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
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
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
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.