R F b y p a s s o n t h e beam coupling impedance o f i n s ulated flan g e s C Z a n n i n i Acknowledgments H Bartosik J Bento N Biancacci F Caspers ID: 915727
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Slide1
Effect of the RF bypass on the beam coupling impedance of insulated flanges
C
.
Z
a
n
n
i
n
i
Acknowledgments:
H. Bartosik, J. Bento, N. Biancacci, F.
Caspers
,
E.
Métral
, G. Rumolo, B. Salvant, C. Vollinger
Slide2Insulated flangesIn circular accelerators with high acceleration rate the fast variation of the main magnetic field induce currents in the ground loop. To overcome the problem one has to cut the vacuum chamber in several sectors and reconnect them with insulated flanges. The insulated flange forms a capacitor which inserted in series with the ground loop constitutes a parallel RLC equivalent circuit.To shift the resonant frequency to a much lower value and to reduce the longitudinal impedance, the so called RF-bypass are connected in parallel to the flange.
Without
RF-bypass
With
RF-bypass
R.
Cappi
, RF bypass on the proton synchrotron vacuum chamber flanges
Slide3Measurements of all PS
B flanges
i
n
the freque
ncy range 100 kHz-17 MHz
Insulated
flanges
Slide4C=1 nF L=10 µH R=100 ΩCbypass=0.4 μF Rbypass=1 Ω
Beam coupling impedance
of
insulated
flanges: example
L
ongitudin
al impedan
c
e
Transverse
i
m
p
e
d
a
n
c
e
Equivalent impedance of the equivalent circuit
Slide5Insulated flangesC=0.01-100 nF L=0.5-15 µH R=1-100 Ω Cbypass=0.4 μF Rbypass=0.5 Ω
Parameter sweep analysis
Resonant frequency of the flange impedance
with (red)
and
without (green)
RF bypass
Slide6Conclusion on the beam coupling impedance of insulated flangesThe RF bypass is expected to shift the impedance spectrum to low frequency (well below the first possible unstable betatron line of the PSB) avoiding possible detrimental effect which could not be excluded in the case without RF bypass. Comment submitted in 2014 about
Insulation and grounding of BSW vacuum chambers EDMS no. 1355024
In terms of beam coupling impedance no issues are expected. In fact, since the insulated flanges will be equipped with RF bypass, the resonant frequency of the equivalent RLC circuit formed by the ground loop and the insulated flange is expected to go down in frequency (well below the first possible unstable
betatron
line) similarly to the present PSB flanges with RF bypass.
Slide7PSB model of insulated flanges with and w
ithout RF
b
y
p
ass
J. Bento
16
L1 R
2
J. Bento
J. Bento
11
L
1
R
4
5
L
1
R
2
Slide8PSB model of insulated flanges with and w
ithout RF
b
y
p
ass
11 L1 R45 L
1 R2
J. Bento
J. Bento
Three bypass circuits in parallel for each flange
C = 1
nF
L = 1.5 µH
R = 3.5 Ω
C
bypass
= 0.4
μ
F
R
bypass
= 0.5
Ω
L
bypass
= 0
Slide9PSB model of insulated flanges with and w
ithout RF
b
y
p
ass
11 L1 R45 L
1 R2
C = 1
nF
L = 1.5 µH
R = 3.5 Ω
C
bypass
= 0.4
μ
F
R
bypass
= 0.5 ΩL
bypass = 100 nH
Impedance magnitude
Slide10PSB model of insulated flanges with and w
ithout RF
b
y
p
ass
Lo
ngitudinal impedance
Slide11Transverse impedancePSB model of in
sulated f
l
a
n
ges with an
d without RF bypass
Slide12PSB model of insulated fla
nges with
a
n
d
without R
F bypass
Slide13PSB model of insulated fla
nges with
a
n
d
without R
F bypass
Slide14PSB model of insulated fla
nges with
a
n
d
without R
F bypass
Slide15PSB model of insulated fla
nges with
a
n
d
without R
F bypass
Slide16SummaryThe beam coupling impedance model of Insulated flanges with and without RF bypasses has been discussedThe impact of bad bypasses on the PSB headta
il growth rates has been estimated
Significant effect
Important to keep the number of bad bypasses as low as possible
Slide17Thank you for your attention
Slide18PSB model of insulated flanges with and w
ithout RF
b
y
p
ass
7
L
1
R
2
10
L
1
R
2
J. Bento
J. Bento
Slide19PSB model of insulated flanges with and w
ithout RF
b
y
p
ass
J. Bento
J. Bento
11
L
1
R
2
16
L
2
R
2
Slide20PSB model of insulated flanges with and w
ithout RF
b
y
p
ass
11
L
1
R
4
16
L
1
R
4
J. Bento
J. Bento
Slide21PSB model of insulated flanges with and w
ithout RF
b
y
p
ass
J. Bento
J. Bento
15
L
2
R
1
16
L
1
R
2
Slide22About short-circuited flanges
R.
Cappi
, RF bypass on the proton synchrotron vacuum chamber flanges
F
o
r
t
h
e
b
e
a
m
c
o
u
p
li
ng impedance point of view is the ideal flange (no contribution
in the PSB fre
q
u
e
n
c
y
r
a
n
g
e
o
f
i
n
t
e
r
e
s
t)