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Archive for June, 2013

Particle Accelerator on a Chip

Tuesday, June 25th, 2013

“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.

 

References
1.  EXPERIMENTAL SEARCH FOR ACCELERATION IN THE MICRO-ACCELERATOR PLATFORM
http://accelconf.web.cern.ch/accelconf/IPAC2013/papers/tupea079.pdf

2.  Particle acceleration on a chip: A laser-driven micro-accelerator for research and industry
http://meetings.aps.org/Meeting/MAR13/Event/187016

3.  The same technology applied as an x-ray source
PROGRESS ON A LASER-DRIVEN DIELECTRIC STRUCTURE FOR USE AS A SHORT-PERIOD UNDULATOR
http://accelconf.web.cern.ch/AccelConf/FEL2012/papers/thpd43.pdf

4.  More on pyroelectric sources
http://copaseticflow.blogspot.com/2013/05/crystal-power-benchtop-fusion-devices.html

5.

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

 

Snooping on Planes from Space!

Thursday, June 13th, 2013

Hot on the heels of recent NSA revelations, the European Space Agency announced today[1] that they’ve put a satellite, Proba-V, in orbit that can track airplane flights from outer space. Unlike the NSA snooping, however, the plane tracking is voluntary, (for the moment), and welcomed.

Proba-V

Proba-V was launched recently and rocketed into orbit inside the same vehicle that carried the Estonian satellite ESTCUBE-1[2]. Proba’s main mission is to track vegetation growth on the planet.  The satellite’s designers provided room for a few extra experiments however. One of the extra experiments was designed to determine if ADS-B[3] signals can be detected from outer space. ADS-B is a radio based vehicle tracking system that is similar to a system developed by the United States Navy and used by ham radio operators known as APRS. Once Proba-V reached a stable orbit, the onboard ADS-B receiver started up, and soon thereafter signals from earthbound planes were detected.

Much like APRS, ADS-B transmitters aboard airplanes broadcast data packets that contain the plane’s location and other pertinent information. The APRS system, relies on automatic radio repeaters to route the data packets into a system of computer servers run by volunteers. Once in the system, the data can be utilized to track the transmitting vehicles. For an example of APRS in action, go to http://goo.gl/16cha, and/or watch the video below of the flight of OH3GMZ-9 path over Helsinki recorded earlier this morning.

Far from being volunteer based, ADS-B is being adopted as an enhancement to the existing air traffic control system and should prove to be more efficient and precise.  In the United States, the majority of planes are required to carry an ADS-B transmitter by the year 2020.

ADS-B adds an inbound channel that APRS doesn’t have. ‘ADS-B in’ users can receive the packets of other nearby aircraft, as well as direct communications.  With the new results from Proba-V, it looks like ADS-B will also be capable of providing space monitored search and rescue data for downed planes that are out of the range of traditional terrestrial radio receiver antennas.

References:
1. Proba-V aircraft tracking announcement
http://www.esa.int/Our_Activities/Technology/Proba_Missions/Proba-V_tracking_aircraft_in_flight_from_orbit

2. ESTCube-1
http://copaseticflow.blogspot.com/2013/05/a-little-news-two-approximations-and.html

3. ADS-B on Wikipedia
http://en.wikipedia.org/wiki/Automatic_dependent_surveillance-broadcast#Relationship_to_surveillance_radar