RF System for Electron Collider Ring
Haipeng Wang
for the team of R. Rimmer and F. Marhauser, SRF Institute
and
Y. Zhang, G. Krafft and S. Derbenev, CASA
Review 09/2010
page
Medium Energy EIC Top Layout
Three compact rings:
• 3 to 11 GeV electron
• Up to 12 GeV/c proton (warm)
• Up to 60 GeV/c proton (cold)
Review 09/2010
page
Electron collider ring figure 8 layout
R=57.495 m
239.167 m
20.000 m
134.989 m
MEIC collider ring
60°
Straights cross angle
Circumference
Arc radius
Figure 8 width
Figure 8 length
Straight length
Insertion straight length
Dipole compacting factor
deg
m
m
m
m
m
m
%
60.000
1000.000
57.495
134.989
379.609
239.167
20.000
60
RF insertion
Low energy
High current
379.609 m
dipole magnet bending radius
average beam current
electron beam energy
synchrotron radiation power per ring
energy loss per turn
radiation power per unit arc length
figure 8 circumference
electron revolution frequency
RF harmonic number
RF cavity's frequency
revolution time
bunch spacing
Review 09/2010
m
A
GeV
MW
MeV
kW/m
m
kHz
MHz
ms
m
57.495
3
5
3.85
1.28
5.331
1000
299.79
2496
748.50
3.3356
0.401
High energy
Low current
57.495
0.13
11
3.91
30.07
5.411
1000
299.79
2496
748.50
3.3356
0.401
page 2
Electron Beam Stacking Structure for 5GeV
From CEBAF
SRF Linac
1.334 ns
(40 cm)
0.750 GHz
<3.3 ps
(<1 mm)
0.4 pC
Microscopic bunch duty factor 2.47x10-3
average current=0.3 mA
10-turn injection
33.3 μs (4 pC)
Stored beam in
collider ring
Macroscopic bunch duty factor 8.33x10-4
40 ms
(~5 times radiation
damping)
25 Hz
revolution time=3.33 μs, 2501 bunches per ring
40 s (1000 bunch trains),
average current=3 A
Review 09/2010
page 3
Existing RF systems in storage rings: normal conducting
Two examples
Rimmer and Allen etc
PEP-II
BESSY
Marhauser and Weihreter etc
Review 09/2010
page 4
Existing RF systems in storage rings: superconducting
Two examples
Design Parameters
cavity parameters
frequency
number of cell
R/Q = Ueff^2/(w*W)
R/Q/cell
Units
Ohm
Ohm
Original CESR-III, Cornell Univ.
CESR-III Cavity
499.765
1
89.0
89.0
Original KEKB, Japan
KEKB-HER cavity
509
1
93.0
93.0
material independent geometry factor G = Rs*Q0
R/Q*G
acitve length
insertion length
operating temperature
Ohm
Ohm
m
m
Kelvin
270.0
24030
0.3
2.86
4.2
250.0
23250
0.243
3.01
4.2
100.8
MHz
BCS surface resistance RBCS
nΩ
97.2
residual surface resistance assumed Rres
nΩ
13.0
13.0
total surface resistance Rs
Q0
shunt impedance (R=Ueff^2/P)
input power (total losses)
Pcavity (surface losses)
Pbeam (beam loading)
Pbeam (beam loading on crest)
average beam current
minimum gap voltage required
accelerating gradient
Qext matched Q0/(1+Pbeam/Pcavity)
coupling factor (Q0/Qext)
total radiated power
energy loss per turn
beam energy
rf effective accelerating voltage
nΩ
MW
MeV
GeV
MV
110.2
5.0E+08
4.5E+04
324.9
0.00761
320.00
324.9
0.55
581.8
1.97
2.00E+05
2.50E+03
1.28
2.33
5.3
2.33
113.8
2.2E+09
2.0E+05
571.2
0.00079
562.50
571.2
1.4
401.8
1.68
8.90E+04
2.47E+04
4.50
3.21
8
3.21
synchronous phase, 0 is on crest
rf peak voltage required
number of cavities needed
insertion length
straigh section length in storage ring
Preliminary Cost Exercise
costs per cavity
total investment costs + RF power
total investment costs (cavities only)
total costs (w/o power bill)
cryoplant
RF to AC power per year
deg
MV
10
2.363
10
3.264
4
11.440
8
24.080
operational costs per year
$
MΩ
kW
kW
kW
kW
A
kV
MV/m
m
m
$
$
$
from BNL per Jim Rose 2008
$1,200,000
$3,395,000
$4,800,000
$13,580,000
Review 09/2010
Padamsee and Chojnacki etc
KEKB-TRISTAN
$
$
could favor SRF after 5-10 years
CESR-III B-cell
could favor SRF after 5-10 years
Furuya and Akai etc.
page 5
RF system in storage ring: Technology of choice
Klystron
power
<600kW for
CW RF power
Power coupler
and RF window
High Current
Low Energy
Synchrotron
radiation power
RF
acceleration
Low RF
Frequency
Beam loading
control
Beam excited
HOMs
Bunch head-tail
instability
Large beam
aperture
High Energy
Low Current
ceramics
Prad  8.8575 105 (m / GeV 3 )
4
4
E (GeV )
I (mA)
 (m)
Low broadband
and narrow
band HOM
impedance
cavity
Superconducting
cavity
High gradient
for CW
Liquid helium
Cooling, 4.2K
Review 09/2010
HOM damping
by waveguide
or coaxial
coupler
Normal
conducting cavity
Warm HOM
windows and
loads
Low gradient
for CW
DI water cooling
<300K
page 6
ferrites
Scaled RF system for MEIC Electron ring: normal conducting
11GeV
Design Parameters
cavity parameters
frequency
number of cell
R/Q = Ueff^2/(w*W)
R/Q/cell
material independent geometry factor G = Rs *Q0
R/Q*G
acitve length
insertion length
operating temperature
BCS surface resistance RBCS
Units
5GeV
Ohm
Ohm
Ohm
Ohm
m
m
Kelvin
nΩ
MEIC3
BESSY type cavity scaled
748.5
1
230.8
230.8
234.0
54007
0.2
0.333
>300
n/a
MEIC4
BESSY type cavity scaled
748.5
1
230.8
230.8
234.0
54007
0.155
0.333
>300
n/a
residual surface resistance assumed Rres
nΩ
n/a
n/a
total surface resistance Rs
Q0
shunt impedance (R=Ueff^2/P)
input power (total losses)
Pcavity (surface losses)
Pbeam (beam loading)
Pbeam (beam loading on crest)
average beam current
minimum gap voltage required
accelerating gradient
Qext matched Q0/(1+Pbeam/Pcavity)
coupling factor (Q0/Qext)
total radiated power
energy loss per turn
beam energy
rf effective accelerating voltage
synchronous phase, 0 is on crest
rf peak voltage required
number of cavities needed
insertion length
straigh section length in storage ring
Preliminary Cost Exercise
costs per cavity
total investment costs + RF power
total investment costs (cavities only)
total costs (w/o power bill)
cryoplant
RF to AC power per year
operational costs per year
nΩ
n/a
30000
6.92
551
333.196
197.457
217.869
0.13
1518.9
10.84
1.81E+04
1.65E+00
6.52
50.12
11
50.124
25
55.305
33
11.0
20.000
n/a
30000
6.92
549
3.913
493.775
544.821
3
164.6
1.17
2.14E+02
1.40E+02
6.42
2.14
5
2.140
25
2.361
13
4.3
20.000
MHz
MΩ
kW
kW
kW
kW
A
kV
MV/m
MW
MeV
GeV
MV
deg
MV
m
m
$
$
$
Marhauser and Weihreter
BESSY:
<100kW
Eacc=6MV/m
Conditioned
up to 30kW
CW in 5 days.
$
$
$
Review 09/2010
page 7
Scaled RF system for MEIC electron ring: superconducting
Only single-cell is preferred due to a heavy
HOM damping requirement in storage ring,
But space is limited.
Units
11GeV
Design Parameters
cavity parameters
frequency
number of cell
R/Q = Ueff^2/(w*W)
R/Q/cell
material independent geometry factor G = Rs *Q0
R/Q*G
acitve length
insertion length
operating temperature
BCS surface resistance RBCS
Ohm
Ohm
Ohm
Ohm
m
m
Kelvin
nΩ
residual surface resistance assumed Rres
nΩ
13.0
13.0
total surface resistance Rs
Q0
shunt impedance (R=Ueff^2/P)
input power (total losses)
Pcavity (surface losses)
Pbeam (beam loading)
Pbeam (beam loading on crest)
average beam current
minimum gap voltage required
accelerating gradient
Qext matched Q0/(1+Pbeam/Pcavity)
coupling factor (Q0/Qext)
total radiated power
energy loss per turn
beam energy
rf effective accelerating voltage
synchronous phase, 0 is on crest
rf peak voltage required
number of cavities needed
insertion length
straigh section length in storage ring
Preliminary Cost Exercise
costs per cavity
total investment costs + RF power
total investment costs (cavities only)
total costs (w/o power bill)
cryoplant
RF to AC power per year
operational costs per year
nΩ
231.01
1.17E+09
1.04E+05
513.7
0.12323
465.43
513.5
0.13
3580.3
19.73
2.80E+05
4.17E+03
6.52
50.12
11
50.12
25
55.305
14
26.734
20.000
231.0
1.17E+09
1.04E+05
544.8
0.00026
493.78
544.8
3
164.6
0.91
5.59E+02
2.09E+06
6.42
2.14
5
2.14
25
2.361
13
24.825
20.000
from BNL per Jim Rose 2008
$1,200,000
$3,395,000
$29,789,600
$84,279,742
MHz
MEIC1
CESR Cavity Scaled, high energy
748.5
1
89
89.0
270.0
24030
0.2
1.91
4.2
218.0
5GeV
MΩ
kW
kW
kW
kW
A
kV
MV/m
MW
MeV
GeV
MV
deg
MV
m
m
$
$
$
$
$
$
Review 09/2010
MEIC2
CESR Cavity Scaled, low energy
748.5
1
89
89.0
270.0
24030
0.2
1.91
4.2
218.0
JLab High Current 750MHz, 5-cell, 1A cavity
Rimmer and Wang etc
could favor SRF after 5-10 years
page 8
Initial HOM Analysis: beam current excitation
S. H. Kim and H.Wang
FFT
•Time averaged HOM power normalized to R/Q (W/W= Amp2) is
current square drive term. It has no information of the cavity but with
assumed HOM damping Qext.
• For example, if we have a HOM resonated at 2.25GHz with R/Q of 10
W and Q external of 100 , we have 1kW HOM power from the beam in
this mode.
• When we design a high current cavity, we have to avoid HOM
frequencies sitting on the beam excitation resonances.
H. Wang etc PAC2005 TPPT086.
Review 09/2010
page 9
Initial HOM damping analysis: Impedance and HOM power
Impedance scaling from BESSY
NC RF cavity in same shape but in different
frequency scale:
• monopole modes around 2.25 GHz have to be
avoid by either changing the cavity shape (safe to
park) or damping totally with Qext< 100,
otherwise 50kW (on resonance HOM power will
come out to the HOM loads.
• Following is an example (H. Wang etc PAC
2005) for JLab High Current 5-cell cavity design
to avoid HOM resonance by choosing different
cavity shapes.
6
180
10
JLab-LL
Re-entrant
JLab-LL-modified
ILC-LL
Rounded Pillbox
Spherical Section
1A, 750MHz CW laser, Qext=10^4
1A, 750MHz CW laser, Qext=10^3
light cone line
5
10
4
10
108
3
10
P=120(W/W)*1.25(W/cell)*5(cell)=750W
2
10
72
1
10
TM030 mode
36
0
2.90
R/Q/cell=1.25(W/cell)
0
10
Time Averaged HOM Power / (R/Q) (W/W)
Phase Advance  (deg)
144
BESSY CWCT copper cavity impedance measurement s
Marhauser and Weihreter, EPAC 2004
-1
2.92
2.94
2.96
2.98
3.00
3.02
3.04
3.06
3.08
10
3.10
Frequency f (GHz)
Review 09/2010
page 10
MEIC electron ring RF system Summary: Pros and Cons
SCRF favors to High Energy, Low Current Operation
Review 09/2010
NCRF favors to Low Energy, High Current Operation
page 11