Two 1500 MHz single cell cavities have been manufactured from two different high purity niobium ingots with very large grains. The ingots have been produced by Reference Metals causing a reduction of niobium material costs because the elaborate sheet manufacturing is being eliminated. The investigation is being conducted to:
- Investigate the effect of grain boundaries on the observed Q-drop in RRR niobium cavities
Both cavities have been tested after removal of about 200 – 300 micron from the surface, which resulted in a very shiny surface. Preliminary results are shown below:
Disc from Ingot “A”
Disc from Ingot “B”
Further tests are planned after post purification.
We are in the process of fabricating a 2.2.GHz single cell cavity, which will use only the center single crystal from ingot “A”, eliminating any grain boundaries. It has been confirmed that an electron beam weld on the single crystal does not break up the crystal into smaller crystallites; therefore this test cavity should give a conclusive answer, whether the observed Q-drop at higher gradients/magnetic fields is influenced by grain boundaries.
In addition a 7-cell high gradient cavity is presently being fabricated from material of ingot ‘A”.