Friday, February 16, 2007

Blue electron light

The blue streak in this photograph shows the dramatic gain in energy made by some of the electrons in a bunch after passing through plasma (ionized gas). The white spot shows the electrons in the bunch that generated the plasma to propel the other electrons to double their energy, to 85 billion electron volts (GeV). The electrons can be photographed because they emit blue light as they pass through air.
Click on image for larger version

Electrons already travel at near light's speed in an accelerator, but physicists from the Stanford Linear Accelerator (SLAC) actually doubled the energy of the electrons, not their speed.

This achievement demonstrates a technology that may drive the future of accelerator design. To reach the high energies required to answer the new set of mysteries confronting particle physics—such as dark energy and the origin of mass—the newest accelerators are vastly larger, and consequently more expensive, than their predecessors. Very high-energy particle beams will be needed to detect the very heavy and very short-lived particles that have eluded scientists so far.

While still in early development stages, the research shows that acceleration using plasma, or ionized gas, can dramatically boost the energy of particles in a short distance.

The electrons first traveled two miles through the linear accelerator at SLAC, gaining 42 billion electron volts (or GeV) of energy. Then they passed through a 33-inch long (84-centimeter) plasma chamber and picked up another 42 GeV of energy. Like an afterburner on a jet engine, the plasma provides extra thrust. The plasma chamber is filled with lithium gas. As the electron bunch passes through the lithium, the front of the bunch creates plasma. This plasma leaves a wake that flows to the back of the bunch and shoves it forward, giving electrons in the back more energy.

The experiment created one of the largest acceleration gradients ever achieved. The gradient is a measure of how quickly particles amass energy. In this case, the electrons hurtling through the plasma chamber gained 3,000 times more energy per meter than usual in the accelerator.

A current experimental limitation is that most of the electrons in a bunch lose their energy to the plasma. Energy out of one part of the beam is put into another part.

During the last two years, the team has improved the plasma acceleration gradient by a factor of 200. One of the next steps is to attempt a two-bunch system, where the first bunch provides all the energy to the trailing bunch. In a full-scale plasma accelerator, physicists would use those second bunches to create high-energy particle collisions in their detectors.

New Accelerator Technique Doubles Particle Energy in Just One Meter
SLAC press release 14/02/07

Supergiant fast X-Ray transients

Credits: ESA This artist's impression shows a high-mass binary system, composed of a supergiant luminous star (in blue) and a compact stellar object, such as a neutron star.

As discovered by ESA's Integral observatory, many of these supergiant systems produce strong and exceptionally fast-rising X-ray outbursts lasting a few hours only, hence their name 'supergiant fast X-ray transients'.

The outbursts may depend on the way stellar material is exchanged between the supergiant star and the compact object.

The light curve at the bottom-right was retrieved by Integral from the supergiant fast X-ray transient source IGR J17544-2619 on 17 September 2003.

The curve shows a very fast X-ray outburst from the compact object, lasting about two hours only, with very fast rise and slow decay. The counterpart of this source is a luminous supergiant, unambiguously identified by ESA's XMM-Newton and NASA's Chandra X-ray observatories.

Credits: JM Blondin, North Carolina State University

This simulated sequence shows the interaction between the stellar material carried by the wind of a supergiant star and its 'receiving' companion - a compact stellar object such as a neutron star. In the vicinity of the compact object it is possible to see the development of a turbulent shocked flow.

Integral reveals new class of ‘supergiant’ X-ray binary stars
LHC - The worlds largest microscope
by Sabine Hossenfelder @ Backreaction

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