Additive manufacturing method for SRF components of various geometries
An additive manufacturing method for forming nearly monolithic SRF niobium cavities and end group components of arbitrary shape with features such as optimized wall thickness and integral stiffeners, greatly reducing the cost and technical variability of conventional cavity construction. The additive manufacturing method for forming an SRF cavity, includes atomizing niobium to form a niobium powder, feeding the niobium powder into an electron beam melter under a vacuum, melting the niobium powder under a vacuum in the electron beam melter to form an SRF cavity; and polishing the inside surface of the SRF cavity.
1. An additive manufacturing method for forming a superconducting radio frequency (SRF) cavity, comprising:
a) atomizing a thin niobium wire in a vacuum under an inert gas atmosphere to form a niobium powder;
b) maintaining said niobium powder in a sealed container in a vacuum under a blanket of inert gas;
c) feeding said niobium powder into the electron beam melter under vacuum;
d) raking the niobium powder over the vertically adjustable surface to form a powder layer;
e) melting the niobium powder under a vacuum in the electron beam melter to form a cross-section of the SRF cavity;
f) lowering said vertically adjustable surface;
g) repeating steps c through f to form additional cross-sections of the SRF cavity; and
h) polishing the inside of the SRF cavity.
2. The method of claim 1 wherein said niobium powder includes a residual resistivity ratio (RRR) of at least 300.
3. The method of claim 1 wherein said niobium powder includes a purity of greater than 99.99%.
4. The method of claim 1 wherein said niobium powder includes a powder size distribution of +30 μm to −100 μm.
5. The method of claim 1 wherein said niobium powder includes a spheroidal morphology.
6. The method of claim 1 wherein said inert gas is argon.
7. The method of claim 1 wherein the vacuum in said electron beam melter is between 10 −5 and 10 −6 Torr.
8. The method of claim 1 wherein said SFR cavity is of monolithic construction.
9. The method of claim 1 wherein said SFR cavity includes a wall and an integral stiffener extending from said wall.
10. The method of claim 9 wherein said integral stiffener is a honeycomb structure.
11. The method of claim 1 wherein the powder layer includes a thickness of 100 μm.
12. The method of claim 11 wherein said polishing the inside of said SRF cavity includes abrasive media.
13. The method of claim 12 wherein said polishing the inside of said SRF cavity includes rotating the cavity at high speed.
14. The method of claim 1 wherein the inside of said SRF cavity is polished to a surface finish of 100 nm or less.
15. The method of claim 9 wherein said wall of said SRF cavity includes a variable wall thickness.
16. The method of claim 1 wherein the atomizing includes melting and converting said thin niobium wire to droplets in a plasma.
17. The method of claim 16 wherein the plasma is an argon plasma.
18. The method of claim 1 wherein melting the niobium powder includes
pre-heating the powder layer with the focused electron beam at low beam current and high scan speed; and
increasing the beam current and decreasing the scan speed of the focused electron beam as needed to melt the powder layer.