Analysis of post wet chemistry heat treatment effects on Nb SRF surface resistance

Most of the current research in superconducting radio frequency (SRF) cavities is focused on ways to reduce the construction and operating cost of SRF based accelerators as well as on the development of new or improved cavity processing techniques. The increase in quality factors is the result of the reduction of the surface resistance of the materials. A recent test on a 1.5 GHz single cell cavity made from ingot niobium of medium purity and heat treated at 1400 C in a ultra-high vacuum induction furnace resulted in a residual resistance of about 1nanoohm and a quality factor at 2.0 K increasing with field up to 5x10^10 at a peak magnetic field of 90 mT. In this contribution, we present some results on the investigation of the origin of the extended Q0-increase, obtained by multiple HF rinses, oxypolishing and heat treatment of all Nb cavities.Comment: To be appear in proceeding of SRF 201

Superconducting Cavities from High Thermal Conductivity Niobium for CEBAF

The Continuous Electron Beam Accelerator Facility (CEBAF) is presently under construction in Newport News, VA.The accelerator consists of approximately 169 meters of 5-cell niobium cavities made from high thermal conductivity niobium with RRR values > 250.Cavities have been manufactured of material from three different suppliers.The material properties like thermal conductivity, residual resistivity and tensile behavior are compared.Results on the performance of these cavities in the presence of high rf fields are reported.Q(sub)0 values as high as 10^10 at 2 K and accelerating gradient of E > 14 MV/m have been achieved

Review of Liquid Helium Level Sensors

Reliability of liquid helium level sensors becomes critical whenever a cryostat needs to be completely welded and accessibility becomes limited. This paper presents a review of the currently available continuous LHe level sensors from the viewpoint of reliability and wide operating temperature range (1.5 - 5.0 K). The only in limited temperature segments 3.0 - 4.6 K and below the lambda-point. Specifications of a new, simple and wide temperature range level sensor which dissipates very low power (~ 6 mW) into the cryogenic system and that can measure level of any cryogenic liquid are also presented here

Thermal and Mechanical Properties of Electron Beam Welded and Heat-Treated Niobium for Tesla

The design accelerating gradient for Tesla SRF cavities is 25 MV/m. For achieving such high accelerating gradients both the field emission and thermal quench limitations have to be eliminated. Post purification of the niobium sheets, cells or the completed cavities is likely to achieve the required gradients. However, such treatments are bound to reduce the mechanical properties of the accelerating structure. In this paper, thermal and mechanical properties of electron beam welded and heat treated high RRR niobium are presented

Superconducting Cavities from High Thermal Conductivity Niobium for CEBAF

The Continuous Electron Beam Accelerator Facility (CEBAF) is presently under construction in Newport News, VA.The accelerator consists of approximately 169 meters of 5-cell niobium cavities made from high thermal conductivity niobium with RRR values > 250.Cavities have been manufactured of material from three different suppliers.The material properties like thermal conductivity, residual resistivity and tensile behavior are compared.Results on the performance of these cavities in the presence of high rf fields are reported.Q(sub)0 values as high as 10^10 at 2 K and accelerating gradient of E > 14 MV/m have been achieved

Several Technical Measures to Improve Ultra-High and Extreme-High Vacuum

Achieving UHV/XHV with out high temperature bake outs is becoming essential in many applications. In this study, we investigated the use of inexpensive silica and titanium oxide thin film coatings on UHV/XHV chambers/components to reduce the adsorption of water on the chamber walls. Water can be cracked into oxygen and hydrogen in the material and act as one of the sources of hydrogen. We have also implemented backing of the turbo pump with an ion pump for reducing the vacuum chamber pump down times into UHV/XHV pressure range. The results of these investigations are summarized in this paper

A path to higher Q0 with large grain niobium cavities

The improvement of the quality factor Q{sub 0} of superconducting radio-frequency (SRF) cavities at medium accelerating gradients ({approx} 20 MV/m) is important in order to reduce the cryogenic losses in continuous wave accelerators for a variety of applications. In recent years, SRF cavities fabricated from ingot niobium have become a viable alternative to standard high-purity fine-grain Nb for the fabrication of high-performing SRF cavities with the possibility of significant cost reduction. Initial studies demonstrated the improvement of Q{sub 0} at medium field in cavities heat treated at 800-1000 C without subsequent chemical etching. To further explore this treatment procedure, a new induction furnace with an all-niobium hot-zone was commissioned. A single-cell 1.5 GHz cavity fabricated from ingot material from CBMM, Brazil, with RRR {approx} 200, was heat treated with the new furnace in the temperature range 600-1200 C for several hours. Residual resistance values 1-5 nano-ohm have been consistently achieved on this cavity as well as Q{sub 0} values above {approx} 2 x 10{sup 11} at 2 K and 100 mT peak surface magnetic field. Q{sub 0}-values of the order of 10{sup 11} have been measured at 1.5 K

ANALYSIS OF POST-WET-CHEMISTRY HEAT TREATMENT EFFECTS ON NB SRF SURFACE RESISTANCE

Abstract Most of the current research in superconducting radio frequency (SRF) cavities is focused on ways to reduce the construction and operating cost of SRF-based accelerators as well as on the development of new or improved cavity processing techniques. The increase in quality factors is the result of the reduction of the surface resistance of the materials. A recent test [1] on a 1.5 GHz single cell cavity made from ingot niobium of medium purity and heat treated at 1400 C in a ultra-high vacuum induction furnace resulted in a residual resistance of ~ 1n and a quality factor at 2.0 K increasing with field up to ~ 5×10 10 at a peak magnetic field of 90 mT. In this contribution, we present some results on the investigation of the origin of the extended Q 0 -increase, obtained by multiple HF rinses, oxypolishing and heat treatment of "all Nb" cavities