Prototype of single ion heat engine created

Scientists at Johannes Gutenberg University Mainz (JGU) and the University of Erlangen-Nuremberg are working on a heat engine that consists of just a single ion. Such a nano-heat engine could be far more efficient than, for example, a car engine or a coal fired power plant. A usual heat engine transforms heat into utilizable mechanical energy with the corresponding efficiency of an Otto engine amounting to only about 25 percent, for instance. The proposed nano-heat engine consisting of a single calcium ion would be much more efficient. The main aim of the research being conducted is to better understand how thermodynamics works on very small scales. A pilot prototype of such a single-ion heat engine is currently being constructed at Mainz University.

As the physicists explain in an article recently published in the journal Physical Review Letters , the efficiency of heat engines powered by thermal heat reservoirs is determined by the second law of thermodynamics, one of the fundamental concepts in physics. It was as far back as 1824 that Frenchman Nicolas Carnot calculated the maximum possible efficiency limit of such engines, now known as the Carnot limit.

In the case of the newly proposed nano-heat engine, the scientists have been theoretically able to exceed the classic Carnot limit by manipulating the heat baths and exploiting nonequlibrium states. Calculations and simulations made about a year ago showed for the first time that the thermo-dynamic flow in an internal combustion engine could be reproduced using individual ions. The idea was to use a calcium 40 ion, which has a diameter a million times smaller than that of a human hair, for this purpose. "Individual ions can basically act as the piston and drive shaft or, in other words, represent the entire engine," explained Johannes Roßnagel of the Quantum, Atomic, and Neutron Physics (QUANTUM) work group of the JGU Institute of Physics. Individual ions have already been captured in Paul traps and, using laser beams and electrical fields, not only cooled and heated but also compressed. "This means we are able to manipulate the pulse location distribution for optimum efficiency," added Roßnagel.

"Exceeding the Carnot limit for a standard heat engine thus does not violate the second law of thermodynamics but instead demonstrates that the use of specially prepared, non-thermal heat reservoirs also makes it possible to further improve efficiency." In their publication, the physicists calculated the general Carnot limit for this situation. As the mechanical capacity of a single ion machine is extremely low, it can probably only be used in heating or cooling nano systems.

The intention is now to actually develop the proposed single ion heat engine in initial experiments and construct a prototype in the laboratory.

In Photo: A single trapped ion in a linear Paul trap with special geometry: The heat engine is being realized by the divergent bars; the squeezing is being caused by establishing special electrical fields.

Alternative Energy Breakthrough First Magma-Enhanced Geothermal System In The World Developed In Iceland

In 2009, a borehole drilled at Krafla, northeast Iceland, as part of the Icelandic Deep Drilling Project (IDDP), unexpectedly penetrated into magma (molten rock) at only 2100 meters depth, with a temperature of 900-1000 degree Celsius. The borehole, IDDP-1, was the first in a series of wells being drilled by the IDDP in Iceland in the search for high-temperature geothermal resources.

The January 2014 issue of the international journal Geothermics is dedicated to scientific and engineering results arising from that unusual occurrence. This issue is edited by Wilfred Elders , a professor emeritus of geology at the University of California, Riverside, who also co-authored three of the research papers in the special issue with Icelandic colleagues.

"Drilling into magma is a very rare occurrence anywhere in the world and this is only the second known instance, the first one, in 2007, being in Hawaii," Elders said. "The IDDP, in cooperation with Iceland's National Power Company, the operator of the Krafla geothermal power plant, decided to investigate the hole further and bear part of the substantial costs involved."

Accordingly, a steel casing, perforated in the bottom section closest to the magma, was cemented into the well. The hole was then allowed to heat slowly and eventually allowed to flow superheated steam for the next two years, until July 2012, when it was closed down in order to replace some of the surface equipment.

"In the future, the success of this drilling and research project could lead to a revolution in the energy efficiency of high-temperature geothermal areas worldwide," Elders said. He added that several important milestones were achieved in this project: despite some difficulties, the project was able to drill down into the molten magma and control it; it was possible to set steel casing in the bottom of the hole; allowing the hole to blow superheated, high-pressure steam for months at temperatures exceeding 450 degree Celsius, created a world record for geothermal heat (this well was the hottest in the world and one of the most powerful); steam from the IDDP-1 well could be fed directly into the existing power plant at Krafla; and the IDDP-1 demonstrated that a high-enthalpy geothermal system could be successfully utilized.

"Essentially, the IDDP-1 created the world's first magma-enhanced geothermal system," Elders said. "This unique engineered geothermal system is the world's first to supply heat directly from a molten magma."

Elders explained that in various parts of the world so-called enhanced or engineered geothermal systems are being created by pumping cold water into hot dry rocks at 4-5 kilometers depths. The heated water is pumped up again as hot water or steam from production wells. In recent decades, considerable effort has been invested in Europe, Australia, the United States, and Japan, with uneven, and typically poor, results.

"Although the IDDP-1 hole had to be shut in, the aim now is to repair the well or to drill a new similar hole," Elders said. "The experiment at Krafla suffered various setbacks that tried personnel and equipment throughout. However, the process itself was very instructive, and, apart from scientific articles published in Geothermics, comprehensive reports on practical lessons learned are nearing completion."

The IDDP is a collaboration of three energy companies — HS Energy Ltd., National Power Company and Reykjavik Energy — and a government agency, the National Energy Authority of Iceland. It will drill the next borehole, IDDP-2, in southwest Iceland at Reykjanes in 2014-2015. From the onset, international collaboration has been important to the project, and in particular a consortium of U.S. scientists, coordinated by Elders, has been very active, authoring several research papers in the special issue of Geothermics.