Manufacturing Bits: Oct. 13

Exploring plasmas with lasers
The Department of Energy’s SLAC National Accelerator Laboratory has upgraded its high-power laser system to 200 terawatts of power, roughly 100 times the world’s total power consumption compressed into tens of femtoseconds.

The peak power before the upgrade was 30 terawatts. The upgraded laser will be coupled with SLAC’s X-ray laser, dubbed the Linac Coherent Light Source (LCLS). The LCLS takes X-ray images of atoms, molecules and other structures. It measures matter using high-power pulses at temperatures reaching millions of degrees.

The upgraded laser will be used to study how materials transform under stress at the atomic level. It will also be used to understand the physics of nuclear fusion.

Researchers can also use its pulses to drive a variety of particle beams. This, in turn, will allow researchers to explore plasmas. Plasmas are considered a fourth state of matter, according to SLAC. They are not solids, liquids or gases. Plasmas consist of a gassy soup of charged particles.

An upgraded high-power laser is designed to synchronize with X-rays for high-temperature, high-pressure experiments in this large chamber. (Source: SLAC)

The upgraded laser system makes use of a titanium-sapphire crystal. Measuring more than three inches in diameter, the crystal stimulates and amplifies light from another laser. Then, the light is focused to a spot at just millionths of an inch across.

This month, the upgraded high-power laser will be available to researchers at 100 terawatts. The laser will fire one pulse every 3.5 minutes at 100 terawatts, with a pulse length of about 40 femtoseconds.

The plan is to ramp up its intensity over time towards 200 terawatts. At that power, it will fire one shot every seven minutes. “This will give us more insight into the processes at work, from the atomic to electronic states,” said Eduardo Granados, a laser scientist at SLAC, on the agency’s Web site.

Miniature particle accelerators
DESY, the Max Planck Society, the University of Hamburg and others have built the world’s first prototype of a miniature particle accelerator, a single module that is 1.5 centimeters long and one millimeter thick.

The technology could one day enable the development of compact free-electron X-ray laser (XFEL) and electron sources. This, in turn, could be used for materials research and medical applications.

Terahertz accelerator module can fit into two fingers. (Credit: DESY/Heiner Müller-Elsner)

Traditionally, particle accelerators rely on electromagnetic radiation at the RF range. The miniature particle accelerator uses terahertz radiation, as opposed to RF.

Terahertz radiation lies between infrared radiation and microwaves, according to the Deutsches Elektronen-Synchrotron (DESY) organization. The wavelength of the terahertz radiation used by researchers is around one thousand times shorter. And so, terahertz technology could miniaturize a system by at least a factor of 100.

In the lab, researchers devised a micro-structured accelerator module. They fired electrons into the module using an electron gun. Then, the electrons were accelerated by terahertz radiation, which was fed into the module.

The tiny accelerator was able to increase the energy of the particles by seven kiloelectronvolts (keV). “This is not a particularly large acceleration, but the experiment demonstrates that the principle does work in practice,” said Arya Fallahi of CFEL, a cooperation between DESY, the University of Hamburg and the Max Planck Society. “The theory indicates that we should be able to achieve an accelerating gradient of up to one gigavolt per meter.”

Over time, CFEL plans to build a compact, experimental XFEL using terahertz technology. XFEL systems generate flashes of laser light. This is done by sending electrons from a particle accelerator down an undulating path.

This is the principle that will be used by the X-ray laser European XFEL, a free-electron laser that is currently being built by an international consortium. The entire facility will be more than three kilometers long. In contrast, the experimental XFEL using terahertz technology is expected to be less than a meter long.

Equipping a laser facility
In a separate announcement, the first instrument component has been installed at the European XFEL. The first component is a support tower for a high-precision robot. A single tower weighs three tons and is four meters tall.

The tower will hold a sensitive detector for the so-called Femtosecond X-Ray Experiments (FXE). The FXE instrument will be an experiment station for femtochemistry, the field that studies chemical reactions at timescales of around a quadrillionth of a second.

The European XFEL will be constructed and operated by the European XFEL GmbH, a non-profit group. The facility will begin operations in 2017.

FXE group members installing the robot tower. Source: European XFEL)