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The accelerating gradients in superconducting RF cavities can be limited by excessive temperature rise on the inner surface. In some circumstances, such as high RF frequency or anomalous losses, improved heat transfer at the niobium-helium interface can increase the achievable gradient. Different surface morphology techniques have been applied to reduce the limitation at the thermal interface. These techniques include varying surface roughness and forming cooling channels (embedded fins) in the surface. Heat transfer measurements on several niobium samples of different surface states, but same bulk purity at both Helium I and II (super-fluid) temperature regimes are planned. Initial measurements to validate the experimental setup on one sample are presented. Comparison of the test measurements is made with the existing literature data. The surface characterization uses a high-resolution 3D optical nano-scope. Finally, the influence of these interface surface techniques on the performance of the cavities will be discussed. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

The low energy beam transport (LEBT) system in the front-end of the Rare Isotope Accelerator (RIA) uses a 70 kV platform to pre-accelerate the ion beam from a 30 kV Electron Cyclotron Resonance (ECR) ion source, followed by an achromatic charge selection system. The selected beam is then pre-bunched and matched into the entrance of a Radio Frequency Quadrupole (RFQ) with a multi-harmonic buncher. To meet the beam power requirements for heavy ions, high current (several mA), multi-species beams will be extracted from the ECR. Therefore, it is crucial to control space charge effects in order to obtain the low emittance beam required for RIA. The PARMELA code is used to perform the LEBT simulations for the multi-species beams with 3D space charge calculations. The results of the beam dynamics simulations are presented, and the key issues of emittance growth in the LEBT and its possible compensation are discussed. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]