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Particle Accelerator on a Chip

“Chip sized particle accelerators within a year!”

That was R. B. Yoder of Goucher College, and G. Travish of UCLA’s prediction reported[2] at the March 2013 meeting of the American Physical Society. Their project may not have come to fruition yet, but its simple design and ingenuity alone make it worth talking about. The team used several rather common technologies and concepts in advanced ways that they hope will ultimately produce relativistic electron beams on the benchtop.

Old School Linacs
First, a word about a more standard type of particle accelerator, the linear particle accelerator, also known as a linac.  Inside a linac an electron travels through a series of drift tubes.  Radio frequency currents are driven onto these tubes.  While the electron is inside the tube, it is shielded from the oscillating electric field being driven on the outside of the tube.  However, if synchronized correctly when it hits the edge of a tube, it sees a repulsive negative field at the edge of the tube it just exited and an attractive positive field at the entrance to the tube it is about to enter.  These fields create an electric potential that accelerates the electron into the next tube.  By tailoring the length of the drift tubes to correspond to the distance the electron can travel during a cycle of the oscillating electric field, the electron is successively accelerated at each gap, (picture 1[5]).


Linac on a chip
Yoder and Travish’s design works in a similar way.   The major difference is that the accelerating electric field is provided not by radio frequency vacuum tubes as in the case of standard linacs, but by the electromagnetic field created by much higher frequency laser beams.  The higher frequency of the lasers allows for a much shorter accelerating structure.  The lasers are polarized so their electric field is parallel to the path traversed by the accelerated electrons.  The equivalent of a diffraction grating is use to limit where the accelerating field for the lasers is present in the accelerator, (see the figure below [1]), providing an analogous drift tube like structure.

The micro-accelerator technology hasn’t been proven to work yet, but it has great potential, (lame pun intended).  One of the key hurdles to overcome is the injection of electrons into the structure.  Initial experiments have been done using electron beams at Work on this has been done using the electron accelerator at the Stanford Linear Accelerator Center.  One possible on-chip source of electrons involves the use of pyroelectric crystals similar to the ones used in benchtop neutron sources also developed at UCLA[4].  Stay tuned for more updates on the micro-accelerators progress.



2.  Particle acceleration on a chip: A laser-driven micro-accelerator for research and industry

3.  The same technology applied as an x-ray source

4.  More on pyroelectric sources


Title High Energy Accelerators
Volume 2 of Interscience tracts on physics and astronomy, 2
Issue 2 of Tracts on physics and astronomy
High-energy accelerators
Author Milton Stanley Livingston
Publisher Interscience Pubs., 1954


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