US scientists have unveiled details of a project that aims to develop Star Trek-style ray guns that could keep "security adversaries" out of Department of Energy (DoE) nuclear sites.

The DoE Office of Security and Safety Performance Assurance, together with the Department of Defense, is "exploring the potential" of directed energy weapons based on millimetre-wave rays.

Dubbed Active Denial Technology (ADT), the systems are an emerging class of non-lethal weaponry using 95GHz millimetre-wave directed energy.

According to the DoE the technology is capable of rapidly heating human skin to a pain level that has been demonstrated as "very effective at repelling people" without apparently burning the skin or causing other secondary effects.

ADT emits a 95GHz non-ionizing electromagnetic beam of energy that penetrates approximately 1/64 of an inch into human skin tissue, where nerve receptors are concentrated.

Within seconds, the beam will heat the exposed skin tissue to a level where intolerable pain is experienced and natural defence mechanisms take over.

This intense heating sensation stops only if the individual moves out of the beam's path or the beam is turned off.

The sensation caused by the system has been described by test subjects as feeling like touching a hot frying pan or the intense radiant heat from a fire. Burn injury is prevented by limiting the beam's intensity and duration.

Sandia National Laboratories, a National Nuclear Security Administration lab, will investigate how the technology can be used on "adversaries" by developing a small ADT system to protect US nuclear sites.

To help solve the many technical issues associated with the project, Sandia has partnered with Raytheon and the Air Force Research Laboratory as both organisations have significant experience with earlier ADT developments.

In the mid 1990s the US Air Force funded development of an ADT prototype which resulted in several ongoing projects, such as the Joint Non-Lethal Weapons Directorate's Vehicle Mounted Active Denial System and the Office of Force Transformation's project Sheriff.

In 2004, Sandia conducted simulations of how the smaller ADT system might be used and how it would perform against "adversary attack scenarios" within a nuclear facility using the Joint Conflict and Tactical Simulation software modelling tool.

"Recently there has been significant progress with this project," said Willy Morse, Sandia's principal investigator.

"On 5 May we took acceptance of a prototype system built by Raytheon's Advanced Electromagnetic Technologies centre in partnership with CPI and Malibu Research. Initial characterisation and performance tests were completed at the end of May."

A second-generation small-size ADT system is expected to be fielded at several DoE nuclear facilities as early as 2008.

Millimetre-wave "human effectiveness testing", initiated in 2001, has demonstrated ADT as effective and safe without any long-term effects, according to the Department of Defense.