Physics Department

Lancaster University

Cavity development

Rebecca Seviour

Physics Department

Lancaster University

Operating Cavities in an Magnetic field

Physics Department

Lancaster University

Where do the electrons go......

7 μ

6 μ

Initial Particle Data Input

(X,Y,Z) (Vx,Vy,Vz)

Use Comsol to Extract (E, B)

Field Parameters

Compute New Particle Data

by Integration

Extraction of Particle Data

at Point of Impact

FEA Analyses at the Point of

Impact

Secondary Electron Emission

Physics Department

Lancaster University

Physics Department

Lancaster University

As received

Ra(nm) 101

Rq(nm) 136

Electropolished

Ra(nm) 89

Rq(nm) 118

Physics Department

Lancaster University

Before

As received Electropolished

Physics Department

Lancaster University

Need to do the experiment to prove .......

Physics Department

Lancaster University

R.L.Geng, PAC 2003

Q

E Field (Mv/m)

Generic Problem

Physics Department

Lancaster University

FP7 – EuCard Thin Films Examining phenomena limit current performance and investigating alternative coating techniquesSeveral mechanisms for the thin film Q-drop[i]ii],[iii];

mfp

NbHigh Rinterface

Low

200 MHz , ~ 40 nmLayer thickness ~ 10 m

Physics Department

Lancaster University

Physics Department

Lancaster University

CERN, Nb on Cu

Nb

High Rinterface

Physics Department

Lancaster University

Renormalisation of N by induced condensate (Proximity Effect)

Quasiparticle current

Contribution from conversion of low energy quasiparticle current into condensate current (Andreev Reflection)

Superconductor

Normal ConductorNb

High Rinterface

Physics Department

Lancaster University

0 100 200 300 400 500 600 700012345678

AFM profile

position along the path / nm

Heig

ht /

nm

Nb (850 nm) on Si

AFM photodetector

Tip piezo

Sample piezotransducer

Microfabricated cantilever

AFM tip

laser

Sample

• Such elasticity variations are linked with – Local surface and subsurface material

composition– Subsurface strain variations (they affect local

elastic moduli via third order elastic constants)

• UFM allows surface topography to be mapped simultaneously with the material composition and strain

Ultrasonic Force Microscope: Measuring Strain and Elasticity

mfp

Physics Department

Lancaster University

Physics Department

Lancaster University

Physics Department

Lancaster University

Towards a High Temperature SC RF Cavity ?

Conventional SCRF (Nb) – Require He Cryosats (< 4 K)

HTc SC - Operate >30 K

HTc SC RF - Minehara (1990) considered HTc RF Cavity resonator

made from isostaticaly pressed YBCO & BSCCO.Achieving Q > 10^6 at 30K.

- Others considering the use of HTC Thin Film

Physics Department

Lancaster University

Bulk HTS Cavity limited by several factors,

HTS have high residual resistance ratios, f

Transport properties very sensitive to imperfections.

This gives rise to low current in the superconductor.

HTS are extremely sensitive to the right stoichiometry and oxygen content.

Physics Department

Lancaster UniversitySome experimental RF work has been done on Proximity effect

- Sputtered Cu on Nb

- Rs of Cu reduced > 50% - SC is shielded from magnetic field

Physics Department

Lancaster UniversityExperiment

Detachable wall

Detachable wall

Coaxial coupler

Hybrid wall

Normal Metal

HTS

2 Hybrid walls

• Working at 10 GHz (small sizes for ALD), create a number of hybrid proximity effect walls for evaluation ( Q, Rs, λ, ξ, , surface properties: stress, strain, elasticity)

• repeat Cu /Nb experiments

• asses various HTC (Magnisium Diboride, BaKBiO)

• asses various N metals (silver, lead, Cu)

• Try various coating techniques