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