femto – Lightsources.org

New beamline for electron bunch diagnostics

2019/04/252019/05/02

A new diagnostic beamline connected directly to the MAX IV linear accelerator is under construction.

It will enable time-resolved characterization of primarily the ultrashort electron bunches for the FemtoMAX beamline but will also be useful for other time-resolved experiments. The design of the highly specialized beamline components is to a large part done in-house.
Head up and tail down
The linear accelerator accelerates electrons up to high energies. Short bunches containing 10⁹ electrons are delivered from the linear accelerator to make X-ray pulses for the FemtoMAX beamline. The duration of the bunches is in the femtosecond (10^-15 s) regime to enable high temporal-resolution measurements at the beamline. The short duration makes the bunches very challenging to characterize with time resolution as conventional detection devices are too slow.
In the new setup, two so-called transverse deflecting cavities (TDC) will make the acquisition of time-resolved data possible. They will in principle add an electromagnetic field that deflects the head of the electron bunch upwards and the tail down so that the first electrons hitting the beam profile analyzer will end up at the top of the screen and the last ones will end up at the bottom. The resulting streak gives a time-resolved measurement of the shape of the bunch but the method will also be used to characterize for example how emittance and energy vary as a function of time.
– Today we rely on calculations and relative measurements for the bunch length delivered to FemtoMAX says project leader Erik Mansten, the TDC is a way for us to verify what we deliver. It also helps us preparing the linac for a possible free electron laser in the future.

>Read more on the MAX IV website

Image: These copper disks are going to become transverse deflecting cavities for the new diagnostic beamline.

Capturing protein motion at FemtoMAX

2019/04/052019/04/09

Your body contains a large variety of different proteins. They are big, complex molecules with diverse functions, from transporting oxygen in your blood to making your muscles contract.

Many proteins change their shape and move as they perform their task. A research team from the University of Gothenburg recently visited the beamline FemtoMAX to develop a method for studying moving proteins. They use electric fields to stimulate motion of the proteins in a sample while imaging them with the X-ray beam.
To study how proteins move, we need something to nudge them and then image them after they have changed position. Certain proteins are activated by light and in that case, the researchers can hit them with a laser pulse to provoke the motion. However, that is far from always the case. In the method being developed by the Gothenburg team, the proteins are instead subjected to an electric field that make them move.
The field is synchronized to the short, femtosecond scale (10^-15 s) X-ray pulses delivered at beamline FemtoMAX. Each X-ray pulse hitting the sample is like taking a photograph using extremely short shutter speed, just like trying to get sharp images of players on a football field. The X-ray pulses at FemtoMAX are short enough to let the researchers capture the instantaneous position of the protein. By varying the time between the electric field and the X-ray pulse they can see different stages of the movement and even put the frames together as a movie of the protein motion.

Linac team has reached major milestones

2018/07/052018/07/05

A big milestone was reached for the MAX IV linear accelerator end of May 2018.

The electron bunches accelerated in the linac was compressed to a time duration below 100 femtoseconds (fs). That means that they were shorter than 1*10^-13s. In fact, we could measure a pulse duration as low as 65 fs FWHM.

The RMS bunch length was then recorded at 32 fs. These results were achieved using only the first of the 2 electron bunch compressors in the MAX IV linac and shows not only that we can deliver short electron bunches, but also that the novel concept adopted in the compressors is working according to theory and simulations.

The ultra-short electron pulses are used to create X-ray pulses with the same short time duration in the linac based light source SPF (Short Pulse Facility). These bursts of X-rays can then be used to make time resolved measurements on materials, meaning you can make a movie of how reactions happen between parts of a molecule.

Picture: Linac team at MAX IV.

World’s fastest water heater

2018/05/142018/05/22

Scientists explore exotic state of liquid with X-ray laser

Scientists have used a powerful X-ray laser to heat water from room temperature to 100,000 degrees Celsius in less than a tenth of a picosecond (millionth of a millionth of a second). The experimental set-up, that can be seen as the world’s fastest water heater, produced an exotic state of water, from which researchers hope to learn more about the peculiar characteristics of Earth’s most important liquid. The observations also have practical use for the probing biological and many other samples with X-ray lasers. The team of Carl Caleman from the Center for Free-Electron Laser Science (CFEL) at DESY and Uppsala University (Sweden) reports its findings in the journal Proceedings of the National Academy of Sciences (PNAS).

The researchers used the X-ray free-electron laser Linac Coherent Light Source LCLS at the SLAC National Accelerator Laboratory in the U.S. to shoot extremely intense and ultra-short flashes of X-rays at a jet of water. “It is certainly not the usual way to boil your water,” said Caleman. “Normally, when you heat water, the molecules will just be shaken stronger and stronger.” On the molecular level, heat is motion – the hotter, the faster the motion of the molecules. This can be achieved, for example, via heat transfer from a stove, or more directly with microwaves that make the water molecules swing back and forth ever faster in step with the electromagnetic field.

Image: After about 70 femtoseconds (quadrillionths of a second) most water molecules have already split into hydrogen (white) and oxygen (red).
Credit: Carl Caleman, DESY/Uppsala University