Micron cubed particle beam characterization via ionization-based techniques

Speaker: Dr. Roxana Tarkeshian (Bern University)

In future collider concepts, particle beams may be focused to sub-micrometer transverse beam sizes to maximize the luminosity of the collider and ultrashort beam durations may aid to minimize the amount of Beamstrahlung that would impact the performance of accelerator and detectors. Free electron lasers (FELs) rely on high brightness beams and maximizing the so-called ρ-parameter (a measure of the brightness) is crucial for optimizing self-amplified spontaneous emission (SASE) performance control.

The compactness of the micron sized beams of such high performance machines makes measuring and controlling a major challenge and novel advanced diagnostic techniques are required to run such accelerators. While the total charge can be readily measured with existing technologies, new concepts are required to access the relevant regimes of few femtosecond beam duration and few micron transverse beam sizes. An indirect technique to reconstruct particle beam properties relies on photo-ionization of gases induced by intense FEL pulses, produced by the intense electron beams, combined with streaking techniques. To address the challenge of measuring and optimizing intense particle beams for ultra-bright beams we propose and have carried out an in-depth analysis of an adaption of this concept. In contrast with photo-ionized processes, when using intense particle beams to ionize a gas, very different physics is manifested due to the large unipolar fields of the charged particle beam that impart a significant momentum to the plasma electrons. As they escape with high radial velocities, they leave the ions unshielded. This non- neutral plasma undergoes Coulomb explosion and the resulting dynamics offers new avenues for direct particle beam characterization. By characterizing the tunnel ionization induced species beam properties can be retrieved. In addition, the exponential dependency of tunnel ionization on the particle beam's radial space- charge field, and thus its charge density, results in a sensitive monitor that can measure micron cubed particle beams with unprecedented resolution (few 10’s of nm level). Achieving such resolution is challenging or simply not possible with today’s methods, let alone on a single shot basis that is minimally invasive. We will discuss further improvements in real time measurements and resolution that can be achieved by integrating laser based techniques. As such this method would provide a low-cost alternative technique for collider beamcharacterization. The result of elaborate numerical modeling, experimental planning at radio-frequency and  promised plasma FEL facilities, LCLS at SLAC and BELLA center at LBNL, will be presented.

Start time: 2:30 p.m.

Coffee will be served before the seminar, at 2:15 p.m.

Registration for this event is currently open.