1 / 13

Low Temperature Near-Surface Diffusion: Infusion in High-Q, High-Gradient SRF Cavity Nb-Ti-N2

This research explores the phenomenon of low temperature near-surface diffusion, known as "infusion", in high-Q, high-gradient superconducting radio frequency (SRF) cavities made of Nb-Ti-N2. Previous studies have shown that infusion can increase the cavity's quality factor (Q0) at medium field ranges, but the underlying mechanisms are not fully understood. The research aims to investigate the effects of low-temperature baking and gas infusion on the cavity's performance, with a focus on oxygen diffusion, near-surface hydrogen reduction, nano-hydride precipitations, and vortices.

isham
Download Presentation

Low Temperature Near-Surface Diffusion: Infusion in High-Q, High-Gradient SRF Cavity Nb-Ti-N2

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. JLabWork on Low Temperature Near-Surface Diffusion aka “Infusion” High Q, High Gradient SRF cavity Nb Ti N2 PashupatiDhakal

  2. Let’s Re(Search), Before 2012/13 • Low temperature baking (LTB) was the final step before rf test primarily to cure high field Q-slope. • It results in increase in residual resistance while reducing BCS surface resistance, no significant benefit at medium gradient. • No unanimous model is available but its linked to “oxygen diffusion”, “near surface hydrogen reduction”, “nano-hydride precipitations”, “vortices” and etc……… R. Geng

  3. Let’s Re(Search), After 2013 • Increase in Q0 in medium field range (<25 MV/m) with increasing RF field, due to near surface material diffusion (Ti and N2). • Limited theoretical work to explain the Q-rise phenomenon, but the available data and models suggest that the effect is due to decrease in BCS surface resistance with RF field. • The idea of increasing Q0 at higher field reported by FNAL and reproduced in some labs with low temperature baking in nitrogen (without nitrogen • With some “Recipes” of LTB in nitrogen, the Q-rise phenomenon were observed in medium field and quench field is extended to higher gradient.

  4. Earlier Results “LTB with N2” • 1.5 GHz single-cell fine-grain Nb cavity (RRR>300) • N-infusion: 800 °C/3h, N2 at ~25 mTorr at 290°C, cooling to hold temperature maintained for 48 h P. Dhakalet al., Phys. Rev. Accel. Beams. 21, 032001 (2018)

  5. Earlier Results “LTB with N2” LG LG FG • Temperature measured at inside wall of furnace • The higher gas injection temperature • Cavity surface temperature unknown • No active RGA monitoring during the gas injection • Able to get some high Q with high Eacc

  6. Furnace Upgrade Ari Palczewski Thermocouple attach to cavity surface RGA monitoring during gas injection

  7. In the mean time….. 75C magic bake reported during last TTC at Reiken from FNAL Baseline-EP +75C/4hrs+120C/48hrs Typical baked cavity !

  8. In the mean time….. 75C magic bake reported during last TTC at Reiken from FNAL Baseline-EP +75C/4hrs+120C/110hrs Typical baked cavity !

  9. Back to “LTB with N2”

  10. Back to “LTB with N2” Previously with same recipe Next: Health evaluation of furnace and components

  11. Back to “LTB with N2” No degradation in Eacc and small Q degradation above 25 MV/m could be due to some MP/FE activities

  12. Summary • Earlier “Infusion” were reproducible when gas injected at higher temperature. • ~75C hold for 4 hours during 120 C baking didn’t appear to be beneficial over the conventional 120C bake (statistics of 2 rf test). • Furnace itself appeared to be clean after the recent upgrade evident from the rf(single cavity) test. • First infusion run after furnace upgrade wasn’t as expected, probably due leak/contamination to gas injection line. • Work in progress to prepare some baseline cavities and infusion run once the furnace issue resolved.

More Related