Sebastian Pfotenhauer

Laser-plasma acceleration of quasi-monoenergetic protons from microstructured targets

Particle acceleration based on high intensity laser systems (a process known as laser–plasma acceleration) has achieved high quality particle beams that compare favourably with conventional acceleration techniques in terms of emittance, brightness and pulse duration. A long-term difficulty associated with laser–plasma acceleration—the very broad, exponential energy spectrum of the emitted particles—has been overcome recently for electron beams. Here we report analogous results for ions, specifically the production of quasi-monoenergetic proton beams using laser–plasma accelerators. Reliable and reproducible laser-accelerated ion beams were achieved by intense laser irradiation of solid microstructured targets. This proof-of-principle experiment serves to illuminate the role of laser-generated plasmas as feasible particle sources. Scalability studies show that, owing to their compact size and reasonable cost, such table-top laser systems with high repetition rates could contribute to the development of new generations of particle injectors that may be suitable for medical proton therapy.

Guidelines for Quality Provision in Cross-Border Higher Education

The Guidelines for Quality Provision in Cross-border Higher Education were developed and adopted to support and encourage international cooperation and enhance the understanding of the importance of quality provision in cross-border higher education. The purposes of the Guidelines are to protect students and other stakeholders from low-quality provision and disreputable providers (that is, degree and accreditation mills) as well as to encourage the development of quality cross-border higher education that meets human, social, economic and cultural needs. Based on a survey about the main recommendations of the Guidelines, this report monitors the extent to which OECD countries and a few non-member partners complied with its recommendations in 2011. Twenty-three responses were obtained from 22 Members.

All-optical measurement of the hot electron sheath driving laser ion acceleration from thin foils

We present experimental results from an all-optical diagnostic method to directly measure the evolution of the hot-electron distribution driving the acceleration of ions from thin foils using high-intensity lasers. Central parameters of laser ion acceleration such as the hot-electron density, the temperature distribution and the conversion efficiency from laser pulse energy into hot electrons become comprehensively accessible with this technique.

A method of determining narrow energy spread electron beams from a laser plasma wakefield accelerator using undulator radiation

In this paper a new method of determining the energy spread of a relativistic electron beam from a laser-driven plasma wakefield accelerator by measuring radiation from an undulator is presented. This could be used to determine the beam characteristics of multi-GeV accelerators where conventional spectrometers are very large and cumbersome. Simultaneous measurement of the energy spectra of electrons from the wakefield accelerator in the 55–70 MeV range and the radiation spectra in the wavelength range of 700–900 nm of synchrotron radiation emitted from a 50 period undulator confirm a narrow energy spread for electrons accelerated over the dephasing distance where beam loading leads to energy compression. Measured energy spreads of less than 1% indicates the potential of using a wakefield accelerator as a driver of future compact and brilliant ultrashort pulse synchrotron sources and free-electron lasers that require high peak brightness beams.

Panacea or diagnosis? Imaginaries of innovation and the ‘MIT model’ in three political cultures

Innovation studies continue to struggle with an apparent disconnect between innovation’s supposedly universal dynamics and a sense that policy frameworks and associated instruments of innovation are often ineffectual or even harmful when transported across regions or countries. Using a cross-country comparative analysis of three implementations of the ‘MIT model’ of innovation in the UK, Portugal and Singapore, we show how key features in the design, implementation and performance of the model cannot be explained as mere variations on an identical solution to the same underlying problem. We draw on the concept of sociotechnical imaginaries to show how implementations of the ‘same’ innovation model – and with it the notion of ‘innovation’ itself – are co-produced with locally specific diagnoses of a societal deficiency and equally specific understandings of acceptable remedies. Our analysis thus flips the conventional notion of ‘best-practice transfer’ on its head: Instead of asking ‘how well’ an innovation model has been implemented, we analyze the differences among the three importations to reveal the idiosyncratic ways in which each country imagines the purpose of innovation. We replace the notion of innovation as a ‘panacea’ – a universal fix for all social woes – with that of innovation-as-diagnosis in which a particular ‘cure’ is ‘prescribed’ for a ‘diagnosed’ societal ‘pathology,’ which may in turn trigger ‘reactions’ within the receiving body. This approach offers new possibilities for theorizing how and where culture matters in innovation policy. It suggests that the ‘successes’ and ‘failures’ of innovation models are not a matter of how well societies are able to implement a sound, universal model, but more about how effectively they articulate their imaginaries of innovation and tailor their strategies accordingly.

Scaling of the proton density reduction scheme for the laser acceleration of proton beams with a narrow energy spread

The laser acceleration of proton beams with quasi-monoenergetic features in the energy spectra from microdot targets is investigated by numerical simulation. The formation of these spectral peaks is strongly dependent on the interplay between different ion species in the target. The scaling of the spectral peaks energy, and number of protons in the spectral peak, with both microdot composition and laser intensity is considered. Particular attention is given to determining the proton concentration below which the number of protons in the spectral peak rapidly diminishes. It is shown that at proton concentrations of 1-5ncrit a spectral peak is produced that reaches an energy up to 70% of the maximum proton energy, whilst still containing more protons than would be produced by a conventional target in this energy range.

Staged laser ion acceleration

We report experimental results proving the possibility to use laser-driven ion acceleration in an additive manner. The observed proton spectra show well-defined characteristic modulations and this process was found to work extremely stable and controllable.

Synchrotron radiation from laser-accelerated monoenergetic electron beams

We present the production of incoherent synchrotron radiation from laser-accelerated electrons propagating through an undulator. Simultaneously recorded electron and photon spectra fit well to undulator theory. Future prospects are ultrashort laser-based synchrotron light sources.

Laser-based Particle Acceleration

The acceleration of charged particles relies on the use of longitudinal electric fields. These fields are typically generated either via capacitors as static electric fields, or via microwaves carried in resonators. Accelerator devices of this sort are, however, constrained by their material damage thresholds: If the electric field in the cavities exceeds ~ 50 MV/m, conduction band electrons from the material are field-ionized, leading to a breakdown of the accelerator. As a consequence, the energy gain per unit length in conventional accelerators is limited, and high particle energies can only be realized through additional acceleration length, which explains the sometimes impressively large dimensions of state-of-the-art accelerators. This chapter is dedicated to a radically new approach towards particle acceleration based on laser-produced plasma. In contrast to conventional accelerator cavities, plasmas can generate and support electric fields up to TV/m. In the present case, the plasma is created by an ultra-short, ultra-intense laser pulse impinging on a target, whereupon the free particles interact immediately with the strong electromagnetic fields of the laser. Since the energy density of such ultra-short pulses is extremely high, efficient energy coupling processes exist between the laser field and the plasma, and the particle may gain substantial kinetic energy within very short distances. As of today, laser-plasma accelerators are capable of producing beams of 1 GeV electron energy over 3 cm of acceleration length (Leemans et al., 2006; Karsch et al., 2007), as well as ion beams of several 10 MeV per nucleon over a distance of some ten microns (Snavely et al., 2000). These laser-produced particle beams possess a number of outstanding properties, such as ultra-short pulse duration of the order of the laser pulse (Pukhov & Meyer-ter-Vehn, 2002; van Tilburg et al., 2006; Fuchs et al., 2006), high peak currents and excellent emittance values (Cowan et al., 2004). Given these unique beam properties and the compactness of the acceleration scheme, the field of laser-based particle acceleration has recently attracted much attention for its great potential for exciting new applications in fundamental and applied physics. The present chapter will be organized as follows: First, we briefly review the principle of chirped pulse amplification as the fundamental optical technology underlying the

Monoenergetic proton beams from laser plasmas

We report the first production of quasi-monoenergetic proton beams using laser plasmas. Supported by scalability studies, this puts laser plasma acceleration clearly in the scope of medical application.