ALBUQUERQUE, NM – Ever since the first human placed a bare hand on an uninsulated power line, people have refrained from personally testing energetic materials. Even metal meters can melt at high voltage.
Now, using a crystal smaller than a dime and a laser smaller than a shoebox, a team at Sandia National Laboratories safely measured 20 million volts without physically contacting the electrical flow.
“No one had directly measured such high voltages in the world before our experiment,” Sandia scientist Israel Owens said of his team’s unique electrical and optical work, recently published in Scientific reports of nature. “To measure high voltages, the technique is safe, efficient and inexpensive. “
“When you have high voltage over short distances, the sensors fail,” said Sandia manager Bryan Oliver. “Israel’s diagnosis can survive these high electric fields and thus allow us to determine the voltage in an environment where this was not previously possible.”
The realization, which multiplies each electric field reading by the same constant to determine the voltage, opens the door to several possible applications.
The work took place at Sandia’s high-energy radiation mega-volt electron source, or HERMES III, where the building-sized accelerator converts powerful electrical pulses into energetic photons called gamma rays.
“Being able to measure Hermes III’s output voltage instead of calculating it allows us to accurately define gamma ray energies,” Owens said. “And our crystal laser system does this without disturbing the environment for the experiment.”
Benefits of accurately measuring gamma ray energy
The HERMES accelerator generates a high-energy electron beam which is stopped by a very dense material and converted into a flux of gamma rays, the most energetic part of the electromagnetic spectrum. These rays have a wide variety of uses, including sterilizing hospital equipment, pasteurizing food, medical imaging, smoke detectors, measuring the thickness of very thin materials and more.
Since nuclear weapons also generate gamma rays, their creation in a laboratory can determine whether military and civilian equipment could continue to function when exposed to these energy flows.
Accurately achieving the desired output of gamma rays requires calibration with the voltages that produced them; hence the need for a sensor capable of measuring high voltages without being destroyed.
The idea of using lasers as remote measurement tools is not new, Owens said. Infrared laser sensors are used remotely to safely measure forehead temperature. Laser rangefinders can determine the size of a room without the owner surveying the distance.
“Our procedure is a little different: we don’t point the laser directly at an object to measure its voltage,” he said. “We determine this information by using our laser simply to interrogate a secondary object – a lithium niobate crystal.”
Tiny crystals altered by huge energy fields
The crystal, less than half an inch long, is placed so that the electric field passes through it from the side, perpendicular to the polarized laser beam traveling along the axis of the crystal.
The electric field changes the crystal’s ability to transmit light by causing its photons to travel at different speeds in the vertical and horizontal directions of the polarized beam. This causes the polarized light to rotate, changing the amount entering the photodetector. This instrument converts the intensity of the laser beam into a single voltage which can be read on an oscilloscope.
“The voltage measured on the oscilloscope is directly related to the strength of the electric field from which the voltage can be calculated,” Owens said. “In our experiments, tens of megavolts translated into hundreds of millivolts on the oscilloscope. (A megavolt is a million volts; a millivolt is a thousandth of a volt.)
“The signal is already in the correct form, and we just need to multiply by a fixed constant. There is also no need for tedious calibrations or complicated post-processing to determine electric fields and voltages.
The high voltages measured with the new sensor closely matched what was expected by calculations and other proxy measurements, Owens said.
Accurate measurement of gamma ray energy might be just one of the benefits of the new measurement technique, Owens said.
“At the moment it is a laboratory device for research, but as its development progresses it could end up in various accelerator installations where a series of crystals could provide readings of. tension in several remote places, ”he said.
The technique would also work, he said, for the power transmission industry, vehicle manufacturers, lightning research centers “or anywhere you want to remotely measure or monitor a source of light. ‘very high energy,’ Owens said. The device could also “see” an electrical short in a remote wall due to the disturbance of the electromagnetic field surrounding the current carrying wire, which would allow non-invasive detection of a fault in the circuits.
This research was funded by the National Nuclear Security Administration.
Sandia National Laboratories is a multi-mission laboratory operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc., on behalf of the National Nuclear Security Administration of the US Department of Energy. Sandia Labs has major research and development responsibilities in nuclear deterrence, global security, defense, energy technology, and economic competitiveness, with primary facilities in Albuquerque, New Mexico, and Livermore, California.
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Electro-optical measurement of intense electric field on a high energy pulsed power accelerator
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