Portland, Ore. -- It won't power the starship Enterprise, but an experimental "dilithium crystal" pyroelectric technology is said to enable compact nuclear fusion.
Engineers at Rensselaer Polytechnic Institute (Troy, N.Y.) said they have opposed two oppositely charged centimeter-sized lithium tantalate crystals to create a fusion device that can operate off a battery at room temperature.
"In a [conventional] fusion device de- signed to produce energy, the release of high-energy ions further heats the plasma, thereby sustaining the reaction. We get the same amount of energy out of the fusion reaction, but we cannot use it to sustain the reaction," said the technique's inventor, associate professor Yaron Danon.
"Instead, we plan to use the energy emitted to create a portable neutron source that has applications in non- destructive testing or, possibly, explosive-mine detection," he said.
Indeed, Danon predicts that different application areas will benefit from the four types of high-energy particles that a pyroelectric crystal accelerator can emit: high-energy electrons, ions, neutrons and X-rays. The electrons that pyroelectric crystals produce could be used for therapeutic purposes, such as cancer treatments, he said. With some improvements, the high-energy emissions might be used to inspect cargo or scan luggage.
Danon performed his research for the Department of Energy with Jeffrey Geuther and Frank Saglime, doctoral candidates in nuclear engineering.
How it works
In the traditional fusion-reactor, high temperatures impart enough energy to initiate nuclear fusion in a superheated plasma. Instead of millions of degrees of heat and a magnetic field to contain the plasma, dilithium-crystal fusion uses 100- kilovolt electric fields to accelerate heavy hydrogen (deuterium) molecules onto a target, achieving nuclear fusion without high-temperature plasmas or low-temperature cryogenic cooling.
The fusion device depends on the piezoelectric-like response of lithium tantalate crystals. Heating (or cooling) the crystals induces a 100,00-V electric field in each crystal. A pyroelectric crystal is an insulator, but its lattice structure responds to heat by causing all the electrons to rush to one side of the crystal, leaving behind positively charged holes on the opposite face.
"When you heat or cool the crystal . . . it becomes polarized," Danon explained. "Because the crystal is an insulator, when it becomes polarized it essentially becomes a charged capacitor. The voltage output is the charge, which is big, divided by the capacitance, which is very, very small, thereby making the voltage swing huge--over 100,000 V on the face of each crystal."
Traditional portable neutron sources are at least a foot long and require a high-voltage power supply that can deliver 250,000 electron-volts. Instead, dilithium-crystal fusion reactors deliver a 200,000-V electric field by opposing two pyroelectric crystals to double the acceleration field. Whenever the pyroelectric crystals are heated or cooled in a low-pressure environment, they naturally produce the high-voltage field.
"We don't require external high-voltage power supplies--we can use a battery to send just a few watts to heat the crystal to get its high-voltage output," said Danon. "The other nice thing is that our device is only about 15 x 15 centimeters, and we have not even tried to scale it down yet. We predict our next-generation device can be much smaller. The pyroelectric crystals themselves are only about 2 x 1 cm."
By using the field to accelerate deuterium oxide atoms between the opposing crystals, the engineers fused two deuterium atoms into helium, releasing the excess energy as high-energy neutron particles--the hallmark of nuclear fusion.