Test facility hones in on impact of nuclear explosions in space

by Tina Barton
Arnold Engineering Development Center Public Affairs

04/19/01 - ARNOLD AIR FORCE BASE, Tenn. (AFPN) - Determining how nuclear explosions in space affect U.S. defense systems is what an Arnold Engineering Development Center team hope to determine using its new plasma radiation source "cold" X-ray test capability.

Completed in 1999 in partnership with the Defense Threat Reduction Agency, the decade-quad simulator produces the X-ray portions of a nuclear explosion within a highly shielded test cell. The entire test lasts approximately 40 nanoseconds, or about the time it takes light to travel across a large room.

The simulator consists of a pulse power train with 288 high-energy storage capacitors that store electrical energy for a short time before producing X-rays.

In 2000, the nuclear weapons effect team added four Bremsstrahling diodes that produce up to 20 krads of "hot" X-rays over a 2,250 square-centimeter area for testing larger systems like communication satellites, ground-based interceptor sensors and missiles.

During a hot X-ray test, operators charge capacitors to levels of up to 100,000 volts of electricity. Then, they discharge the capacitors through the diodes to produce a 10 terawatt-pulse electron beam which impacts on a target producing the "hot" X-ray pulse.

Sensors on or near the test article measure and document the amount and type of X-rays produced. The entire sequence takes approximately two minutes.

"These X-rays deeply penetrate space systems and damage the internal components such as cables, computer circuits and processor boards," said Dr. Larry Christensen, one of the AEDC plasma physicists supporting the testing effort.

The latest upgrades produce "cold" X-rays by replacing the four Bremsstrahling diodes with a water coupler that funnels the electric current from the individual modules into a single load.

"Cold X-rays do not penetrate as effectively as hot X-rays, but 'land' on surfaces of satellite optical components such as telescopes, mirrors and lenses," Christensen said. "By depositing their energy at the surface of the test article, they can damage those components by marring the telescope lens or mirror coatings."

During cold X-ray testing, a conducting medium, such as aluminum wire or argon gas, is loaded into the center of the plasma radiation source coupler opening. Then, using the same process as hot X-ray testing, 10 million amps of electricity flows through the medium creating temperatures hot enough to vaporize it and strip "K-shell" and "L-shell" electrons from its molecules. The electrons produce the cold X-ray when they give up energy and fall back into their orbit.

"Since a nuclear explosion produces a broad spectrum of X-rays, including both 'hot' and 'cold,' we need to test with both types to accurately simulate the potential effects," said Lavell Whitehead, project manager and nuclear weapons effect team coach.

"Because different nuclear bombs emit different X-ray spectrums, our goal is to produce a spectrum that matches the type able to effect the customer's test article," he said.

Different mediums can be used depending on the X-ray spectrum being simulated, according to Whitehead,

"In the [testing] quad, different conducting mediums produce different X-ray spectrums, Whitehead said. "When our customer brings a test article in for testing, we determine which spectrum's could effect the system and then decide which conducting medium will produce that particular spectrum."

The nuclear weapons effect team will conduct its final cold X-ray check during April. The first test using the new capability will be the telescope portion of an exoatmospheric kill vehicle and is scheduled near the end of the fiscal year. (Courtesy of Air Force Materiel Command News Service)