For the GBAR (Gravitational Behaviour of Antihydrogen at Rest) experiment at CERN’s Antiproton Decelerator (AD) facility we have constructed a source of slow positrons, which uses a low-energy electron linear accelerator (linac). The driver linac produces electrons of 9 MeV kinetic energy that create positrons from bremsstrahlung-induced pair production. Staying below 10 MeV ensures no persistent radioactive activation in the target zone and that the radiation level outside the biological shield is safe for public access. An annealed tungsten-mesh assembly placed directly behind the target acts as a positron moderator. The system produces $5\times 10^7$ slow positrons per second, a performance demonstrating that a low-energy electron linac is a superior choice over positron-emitting radioactive sources for high positron flux.

对于在CERN的反质子减速器（AD）设施上进行的GBAR（静止氢反重力行为）实验，我们构建了一个慢正电子源，它使用低能量电子线性加速器（线性加速器）。驱动器直线加速器产生9 MeV动能的电子，由致辐射诱导的成对产生产生正电子。保持在10 MeV以下可确保目标区域内没有持续的放射性活化，并且生物屏蔽外的辐射水平对于公众是安全的。直接置于目标后面的退火钨网组件充当正电子缓和器。系统产生$5\times \mathrm{1个}{0}^7$ 每秒正电子速度慢，这一性能表明，对于高正电子通量而言，低能量电子直线加速器是优于正电子发射放射源的最佳选择。