Nearly the Speed of Light in One Millimeter: Presenting a New Type of Particle Accelerator
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Nearly the Speed of Light in One Millimeter: Presenting a New Type of Particle Accelerator:
In conventional particle accelerators, strong radio waves are guided into specially shaped metal tubes called resonators. The particles to be accelerated - which are often electrons - can ride these radio waves like surfers ride an ocean wave. But the potential of the technology is limited: Feeding too much radio wave power into the resonators creates a risk of electrical charges that can damage the component. This means that in order to bring particles to high energy levels, many resonators have to be connected in series, which makes today's accelerators in many cases kilometers long.
That is why experts are eagerly working on an alternative: plasma acceleration. In principle, short and extremely powerful laser flashes fire into a plasma - an ionized state of matter consisting of negatively charged electrons and positively charged atomic cores. In this plasma, the laser pulse generates a strong alternating electric field, similar to the wake of a ship, which can accelerate electrons enormously over a very short distance. In theory, this means facilities can be built far more compact, shrinking an accelerator that is a hundred meters long today down to just a few meters. "This miniaturization is what makes the concept so attractive," explains Arie Irman, a researcher at the HZDR Institute of Radiation Physics. "And we hope it will allow even small university laboratories to afford a powerful accelerator in the future."
But there is yet another variant of plasma acceleration where the plasma is driven by near-light-speed electron bunches instead of powerful laser flashes. This method offers two advantages over laser-driven plasma acceleration: "In principle, it should be possible to achieve higher particle energies, and the accelerated electron beams should be easier to control," explains HZDR physicist and primary author Thomas Kurz. "The drawback is that at the moment, we rely on large conventional accelerators to produce the electron bunches that are needed to drive the plasma." FLASH at DESY in Hamburg, for instance, where such experiments take place, measures a good one hundred meters.
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