Passivated niobium cavities
A niobium cavity exhibiting high quality factors at high gradients is provided by treating a niobium cavity through a process comprising: 1) removing surface oxides by plasma etching or a similar process; 2) removing hydrogen or other gases absorbed in the bulk niobium by high temperature treatment of the cavity under ultra high vacuum to achieve hydrogen outgassing; and 3) assuring the long term chemical stability of the niobium cavity by applying a passivating layer of a superconducting material having a superconducting transition temperature higher than niobium thereby reducing losses from electron (cooper pair) scattering in the near surface region of the interior of the niobium cavity. According to a preferred embodiment, the passivating layer comprises niobium nitride (NbN) applied by reactive sputtering.
1. A process for the production of a niobium cavity exhibiting high quality factors at high gradients comprising:
A) removing surface oxides from the interior of the niobium cavity;
B) removing gases absorbed in the bulk niobium by high temperature treatment of the cavity under high vacuum to achieve hydrogen outgassing; and
C) assuring the long term chemical stability of the niobium cavity by applying a passivating layer of a superconducting material having a superconducting transition temperature higher than that of niobium.
2. The method of claim 1 wherein the removal of surface oxides is accomplished by plasma treatment under a vacuum.
3. The method of claim 1 wherein the removal of gases is accomplished by heating the cavity to a temperature of between about 600 and 900° C. under a vacuum below about −6 mbar.
4. The method of claim 2 wherein the removal of gases is accomplished by heating the cavity to a temperature of between about 600 and 900° C. under a vacuum below about −6 mbar.
5. The method of claim 1 wherein the passivating layer of a superconducting material having a superconducting transition temperature higher than niobium is applied by the reactive sputtering of a mixture of nitrogen and argon to obtain a passivating layer of niobium nitride.
6. The method of claim 2 wherein the passivating layer of a superconducting material having a superconducting transition temperature higher than niobium is applied by the reactive sputtering of a mixture of nitrogen and argon to obtain a passivating layer of niobium nitride.
7. The method of claim 3 wherein the passivating layer of a superconducting material having a superconducting transition temperature higher than niobium is applied by the reactive sputtering of a mixture of nitrogen and argon to obtain a passivating layer of niobium nitride.
8. The method of claim 4 wherein the passivating layer of a superconducting material having a superconducting transition temperature higher than niobium is applied by the reactive sputtering of a mixture of nitrogen and argon to obtain a passivating layer of niobium nitride.
9. A niobium cavity exhibiting high quality factors at high gradients prepared by a process comprising:
A) removing surface oxides from the interior of the niobium cavity;
B) removing gases absorbed in the bulk niobium by high temperature treatment of the cavity under high vacuum to achieve hydrogen outgassing; and
C) assuring the long term chemical stability of the niobium cavity by applying a passivating layer of a superconducting material having a superconducting transition temperature higher than that of niobium.
10. The niobium cavity of claim 9 wherein the removal of surface oxides is accomplished by plasma treatment under a vacuum.
11. The niobium cavity of claim 9 wherein the removal of gases is accomplished by heating the cavity to a temperature of between about 600 and 900° C. under a vacuum below about −6 mbar.
12. The niobium cavity of claim 10 wherein the removal of gases is accomplished by heating the cavity to a temperature of between about 600 and 900° C. under a vacuum below about −6 mbar.
13. The niobium cavity of claim 9 wherein the passivating layer of a superconducting material having a superconducting transition temperature higher than niobium is applied by the reactive sputtering of a mixture of nitrogen and argon to obtain a passivating layer of niobium nitride.
14. The niobium cavity of claim 10 wherein the passivating layer of a superconducting material having a superconducting transition temperature higher than niobium is applied by the reactive sputtering of a mixture of nitrogen and argon to obtain a passivating layer of niobium nitride.
15. The niobium cavity of claim 11 wherein the passivating layer of a superconducting material having a superconducting transition temperature higher than niobium is applied by the reactive sputtering of a mixture of nitrogen and argon to obtain a passivating layer of niobium nitride.
16. The niobium cavity of claim 12 wherein the passivating layer of a superconducting material having a superconducting transition temperature higher than niobium is applied by the reactive sputtering of a mixture of nitrogen and argon to obtain a passivating layer of niobium nitride.