Experimental Systems develops high-power beam dump

FRIB will primarily use a 400 kW beam to create rare isotopes. Once the beam hits the production target, only a part of it will undergo nuclear reactions. The majority will emerge from the target as unreacted beam and is stopped in the beam dump. For this purpose, the FRIB Experimental Systems Division has developed a high-power beam dump that uses a rotating water-filled drum to intercept the unreacted beam.

A volume of water inside a rotating thin-walled shell of the drum will absorb beam power of up to 325 kW. The drum has a diameter of 70 centimeters (about 27.5 inches) and a height of 8 centimeters (about 3 inches) in order to distribute the heat and radiation damage the beam will cause. The shell is made of titanium alloy Ti-6Al-4V with a wall thickness of only 0.5 millimeters (about 0.02 inches) in order to limit the power deposited into the wall material.

Fabricating this large-size shell is a challenge with conventional manufacturing processes because of its thin wall and the specific curved shape required to support the high water pressure inside the drum. To meet this challenge, the FRIB team has been investigating different manufacturing approaches. One of the most promising techniques for this task is additive manufacturing, often also referred to as 3D printing.

In recent years, different processes have been developed to 3D print titanium alloys, and the sizes of objects that can be fabricated in this way have increased. The processes and sizes have advanced to a point where such a beam dump shell could be printed in a few pieces now and possibly in a single piece in the near future. Direct Metal Laser Sintering (DMLS) is one of the available processes for additive manufacturing of titanium-alloy. It’s known to produce material with mechanical properties that match or exceed those obtained with conventional techniques. The FRIB Target Systems group used it to fabricate a quarter-scale prototype beam-dump drum they developed. The prototype will be used in tests with the high-energy electron beam at the Budker Institute of Nuclear Physics (BINP) in Novosibirsk.

The entire mechanical setup, including the quarter-scale 3D-printed Ti-6Al-4V beam-dump prototype, was fully tested at the FRIB Laboratory, including pressure testing to the FRIB operating pressure, and rotation testing at the nominal speed. The assembly is now ready for shipment to BINP in Novosibirsk for tests with a high-power electron beam in spring of 2016. These tests will provide results that validate design assumption and how the 3D-printed structure performs under FRIB-like heating conditions.