Miniaturization of Particle Accelerators Using Plasmas
Particle accelerators are some of the largest and most complex scientific instruments ever built. Future accelerators at the energy frontier will be even larger and more expensive, and therefore developing a new technology that would allow for a significant reduction of the accelerator size could also drastically reduce its cost. Plasma-based accelerators have made tremendous progress in the last few years. The production of narrow energy spread, GeV beam have been produced in laser-driven plasma-based accelerators. At the same time, the energy doubling of 42 GeV incoming electrons has been doubled in an 85 cm-long, electron beam-driven plasma wakefield accelerator. This distance is more that 2000 times shorter than the conventional linear accelerator that produced the incoming electrons. These amazing results obtained in proof-of-principle experiments suggest that plasma-based accelerators could one day become the new technology that would miniaturize accelerators and enable new discoveries in particle physics. At the same time these plasma-based accelerators could be used as compact sources of megavolt electrons and protons or ions with applications to research, to medicine for cancer treatment and radioactive isotope production, and to material science. These sources would replace the present large size facilities and become widely available at hospitals, at industrial research laboratories, and at universities. Recent experimental results will be presented and future applications and potential will be discussed.
Plasma-based Radiation Sources
Plasmas can sustain very large electric fields and their characteristics can often be easily adjusted for a particular application by changing their density. For example, the plasma frequency varies from 100 GHz to 10 THz for densities from 1014 cm¬ 3 to 1018 cm¬ 3. Few high-power, tunable sources exist in this frequency domain. While electrostatic plasma waves do not radiate efficiently in vacuum, electromagnetic modes with comparable frequencies can be excited and used as high-power, high-frequency radiation sources. In addition, these large fields can also be used to make externally injected electrons oscillate in a plasma wiggler, and radiate for example in the visible to the x-ray energy range. Various plasma-based radiation sources will be introduced and discussed.
Ultra-fast Beam Diagnostics
Ultra-short electron bunches are of great interest for new radiation source such as the free electron laser (FEL) and for advanced acceleration concepts such as plasma-based particle accelerators. Bunches with time duration in the femtosecond range can be produced, however, electronics are too slow to measure and characterize them. On the other hand, optical pulses as short as a few femtosecond can now be completely characterized using a large array of optical techniques. Therefore, various techniques have been devised to convert the electrical signal of the ultra-short electron bunches into corresponding electromagnetic (em) signal that can then be characterized using optical techniques. However, typical bunch durations are still in the >30 fs range, which places the em signal in the THz to infrared range where material properties are often not well known and change rapidly with frequency. Various ultra-short bunch diagnostic techniques will be described.
Dr. Patric Muggli received his bachelor degree in Physics from the Swiss Federal Institute of Technology (Ecole Polytechnique FÈdÈrale), Lausanne in 1985 with a specialty in plasma physics. He received his Ph.D. from the Physics Department from the Center of Plasma Physics Research of the same school for his work on high power gyrotrons. He then spent three year as a post-doctoral fellow at the University of California Los Angeles (UCLA) department of electrical engineering where he worked on a number of different topics, including plasma-based radiation sources such as the frequency upshifting of radiation using relativistic ionization fronts and DC to AC Radiation (DARC) sources, and the photoemission processes form various elements such as copper, magnesium, diamond and fullerene. He then joined the electrical engineering/electrophysics department of the University of Southern California (USC) as Research Associate. He worked on the pioneering laser wakefield acceleration (LWFA) experiments using the Rutherford Appleton Laboratory (UK) Vulcan laser, the world most powerful short pulse laser at the time. He was appointed as Research Associate Professor at USC in 2000, and Research Professor in 2006. He became one of the lead experimentalists on the SLAC/UCLA/USC collaboration that performs the plasma wakefield acceleration (PWFA) experiments at the Stanford Linear Accelerator Center. This experiment has been very successful in producing very interesting physics results, as well as advancing the PWFA from the level of basic physics experiments to that of a promising technology to significantly reduce the size of a future electron/positron linear collider. Some of the most significant results obtained in these experiments include: the discovery of the refraction of electron beams at a plasma/vacuum interface (P. Muggli et al., Nature 411, 43-43 (03 May 2001)), the first demonstration of the acceleration of positrons in plasmas (B.E. Blue et al., Phys. Rev. Lett. 90, 214801 (2003)), the first demonstration of an energy gain larger than one GeV in a plasma (M. J. Hogan et al., Phys. Rev. Lett. 95, 054802 (2005)), and recently the demonstration of the energy doubling of 42 GeV incoming electrons in only 85 cm of plasma (I. Blumenfeld et al., Nature 445, 741-744 (15 February 2007)). He is also leading PWFA experiments at the Brookhaven National laboratory, where low energy beam are used to demonstrate new concepts in PWFAs. Dr. Muggli is the author or co-author of more that 40 scientific publications in refereed journals, and of numerous conference proceedings papers. These publications are available at http://www-rcf.usc.edu/~muggli/index.html. He has given more that 20 invited presentations at international meetings. He teaches a graduate plasma physics course at USC. His research interests include plasma-based radiation sources, plasma-based plasma accelerators, particle beam physics, and ultra-fast diagnostics of particle beams.