Cavity design for quench study

M. Ge, G. Wu, L. Cooley, M. ChampionFermilab, Batavia, IL, USA

TFSRF Workshop

JLab, Jul 22-25, 2008

MotivationMaterials and surfaces

Surface roughnessImpuritiesOxideGrain boundariesHot-Spots

RF SuperconductivityQuench fieldSurface resistance

A. Romanenko, Surface Analysis of Samples Dissected from a Cavity with a High-Field Q-Slope

LE1-35 T-map at P=14100 uW

a_corrT

H1

H2

H3

H4

H5

H6

H7

H8 H9

H10

C1C2

C3C4

C5

C7C8

C9

C10

Dissected 10 hot and 9 “cold” regions

Optical profilometry – roughness comparisonX-ray photoelectron spectroscopy (XPS) – near-surface (a few nm) elemental composition and chemical stateElectron back-scattered diffraction (EBSD) – crystal orientation mappingAuger electron spectroscopy (AES)Secondary ion mass spectrometry (SIMS)

The samples cut from CEBAF single cell cavity

Motivation

Although FE is not a fundamental problem, but it still happens in many cavity tests.In order to focus on limit-pushing quench study, we want a cavity which could reduce FE interference.

Motivation

108

109

1010

0 5 10 15 20 25 30

SC-035th meas.Qo

Qo

Ep [MV/m]

2007/03/3 Sat

EP(3um)+HF+HPR(TOC=6, Bacteria=0)+Baking(120*C 48hrs)

X-ray start from 15MV/m

limited by FE

Ep=25.2MV/mQ0=4.6E8

108

109

1010

0 5 10 15 20 25 30 35 40

CLSC-034th meas.

Qo

Qo

Esp(MV/m)

2007/02/13 Tue

Esp=37.49MV/mQ0=3.05E9A bad experience in cavity test

FE happened during the testThe defects were found

on equator

Field emission is a continuing problem

DESY cavity experienceL. Lijie’s summary of DESY cavity databank, DESY, 2006

Red represents the FE limitation

Pioneering effortJLab two-cell cavity

G.Ciovati (2003), Preliminary study of electric and magnetic field effects in superconducting Niobium cavities. PAC03.

Design goal

2000 45p p

acc acc

H EE E

<

2000 44( /( / ))45

p

p

HOe MV m

E> =

Design a cavity that quenches before field emission starts(Cavity will quench at Hp=2000 Oe, and start field emission at Ep=45MV/m. )

Shemelin, V. (2007). Low loss and high gradient sc cavities with different wall slope angles. PAC07.

Approach

The angle dramatically

affects the Hp/Eacc.

Go reverse direction from the High gradient cavity design.

TESLA shapeα =13.3 deg

Hp/Ep=23 (Oe/(MV/m))

Shape for quench studyα =39.2 deg

Hp/Ep=45 (Oe/(MV/m))

Tool: SUPERFISH code

Field distribution

Multipacting simulation

The electron energy should be controlled within 40 eV.

Multipacting simulation summary

0

5

10

15

20

25

30

35

40

45

50

55

60

9 9.5 10 10.5 11 11.5 12 12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 18 18.5 19 19.5 20Eacc (MV/m)

Elec

tron

Ener

gy (e

V)

B/A=1TESLA shapeB/A=0.79B/A=0.58

Tool: Fishpact code

MP simulation summary

37.813.10.58“

40.813.10.79“

43.513.41For quench study

31.514.71TESLA

Max Electron Energy(eV)

Eacc(MV/m)

B/ACavity shape

Cavity shape

2B

2A

D/2

α

2a

2b

Lc/2 Lb

Ri

Cavity axisO

25.2

2711472.6

CEBAF shape

4523Hp/Ep (Oe/(MV/m))66.0340.73Hp/Eacc (Oe/(MV/m))1.471.8Ep/Eacc

87118R/Q (Ohm)284270G=Rs·Q (Ohm)

1299.31288.1f0 （MHz）117138Lb（mm）3535Ri (mm)1042B (mm)

17.2542A (mm)18.419b (mm)1612a (mm)

39.213.3α (°)221206.6D (mm)

158.8115.4Lc (mm)

Shape for quench study

TESLA shape

3D draft

Highlights This cavity Will dramatically reduce the FE.It has same total length and beam pipe radium with TESLA single-cell cavity, so it can be fitted in any standard CBP, BCP, EP, HPR, and VTS facilities.It can be used as a tool to optimize the current EP processing.It’s convenient to be cut.It’s easy to be clean. (Clean water is enough for HPR)

Next plan

The cell length of this cavity (158.8mm) is larger than TESLA shape (115.4mm). This might cause some problems in deep drawing

Deep drawing simulation by ANSYS.Pre deep drawing with copper sheets.

Thanks