The Ursa Minor is a fully operational prototype of the next generation of pulsed power technology which employs compact and modular Linear Transformer Drivers (LTD). Ursa Minor uses 21 LTD cavities (see the photo above), adding the voltage from each to produce up to 2.4 million volts. Ursa Minor is the highest voltage LTD of its kind and has more cavities than any other LTD currently in operation.
In its present configuration, Ursa Minor’s 21 cavities are assembled in three groups of seven (in the photo, one cavity has been removed from the rightmost group). The center of each of the 21 cavities is coupled to a coaxial transmission line which delivers the 100 billion watts of LTD electrical power to an electron beam diode. Ursa Minor has been used to produce intense x-rays over a large area, to test bright x-ray sources used for radiographic imaging and to test novel concepts to produce x-rays.
Ursa Minor began as a 7-cavity LTD system built by the High Current Electronics Institute (HCEI) in Tomsk, Russia and was tested at SNL from 2005 to 2009 (the 7 leftmost cavities in the photo). In 2009-11, SNL and National Security Technologies, LLC (NSTec) collaborated to manufacture and procure an additional 14 cavities, increasing the voltage of the system from 800 thousand volts to 2.4 million volts.
In addition to demonstrating the modularity of the LTD technology, this expansion provides the first opportunity to evaluate the suitability of the LTD technology for driving electron beam diodes which produce intense, small x-ray spots for taking radiographic images of thick objects.
In its present configuration, Ursa Minor contains 420 high power capacitors (20 in each cavity), 210 high power switches (10 in each cavity, each connected to 2 capacitors) and 21 magnetic cores (1 in each cavity). The length of the section shown in the photo is 7 meters (22 feet). The cavities are 1.3 meters in diameter.