An accelerator on a chip

Electrical engineers from the Accelerator Physics Group of TU Darmstadt have come up with a concept for a laser-driven electron accelerator so small that it could be produced on a silicon chip. It would be inexpensive and with multiple applications. The design, which was published in Letters of physical examination, is being implemented as part of an international collaboration.

Particle accelerators are usually big and expensive, but that will change soon if researchers do it. The international Accelerator on Chip (AChIP) program, funded by the Gordon and Betty Moore Foundation in the United States, aims to create an electron accelerator on a silicon chip. The basic idea is to replace the metal accelerator parts with glass or silicon and to use a laser instead of a microwave generator as a source of energy. energy. Due to the greater charge capacity of the electric field glass, the rate of acceleration can be increased and thus the same amount of energy can be transmitted to the particles in a shorter space, reducing the Accelerator by a factor of about 10 compared to traditional accelerators providing the same energy. .

One of the challenges here is that the vacuum channel for electrons on a chip must be very small, which requires that the electron beam be extremely concentrated. The magnetic focusing channels used in conventional accelerators are far too weak for this. This means that a whole new focus method needs to be developed for the accelerator of a chip to become a reality.

In the field of Matter and Radiation Science at the University of Darmstadt, the AChIP Accelerator Physics Group (Faculty of Electrical Engineering and Information Technology, University of Darmstadt), directed by the beginning scientist, Dr. Uwe Niedermayer, recently proposed a decisive solution The laser fields themselves focus the electrons in a channel of only 420 nanometers wide. The concept is based on abrupt changes of the electron phase with respect to the laser, resulting in alternating focusing and deconcentration in both directions in the plane of the chip surface. This creates stability in both directions. The concept can be compared to a ball on a saddle – the ball will fall, regardless of the direction in which the saddle tilts. However, turning the saddle continuously means that the ball will remain stable in the saddle. The electrons in the channel on the chip do the same thing.

Perpendicular to the surface of the chip, a lower focus is sufficient, and a single quadrupole magnet encompassing the entire chip can be used. This concept is similar to that of a conventional linear accelerator. However, for an accelerator on a chip, the electron dynamics has been modified to create a two-dimensional design that can be achieved using lithographic techniques from the semiconductor industry.

Niedermayer is currently visiting scholar at Stanford University; The American University runs the AChIP program with the University of Erlangen in Germany. At Stanford, he collaborates with other ACHIP scientists with the goal of creating an accelerator on a chip in an experimental chamber the size of a shoebox. A commercially available system, adapted by means of complex nonlinear optics, is used as a laser source. The AChIP program, funded until 2020, aims to produce electrons with a mega-electron-volt energy from the chip. This is roughly equivalent to the voltage of a million batteries. An additional goal is to create ultra-short electronic pulses (-15 seconds), as required by the design of a scalable accelerator on a chip developed in Darmstadt.

Applications in industry and medicine

The possible applications of such an accelerator would be those of industry and medicine. An important long-term goal is to create a compact and consistent X-ray beam source for material characterization. An example of medical application would be an accelerator endoscope that could be used to irradiate deep tumors in the body with electrons.

A particular advantage of this new accelerator technology is that chips can be manufactured cheaply in large quantities, which means that the accelerator would be within the reach of the man in the street and that each university could buy your own accelerator lab. Other possibilities include the use of consistent and inexpensive x-ray sources in the photolithographic processes of the semiconductor industry, which would allow a reduction in the size of transistors in computer processors as well as higher degree of integration density.

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"Accelerator on a chip" demonstrated

More information:
Uwe Niedermayer et al. Alternate phase focusing for laser dielectric acceleration, Letters of physical examination (2018). DOI: 10.1103 / PhysRevLett.121.214801