Coupler A new generation of waveguide couplers for standing wave cavities Publication CERNATSNote2011085 Frank Gerigk JeanMichel Giguet Rolf Wegner Patricia ID: 816471
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Slide1
TaCoTuner-adjustable waveguide Coupler
A new generation of waveguide couplers for standing wave cavitiesPublication: CERN-ATS-Note-2011-085
Frank
Gerigk
, Jean-Michel
Giguet
,
Rolf
Wegner
, Patricia
Ugena
Slide2Outlinewhy adjustable couplers for standing wave cavities
principles of couplers and their adjustment‘nozzle’ coupler, T-type coupler, TaCoTaCos for Linac4/SPLTaCo prototype
Advantages and potential applications of
TaCo
09/12/11
TaCo
// Tuner-adjustable waveguide Coupler
2
Slide3Unpredictable Q-value variations
09/12/11TaCo // Tuner-adjustable waveguide Coupler3
EB welding
shrinkage 0.2 to 0.3 mm
dQ
/Q ~ 1%
tuning
elements
dQ/Q
~ 1..2%
surface roughness
dQ
/Q ~ 3..5%
Slide4Why adjustable couplers
Critical coupling of cavities (with beam) to minimise reflected power09/12/11
TaCo // Tuner-adjustable waveguide Coupler
4
coupling factor
(critical coupling:
β
d
= 1)
small adaptation of coupling factor desired to compensate for unpredictable variation
=> safety margin
(often adjustment in one direction only;
proton
Linacs
: cavities often have different dimensions
)
Slide5“nozzle” coupler
09/12/11TaCo // Tuner-adjustable waveguide Coupler5
‘nozzle’ coupler
adaptation
Δ
β
/
β
0
courtesy of Jim Stovall & Craig
Deibele
Slide6T-type coupler
09/12/11TaCo // Tuner-adjustable waveguide Coupler6
adjustment of coupling factor: L
S
principle: compensation of reactance by stub line
Slide7T-type coupler,
adaptation09/12/11TaCo // Tuner-adjustable waveguide Coupler7
1
st
Step:
movable
short circuit
L
S
Slide8T-coupler, adaptation
09/12/11TaCo // Tuner-adjustable waveguide Coupler8
2. machining of appropriate short circuit (vacuum)
(+ copper plating)
delay
3.
installation
(
helicoflex
joint,
30 bolts M12)
Slide9TaCo – Tuner
adjustable w.g. coupler
09/12/11
TaCo // Tuner-adjustable waveguide Coupler
9
plunger tuner
1. Cavity (slightly) detuned to compensate stub line reactance
2. Coupling factor can be decreased as well as increased
Slide10TaCo for LINAC4/SPL
09/12/11TaCo // Tuner-adjustable waveguide Coupler10
x
t
= 350 mm
z
t
= 0 mm
L
S
= 311 mm
ø
t
= 83 mm
R
Rt
= 10 mm
vacuum section
P
in
=1 MW, cavity: E
S
~33 MV/m
Slide1109/12/11TaCo // Tuner-adjustable waveguide Coupler11
TaCo, increase of coupling factor
increase of coupling factor
Slide12TaCo prototype09/12/11
TaCo // Tuner-adjustable waveguide Coupler12
x
t
= 292 mm
z
t
= -345 mm
L
S
= 420 mm
ø
t
= 43 mm
R
Rt
= 2.0 mm
L
t
= 113 mm
P
in
=1 MW
Slide13TaCo // Tuner-adjustable waveguide Coupler
TP= 0.8 ms,frep
= 2 Hz,
ttest
= 72 h
high power test:
P
in
= 1.1 MW,
E
s
,m
= 8 MV/
m
09/12/11
13
TaCo
prototype
no breakdowns
no
multipactor
Slide14Advantages of TaCo
Coupling factor can be increased as well as decreased=> cavity design for desired coupling=> safety margins included in coupler design
TaCo
machined in one process
(T-type: short circuit machined after RF measurements -> delay)
RF matching simple and quick
(final RF contact between coupler and cavity)
Change of beam current => exchange of plunger tuner
Movable tuner => variable coupling during
operation
TaCo
applications: Linac4
/ SPL
26
TaCos
(20 x decrease β
, 5 x increase β, 1 x variable β)
09/12/11
TaCo // Tuner-adjustable waveguide Coupler
14