Machine to capture live pictures of atomic motions

By Biplab Das
Published: Friday 15 December 2006

it may now be possible to capture live pictures of atomic motions in a chemical reaction or marvel at a snapshot of early universe. An international research team is building two huge machines towards these.

"We have developed a novel microwave amplifier and ultra-stable microwave generator for one of the machines known as Laser-based Ultra-fast x -ray Source (lux) which will generate extremely small pulses of x -rays," says Subal Kar who led a team at the department of radio physics and electronics of Calcutta University with John N Corlett of Centre for Beam Physics, Accelerator and Fusion Research Division of University of California, Berkeley, us. The ultra-small pulses of x -rays can probe and shoot atomic motions in any chemical reactions.

The radio frequency cavities (below) will take us back in time when universe was not transparent and help solve several mysteries

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" lux will help biologists study the structures of cell membrane-bound big protein molecules, which are targets for designing many of the drugs," Kar says.

"We have also invented specially designed radio frequency (rf) cavities for muon collider which will churn out high energy neutrinos providing clues to many unexplained cosmic phenomena," he adds. Neutrinos (weighing less than a billionth of a hydrogen atom), a sub-atomic particle, is a vital constituent of the dark matter, which makes up 90 per cent of the matter of the universe. Muon particles are a kind of sub-atomic particle much heavier than an electron, which ultimately decay into high energy neutrinos inside the collider. Both the machines are being made in the us and should be ready by 2008.

Recording movement In lux, beams of electrons are accelerated very close to the speed of light inside the superconducting linear accelerator (linac). Then a set of microwave amplifiers through a specially designed cavity in linac boosts the energy of electrons. After leaving linac, the electrons are exposed to short pulses of laser and magnetic field making electrons emit ultra-fast and ultra-small pulses of x -rays. "Each x -ray pulse lasting for an attosecond (millionth of trillionth of a second), reach end stations which are designed to produce ultra-small pulses of laser to carry out various experiments," explains Kar. In such experiments, a pulse of laser pumps (excites) any nano-sized particles or cells under study, and x -ray pulse probes the tiny particles or cells recording live picture of microscopic events that last for attoseconds. This is to obtain the detailed video snap shots of physical properties of say quantum dots (physical study in one end station), chemical reaction (chemical study in another end station), biological cells (biological study in yet another end station)

The time delay between 'pump' and 'probe' is 10 to 50 femtoseconds (femtosecond equals a thousandth of trillionth of a second) at the end stations. "The ultra-stable microwave generator synchronises the time delay between 'pump' and 'probe'. It will help better understand photosynthesis, which is vital for future energy planning and agriculture," Kar says. lux will even snap images of proliferating cancer cells offering vital clues to their unbridled growth and novel anti-cancer therapies.

Unfolding mysteries The rf cavity for the muon collider research is expected to play a vital role in increasing the energy of muon particles. Within the collider, as high energy protons hit a target of liquid jet of platinum oxide, pions (short-lived sub-atomic particles) pop into existence and quickly decay into muons. Then, through ionisation cooling, muon beams become thin. Energy lost in such cooling is replenished while muon beams pass through a linac containing specially designed rf cavities. "The rf cavities are designed in a way that they pump up the energy of muon beams by 14 million electron volts while pushing the beams a metre along the horizontal direction inside the linac of collider," says Kar.

The bunches of muon particles (positive and negative) are then further accelerated in linac and immediately injected into the collider ring, where energy reaches hundreds of thousands of tera electron volts (1 tera electron volt is equal to 1,000 billion electron volts) triggering muons' decay into high energy neutrinos. "Such neutrinos can unveil secrets of neutron stars (dead stars) and exploding stars (supernovas)," says Kar.

The muon collider research started in 1998, with Lawrence Berkeley National Laboratory as the nodal laboratory, with Fermi Lab and Stanford Linear Accelerator Center of us and kek High Energy Accelerator Research Organization, Japan, and Research Center Karlsruhe, Germany.

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