10 The Largest Accelerators and Colliders of Their Time
631
Table 10.14 Parameters of SuperKEKB, design and typical values in phase 2, comparing to
KEKB with crab crossing, where the effective crossing angle is zero
SuperKEKB
SuperKEKB
KEKB (crab)
Design
June 2018
June 17, 2009
Date
LER
HER
LER
HER
LER
HER
Circumference
3016
m
Beam energy
4.0
7.0
4.0
7.0
3.5
8.0
GeV
Crossing angle
83
22/0 (crab)
mrad
Beam current
3.8
2.6
0.27
0.225
1.64
1.19
A
Bunches
2500
395
1584
Bunch current
1.5
1.0
0.67
0.55
1.03
0.71
mA
Bunch spacing
1.2
~7.2
1.8
m
Hor. emittance
3.2
4.6
1.8
4.6
18
24
nm
RF frequency
509
MHz
Bunch length σ z
6
5
4.6
5.3
8
6
mm
β ∗
x
3.2
2.5
20
10
120
120
cm
β ∗
y
0.27
0.3
3
3
5.9
5.9
mm
Hor. size @ IP
10
11
19
21
147
170
μm
Ver. size @ IP
0.048
0.048
0.56
0.56
0.94
0.94
μm
Piwinski Angle
24.9
18.9
10.0
10.5
(0.60)
(0.39)
σ ∗
x /θ x
0.24
0.27
0.46
0.51
(13.3)
(15.4)
mm
Beam-beam ξ x
0.0028
0.0012
0.125
0.100
Beam-beam ξ y
0.088
0.081
0.030
0.021
0.130
0.090
Luminosity
800
2.3
21.1
/nb/s
1/nb = 10 33 cm −2 s −1
and a typical performance of Phase 2 operation [170] of SuperKEKB are listed in
Table 10.14.
The commissioning in Phase 2 has achieved several milestones of the project:
• Verified the collision with nano beam scheme with Piwinski angle ∼10. Although
the luminosity was still much less than the design or achieved at KEKB, no
fundamental limitations are found. The highest luminosity 56/nb/s was recorded
during Phase 2 [170]. An experimental verification of coherent beam-beam
instability [171] also assures the understanding of the beam-beam effect.
• The upgrade of the injector several new components: RF gun, positron target,
and positron damping ring was basically successful [172].
• The mitigation of e-cloud in the LER has well suppressed the blowup of the
vertical beam size up to 1 A of the stored beam [173].
The key toward the design luminosity is higher stored current with smaller β ∗ s.
Both the stored currents and β ∗ s are still far from the design. Table 10.14 shows
that the achieved β ∗
y is much longer than the length of the interaction area, σ ∗
x /θ x . It
means that the merit of nano-beam scheme has not been obtained yet. One possible
obstacle for higher current and smaller β ∗ s is the robustness of superconducting
631
Table 10.14 Parameters of SuperKEKB, design and typical values in phase 2, comparing to
KEKB with crab crossing, where the effective crossing angle is zero
SuperKEKB
SuperKEKB
KEKB (crab)
Design
June 2018
June 17, 2009
Date
LER
HER
LER
HER
LER
HER
Circumference
3016
m
Beam energy
4.0
7.0
4.0
7.0
3.5
8.0
GeV
Crossing angle
83
22/0 (crab)
mrad
Beam current
3.8
2.6
0.27
0.225
1.64
1.19
A
Bunches
2500
395
1584
Bunch current
1.5
1.0
0.67
0.55
1.03
0.71
mA
Bunch spacing
1.2
~7.2
1.8
m
Hor. emittance
3.2
4.6
1.8
4.6
18
24
nm
RF frequency
509
MHz
Bunch length σ z
6
5
4.6
5.3
8
6
mm
β ∗
x
3.2
2.5
20
10
120
120
cm
β ∗
y
0.27
0.3
3
3
5.9
5.9
mm
Hor. size @ IP
10
11
19
21
147
170
μm
Ver. size @ IP
0.048
0.048
0.56
0.56
0.94
0.94
μm
Piwinski Angle
24.9
18.9
10.0
10.5
(0.60)
(0.39)
σ ∗
x /θ x
0.24
0.27
0.46
0.51
(13.3)
(15.4)
mm
Beam-beam ξ x
0.0028
0.0012
0.125
0.100
Beam-beam ξ y
0.088
0.081
0.030
0.021
0.130
0.090
Luminosity
800
2.3
21.1
/nb/s
1/nb = 10 33 cm −2 s −1
and a typical performance of Phase 2 operation [170] of SuperKEKB are listed in
Table 10.14.
The commissioning in Phase 2 has achieved several milestones of the project:
• Verified the collision with nano beam scheme with Piwinski angle ∼10. Although
the luminosity was still much less than the design or achieved at KEKB, no
fundamental limitations are found. The highest luminosity 56/nb/s was recorded
during Phase 2 [170]. An experimental verification of coherent beam-beam
instability [171] also assures the understanding of the beam-beam effect.
• The upgrade of the injector several new components: RF gun, positron target,
and positron damping ring was basically successful [172].
• The mitigation of e-cloud in the LER has well suppressed the blowup of the
vertical beam size up to 1 A of the stored beam [173].
The key toward the design luminosity is higher stored current with smaller β ∗ s.
Both the stored currents and β ∗ s are still far from the design. Table 10.14 shows
that the achieved β ∗
y is much longer than the length of the interaction area, σ ∗
x /θ x . It
means that the merit of nano-beam scheme has not been obtained yet. One possible
obstacle for higher current and smaller β ∗ s is the robustness of superconducting