Treatments of Niobium A. Camacho*^, A.A. Rossi* and V. Palmieri*^, * - PowerPoint PPT Presentation

Athmospheric Surface Treatments of Niobium A. Camacho*^, A.A. Rossi* and V. Palmieri*^, * INFN – Legnaro National Laboratories ^ University of Padua

Samples or Cavities? Material Study or Cavity construction?

Low research budget  Large amount of cavities 6 6 GHz GHz

Samples Pillbox cavities, etc Real cavities Calorimetric methods 6 GHz cavities Resistive R S Differential 1,5 /1,3 GHz monocells Inductive measurements H c1 Measurement Microstrip Resonators 1,3 GHz 3-cell cavity 1,3 GHz 9-cell cavities

6 GHz CAVITY MINILAB • No electron beam welding, neither for flanges • Obtained by spinning from Nb scraps • Short fabrication time • Fast and low cost BCP and EP treatments • Inexpensive Cryogenics • Quick RF Measurements

6 Ghz Cavity Geometry 36 mm Seamless flanges 20 mm Flange Area = 7 cm 2 [mm]

Mini Mechanical Tumbling SiC ZrO 2 Al 2 O 3 + SiO 2

Mini EP

6 GHz CAVITY MINI-furnace

6 GHz CAVITY MINI-Camera

Ready for the RF measurement

6 GHz CAVITY: MINI-Kapton gasket

Quick RF Measurements The insert has been conceived to even enter into a 450 lt Helium dewar INSERT DEWAR RF measuring system

High Temperature Rapid Metathesis (Nitriding in Mushy State)

The Homologous Temperature T [K] q = T m [K] 0 1 for Nb 2467 °C

T [K] q = T m [K] Premelting Mushy State 0,9 0,96 0,98 1 2196 °C 2357 °C 2412 °C 2467 °C

PureNb NbN2 NbN2a NbN2b NbN3 8 10 NbN4 NbN5 NbN6 NbN8 NbN8Ox NbN9 NbN11 NbN12 NbN13 Q NbN13 3'' BCP NbN14 Bulk Nb 6 Ghz @4,2K 7 10 0 1 2 3 4 5 6 E Pk (MV/m)

High Temperature Rapid Metathesis (Nitriding in Mushy State) The Process is: • Fast ( takes only few sec) • Cheap (Vacuum Technology Free) • Simple (No need of special expertise)

Pr Premelting emelting (also Surf Surface ace melting melting) Even below its melting point ( T m ), quasi-liquid films can be observed on crystalline surfaces

Pr Premelting emelting (also Surf Surface ace melting melting) The thickness of the quasi-liquid film is T - dependent This effect is common for all crystalline materials

NbN Nb NbN 3 mm Nb

 Nb 5 N 6 ; N 4 N 3 Over-Stoichiometric  d -NbN 1-x ;  g -Nb 4 N 3-x Under-Stoichiometric  a -Nb (N) (bcc solid solution)  Niobium

Nb 5 N 6 ; N 4 N 3 d- NbN 1-x ; h -NbN (hexagonal); d ’ - NbN (hexagonal); b -Nb2N (hexagonal); g -Nb 4 N 3-x a -Nb (N) (bcc solid solution) Niobium

Surface layers

T m of Nb Temp emper eratu ture Ti Time me 3 3 – 30 sec 30 sec

d -Nb N g -Nb N

As the d -NbN  g -Nb 4 N 3-x phase transformation is a very fast , quasi-continuous Transition, it cannot be avoided by quenching

The good layer is t he most external one

PureNb NbN13 NbN13 - BCP 3' 8 10 NbN BCP 3’ Q BCP 3 ’ Pure Nb 7 10 0 1 2 3 4 5 6 E Pk (MV/m)

8 10 PureNb NbN NbN He Annealing NbN N 2 Annealing 7 10 Q 6 10 0 1 2 3 4 5 E Pk (MV/m)

NbN @4,2K T = 4,2 K Bulk Nb

High Temperatures for Nb Purification

8 10 5 min at 2300°C 7 10 Q IL - EP Nb 26 Nb 17 IL - EP Nb 1 Classical – EP Nb 27 Classical – EP Classical – EP Nb 37 Classical – EP Nb 13 G 5 min at 2300°C Nb 111 6 10 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 E Pk [MV/m]

Conclusions 1 • 6 Ghz cavities allow a fast and dense statistics

Conclusions 2 • No vacuum required! • 5min @ 2300°C seem to purify Nb • Nitriding performed at Atmospheric pressure • At 4,2 K the Q-value at low field increases of even a factor 5