4th Generation High-Brightness Electron Beam Shaping and Light Source Applications

申请人及其合作者最近构思、获得专利并发表的一种基于等离子体的产生高质量电子束的新概念，将进行实验论证和优化。首先，应开发基于锂、铷、铯等最低电离阈值碱金属蒸气的等离子体源。紧凑型电子束将利用它们的电场使这些蒸汽自电离，然后驱动强烈的等离子体波。这些等离子体波非常适合加速电子，因为与传统加速器相比，这种等离子体波的集体电场可以大四个数量级。同步的超短激光脉冲，峰值强度比最先进的激光等离子体加速器低4个数量级，然后电离其焦点中的第二个气体成分，从而以最小的横向动量直接在等离子体波内释放电子。该气体组分应具有比构成等离子体波的介质（例如氦）更高的电离阈值。激光释放的氦电子现在被聚焦、捕获并在等离子体波中迅速加速。由于释放激光的聚焦强度被最小化，在这种低密度光电阴极等离子体尾流场加速方案中释放的电子是超冷的，并形成最小发射度的束。而发射度对于基于自由电子激光、康普顿后向散射或等离子体中电子振子振荡的电子束光源至关重要。概念验证实验将在汉堡大学进行，并将在德国的激光等离子体加速器设施以及斯坦福直线加速器（SLAC）进行。此外，为了优化方案的加速距离和能量增益，以及方案的稳定性和可调性，还需要研究低电离阈值组件通过激光脉冲和放电的预电离以及释放激光脉冲相对于等离子体波在空间和时间上的平移。最终，该计划将为控制产生前所未有质量的电子束铺平道路，并为医学和基础研究开发紧凑，成本效益高的优质光源。

A novel plasma based concept for generation of electron beams of highest quality which has recently been conceived, patented and published by the applicant and his collaborators shall be experimentally demonstrated and optimized. At first, plasma sources based on lowest-ionization-threshold alkali metal vapors such as lithium, Rubidium and cesium shall be developed. Compact electron beams shall then self-ionize these vapors by virtue of their electric self-fields, and shall then drive an intense plasma wave. These plasma waves are excellently suited to accelerate electrons, since the collective electric fields of such plasma waves can be four orders of magnitude larger as compared to conventional accelerators. A synchronized, ultrashort laser pulse with a peak intensity about four orders of magnitude lower than in state-of-the-art laser-plasma-accelerators shall then ionize a second gaseous component in its focus, thus releasing electrons directly inside the plasma wave with minimal transversal momentum. This gas component shall have a higher ionization threshold than the medium constituting the plasma wave, for example helium. The laser-released helium electrons are now focused, trapped and rapidly accelerated in the plasma wave. Since the focus intensity of the release laser is minimized, the released electrons in this underdense photocathode plasma wakefield acceleration scheme are ultracold and form bunches of minimized emittance. The emittance, in turn, is crucial for electron beam based light sources based on free-electron-lasers, Compton backscattering or betatron oscillations in the plasma. Proof-of-concept experiments shall be developed at University of Hamburg and shall be carried through at laser-plasma-accelerator facilities in Germany, as well as at the Stanford Linear Accelerator (SLAC). Furthermore, preionization of the low-ionization-threshold component via laser pulses and discharges and translation of the release laser pulse in space and time with respect to the plasma wave shall be studied in order to optimize the acceleration distance and energy gain, as well as the stability and tunability of the scheme. Ultimately, the scheme shall pave the way to the controlled generation of electron beams of unprecedented quality, and the development of compact, cost-effective and superior light sources for medicine and fundamental research.