Indiana University       Research & Creative Activity       September 2000 • Volume XXIII Number 2

On the Beam by Nick Riddle

In the concrete warrens of the IU Cyclotron Facility, applied physics is thriving. At slightly less than the speed of light, charged particles are hurling through a network of pipes that resemble the inner workings of an old wireless radio. The particles are aimed at a laptop computer, clamped fast at the end of a pipe like a damsel tied to a railway line.

But this is a serious scientific pursuit. More than that, it’s a business, putting IU’s powerful cyclotron at the disposal of the world’s space and aeronautics industries. The Radiation Effects Research Program (RERP) makes it possible for the likes of NASA and Boeing to answer a pressing question: Can today’s microelectronic circuitry withstand the onslaught of radiation, especially in outer space?

There’s no escaping radiation. Charged ions rain down on us from solar flares; electrons jostle us constantly in the form of electromagnetic radiation. Most of the ions are absorbed by our atmosphere before they reach the earth. But outside of Earth’s atmosphere, the incidence of charged particles is vastly increased. Just one wayward ion with an attitude can unseat the most ambitious space mission.

Members of the Radation Effects Research Program—from left, Ken Murray, Barbara von Przewoski, and Charles Foster—help scientists test a wide variety of devices for use in space, from circuit boards to supercomputers. Photo Tyagan Miller.

“Space is a nasty environment,” says Charles Foster, IUCF staff physicist and director of RERP. “It’s a vacuum, for one thing. There are particles, cosmic rays, heavy ions and fragments of them, which can cause problems, depending on the conditions. The components on semiconductor devices are getting smaller and smaller, andthat makes them individually more sensitive and more susceptible to damage.”

High-velocity ions can permeate a semiconductor device, producing freed electrons and “holes” (when an electron leaves an atom, the resulting ion has a positive electric charge, referred to as a “hole”). These electrons and holes then carry currents within the device. Because semiconductor devices work by carefully regulating the currents flowing through them, any unexpected alterations can wreak havoc. This is especially true of sensitive areas such as memory cells, where information may be altered or erased, or false commands can be generated. In control systems, the alterations can be catastrophic, producing failures in propulsion and navigation. Circuits anywhere can suffer burnout, and systems can be switched irretrievably into the wrong mode (a situation known as “latchup”). More generally, exposure to large quantities of ions can degrade a semicon-ductor’s material, shortening its life considerably.

This all makes “Will this thing work in space?” an urgent question. It’s bad enough when your hard drive crashes at home—a systems failure in outer space is another thing altogether. The question is complicated by radical changes in the economics of space exploration over the past couple of decades.

“A quarter-century ago,” Foster explains, “the military and space sectors drove the development of electronic technology, so they could dictate their needs.”

Now, the commercial market for microelectronics is so huge that military and space consumers account for a mere 1 percent. Consequently, many of the devices taken into space these days are similar, if not identical, to the kinds of gadgets you buy for your own home or office.

Foster cites an example. “Everyone knows about the problems NASA had with the optics on the Hubble spacecraft. But there was also a problem with one of the Hubble’s computers. This computer latched up whenever the spacecraft passed through a band of high-velocity electrons and ions called the South Atlantic Anomaly. The thrusters would fire and make the flight path unstable. So the computer had to be turned off whenever the Hubble passed through the anomaly. In the end, someone had to go up to replace it.”

This, Foster concludes, is the quandary facing the space and military sector: “How do they know, when they buy off-the-shelf systems, that these things will survive the mission? Well, they bring them here and test them.”

The radiation effects program began in 1992, after a number of discussions and experiments over the preceding years. Foster says he had argued for some time that “at some point, funding for basic nuclear physics was going to wind down, and we needed to find other uses for the facility.” In the summer of 1992, Foster and Alan Skees, a student, built a new beam line from the main branch of the facility, complete with an end station.

“It was all done on a shoestring,” says Foster. “The National Science Foundation doesn’t directly fund applied research, but the director of the cyclotron, John Cameron, allowed us to use equipment that was already around.”

Around the same time, Ken Murray, a scientific consultant in California, contacted Foster. “I had been working at UC Davis,” Murray says, “and I’d heard the IU machine was more powerful and better suited to radiation-effects experiments.”

Early attempts at setting up a testing program had not been successful, but after Murray met with Foster and saw the program’s potential, he decided to relocate to Bloomington. Murray brought with him the original version of Beam Monster, a software program he designed to regulate and measure the variables in a radiation test. After extensive modifications, Beam Monster became the control system for the new project. The high demand for use of the IU facility led to the building of a second beam line end station in March 1997, enabling two tests to be carried out simultaneously.

RERP team member Ken Murray (in red shirt) is hidden by a radiation beam line as he adjusts a laptop computer for testing. Photo Charles Foster.

The RERP end station is a cross between a physics lab and a shooting gallery. The device to be tested is placed in the path of a beam and subjected to a series of proton bursts. Murray’s Beam Monster software allows the user to control the beam and to measure the outcome. A printout indicates whether or not the device being tested is “rad hard”—that is, whether it is likely to survive the radiation levels expected. But why use protons, which carry a lower charge, if it’s the heavy ions that cause damage in space?

“Generally, protons cause no direct upsets in microelectronic devices,” Foster acknowledges. “But when a proton interacts with a silicon nucleus, it produces a shower of fragments that includes heavy ions, and these can do damage. Testing with protons is far cheaper and more convenient. What we needed to know was whether the damage rate for heavy ions could be estimated from the proton test results.”

The answer was yes, as two NASA scientists from the Johnson Space Center determined. Patrick M. O’Neill and William X. Culpepper, both regular users of the IUCF beam, developed a proton-based model for testing that gives an approximate idea of heavy ion failure rates and modes. NASA now uses this model extensively and is one of the heaviest users of the RERP. The program’s ever-growing client list also includes Boeing, Lockheed Martin, McDonnell Douglas, Vanderbilt and Princeton universities, and the Naval Research Laboratory.

A tremendous variety of electronic guinea pigs have undergone the proton test, and so far, there have been no unpleasant surprises. Laptops and PCs are frequent subjects. They stand up fairly well to radiation, although their cache memories have a tendency to go on the fritz. A leading brand of printer, intended for use on the space shuttle, fared less well. “Once we hit that with the beam,” Foster remembers, “it spat paper all over the place.” Other devices tested include communications systems, an emergency rocket pack for spacewalks, and a global positioning system designed for use on aircraft.

The Cassini spacecraft and its attached probe were launched on a seven-year journey to Saturn on October 15, 1997. Scientists from NASA used Indiana University's Radiation Effects Research Program facility to do last-minute testing of devices intended for use on the flight. Photo courtesy NASA.

Sometimes the tests have a very quick turnaround. Such was the case with the Cassini mission to Saturn, one of the most expensive and controversial ever mounted, with a price tag of $3.4 billion and a propulsion system involving seventy-two pounds of plutonium—the most ever sent into space. The Cassini spacecraft was due to launch on October 15, 1997. But on September 5, the IUCF got a call from the NASA Jet Propulsion Laboratory requesting emergency access to the beam.

The Cassini team was concerned about the viability of European optocouplers (connections that translate an electrical signal into a light signal and vice versa) and needed to test them with proton irradiation to qualify them for use on the mission. An engineer from NASA JPL arrived on September 6 and began the test that night because Lockheed Martin had already booked the facility during the day. By the early morning of September 8, the tests were completed. The optocouplers were declared “rad hard” and were installed in the Cassini spacecraft, which launched on schedule and is due to arrive in orbit around Saturn in 2004.

The nature of the tests isn’t always so obvious. “What these devices are and what their uses will be, I don’t always know,” says Foster. “If they want to tell me, fine. If not, that’s fine too. They might be guarding commercial or military secrets. Once we had two competing companies who both wanted to test their own versions of the same device, and we had to get one group out before the other one came in.”

The commercial bent of this work doesn’t prevent students from becoming involved. Undergraduates work ten weeks in the summer on a project, which they conclude with a written report and an oral presentation.

“Some of them have made major contributions to the program,” Foster says. “If nothing else, students get a clearer idea of what basic or applied research is all about, and they can make a more informed decision about the path they want to take.”

The path of the program in the future seems assured. As Foster nears retirement, he is preparing IUCF staff physicist Barbara von Przewoski to take over the reins. And the need for radiation testing will only increase. In the 1960s, future Intel chairman Gordon Moore predicted that the number of transistors on a chip would double every year. He was proved right. Today, a microchip the size of a fingernail can accommodate more than nine million transistors—every one a sitting target for pesky charged particles. As long as space missions continue and technology advances, business is not likely to slow down at IU’s RERP facility.

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