Transcript Document 7319546

SuperKEKB
Upgrade project of KEKB
KEK
Yukiyoshi Ohnishi
1
Target of SuperKEKB

Extremely high luminosity B factory
–
–

Luminosity = 1035 ~ 1036 cm-2s-1
Int. L > 1000 /fb/year at SuperKEKB
(Int. L = 100 /fb/year at present machine)
Strategy :
1. Unique
–
Asymmetric energy, double ring collider, finite x-angle, high
beam current, extremely low beta & short bunch, crab crossing
2. Upgrade
–
–

Scrap & Build
Application of existing components
Major upgrade in 2006-2007
2
Y. Ohnishi (KEK)
History of peak luminosity in last 25 years
1035 is good prediction for the future !
SuperKEKB
1035 cm-2s-1
2007 year ~ ?
3
Y. Ohnishi (KEK)
Motivation


KEKB will loose its competitiveness in 2005-2007.
Competitors in 5 years
– LHC-B, BTeV, (SuperPEP-II)
– Luminosity of LHC-B/BTeV corresponds to 1036 cm-2s-1 e+ecollider.

Physics motivation
1. PRECISION TEST of Kobayashi-Maskawa scheme
2. Search for NEW SOURCE of Flavor Mixing and CP Violation
3. Study of the FLAVOR STRUCTURE of SUSY, identification of
SUSY breaking mechanism

KEKB is R&D machine for SuperKEKB.
4
Y. Ohnishi (KEK)
Machine parameters of SuperKEKB

Luminosity formula :
L

Ne Ne f
* * RL
4 x y
Beam-beam tune shift parameters :
x ,ye
N e  x ,ye

R x , y
*
*
*
2 e  x ,y  x   y 
re
*

Assumed that the "transparency" conditions :
 e Ie   e Ie ,  e   e , etc.
 Alternative expression of luminosity :
Ie y  RL
L
1 r  * 
2ere
 y  R y
e
*y  y  *y
r * 

x  x  *x
“Optimal coupling”
5
Y. Ohnishi (KEK)
Machine parameters of SuperKEKB (cont'd)

Luminosity is proportional to :
Ibeam   y
 y*

x
RL
R y
Luminosity
reductions
Brute Force Concept :
–
Higher beam current
 function at I.P
– Smaller beta
(as well as short bunch length)
– Larger beam-beam parameters
6
Y. Ohnishi (KEK)
Luminosity reductions
Half crossing angle: qx = 15 mrad
 Horizontal beta at I.P: x* = 30 cm
 Vertical beta at I.P: y* = 3 mm
 Emittance : 33 nm (6.4 % coupling)

qx = 15 mrad
x* = 15 cm
x* = 30 cm
RL/Ry = 0.8
(KEKB : ~1)

RL : Luminosity reduction due to geometrical
 R : Tune shift reduction
 RL/Ry is a function of crossing angle, beta, emittance, bunch length.
7
Y. Ohnishi (KEK)
Strategy of SuperKEKB

Primary target of luminosity is 1035 cm-2s-1.
–
–
–
–
Beam-beam parameter : ~ 0.05 (experience at KEKB)
Vertical beta at I.P : 3 mm (bunch length : 3 mm)
Beam current : 9.4 A (LER) x 4.1 A (HER)
Half crossing angle : 15 mrad
Brute force concept

1036 cm-2s-1 is also considered.
– Extensibility in the future is important.

Political issue should NOT KILL 1035 cm-2s-1
machine.
8
Y. Ohnishi (KEK)
Machine parameters of SuperKEKB (detail)
SuperKEKB
Horizontal emittance
Vertical emittance
x-y coupling
Beam current
Number of bunches
Bunch current
Bunch spacing
Half crossing angle
Luminosity reduction R L
x reduction R x
y reduction R y
Bunch length
Radiation loss U 0
Betatron tunes x/ y
Beta at IP x*/y*
Beam-beam parameters
x/y
Beam lifetime
LER
33
2.1
6.4
9.4
HyperKEKB
HER
33
2.1
6.4
4.1
LER
33
0.33
1
17.2
5018
1.87
0.817
Luminosity
3
3.48
44.515/41.57
30/0.3
0.068/0.05
~150
1
HER
33
0.33
1
7.8
5018
3.43
0.6
15
0.748
0.691
0.916
3
1.23
45.515/43.57
30/0.3
0.068/0.05
~150
SuperPEP-II
1.55
LER
92
0.92
1
27
3400
7.94
0.6
0
HER
92
0.92
1
9.3
3400
2.74
unit
nm
nm
%
A
mA
m
mrad
0.65
0.83
3.5
3.5
1.8
1.75
mm
MeV/turn
15/0.3
15/0.3
15/0.15
15/0.15
cm
0.1~0.2
0.1
min
4~10
Head-on collision
(effective)
Need crab cavity
S-S, S-W simulation
10
10
35
/cm 2 /sec
Energy : 3.1/9 GeV
Options April 2002
from SBF Luminosity
9
Y. Ohnishi (KEK)
High beam current







RF system
Vacuum system
Photoelectron cloud effect
Fast ion instability (FII)
Bunch by bunch feedback system
Higher order mode (HOM)
Injector linac
10
Y. Ohnishi (KEK)
RF system

Requirements :
K. Akai et al.
– Large amount of RF power
– Very large HOM loss at cavities
– Heavy beam-loading

Strategy : Existing RF system is used as much
as possible.
 RF frequency : 509 MHz (same as KEKB)
 Cavity : ARES (LER) / ARES+SCC (HER)
– Improvements and modifications are needed.
– ARES (NC cavity) / SCC (SC cavity)
11
Y. Ohnishi (KEK)
The ARES cavity
Accelerator Resonant coupled with Energy Storage
Tw o SiC bullets per Waveguide
HOM damper
Input Coupler
Port
RF Paramete rs
of
the š/2 Accelerating Mode
Ua : Us = 1 : 9
R / Q
= 15 ž
Q
= 1.1 x 1 0 5
High-Powe r Performanc e
š / 2 - mode bas ics
2
Ua / Us = k s / ka
2
0.1
š/2 mode
0.0 1
Pumping Port
Pc = 150 kW / ARES Ca vity
generating
V c = 0.5 MV (KEKB Des ign)
0.0 01
Ma ximum Continuous
Pc = 380 kW
Ma ximum for 2 0 minutue s
Pc = 450 kW
0.0 001
495
š m ode
QL-100
0 m ode
QL-100
500
505
510
515
520
freque ncy /MHz
Coupling Cavity Damper
Storage Cavity
Tw o SiC bullets per Waveguide
Tuner Port
Accelerating Cavity
Tuner Port
Mo de Shif tin g
Gro ove
HOM damper
Eight SiC tiles per Groove
Coupling Cavity
12
Y. Ohnishi (KEK)
Superconducting Damped Cavity for KEKB
T. Fu ru ya
DOOR KNOB TRANS FORME R
INPUT COU PLE R
GATE VAL VE
L He
GATE VAL VE
FR EQUE NCY
TUNE R
HOM D AMPER
( SBP)
HOM D AMPER
(LBP)
Nb
CAVITY
ION P UMP
N 2 S HIEL D
0
0.5
1m
13
Y. Ohnishi (KEK)
Modification of RF system



Total beam power is higher than KEKB by factor 4.
Need high power fed to each cavity.
Increase number of RF stations. ~ Double RF.
– Half of wigglers in LER is replaced to RF cavities.
14
Y. Ohnishi (KEK)
RF system parameters
Ring
Beam current (A)
Wigg ler magnets
Energy loss/turn (MeV)
Loss factor (V/pC)
Radiation loss power (MW)
Parasitic loss power (MW)
Total beam power (MW)
Total RF voltage (MV)
Cavity type
No. of cavities
Voltage /cav. (MV)
Input coupling
Loaded-Q value (x10E4)
Beam power /cav. (kW)
Wall loss /cav. (kW)
Detuning frequency (kHz)
Klystron power (kW)
No. of klystrons
Total AC plug power (MW)
LER
9.4
yes (half)
1.2
40
11.3
7.1
18.4
14
ARES
28
0.5
5.4
1.7
660
150
71
850
28
40
HER
4.1
no
3.5
50
14.3
1.7
16.0
23
KEKB
ARES SCC
16
12
0.5
1.3
5.4
1.7
4.0
660
460
150
31
74
850
16
23
480
12
10
(Total)
ARES / SCC
44 / 12
30/8
56
73
23
45
15
Y. Ohnishi (KEK)
Layout of RF stations
D1
D2
5 buildings should be added.
D4
D5
new
D8
new
D10
LER-RF
(ARES)
new
new
D11
HER-RF
(SCC)
(Each building for
4〜6 RF units.)
HER-RF
(ARES)
new
D7
16
Y. Ohnishi (KEK)
Heavy beam-loading on the accelerating mode

Longitudinal instability
Growth rate of the -1 mode caused by large detuning is very
high (~104), even with ARES and / or SCC.
– Strong damping by feedback with comb filter is
inevitable.
– Zero-mode stabilization should also be improved.

Beam phase modulation due to abort gap
Abort gap of KEKB has been reduced (1 ms → 0.5 ms).
– Further reduction to 0.2 ms is required.
Δφ = 5.2° (LER 9.4A @0.2 ms gap)
17
Y. Ohnishi (KEK)
R&D issues for RF

HOM dampers
– as well as Input couplers and Damper at C-cavity

Impedance estimation

RF control
– Feedback for zero mode and -1, -2 modes

Klystron and high-power system
– Reduce crowbar trips
– Improve reliability of dummy loads

Beam test of improved system
18
Y. Ohnishi (KEK)
Vacuum system

Ante-chamber
–
–
–
–
–

Y. Suetsugu et al.
Reduce power density of synchrotron radiation at Wall.
Reduce effect of photoelectron cloud.
Low impedance / no pumping port in beam chamber
High linear pumping speed (Target : 100 l/s/m)
Solenoid winding before installation (e+ ring)
Bellows
– No heating or discharge problem due to HOM
– Need low impedance

Movable masks
– No damage of mask head due to beam hitting
– No HOM heating
– Need low impedance

HOM absorber chamber
19
Y. Ohnishi (KEK)
Design of Ante-chamber
LER arc section
[Ion pump section]
Cooling water
Pump
Ante-chamber
Beam
NEG
strip
Cooling water
SR
IP, NEG feed through
LER
20
Y. Ohnishi (KEK)
Design of Ante-chamber (cont'd)

Very large SR power

No photon stop

Ante-chamber for LER
– Max. SR power line density : 29 kW/m
– Power density :
40 W/mm2

(KEKB)
(14.8 kW/m)
(37 W/mm2)
Ante-chamber for HER
– Max. SR power line density : 25 kW/m
– Power density :
40 W/mm2
(5.8 kW/m)
(14.5 W/mm2)
21
Y. Ohnishi (KEK)
Ante-chamber R&D

Ante-chamber with photon stop (Prototype 2001)
Photon Stop
positron beam
Quadrupole
[QF2P.33]
Photoelectron
Monitor
Bending
[B2P.73]
22
Y. Ohnishi (KEK)
Ante-chamber R&D (cont'd)


Prototype has been tested in LER at KEKB.
Photoelectrons in beam chamber are measured.


Number of electrons
measured by a
photoelectron monitor
reduced to about 1/7
compared to the usual
single chamber.
Solenoid is still effective
to reduce number of
electrons by 1/2.
23
Y. Ohnishi (KEK)
Ante-chamber R&D (cont'd)
Prototype 2003




R&D for production procedure (BINP, Russia)
No photon stops (special material : GlidCop etc.)
New prototype will be installed during this summer.
Confirm reduction of photoelectrons in beam chamber.
24
Y. Ohnishi (KEK)
New Bellows with RF-shield (Comb structure)
Reduction of impedance sources





Low HOM leakage
High thermal strength
Loss factor : 1/4 of present
bellows
No multipactering
Less flexibility :
– expansion < ± 3 mm
– offset < ~ 0.2 mm
– bending angle < ± 2 deg.
2 mm
RF-shield
1 mm
10 mm
25
Y. Ohnishi (KEK)
New Bellows with RF-shield (cont'd)
Machining is available.
Application to ante-chamber
26
Y. Ohnishi (KEK)
Movable mask R&D

Heating of components near mask:
– Chamber type (Version 4) as KEKB is better. But,
• Heating of bellows is a problem.
– Beam steering scheme solves the troubles of bellows.
– Long tapers will reduce TE mode HOM power.
• How does the mask head harmonize the ante-chamber
structure ?
Version 4

HOM absorbers near the mask
head is needed.
 Plunger type (Version 5) is
another option.
27
Y. Ohnishi (KEK)
HOM absorber chamber (slot type)
Effective for TE mode HOM that causes heating of bellows.
 Tested at KEKB

SiC rod
28
Y. Ohnishi (KEK)
Small beta function at I.P

Optics
– flat beam
– beta functions : x* / y* = 30 cm / 3 mm

Interaction region (IR) design
– QCS, special magnets (QC1, QC2)

Dynamic aperture
29
Y. Ohnishi (KEK)
Optics at IR
H. Koiso et al.
LER

HER
beta function at I.P : x* / y* = 30 cm / 3 mm
30
Y. Ohnishi (KEK)
Layout of beam lines at IR
N. Ohuchi et al.
Half crossing angle :
15 mrad
Final focusing quadrupoles (QCS) locate at the position as close to the IP as possible.
Pos. from the IP Super-KEKB
KEKB
QCS-R 1163.3 mm
1920 mm
QCS-L 969.4 mm
1600 mm
The QCS magnets are overlaid with the compensation solenoids (ES).
compact & short in z
31
Y. Ohnishi (KEK)
QCS (Left)
QCS (Right)
QCS
ESL
ESR
QCSR
QCSL
50
50
HER
LER
HER
100
-100
-100
100
LER
-50
-50
ESR
QC1 (Left)
QC1 (Right)
Option 1: Superconducting
magnet
50
LER
HER
100
-100
ø100
200
-100
-50
100
200
250
Option 2: Normal-conducting
magnet
32
Y. Ohnishi (KEK)
Field distortion in Belle detector
Bz (central field), T
L (coil length), m
ESR
3.00
1.20
ESL
2.77
0.752
Electro-magnetic force acting on ESR and ESL from the Belle (in zdirection)
Super-KEKB
ESR: 42288 N (4.3 tons)
ESL: -134820 N (13.8 tons)
KEKB
ESR: 7050.5 N (0.7 tons)
ESL: -23505 N (2.4 tons)
33
Y. Ohnishi (KEK)
Dynamic aperture

LER
injection


6-D tracking simulation with SAD
No lattice errors
Field distributions of the
detector, compensation
solenoids, QCSs along
longitudinal direction are
given by slices of 4 cm
thickness with const.
field.
Multipole components
not included.
Natural chromaticity :
– -87.9 (horizontal)
– -132.2 (vertical)
Dynamic aperture of LER lattice satisfies the requirement for the
injection and lifetime (Touschek ~230 min).
34
Y. Ohnishi (KEK)
Short bunch length

Higher order mode (HOM)
– Impedance estimation

Coherent synchrotron radiation (CSR)
 Optics design
– Momentum compaction factor (a) : -2 ~ +4x10-4
– Negative alattice may help to reduce bunch length.
35
Y. Ohnishi (KEK)
Beam lifetime at 1035 cm-2s-1

Luminosity lifetime
–
–
–
–

dN/dt = -L
Cross section of radiative Bhabha: 2.14x10-25 cm2
Loss rate : 0.34 mA/s
LER/HER : 460/200 min
Vacuum lifetime
– ~10 hours (? depends on vacuum system)

Touschek lifetime
– LER/HER : 230/1650 min (estimated from dynamic aperture)

Overall lifetime of LER/HER : > ~150 min (inc. beam-beam)
– Loss rate : 1 mA/s (LER)/ 0.46 mA/s (HER)

Continuous injection
– Need 5Hz ~ 10 Hz repetition (70% injection efficiency)
36
Y. Ohnishi (KEK)
Requirements to linac injector at SuperKEKB
1.
e+ beam energy
3.5 → 8.0 GeV
T. Kamitani et al.
Energy switch :
8.0 GeV e- / 3.5 GeV e+ → 8.0 GeV e+ / 3.5 GeV e(a) This helps to reduce beam blowup due to photoelectron effects.
(b) e- charge > e+ charge
2.
Injection charge
1.0 → 5.0 nC (e-)
0.6 → 1.2 nC (e+)
For larger stored current :
1.1A e- / 2.6 A e+ → 9.4 A e- / 4.1 A e+
3.
Simultaneous Injection (both e+/e-)
4.
Smaller e+ emittance
37
Y. Ohnishi (KEK)
Higher acceleration field scheme for 8 GeV e+
e+ Damping
Ring for lower
emittance
2-Bunches for Simultaneous Injection
1-st bunch -> e- Injection
2-nd bunch -> e+ production
B
A
eGun
Damping
Ring
1.7-GeV
J-arc for e–
S-band accl. units are replaced
with C-band units.
Accl. Field 21 -> 41 MV/m
E(e+)=1.0 GeV
Q(e+)=1.2nC
e+ target
C
1
E(e–)=3.5 GeV,
Q(e–)=10 nC
to target
Q(e–)=5 nC
for Injection
2
3
4
5
E(e+)=8.0 GeV,
Q(e+)=1.2 nC
HER
New C-band units
LER
E(e–)=3.5GeV,
Q(e–)=5 nC
(Beam recirculation scheme is also under consideration, but skipped here.)
38
Y. Ohnishi (KEK)
KEKB injector linac accelerator unit
S-Band to C-Band
Present S-band accelerator unit
Wave guide
Wave guide
S-band
SLED
Pulse
Modulator
New C-band accelerator unit
S-band
Klystron
S-band accelerating structures
Wave guide
C-band
SLED
C-band
SLED
Pulse C-band
Modul- Klystron
ator
Pulse
Modulator
C-band
Klystron
C-band accelerating structures
39
Y. Ohnishi (KEK)
C-band components R&D status
• Toward 2003 Summer beam test at KEKB Linac
(1 Pulse Modulator + 1 Klystron + 1 Accel. structure 1m-long)






Klystron (Toshiba 50 MW C-band Klystron )
Pulse Modulator (Compact type)
Sub-booster klystron (satellite 40 kW Klystron is modified to 5712 MHz)
Already Fabricated
Accelerating structure #1 (2pi/3-mode, scaled down from S-band)
Under Engineering design (parameter tuning)
Wave guides, RF Window, Flange
Under fabrication
3-dB Hybrid, Dummy load
Under Engineering design (parameter tuning)
• Toward 2004 Spring beam test at KEKB Linac
(1 Pulse Modulator + 1 Klystron + 1 RF compressor
+ 2 Accel. structures 1m-long)


Accelerating structure #2 (New power coupler design)
Under basic design
RF pulse compressor (LIPS-type TE038-mode)
Under basic design
40
Y. Ohnishi (KEK)
Compact pulse modulator
C-band Klystron
Test accel. cavity RF measurement
41
Y. Ohnishi (KEK)
Toward higher luminosity

Crab crossing
– Beam-beam simulations
– Design of crab cavity for 1-2 A (KEKB)
– Design of crab cavity for 10 A

Four beams (neutralization)
– Analytic calculation
– Beam-beam simulations

Round beam
– Not considered yet.
42
Y. Ohnishi (KEK)
Beam-beam simulation





Target luminosity : 1035 ~ 1036 cm-2s-1
Number of bunches : 5000
Energy : 3.5 GeV (LER) / 8 GeV (HER)
Beam current : I(HER) = (3.5/8) x I(LER)
Weak-strong simulation
K. Ohmi et al.
x = 0.5156
qx = 0 mrad
qx = 15 mrad
x = 0.5156
x = 0.5256
x = 0.5356
x = 0.549
43
Y. Ohnishi (KEK)
Crab cavity
K. Hosoyama and K. Akai et al.




Squashed cell operating in
TM2-1-0 (x-y-z)
Coaxial beam pipe + HOM
dampers
Designed for 1〜2A beam
Present design for KEKB
Notch filter
–
–
–

Heavy damping of all HOM’s except TM1-1-0.
Smaller loss factor
More power to damper is allowed than the
present scheme.
Cure high-Q TM1-1-0
–
(axial view)
Absorbing
material

Squashed cell operating in TM2-1-0
HOM damping using wave guides
without coaxial beam pipe damper
Frequency control, Feedback w/ parallel comb
filter
Absorbing
material
inner conductor
Coaxial beam pipe
Cooling for
inner conductor
"Squashed cell"
Squashed Crab cavity for B-factories
(K. Akai et al., Proc. B-factories, SLAC-400 p.181 (1992).)
New design for SuperKEKB
44
Y. Ohnishi (KEK)
Crab crossing
A. Morita et al.



Crab crossing is powerful scheme to achieve high luminosity.
It is hard to develop crab cavity for extremely high beam current.
Test of crab crossing at KEKB in 2005
KEKB HER
– 1 crab : 11 mrad / HER x= 200 m
KEKB HER
Nikko straight section
Crab cavity
Need magnet
reconfiguration
45
Y. Ohnishi (KEK)
Crab crossing (cont’d)

Dynamic aperture can be kept as same as the case w/o crab
cavity at KEKB.
KEKB
(operation)
w/o crab cavity
w/ crab cavity
46
Y. Ohnishi (KEK)
Summary


R&D of SuperKEKB is going on.
Long-term plan of KEKB includes SuperKEKB.
– KEKB has already achieved L = 9.5 x 1033 cm-2s-1. (design:1034)



New components and schemes to achieve higher
luminosity have been or will be tested at KEKB.
Expression of Interest was written in Jan. 2002.
Workshops on higher luminosity B-Factory were held.
– Aug. 2001, Jan. 2002, Aug. 2002, Feb. 2003

Letter of Intent will be written this year.
 Thanks to a lot of efforts of volunteers working on KEKB.
47
Y. Ohnishi (KEK)