If you're ever tempted to think that the city's messiest politics are found only on Capitol Hill, have a chat with energy expert Robert L. Hirsch, whose termination from the Rand Corp. last fall still rankles him. His behind-the-scenes tale of a policy report gone awry is awash in policy disagreements and charges and countercharges.

Rand hired Hirsch in January 2001, and he began work on the report "Energy Technologies for 2050," a $200,000 study commissioned by the Department of Energy's Fossil Energy Program. His mission was to develop a methodology that could be used to evaluate the viability of energy technologies over the next 50 years. Then in October, Hirsch was fired.

On that much, Hirsch and Rand agree. It's what happened in between that's controversial.

Hirsch, now head of the National Research Council's Board on Energy and Environmental Systems, said Rand was trying to squash his report because its preliminary conclusions were unpalatable to DOE, Rand's client.

"When management plays around with you for a couple of weeks and then takes [your report] away to give it to somebody else and tells you that the report will go out without the two sections that offended people in DOE -- to me, that's prima facie evidence of a cover-up," Hirsch said. "If that's not the case, I don't know what is."

That wasn't the case to Rand. "The problems were with the methodology, not the results," said James Dewar, a senior Rand official and methodology expert who shored up the report. "If the methodology was sound and that's how the results came out, we'd have no problem. Rand certainly doesn't shy away from saying something uncomfortable to its clients."

In the report, Hirsch, an engineer who has worked at DOE and Arco Oil and Gas Co., developed a preliminary methodology and tried it on three technologies: solar cells, fusion and coal gasification. His early conclusions were that coal gasification is close to being practical, fusion research is on the wrong track and solar cells are impractical for large-scale use.

He said that rubbed DOE the wrong way, contending the agency is heavily invested in fusion and loath to be seen as being against renewable energy.

A DOE spokesman said the agency did advise Rand of its concerns, but that these regarded the work's quality and "a misapplication of the study's parameters."

"Out-of-date data and inappropriate market assumptions led the analyst to reach strongly negative judgments for both photovoltaic and fusion," said a DOE summary of the study and controversy. "While the study reached positive conclusions for the coal-based technology, its serious shortcomings in analyzing the other two technologies led [Fossil Energy] -- and subsequently other DOE offices -- to question the study's overall technical and analytical quality."

Hirsch said he was abruptly fired for sharing a draft of the report, which he admits doing as a last resort, saying he feared the conclusions would not get out otherwise. Rand officials said they cannot comment on the reasons for the firing.

The government recently published a white paper on energy, citing economics and waste as reasons for turning its back on nuclear power. It said that by 2020 a fifth of the country's electricity should be generated from renewable energy sources, such as wind, wave and solar power. It pledged an extra £60m for such technologies, increasing its total spending on renewable energy to about £350m over four years.

However, the Science and Technology Committee believes that these funds lack focus and are insufficient, both in absolute terms and in comparison with the UK's competitors. "There is a superabundance of funding bodies, resulting in fragmentation of effort and confusion in academia and industry," its report says. "Where UK technologies are developed, we found the private sector unwilling to develop these technologies while the government is failing to step in to take them forward or provide the necessary incentives to encourage private companies."

The committee recommends the formation of a "Renewable Energy Authority" to identify and develop those technologies that are best suited to Britain's natural resources and skills. "We believe that the focus should be on offshore technologies - wind, wave and tidal - and nuclear fission and fusion," it says.

The committee also criticizes the government's economic incentives for the take up of renewable technologies, and proposes setting up a taxation system to reward "carbon-free" or "carbon-neutral" sources. "We believe that nuclear fission should enjoy the full status of a carbon-free technology," it says. "Renewable sources of power are not coming on stream fast enough and nuclear power must fill the gap."

Author
Edwin Cartlidge is News Editor of Physics World

Then came quantum mechanics. Classical thermodynamics tends to work for large numbers of atoms or molecules, which means that some quantum systems can at first appear to violate its basic laws. Now Marlan Scully and co-workers at Texas A&M University and Herbert Walther at the Max-Planck Institute for Quantum Optics in Garching have proposed a "quantum Carnot engine" that displays features that are simply not possible with a classical engine. In particular, their quantum engine can extract work from a single heat bath (M O Scully et al. 2003 Science 299 862-864 -- see #4 below - Ed.).

Quantum steam

Carnot's conceptual heat engine operated in cycles such that there is no change in the internal energy of the working fluid - such as steam - during a cycle. More heat is converted to work as the number of operating cycles increases, without the engine itself being a source of any work. In particular he considered a reversible closed cycle consisting of two isothermal (constant temperature) processes and two adiabatic (no external exchange of heat) processes. He showed that no heat engine operating between two temperatures could be more efficient than a Carnot cycle. But he was wrong.

The "steam" in the new quantum Carnot engine considered by Scully and colleagues comes in the form of photons. The radiation pressure from the photons drives a piston in an optical cavity, which also doubles as one of the cavity mirrors. The other cavity mirror is used to exchange heat with a heat sink at temperature T₁. A second heat bath at a higher temperature T₂ is required as a source of heat for the radiation, in analogy with the classical Carnot engine.

Scully and co-workers take this source of heat to be a stream of hot atoms, which flows through the cavity and exchanges energy with the photons through emission and absorption processes. These atoms flow out of the cavity at a cooler temperature and are then reheated in a second cavity known as a "hohlraum". Once the atoms have been heated to T₂ they are re-injected into the first cavity for the next cycle of the quantum Carnot engine.

Quantum coherence

The new twist in the quantum engine occurs when the bath atoms have three states instead of two, which can result in what is called quantum coherence. If there is a non-vanishing phase difference between the two lowest atomic states, then the atoms are said to have quantum coherence. This can be induced by a microwave field with a frequency that corresponds to the transition between the two lowest atomic states.

And the second law?

Furthermore, extracting work from a quantum Carnot engine does not violate the second law of thermodynamics because the quantum coherence also costs extra entropy, which ensures that the overall entropy of the system is always increasing.

Practicalities aside, a quantum Carnot engine may one day provide a "quantum afterburner" that will increase the efficiency of a conventional combustion engine. Such a hybrid device would exploit the temperature difference between the combustion and exhaust phases of the four-stroke Otto cycle ("The energy-saving quantum afterburner" Physics World March 2002 p6 -- See #5 below - Ed.).

The point is that atoms with quantum coherence constitute a substance that is fundamentally different from conventional working fluids such as steam or Freon, which allows us to extend our understanding of thermodynamics at the interface of classical and quantum physics.

Author
Peter W Milonni is at the Los Alamos National Laboratory, New Mexico, US (Dr. Milonni is also author of the highly recommended, future energy textbook for ZPE engineers: The Quantum Vacuum, Academic Press, 1994 - Ed.)

Science, Vol. 299, Issue 5608, 862-864, February 7, 2003 Marlan O. Scully,¹² M. Suhail Zubairy,¹³ Girish S. Agarwal,¹⁴ Herbert Walther² (excerpt)

We present here a quantum Carnot engine in which the atoms in the heat bath are given a small bit of quantum coherence. The induced quantum coherence becomes vanishingly small in the high-temperature limit at which we operate and the heat bath is essentially thermal. However, the phase associated with the atomic coherence, provides a new control parameter that can be varied to increase the temperature of the radiation field and to extract work from a single heat bath. The deep physics behind the second law of thermodynamics is not violated; nevertheless, the quantum Carnot engine has certain features that are not possible in a classical engine.

Carnot showed that every heat engine has the same maximum efficiency, determined only by the temperatures of the high-temperature energy source at T_h and the low-temperature entropy sink at T_{c .} Specifically, the Carnot efficiency for converting heat into work is given by E = 1 T_c/T_h. It follows that no work can be extracted from a single heat bath when T_c = T_h.

Here, we propose and analyze a new kind of quantum Carnot engine powered by a special quantum heat bath, which allows us to extract work from a single thermal reservoir. In this heat engine, radiation pressure drives the piston. Thus the radiation is the working fluid (analogous to steam), which is heated by a beam of hot atoms (analogous to coal).

Scully considered a simplified version of the Otto cycle, a sequence of operations similar to that carried out by a standard car engine. In this four-step cycle, a hot gas expands in a cylinder doing useful work before it loses heat to its surroundings; then it is compressed and heated again.

But Scully added two extra steps. After the heat has dissipated the gas is passed through a laser-maser cavity at constant temperature, where it deposits useful energy. This cavity is then reheated once the system as a whole has been reheated, again at a constant temperature.

The crux of Scully's system is that the heating of the cavity does not raise the kinetic energy of the atoms in the gas, as the normal heating stage does. Instead it increases the internal energy levels of the atoms, making them emit photons. Scully calculated that this liberated quantum energy was greater than the extra work that would have been produced if the additional heat had instead been ploughed into a normal four-stage cycle.

Scully points out that this result does not violate any laws of thermodynamics. He also analysed an equivalent system in a Carnot cycle - which, unlike the Otto cycle, runs at the highest efficiency permitted by thermodynamics - and found that quantum mechanics could not be used to improve the engine's performance.

He hints that he has already worked out how to test his idea in the lab and that he has conceived several novel laser systems. His idea has been dubbed a 'quantum afterburner' because of its parallel with the devices that extract useful energy from the exhaust of a jet engine.

Author
Edwin Cartlidge is News Editor of Physics World