Accelerators for nano- and biosciences

30 September 2002

Practical, affordable yet unique and exciting new accelerator facilities could advance vital research capabilities for nano- and bioscience, says Swapan Chattopadhyay.

From a historical perspective, large particle-accelerator facilities entered the scientific arena as grand instruments that enabled us to understand the fundamental workings at the heart of matter. Ever since Ernest Orlando Lawrence’s invention of the cyclotron in 1930, we have witnessed the scientists’ obsession with increasingly higher-energy particle beams to probe deeper into the nucleus, the nucleons and the elementary particles to understand the fundamental forces and processes at work. The result has been a scientific culture and sociology that defined the so-called “big science”, with numerous spin-off benefits to society at large (such as large international collaborations and information networking via the creation of the World Wide Web). On the flip side, however, the economics, sociology and politics relevant to the envisioned next big accelerator facility addressing the frontier of particle physics are daunting to the point of paralyzing the field and driving its artisans – especially accelerator scientists – to extinction.

The value of accelerator science and technology is not limited to high-energy physics; witness the flourishing of accelerator-based synchrotron radiation sources worldwide that serve a much broader scientific community. While the energy of speed-of-light particles is an important parameter that determines the resolution with which we can see things in the microscopic world (whether using the particles directly or using the synchrotron radiation they generate when bent in a magnetic field), the intrinsic value of a particle beam goes far beyond its mere energy. It provides bursts of energy in suitably packaged pulses in space and time that have critical applications in today’s emerging sciences of the nano- and bioworld. Such critical characteristics as the brightness, time structure, spatial dimensions, polarization, coherence, simultaneous and concurrent use of synchronized multiple light and particle beams are all important factors that can be tailored to address many relevant fundamental scientific issues of our times. And a careful examination shows that indeed it is possible to conceive affordable mezzo-scale unique accelerator facilities that can produce creative space-time patterns of particle and/or wave energy to address specific issues that cannot be done otherwise.

Different worlds

What are some of the critical issues in nano- and biosciences today? The nanoworld is concerned with designing microscopic structures on a nanometre scale atom-by-atom and understanding the properties of these intermediate structures – made naturally or in the laboratory – which exhibit classical and quantum behaviour in a special and peculiar way. The relevant space dimensions are micrometres to nanometres, and the timescales for fundamental processes in the nanoworld range from picoseconds for vibrational electronic phenomena to femtoseconds for collective surface atomic nucleus motion and attoseconds for truly quantum single atomic phenomena. The bioworld is concerned with larger biomolecules where the energy transfer and topological deformations within the longer, functional biomolecules, such as proteins, demand suitable bursts of energy to initiate the energy-transfer mechanisms and ultrashort pulses to probe and image the molecules while still in a functional state, before being destroyed by the pulsed energy of the beam. An electron beam of up to a few giga-electron-volts in particle energy can be manipulated to produce pulses of electromagnetic waves from a picosecond to an attosecond in duration, and focused from a few micrometres to a few nanometres with wavelengths that can probe atomic motion. Such modest practical accelerator facilities are clearly possible for accelerator science and technology today. As an example I can only point to the exciting possibilities now opening up with various energy-recovered linear-accelerator concepts, short wavelength, high-power and high-brightness free-electron lasers, and various ultrashort/ultrafast pulse-production and slicing techniques actively pursued at major laboratories (such as DESY, PSI, Daresbury, Spring-8, Jefferson Lab, Cornell, Berkeley, SLAC, BNL and ANL).

Today’s scientists working with light and speed-of-light particles grapple with classical power electromagnetics; microwave superconductivity; surface physics of metals and dielectrics; laser physics and technology; atomic physics of semiconductors; atomic and surface phenomena under extreme high fields (1-100 GV/m); precise detection of near-field and far-field radiation; nonlinear phenomena; studies of controlled high-density plasma waves; and the whole spectrum of space-time phenomena ranging from milliseconds to attoseconds and centimetres to nanometres. The transition from electronics (GHz) to optronics (THz) to photonics (PHz) is visible on the horizon – it is no longer only the domain of traditional physics and/or electrical engineering. We need to recognize this situation and seek to engage experts from all these disciplines to make a difference in the world. Let’s extend our vision outwards from the world at femtometres to embrace the nano- and bioworld, where we have much to contribute. The accelerator community should take an active role in understanding the needs of the nano- and biosciences, and in educating the scientific community, government agencies and society via proper articulation of the tremendous hidden potential for bringing these capabilities to fruition.

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