This assumess brem from the ring itself is negligible. Energy loss is from any interaction between ions that doesnt result in fusion. This includes stuff that w

This assumess brem from the ring itself is negligible. Energy loss is from any interaction between ions that doesnt result in fusion. This includes stuff that would scatter ions out of the beam in reality, but in the charitable model its assumed their momenta are immediately reset to the most desirable value with perfect efficiency. In reality this would not be possible due to phase space considerations (Liouville theorem)