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UW team crafts a cooler to study X-rays

April 27, 1998

Illustration by Brian Strassburg

For a more detailed story about this project, including photographs of the Adiabatic Demagnetization Refrigerator, please visit the Space Science and Engineering Center Web site.

Building space flight hardware sounds pretty glamorous to a lot of us: working with state-of-the-art equipment to create instruments that will fly in outer space, enhancing humankind’s understanding of the universe. But when you get down to the nitty gritty, it can be far less so.

Ask Tony Wendricks about spending an evening in a Chicago motel room spreading wires so they could be properly plated. Ask Dave Jones about threading those same wires, 1,600 of them, one by one through a tiny grid. Wendricks and Jones work in the not-so-glamorous trenches of a project in the Space Science and Engineering Center, building a high-tech refrigerator of sorts that will fly on a satellite gathering information about X-rays from outer space.

The project has been daunting from the start. When the group, which also includes Mike Dean and Mark Mulligan, first met with the Principal Investigator, Dan McCammon of the physics department, Wendricks remembers thinking, “Can we even do this?” The refrigerator uses a magnetic field and salt crystals to cool gold wires, which had to be strung, without touching each other, in a container the size of a soda can.

The hardware, known as the Adiabatic Demagnetization Refrigerator, will fly on the Astro-E satellite, a joint Japanese-NASA X-ray astronomy project. The refrigerator will be used to cool one of the satellite’s X-ray detectors to almost absolute zero. By keeping the detector’s temperature low, the heat generated by a single X-ray photon can be detected and measured, which can lend insights into black holes, white dwarves, supernovas and a myriad other phenomena.

The refrigerator cools by manipulating the magnetic alignment of the salt crystal molecules with a large magnet. The satellite detector will connect to the crystals using gold wire and gold-plated rods, which will enable the device to cool the detector to 0.065 degrees Kelvin.

The team had to figure out how to keep the apparatus from being eaten away by the corrosive soup needed to form salt crystals. Only gold and stainless steel could stand up to the sulfuric-acid-based solution. After much trial and error, the team finally hit on a way to string the 1,600 gold wires using a perforated disk, which looks like a piece cut from a colander.

Construction brought other problems: A $4,000 spool of gold wire proved not to have the conductivity needed. The first try at heating the wires resulted in their clumping together. “They stuck together like a plate of overcooked spaghetti,” says Jones. Gold wire isn’t the kind of thing that you throw in the trash, so Wendricks and Jones painstakingly peeled the strands apart using tweezers.

Wendricks also spent an evening spreading apart the wires, which turned out to be too tightly bunched to allow their soldered connections to the apparatus to be gold-plated. Once a Chicago gold-plater had done that, the wires had to be installed on the refrigerator, a process that involved stringing the wires with tweezers through two disks on the unit — as Jones says, like “threading 1,600 needles . . . twice,”

Now Wendricks and Jones are growing salt crystals, which requires pouring a solution of ground salt crystals and sulfuric acid into the refrigerator “can,” four times a day, including a pour at 6 a.m. and one at midnight. It will take a week to two weeks to accumulate the crystals into a tiny salt pill.

Once the salt crystals are grown, the refrigerator will be tested by UW’s space physics department before heading to NASA’s Goddard Space Flight Center for more testing. Eventually, it will end up in Japan where the launch of the Astro-E is planned for the year 2000.

When it finally gets to space, the product of the UW team’s labor will keep the detector operating smoothly for at least two years.

Tags: research