustion of H2 and NH3 at different air‐fuel equivalence ratios and initial H2 concentrations in the fuel gas were experimentally studied. NH3 burning velocity improved because of increased amounts of H2 atom in flame with the addition of H2. NH3 burning velocity could be moderately improved and could be applied to the commercial gas engine together with H2 as fuels. H2 has an accelerant role in H2–NH3–air combustion, whereas NH3 has a major effect on the maximum burning velocity of H2–NH3–air. In addition, fuel‐NOx has a dominant role and thermal‐NOx has a negligible role in H2–NH3–air combustion. Thermal‐NOx decreases in H2–NH3–air combustion compared with pure H2–air combustion. NOx concentration reaches its maximum at stoichiometric combustion. Furthermore, H2 is detected at an air‐fuel equivalence ratio of 1.00 for the decomposition of NH3 in flame. Hence, the stoichiometric combustion of H2 and NH3 should be carefully considered in the practical utilization of H2 and NH3 as fuels. H2 as fuel for improving burning performance with moderate burning velocity and NOx emission enables the utilization of H2 and NH3 as promising fuels. Copyright © 2014 John Wiley & Sons, Ltd.

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We report preliminary results on the analysis of the three-body Υ( 10860) → B Bπ, Υ(10860) → [B B * + c.c.]π and Υ(10860) → B * B * π decays including an observation of the Υ(10860) → Z ± b (10610)π ∓ → [B B * + c.c.] ± π ∓ and Υ(10860) → Z ± b (10650)π ∓ → [B * B * ] ± π ∓ decays as intermediate channels. We measure branching fractions of the three-body decays to be B(Υ(10860) → [B B * + c.c.] ± π ∓ ) = (28.3 ± 2.9 ± 4.6) × 10 −3 and B(Υ(10860) → [B * B * ] ± π ∓ ) = (14.1 ± 1.9 ± 2.4) × 10 −3 and set 90% C.L. upper limit B(Υ(10860) → [B B] ± π ∓ ) < 4.0 × 10 −3 . We also report results on the amplitude analysis of the three-body Υ(10860) → Υ(nS)π + π − , n = 1, 2, 3 decays and the analysis of the internal structure of the three-body Υ(10860) → h b (mP )π + π − , m = 1, 2 decays. The results are based on a 121.4 fb −1 data sample collected with the Belle detector at a center-of-mass energy near the Υ(10860).

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An excited-state intramolecular proton transfer (ESIPT) fluorophore, 2,6-bis(benzothiazol-2-yl)phenol, was modified with alkoxy groups at the 4-position to obtain the methoxy (OMe), ethoxy (OEt), propoxy (OPr), and butoxy (OBt) derivatives. The derivatives exhibit bright red fluorescence in chloroform, giving the same fluorescence spectra with a maximum (λ max ) at 619 nm. However, in the crystalline state, the λ max values of OMe and OEt are bathochromically shifted, producing a deeper red color, whereas those of OPr and OBt are hypsochromically shifted producing an orange color. X-ray analysis of the OMe and OPr crystals shows that OMe molecules interact strongly with each other through sulfur-sulfur contacts, whereas the OPr molecules are stacked in an eclipsed arrangement. Assuming that the OMe and OPr crystals are J-and H-aggregates, respectively, the difference in solid-state fluorescence could be explained by the Davydov exciton coupling theory. The OEt derivative was the best solid-state red fluorophore (λ max = 633 nm) with a fluorescence quantum yield of 0.32. Therefore, ESIPT fluorophores are promising for developing a highly efficient solid-state red-emitting material with relatively small π-conjugation and no bulky groups.

Recent progress on the high power gyrotron development in JAEA is presented. The gyrotron is featured to have a triode-type magnetron injection gun, a cylindrical resonator working at 170 GHz with TE31,8 mode, a water-cooled diamond window and a depressed collector. After the demonstration of the ITER basic performance, the gyrotron has been operated for 3 years, and recorded ∼200 GJ of total output energy. Next, a gyrotron which oscillates in higher order resonator mode, TE31,12, is designed and fabricated to study the long pulse oscillation at greater than 1 MW. In parallel, feasibility studies of a CW-power modulation for neoclassical tearing mode stabilization, a dual frequency gyrotron and a rapid frequency control are carried out. It is shown that these gyrotrons will be available with current technology.