Institute of High Energy Physics, Chinese Academy of Sciences

Cao J., Wang M., Pei Y., Li Q., Zhao L., Xu Q., Zhang M., Yang H., Ning F.

Chen Y., Guo L., Jia Q., Xie X., Zhu W., Wang P.

The research on the thermal insulation performance of experimental systems in the liquid helium temperature range is relatively scarce. This paper presents the theoretical design and establishment of a liquid helium storage system for insulation research, consisting of a liquid helium Dewar, a daily boil-off rate test subsystem, and a helium recovery subsystem. The passive thermal insulation structure consisted of a multilayer insulation (MLI) system with hollow glass microspheres serving as spacers. Based on self-built data acquisition, experiments were conducted to investigate the liquid helium insulation characteristics of an experimental system. A theoretical thermal analysis of the Dewar was conducted, resulting in the derivation of an expression for the heat leak of the Dewar. The analysis indicates that the evaporation capacity from the liquid helium Dewar was significantly affected by the structure of the neck tube. The overall relative error between the simulated and experimental temperature distribution of the insulation layer is 14.3%, with a maximum error of 22.3%. The system had an average daily boil-off rate of 14.4%, a heat leakage of 7.5 W, and a heat flux of 2.254 W/m2, while the effective thermal conductivity of the MLI with hollow glass microspheres was determined to be 2.887 × 10−4 W/(m·K). Furthermore, the apparent thermal conductivity between different layers of MLI significantly fluctuated with increasing temperature, ranging from a maximum of 5.342 × 10−4 W/(m·K) to a minimum of 1.721 × 10−4 W/(m·K).

Wang J., Zeng M., Li D., Gao J.

In recent years, the field of positron acceleration in plasma wakefield accelerators has witnessed rapid theoretical advancements, and several effective schemes have been proposed. In these studies, longitudinally uniform plasma is taken into account, with the positron beam located at the start of the second wakefield bubble. The electron filament near the positron beam provides Coulomb attraction force for the guiding of the positron beam. However, the influence of vacuum-plasma transition on positron beams has not been considered yet, where wakefield bubble is larger than that in the density plateau region, and the positron beam is in the defocusing region. In this paper, we study the evolution of positron beam size in the vacuum-plasma transition region and find out that the transition is detrimental to low-energy positron beams. Wide drive beams with relatively large transverse sizes are proposed as a possible solution to this difficulty. Published by the American Physical Society 2025

Mojahed M.A., Schmitz K., Xu X.

Wash-in leptogenesis is an attractive mechanism to produce the baryon asymmetry of the Universe. It treats right-handed-neutrino interactions as spectator processes, on the same footing as electroweak sphalerons, that reprocess primordial charge asymmetries in the thermal plasma into a baryon-minus-lepton asymmetry. The origin of these primordial charges must be accounted for by new CP-violating dynamics at very high energies. In this paper, we propose such a scenario of chargegenesis that, unlike earlier proposals, primarily relies on new interactions in the gravitational sector. We point out that a coupling of a conserved current to the divergence of the Ricci scalar during reheating can lead to nonzero effective chemical potentials in the plasma that, together with a suitable charge-violating interaction, can result in the production of a primordial charge asymmetry. Gravitational chargegenesis represents a substantial generalization of the idea of gravitational baryogenesis. We provide a detailed analysis of a generic and minimal realization that is consistent with inflation and show that it can successfully explain the baryon asymmetry of the Universe. Published by the American Physical Society 2025

Song X.

The possibility of compact stars as hideouts for color-spin-locked (CSL) quark matter (QM) is investigated in both the MIT bag model and the Nambu-Jona-Lasinio (NJL) model. Within the framework of the NJL model, the idea of absolutely stable quark matter and the existence of the conventional pure quark star (QS) are not supported; in addition, there appears to be no stable hybrid configuration above 2M⊙ as the hideout for CSL QM. The stable configurations of massive strange quark stars could be reproduced in the MIT bag model with QCD corrections being taken into account; moreover, they could act as the hiding place for the CSL QM. An interesting scenario is proposed that the phase transition to the CSL phase could occur in the cooling process. The CSL quark matter is an electromagnetic (EM) superconductor of type I, and a complete Meissner effect is expected. However, the analysis for this sizable superconductor indicates that most of the magnetic field is frozen inside the quark core with a critical strength, while in some special cases a small fraction could be expelled from a thin layer near the surface in a short time. The analysis on energetics and timescale suggests that this process could act as an inducement mechanism to power typical fast radio bursts, but as a single source of energy, it is unlikely to generate other EM emissions such as gamma-ray bursts and giant flares. Published by the American Physical Society 2025

Yang Y., Bi X., Yin P.

Yang C., Yao J., Meng S., Wang P., He M., Li P., Xiao P., Xiao J., Liu Y., Li Z.

Xu R., Xia X., Han Z., Wang D., Ji G., Wang H., Cui X., Liu Y., Shi X., Jiang W., Fan R., Liang H.

Ma X., Ma Y., Li Z., Zhang Y., Zhang J., Wei W., Li H., Ji X., Liu P., Chen Y.

Yang X., Ji X., Zhu K., Zhang S., Li H., Yu Z., Xiao P., Shi Y., Ma X.

Xu C., Zhang H., Zhou J., Chen Y., Yan Z., Liang Z., Wu T., Hu J., Wei W., Zhang Y.

Li H., Ye M., Xie X., Liu S., Huang S., Jiang X., Hu J.

Xu C., Zhou J., Zhang H., Zheng W., Zhou Y., Dong S., Dong J., Lu Y., Ouyang Q.

Wu Y., Yu Z., Zhang S., Chen C., Zhang H., Li F., Gu M., Zhu K.

Zhao X., Ke Y., Xie S., Sun M., Jiang H., Li B., Wang X.

Solid-state precipitation is an effective strategy for tuning the mechanical and functional properties of advanced alloys. Structure design and modification necessitate good knowledge of the kinetic evolution of precipitates during fabrication, which is strongly correlated with defect concentration. For Fe-Ga alloys, giant magnetostriction can be induced by the precipitation of the nanoscale tetragonal L60 phase. By introducing quenched-in vacancies, we significantly enhance the magnetostriction of the aged Fe81Ga19 polycrystalline alloys to ∼305 ppm, which is close to the level of single crystals. Although vacancies were found to facilitate the generation of the L60 phase, their impact on the precipitation mechanism and kinetics has yet to be revealed. This study combined transmission electron microscopy (TEM) and time-resolved small-angle neutron scattering (SANS) to investigate the precipitation of the L60 phase during the isothermal aging at 350 and 400 °C, respectively. The evolution of L60 nanophase in morphology and number density in as-cast (AC) and liquid nitrogen quenched (LN) Fe81Ga19 alloys with aging time were quantitatively compared. Interestingly, the nucleation of the L60 phase proceeds progressively in AC while suddenly in LN specimens, indicating the homogenous to heterogeneous mechanism switching induced by concentrated vacancies. Moreover, excess vacancies can change the shape of nanoprecipitates and significantly accelerate the growth and coarsening kinetics. The magnetostrictive coefficient is optimized when the size (long-axis) of L60 precipitates lies between 100 and 110 Å with a number density between 3.2–4.3 × 10–7 Å–3. Insight from this study validates the feasibility of achieving high magnetoelastic properties through precise manipulation of the nanostructure.