The possibility of using 1288 MHz (L-band) SRF elliptical cavities to accelerate heavy ion multi-charge-state (up to 5 charge states) beams is being investigated for accelerating energy higher than 200 MeV/u. This cavity can be a potential energy upgrade for heavy ions linac accelerators such as the Facility for Rare Isotope Beams (FRIB) in the United States of America and Rare Isotope Science Project (RISP) in Korea. One of possible disadvantages of the L-band frequency structure is its small longitudinal acceptance. It should be sufficiently large for transporting the ions with the limited beam loss ensuring accelerator hands-on maintenance.A first simple analytic study was performed and it showed a promising result with 1288 MHz linac. In addition, from beam loss point of view, the study deduced that 1288 MHz linac frequency could be the limit for medium-beta heavy ion up to five charge states beam accelerators. This work is the result of the detailed beam dynamics simulation for the linac performance using TRACK code to confirm the analytic result. The result shows that the longitudinal acceptance is large enough for medium-beta heavy ion with five charge state beams. Usually accelerator upgrade projects have limitations such as environment, space, and cryogenic cooling plant. Thus, high frequency and high gradient cavity is demanded to resolve such limitations. Exploiting cavity nitrogen doping technology would be beneficial for efficient cryogenics.Nitrogen doping technology has shown that it is more beneficial for higher frequencies cavities. This impact on BCS surface resistance (RBCS). RBCS is proportional to the frequency squared, nitrogen doping technology benefit is larger in the higher frequencies. For instance, the benefit is larger at 1300 MHz cavity than low frequency cavities such as 650 MHz cavity. That is due to the fact that BCS surface resistance, RBCS (depends on temperature and electron mean free path of the niobium material) is higher than the residual surface resistance, Rres (Temperature independent) in higher frequencies. The Research and Development (R&D) of nitrogen doping technology is still on going. However our neon doping proposal to give us more insight on the physics of nitrogen doping of RF surfaces and confirm or refute the assumption that the interstitial nitrogen atoms play the role of improving the cavity intrinsic quality factor not the nitrogen nitride (NbN) chemical compositions hasn't been implemented yet, it is still an open question.
Read
