Bright sources of high-energy electromagnetic radiation are widely employed in fundamental research, industry and medicine^1,2. This motivated the construction of Compton-based facilities planned to yield bright gamma-ray pulses with energies up to³ 20 MeV. Here, we demonstrate a novel mechanism based on the strongly amplified synchrotron emission that occurs when a sufficiently dense ultra-relativistic electron beam interacts with a millimetre-thickness conductor. For electron beam densities exceeding approximately 3 × 10¹⁹ cm⁻³, electromagnetic instabilities occur, and the ultra-relativistic electrons travel through self-generated electromagnetic fields as large as 10⁷–10⁸ gauss. This results in the production of a collimated gamma-ray pulse with peak brilliance above 10²⁵ photons s⁻¹ mrad⁻² mm⁻² per 0.1% bandwidth, photon energies ranging from 200 keV to gigaelectronvolts and up to 60% electron-to-photon energy conversion efficiency. These findings pave the way to compact, high-repetition-rate (kilohertz) sources of short (≲30 fs), collimated (milliradian) and high-flux (>10¹² photons s⁻¹) gamma-ray pulses.

高能电磁辐射的光明来源广泛用于基础研究，工业和医学^1,2。这激励了基于Compton的设施的建设，该设施计划产生能量高达³ 20 MeV的明亮伽马射线脉冲。在这里，我们展示了一种基于强烈放大的同步加速器发射的新颖机制，当足够密集的超相对论电子束与毫米厚度的导体相互作用时，就会发生这种现象。对于电子束密度超过大约3×10 ¹⁹  cm ^-3的情况，会发生电磁不稳定，并且超相对论电子会通过高达10 ⁷ –10 ^8的自生电磁场传播高斯。这导致产生准直的伽马射线脉冲，其峰值亮度高于每0.1％带宽10 ^25个光子s ^-1 mrad ^-2 mm ^-2，光子能量范围从200 keV到千兆电子伏，电子对电子的最高60％光子能量转换效率。这些发现为紧凑的，高重复频率（千赫兹）的短（≲30 fs），准直（毫弧度）和高通量（> 10 ¹²光子s ^-1）伽马射线脉冲源铺平了道路。