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Challenges and limitations in development of the mid-infrared room temperature CW operated diode lasers with wavelength longer than 2 μm are discussed. The major breakthrough in terms of high power performance in this spectral range was achieved with type-I true quaternary InGaAsSb heavily compressively strained QW GaSb-based lasers. We have demonstrated 1 W CW at 2.5 μm, 500 mW and 160 mW CW at 2.7 and 2.8 μm, respectively. High power 2.3 μm linear laser arrays output 10W CW at room temperature. Experimental results show that there is no fundamental limitation to extend CW RT operating wavelength of these devices to over 3 μm spectral region. It is carrier leakage and material quality issues that limit device performance at wavelength longer than 2.5 μm. The role of Auger recombination is not decisive in type-I MQW GaSb-based lasers. We speculate that it is high differential gain and, as a result, low threshold carrier concentration that can account for muted effect of Auger on type-I GaSb-based laser performance. Dilute-nitride GaSb-based type-I QWs are proposed for development of CW room temperature operated lasers in spectral range 3 - 4 μm.

The proton accelerator of the China Initiative Accelerator Driven Subcritical System (CiADS) adopts the continuous wave (CW) and superconducting technical route, and it may accelerate 5 mA proton beam to 500 MeV in energy. In this paper, the baseline physics design of the superconducting section (SC) and some design choices are discussed, and the error study results are also presented.

The beam power of the CEPC Collider is about 60 MW, so an efficiency of an RF power source is very important for cost of project implementation. The most popular source for an accelerator is a klystron, which has the advantage that it can be operated at high power with a reasonable high efficiency. IHEP is developing 650 MHz klystron with 800 kW CW output power and 80% efficiency. To reach this goal, a couple of klystron prototypes will be manufactured in the near future. The first prototype is completely manufactured by Institute of Electronics (IE) and GLVAC Company and the first step of high-power conditioning and commissioning is also completed in IHEP. The design schemes of high-efficiency klystron are also in progress.

A high-power superconducting linac with an energy of 30MeV and a beam current of 100mA has been proposed and designed. The primary challenge lies in beam loss control and a robust lattice structure to ensure stable operation. This paper discusses the physics design study, design principles and simulation results considering machine errors. Extensive multiparticle simulations (a cumulative statistic of $1\times 10^5$ macroparticles) demonstrated that this linac, operating at 100mA, could maintain beam losses lower than 1W/m in error scenarios.

We review our recent progress on power scaling of THz pulses generated from several nonlinear-optical crystals. By using a high-resistivity GaP crystal, we have significally increased the output peak power to as high as 722 W. By stacking three GaP wafers, we have further increased the highest output peak power to 2.36 kW. On the other hand, by using CO₂ laser pulses, we have obtained the average output power of 260 μW. We have also used these laser pulses to scale up the output power for the THz pulses to 29.8 μW by stacking GaAs wafers. Indeed, by stacking up to ten wafers, we have increased the output power by a factor of 160. Finally, by using ultrafast laser pulses, we have achieved record-high output powers for the THz pulses generated from multi-period periodically-poled LiNbO₃ crystals based on a backward configuration. The highest output power measured by us so far is 10.7 μW.

This review summarizes projects and studies on circular accelerators proposed for driving subcritical reactors. The early isochronous cyclotron cascades, proposed about 20 years ago, and the evolution of these layouts up to the most recent solutions or designs based on cyclotrons and fixed field alternating gradient accelerators, are reported. In addition, the newest ideas and their prospects for development are discussed.

The key factor to the miniaturization of piezoelectric devices is power density, which is limited by the heat generation or loss mechanisms. There are three loss components in general in piezoelectric vibrators/resonators, i.e., dielectric, elastic and piezoelectric losses. The mechanical quality factor, determined by these three factors, is the Figure Of Merit (FOM) in the sense of loss or heat generation. In this paper, we introduce a new loss phenomenology and innovative measuring methods based on the theory. First, quality factors at resonance and antiresonance for the k₃₁, k₃₃, k_t and k₁₅ vibration modes are derived theoretically, and the methodology for determining loss factors in various orientations (i.e., loss anisotropy) is provided. For simplicity, we focus on materials with ∞ mm (equivalent to 6 mm) crystal symmetry for deriving the loss factors of a polycrystalline ceramic, and 14 different loss factors among 20 in total can be obtained from the measurements. Second, we propose the experimental methods for measuring both mechanical quality factors Q_A and Q_B at the resonance and antiresonance modes: a continuous admittance/impedance spectrum measuring method (traditional with temperature rise) and a burst mode (to circumvent the temperature effect).

Challenges and limitations in development of the mid-infrared room temperature CW operated diode lasers with wavelength longer than 2 μm are discussed. The major breakthrough in terms of high power performance in this spectral range was achieved with type-I true quaternary InGaAsSb heavily compressively strained QW GaSb-based lasers. We have demonstrated 1 W CW at 2.5 μm, 500 mW and 160 mW CW at 2.7 and 2.8 μm, respectively. High power 2.3 um linear laser arrays output 10W CW at room temperature. Experimental results show that there is no fundamental limitation to extend CW RT operating wavelength of these devices to over 3 μm spectral region. It is carrier leakage and material quality issues that limit device performance at wavelength longer than 2.5 μm. The role of Auger recombination is not decisive in type-I MQW GaSb-based lasers. We speculate that it is high differential gain and, as a result, low threshold carrier concentration that can account for muted effect of Auger on type-I GaSb-based laser performance. Dilute-nitride GaSb-based type-I QWs are proposed for development of CW room temperature operated lasers in spectral range 3 - 4 μm.

This review summarizes projects and studies on circular accelerators proposed for driving subcritical reactors. The early isochronous cyclotron cascades, proposed about 20 years ago, and the evolution of these layouts up to the most recent solutions or designs based on cyclotrons and fixed field alternating gradient accelerators, are reported. In addition, the newest ideas and their prospects for development are discussed.