esls-rf meeting 2004 status of the hom damped cavity project e. weihreter / bessy project funded by...
TRANSCRIPT
ESLS-RF Meeting 2004
Status of the HOM Damped Cavity Project
E. Weihreter / BESSY
Project funded by the EC under contract HPRI-CT-1999-50011
for the HOM Damped Cavity CollaborationBESSY, Daresbury Lab, DELTA, MaxLab, NTHU
♦ Cavity concept and design goals
♦ Simulations and impedance measurement results
♦ Prototype cavity conditioning and first beam tests
♦ What lessons have we learned so far?
♦ Further developments
♦ Summary and outlook
ESLS-RF Meeting 2004
Fundamental mode frequency f = 500 MHz
Insertion length L 0.7 m
Shunt impedance R 4 M
Max. thermal power P = 100 kW
Compact design to fit into existing SR source tunnels
Cavity ConceptDesign Goals
ESLS-RF Meeting 2004
Simulation Models
S11=1
~ 106 mesh points 2-3 days cpu time
~18* 106 mesh points 6-7 weeks cpu time
ESLS-RF Meeting 2004
Simulations and Impedance Measurement Results
Tapered CWCT
Homogenious waveguidewith S11 = 1 boundary
ESLS-RF Meeting 2004
Threshold impedances for different rings
sb
s
HOMC
thresh
I
QE
fNZ
0
||,
.||
211
yxyxbrevC
threshyx If
E
NZ
,,
0.,
21
ESLS-RF Meeting 2004
Tuning and Cavity Test at ZANON S.p.A. / Italy
ESLS-RF Meeting 2004
Measured Impedance Spectra of
ESLS-RF Meeting 2004
Measured Cavity Parameters
Parameter
3D MWS Simulation
Standard/New Method
Measurement
f0 (MHz) 500.98 499.65
Q0 32557 / 28410 26692
Reff/Q0 (Ω)
114.5 115.4
Reff (MΩ) 3.73 / 3.25 3.1
Nominal Frequency 499.65 MHz
Tuning Range 2 MHz
Shunt Impedance 3.1 MΩ
Unloaded Q 26692
Thermal Power Capability 100 kW
Longitudinal HOM Impedance
≤ 4.8 kΩ
Transverse HOM Impedance
≤ 180 kΩ/m
Waveguide cut-off 615 MHz
Coupling Range 0-8
Insertion Length 50 cm
Beam Hole DiameterTE11 cut-offTM01 cut-off
743.742.31
mmGHzGHz
Resonant frequency vs. plunger positionas measured and calculated.
ESLS-RF Meeting 2004
Prototype Cavity Conditioning
Peak and average cavity input power during
RF conditioning (pvac< 5*10-7 mb) Vacuum conditioning procedure
Increase in vacuum pressure around 200W and 600 W,however no serious multipacting thresholds observed
ESLS-RF Meeting 2004
Cavity installed in the DELTA Ring
ESLS-RF Meeting 2004
First Beam Observations at 1480 MeV
DORIS Cavity
HOM Damped Cavity
CBM 55 is not driven by the cavity !!
ESLS-RF Meeting 2004
DORIS Cavity beam spectrum at low energy
Final beam tests: measurement of coupled bunch instability thresholds at 540 MeV
ESLS-RF Meeting 2004
What lessons have we learned so far ?
♦ The tapered waveguides are the most critical components of the cavity
∙ about 60% of total manufacturing costs
∙ small tolerances
∙ vacuum brazing is a subtle technique, to be avoided where possible
♦ Engineering layout of e-beam welds and quality control during manufacturing must be improved
♦ Gaps between the ridges and the waveguide port wall should not be longer than 80 mm to avoid resonances coupling to the fundamental mode
♦ A CF 63 flange should be added at the end of the tapered waveguide
♦ Homogenous damping waveguides allow further reduction of HOM impedances
ESLS-RF Meeting 2004
Avoid long gaps coupling to fundamental mode
gap
ESLS-RF Meeting 2004
Further Development: Homogenious ferrite loaded waveguide
0.6 0.8 1 1.2 1.4
F req u en cy (G H z)
0
0.2
0.4
0.6
0.8
1
S11
---L = 1 5 0 m m (m esh 5 8 6 1 )---L = 2 0 0 m m (m esh 8 4 9 3 )---L = 2 5 0 m m (m esh 1 0 3 2 2 )---L = 3 0 0 m m (m esh 1 1 6 4 3 )---L = 3 5 0 m m (m esh 1 7 0 5 8 )N ew ferrite p a ra m eter ,T = 3 .2 m m ,C o v er-M o d el
D ifferen t L en g th o f F err ite(C -4 8 ,N i-Z n ) w ith Q u a rter C over-M odel (d iscrete)
0.5 1 1.5 2 2.5 3
F req u en cy (G H z)
0
0.2
0.4
0.6
0.8
1
S11
E x p erim en t m ea su rem en t(co v ered m o d el,g a te1 1 n s~3 0 n s)E x p erim en t m ea su rem en t(co v ered m o d el,w ith o u t set g a te)E x p erim en t m ea su rem en t(N O -co v ered m o d el,g a te1 0 .1 3 2 n s~1 0 0 n s)H F S S S im u la tio n resu lt(co v ered m o d el)
T o C o m p a re W ith E x p erim en t a n d S im u la tio n R esu lt
ESLS-RF Meeting 2004
TDR measurement set-up
CWCT used as adapter
Ferrite load
Circular ridged waveguide
Low power model of a homogenous ridged waveguide load
ESLS-RF Meeting 2004
Summary
♦ A HOM damped prototype cavity has been built and tested under low and high power conditions
♦ Impedance measurements show that longitudinal HOM impedances < 4.8 kΩ transverse HOM impedances < 180 kΩ/m fundamental mode impedance 3.1 MΩ
♦ Measurements are in good agreement with calculations: Simulation tools are reliable
♦ Successful high power operation up to 30 kW thermal power, no serious multipacting thresholds found
♦ Technical improvements modifications e-beam welds, avoid vacuum brazing where possible reduced gaps between ridges and CWCT port CF 63 flange at the end of the CWCT ♦ Conceptual and technical layout has been verified. Cavity design is ready for use.
Outlook
♦ Final beam test of the cavity in DELTA at 540 MeV early in 2005 ♦ Development of a high power prototype for a homogenious wavegude load is under way to reduce manufacturing cost and further reduce HOM impedances by a factor 3-4