The Laboratory for Experimental Nuclear Astrophysics (LENA), located at the Triangle Universities Nuclear Laboratory (TUNL), is noted internationally for its precision nuclear reaction rate measurements of rare astrophysical processes. These are critical to stellar nucleosynthesis of heavier elements from hydrogen and helium. To recreate stellar conditions at LENA requires very intense beams and highly selective detection techniques. The acceleration system at LENA has already produced proton currents on target up to 2.5 mA, the most intense beams worldwide in any laboratory where such studies are underway.
On a path to even higher beam intensity, UNC Professors Art Champagne and Tom Clegg worked with graduate student, Andrew Cooper, and undergraduate, Ivan Pogrebnyak, to design, construct, and use success¬fully a more robust acceleration column capable of accelerating ~30 milliamperes of protons to energies up to 240 keV (that’s 7.2 kW of beam power!).
The new column is depicted between the yellow solenoidal magnet around the ion source and the blue solenoidal magnetic lens used to focus the emerging proton beam toward the target. Both the ion source and new column were designed and constructed locally, using precision parts fabricated in our departmental instrument shop at UNC.
Three axial insulating rods are used to support the column and compress O-ring vacuum seals between its electrodes and ceramic insulators. Internal trans¬verse magnetic fields along the entire column length suppress backstreaming electrons which had previously produced dangerous levels of bremsstrahlung X-rays. Two channels of chilled flowing deionized water along the column now provide simultaneously both a high resistance path for column current to establish the uniform acceleration field gradient, and active cooling for the intervening column electrodes.