The Oak Ridge National Laboratory’s (ORNL) new accelerator-based Spallation Neutron Source (SNS) is a facility that provides the most intense pulsed neutron beams in the world for scientific research and industrial development.
When ORNL sought to improve the cooling jacket for the aluminum nitride plasma chamber that produces ions for the SNS, it chose Ensinger Inc extruded TECAPEEK made with VICTREX PEEK polymer in place of polycarbonate because of the material’s dimensional stability under pressure, low radio frequency (RF) losses, and its ability to be precisely machined resulting in a new one-part design solution.
The plasma chamber containing the RF-driven multicusp ion source measures about 76mm (3 inches) in diameter and 178mm (7 inches) in length. The ions produced are formed into a pulsed beam and accelerated to very high temperatures. “The plasma puts a nominal 3kW heat load on the plasma chamber which must be cooled,” said Robert Welton, PhD, of SNS. “The function of the cooling jacket is to cool the plasma chamber by channeling water around it.”
The original cooling jacket was a two-part design made with a polycarbonate material. It failed because of cracking and poor tolerances; the application was exceeding what the material could handle. Another contributing factor was the high amount of machining that went into creating the two parts added a tremendous amount of internal stress. Ensinger, in consultation with their distributor AIN Plastics, a division of ThyssenKrupp, offered ORNL a one-part design solution using VICTREX PEEK polymer for the cooling jacket.
“ORNL was skeptical at first,” said Timothy Mercurio, Southeast Sales and Marketing Manager for AIN. “They couldn’t believe it could be done given the overall complexity of the parts to be combined. But we knew we had the right material with VICTREX PEEK polymer, and the right company to do the machining in American Industrial Plastics (AIP) of Daytona Beach, Florida. Because of AIP’s machining capabilities we were able to create a worry-free, one-part cooling jacket using VICTREX PEEK polymer. AIP precision machined the newly designed cooling jacket that carried tolerances of ± 001.”
Given the critical nature of the application, VICTREX PEEK polymer offered a number of essential properties including: low thermal conductivity to prevent the ions from reaching high temperatures, radiation resistance because x-rays are present, chemical resistance to prevent reduction by hydrogen, and electrical properties because of low RF losses.
For many research problems, having neutrons available in a series of pulses is better than having a continuous neutron source. SNS produces pulses that contain neutron intensities 20 to 100 times higher than that obtainable from the best continuous sources. “Just as we prefer a bright light to a dim one to read the fine print in a book, SNS gives researchers more detailed snapshots of even the smallest samples of physical and biological materials,” explained Welton. “Most people don't know it, but neutron-scattering research has a lot to do with our everyday lives. For example, things like medicine, food, electronics, and cars and airplanes have all been improved by neutron-scattering research.”
“AIP was invaluable in delivering one of the most complex, precision machined parts I’ve ever seen,” added Mercurio. “This was one of the best manufacturing team efforts I’ve ever been involved with. Without the material and technical expertise from Victrex, Ensinger and AIP, we could not have solved the problems and met the challenges that ORNL set forth.”
For more information, www.victrex.com