Schätz T, Schramm U, Habs D
Sektion Physik, LMU München, Garching, Germany.
Nature. 2001 Aug 16;412(6848):717-20. doi: 10.1038/35089045.
By freezing out the motion between particles in a high-energy storage ring, it should be possible to create threads of ions, offering research opportunities beyond the realm of standard accelerator physics. The usual heating due to intra-beam collisions should completely vanish, giving rise to a state of unprecedented brilliance. Despite a continuous improvement of beam cooling techniques, such as electron cooling and laser cooling, the ultimate goal of beam crystallization has not yet been reached in high-energy storage rings. Electron-cooled dilute beams of highly charged ions show liquid-like order with unique applications. An experiment using laser cooling suggested a reduction of intra-beam heating, although the results were ambiguous. Here we demonstrate the crystallization of laser-cooled Mg+ beams circulating in the radiofrequency quadrupole storage ring PALLAS at a velocity of 2,800 m s-1, which corresponds to a beam energy of 1 eV. A sudden collapse of the transverse beam size and the low longitudinal velocity spread clearly indicate the phase transition. The continuous ring-shaped crystalline beam shows exceptional stability, surviving for more than 3,000 revolutions without cooling.
通过在高能储存环中冻结粒子间的运动，应该有可能制造出离子束，从而提供超出标准加速器物理领域的研究机会。通常由束内碰撞引起的加热应该会完全消失，从而产生一种前所未有的高亮度状态。尽管束冷却技术（如电子冷却和激光冷却）不断改进，但高能储存环尚未实现束结晶的最终目标。电子冷却的高电荷离子稀释束表现出类似液体的有序性，具有独特的应用。一项使用激光冷却的实验表明束内加热有所减少，尽管结果并不明确。在此，我们展示了在射频四极储存环PALLAS中以2800米/秒的速度循环的激光冷却Mg+束的结晶，这对应于1电子伏特的束能量。横向束尺寸的突然缩小和低纵向速度展宽清楚地表明了相变。连续的环形结晶束表现出非凡的稳定性，在没有冷却的情况下存活了超过3000圈。
