Transcript Round Beams - Novosibirsk

Round Beam Collisions
at
VEPP-2000
Dmitry Berkaev, Alexander Kirpotin, Ivan Koop, Alexander Lysenko, Igor Nesterenko,
Alexey Otboyev, Evgeny Perevedentsev, Yuri Rogovsky, Alexander Romanov,
Petr Shatunov, Yuri Shatunov, Dmitry Shwartz, Alexander Skrinsky, Ilya Zemlyansky
Novosibirsk
21.09.2011
Layout of VEPP-2000 complex
ILU
2.5 MeV
Linac
CMD-3
VEPP-2000
B-3M
250 MeV
synchrobetatron
BEP
e–, e+
booster
825 MeV
RF
2m
e–e+
convertor
SND
Collider overview
L = 24.39 m
facc= 172 MHz
Vacc= 120 kV
E=0.2 – 1 GeV
Bbend = 2.4 T
Bsol = 13 T
β*=2 – 10 cm
σs = 3 cm
ε=1.4•10-7mrad
νx,z= 2.1; 4.1
α= 0.036
ξ = 0.15
N± = 1011
L=1•1032cm-2s-1
The Concept of Round Colliding Beams
Small and equal β-functions at IP:
 x  z
Equal beam emittances:
x  z
Equal betatron tunes:
x  z
Angular momentum conservation M y  xz  xz
z
y
x
VEPP-2000 lattice
Round beam options
z
“Flat”
“Normal
Round”
“Single
möbius”
“Double
möbius”
x
Positron beam lifetime
(I+ = 20 mA)
Machine tuning
Closed orbit corrections
Pick-ups Orbit Response Matrix to focusing offsets (4⊗32)
SVD analysis
steering coil corrections
2-3 iterations + minimizing of ƩIcor
correctors setting
Δx; Δz ≃ ± 0.2 mm
Lattice corrections
BPMs ORM to steering coils modulations (20⊗36)
SVD analysis
focusing corrections (quads +solenoids)
3–4 iterations
lattice setting
β*; zero dispersion outside achromats;
Coupling compensation
1.5 Tm field of CMD detector + solenoids compensating coils
3 families of skew quads
ν1 – ν2 < 0.003
Lattice corrections
βx, βz (cm)
βx, βz (cm)
βx, βz (cm)
Dx (cm)
after
3 iterations
after
4 iterations
Dispersion
Lattice and beam sizes
(I± <1mA)
 1  2.15;  2  4.15
10
”Week-strong” beam-beam
(“dynamic beta and emittance”)
I+=3 mA; I-=48 mA
11
“Strong-strong” beam-beam
(“dynamic beta and emittance”)
I+=61.8 mA; I-=53.2 mA
Threshold current vs.tune
(“week-strong”)
ξ = N re
4πγε =0.1
Luminosity measurements
Bhabha scattering in the SND and СMD detectors
Θscatt ≥ 0.5
Main disadvantage ⇛ low counting rate
n
≃ 10 Hz at L=1•1031 cm-2s-1
f 0  N  N
Basic formulae of the luminosity: L 
4    
Beam profile measurements at 16 points ⇛   ( x )2  ( z ) 2
with dynamic β-functions and beam emittance, but under
assumption: no other lattice distortions besides counter beam.
Time of measurement ≃ 1 s at any energy.
Luminosity measurements
(E = 837 MeV; Run 2011)
L⁎10-30 (cm-2s-1)
t (sec)
Luminosity at run 2011
(CMD data)
ramping
Ldt

20
(
pb
)

⇛
1
16
Luminosity vs.ξ
ξ=
N  re
4πγε
Positron beam size
vs
ξ
ξ=
N  re
4πγε
Radiative polarization
1.0
ζ
-
+
1.0
3
Bs Bs  10
ζ
0.8
GeV
+
0.8
0.6
0.6
0.4
0.4
0.2
GeV
0.2
0
0.4
0.6
0.8
1.0
0.4
0.6
0.4
1.0
0.8
τpp 104
102
102
1
1
+
10-2
GeV
0
τp 104
sec
Bs Bs  102
ζ
-
sec
10-2
0.6
0.8
1.0
τp
19
Beam energy calibration
f d  10( Hz sec)
E = 750.67 ± 0.03 MeV
f d   10( Hz sec)
f d  1( Hz sec)
fd (kHz)
 E(MeV) 
fd = 
-1 f 0
 440.6484 
20
BEP upgrade (1GeV)
26.0 кГс
9,5 кА
Conclusion
Round beams give a serious luminosity enhancement.
The beam-beam parameter achieves a value ξ= 0.15 .
VEPP-2000 started up for data taking with 2 detectors.
Precise beam energy calibration is in progress.
To reach the target luminosity, more positrons are
needed.
Booster BEP upgrade for beam transfer at 1GeV is
being prepared.
Thanks for your attention!
Novosibirsk
21.09.2011