5 research outputs found
Thermocurrents and their Role in high Q Cavity Performance
Over the past years it became evident that the quality factor of a
superconducting cavity is not only determined by its surface preparation
procedure, but is also influenced by the way the cavity is cooled down.
Moreover, different data sets exists, some of them indicate that a slow
cool-down through the critical temperature is favourable while other data
states the exact opposite. Even so there where speculations and some models
about the role of thermo-currents and flux-pinning, the difference in behaviour
remained a mystery. In this paper we will for the first time present a
consistent theoretical model which we confirmed by data that describes the role
of thermo-currents, driven by temperature gradients and material transitions.
We will clearly show how they impact the quality factor of a cavity, discuss
our findings, relate it to findings at other labs and develop mitigation
strategies which especially addresses the issue of achieving high quality
factors of so-called nitrogen doped cavities in horizontal test
Advanced surface treatments for medium-velocity superconducting RF cavities for high accelerating gradient continuous-wave operation
Nitrogen-doping and furnace-baking are advanced high-Q0 recipes developed for
1.3 GHz TESLA-type cavities. These treatments will significantly benefit the
high-Q0 linear accelerator community if they can be successfully adapted to
different cavity styles and frequencies. Strong frequency- and geometry-
dependence of these recipes makes the technology transfer amongst different
cavity styles and frequencies far from straightforward, and requires rigorous
study. Upcoming high-Q0 continuous-wave linear accelerator projects, such as
the proposed Michigan State University Facility for Rare Isotope Beam Energy
Upgrade, and the underway Fermilab's Proton Improvement Plan-II, could benefit
enormously from adapting these techniques to their beta_opt = 0.6 ~650 MHz
5-cell elliptical superconducting rf cavities, operating at an accelerating
gradient of around ~17 MV/m. This is the first investigation of the adaptation
of nitrogen doping and medium temperature furnace baking to prototype 644 MHz
beta_opt = 0.65 cavities, with the aim of demonstrating the high-Q0 potential
of these recipes in these novel cavities for future optimization as part of the
FRIB400 project R&D. We find that nitrogen-doping delivers superior Q0, despite
the sub-GHz operating frequency of these cavities, but is sensitive to the
post-doping electropolishing removal step and experiences elevated residual
resistance. Medium temperature furnace baking delivers reasonable performance
with decreased residual resistance compared to the nitrogen doped cavity, but
may require further recipe refinement. The gradient requirement for the FRIB400
upgrade project is comfortably achieved by both recipes.Comment: 16 pages, 5 figure
Recommended from our members
Advances of the FRIB project
The Facility for Rare Isotope Beams (FRIB) Project has entered the phase of beam commissioning starting from the room-temperature front end and the superconducting linac segment of first 15 cryomodules. With the newly commissioned helium refrigeration system supplying 4.5K liquid helium to the quarter-wave resonators and solenoids, the FRIB accelerator team achieved the sectional key performance parameters as designed ahead of schedule accelerating heavy ion beams above 20MeV/u energy. Thus, FRIB accelerator becomes world's highest-energy heavy ion linear accelerator. We also validated machine protection and personnel protection systems that will be crucial to the next phase of commissioning. FRIB is on track towards a national user facility at the power frontier with a beam power two orders of magnitude higher than operating heavy-ion facilities. This paper summarizes the status of accelerator design, technology development, construction, commissioning as well as path to operations and upgrades
ANALYSIS OF STRUCTURAL SECRECY OF MULTI-FREQUENCY SIGNALS OF BROADBAND COMMUNICATION SYSTEMS
Recommended from our members
Advances of the FRIB project
The Facility for Rare Isotope Beams (FRIB) Project has entered the phase of beam commissioning starting from the room-temperature front end and the superconducting linac segment of first 15 cryomodules. With the newly commissioned helium refrigeration system supplying 4.5K liquid helium to the quarter-wave resonators and solenoids, the FRIB accelerator team achieved the sectional key performance parameters as designed ahead of schedule accelerating heavy ion beams above 20MeV/u energy. Thus, FRIB accelerator becomes world's highest-energy heavy ion linear accelerator. We also validated machine protection and personnel protection systems that will be crucial to the next phase of commissioning. FRIB is on track towards a national user facility at the power frontier with a beam power two orders of magnitude higher than operating heavy-ion facilities. This paper summarizes the status of accelerator design, technology development, construction, commissioning as well as path to operations and upgrades