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Crab crossing at KEKB. K. Ohmi, KEK Beam-beam workshop 2-4, July, 2007, SLAC. T. Abe, T. Agho, K. Akai, M. Akemoto, A. Akiyama, M. Arinaga, K. Ebihara, K. Egawa, A. Enomoto, J. Flanagan, S. Fukuda, H. Fukuma, Y. Funakoshi, K. Furukawa, T. Furuya, K. Hara, T. Higo, S. Hiramatsu, - PowerPoint PPT Presentation
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Crab crossing at KEKB
K. Ohmi, KEK
Beam-beam workshop
2-4, July, 2007, SLAC
T. Abe, T. Agho, K. Akai, M. Akemoto, A. Akiyama, M. Arinaga, K. Ebihara, K. Egawa, A. Enomoto, J. Flanagan, S. Fukuda, H. Fukuma, Y. Funakoshi, K. Furukawa, T. Furuya, K. Hara, T. Higo, S. Hiramatsu, H. Hisamatsu, H. Honma, T. Honma, K. Hosoyama, T. Ieiri, N. Iida,
H. Ikeda, M. Ikeda, S. Inagaki, S. Isagawa, H. Ishii, A. Kabe, E. Kadokura, T. Kageyama,K. Kakihara, E. Kako, S. Kamada, T. Kamitani, K. Kanazawa, H. Katagiri, S. Kato, T. Kawamoto, S. Kazakov, M. Kikuchi, E. Kikutani, K. Kitagawa, H. Koiso,
Y. Kojima, I. Komada, T. Kubo, K. Kudo, N. Kudo, K. Marutsuka, M. Masuzawa, S. Matsumoto, T. Matsumoto, S. Michizono, K. Mikawa,
T. Mimashi, S. Mitsunobu, K. Mori, A. Morita, Y. Morita, H. Nakai, H. Nakajima, T. T. Nakamura, H. Nakanishi, K. Nakanishi, K. Nakao, S. Ninomiya, Y. Ogawa, K. Ohmi, S. Ohsawa, Y. Ohsawa, Y. Ohnishi,
N. Ohuchi, K. Oide, M. Ono, T. Ozaki, K. Saito, H. Sakai, Y. Sakamoto, M. Sato, M. Satoh, K. Shibata, T. Shidara, M. Shirai, A. Shirakawa,
T. Sueno,M. Suetake, Y. Suetsugu, R. Sugahara, T. Sugimura, T. Suwada, O. Tajima, S. Takano, S. Takasaki, T. Takenaka, Y. Takeuchi, M. Tawada, M. Tejima, M. Tobiyama, N. Tokuda,
S. Uehara, S. Uno, Y. Yamamoto, Y. Yano, K. Yokoyama, Ma. Yoshida, Mi. Yoshida, S. Yoshimoto, K. Yoshino,
KEK, Oho, Tsukuba, Ibaraki 305-0801, JapanE. Perevedentsev, D. N. Shatilov, BINP, Novosibirsk, Russia
Input Coupler Liq. Helium Vessel
Stub Support
Coaxial Coupler
Copper Bellows80 K Liq. Nitrogen Shield
Notch Filter
RF Absorber
Aluminum End Plate
Aluminum End Plate
SUS Support Pipe
Crab Crossing @ KEKB
Crossing angle 22 mrad
Head-on (crab)(Strong-strong simulation)
Crab Crossing can boot the beam-beam parameter higher than 0.15 !
Crab cavities were successfully produced and beam study has started
in Feb. 2007.
K. Ohmi
K. Hosoyama, et al
Crab Cavities in the KEKB Rings
LER
HER
1 cavity per ring
Single Crab Cavity Scheme
1 crab cavity per ring.
saves the cost of the cavity and cryogenics.
avoids synchrotron radiation hitting the cavity.
•Beam tilts all around the ring.
•z-dependent horizontal closed orbit.
•tilt at the IP:
Crab cavity creates a dispersion, (x,px)=(’)z
• Periodic solution at crab cavity.
• Synchrotron radiation damping realizes an equilibrium orbit (closed orbit) and beam size with periodic condition.
• (,') is transferred as
• (,') is matched at IP as follow
€
ς (s)
ς '(s)
⎛
⎝ ⎜
⎞
⎠ ⎟= M0
ς (s)
ς '(s)
⎛
⎝ ⎜
⎞
⎠ ⎟+
0
edVcrb dz
⎛
⎝ ⎜
⎞
⎠ ⎟
€
ς (s2)
ς '(s2)
⎛
⎝ ⎜
⎞
⎠ ⎟= M21
ς (s1)
ς '(s1)
⎛
⎝ ⎜
⎞
⎠ ⎟
€
ς (s*)
ς '(s*)
⎛
⎝ ⎜
⎞
⎠ ⎟=θcrs0
⎛
⎝ ⎜
⎞
⎠ ⎟
Remember the ordinary dispersion, (x,px)=(’)
Parameterization of 6x6 revolution matrix
€
x 2 xpx xy xpy xz xδ
px2 pxz px py pxz pxδ
y 2 ypy yz yδ
py2 pyz pyδ
z2 zδ
δ 2
⎛
⎝
⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟
= HRB
εx 0 0 0 0 0
0 εx 0 0 0 0
0 0 εy 0 0 0
0 0 0 εy 0 0
0 0 0 0 εz 0
0 0 0 0 0 εz
⎛
⎝
⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟
B tR tH t
€
V = HRB
€
M =VUV −1
€
U =
cosμ x sinμ x 0 0 0 0
-sinμ x cosμ x 0 0 0 0
0 0 cosμ y sinμ y 0 0
0 0 -sinμ y cosμ y 0 0
0 0 0 0 cosμ z sinμ z0 0 0 0 -sinμ z cosμ z
⎛
⎝
⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟
€
R =
μ 0 R4 −R2 0 0
0 μ −R3 R1 0 0
−R1 −R2 μ 0 0 0
−R3 −R4 0 μ 0 0
0 0 0 0 1 0
0 0 0 0 0 1
⎛
⎝
⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟
€
H =
1− ax ζ x η x1− ax ζ 'x η 'x
1− ay ζ y η y1− ay ζ 'y η 'y
−η 'x η x −η 'y η y 1 0
ζ 'x −ζ x ζ 'y −ζ y 0 1
⎛
⎝
⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟
€
B =
β x 0 0 0 0 0
−α x β x 1 β x 0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
⎛
⎝
⎜ ⎜ ⎜ ⎜ ⎜ ⎜ ⎜
⎞
⎠
⎟ ⎟ ⎟ ⎟ ⎟ ⎟ ⎟
K. Ohmi, K. Hirata, K.Oide, PRE 54, 751, 1994
Crab Phase Scan (LER)
Horizontal orbit distortion by a crab kick measured with 453 BPMs.
Dependence of the horizontal kick the crab cavity of the rf phase. The kick angles estimated from the orbit response agree well those from the setting voltage of the crab cavity by 3.6%.
crab
V(z=0) gives a dipole kick.
Beams has indeed tilted!
LER HER
inside of the rings
outside of the rings
- Observation with Streak Cameras (H. Ikeda et al, FRPMN035)
The streak camera
longitudinal
horizontal
Vcrab Scan (HER)
3.6 mrad
Luminosity Ratio
Vertical beam size
Beam lifetime
design
H. Koiso
HERHER
LERLER
Warmupto 300K
Crab cav.detuned
IHER = 0.7 A, ILER = 1.3
A, L > 1034 with
crab crossing.
Working Point of Tunes
K. Ohmi, et al.Phys. Rev. ST Accel. Beams 7, 104401(2004)
We are here.
Simulations give good guidelines.
Head-on 22 mrad crossing
LER
HER
Achievable luminosity for various emittance cases
x=18/24nm (3/14)x=24/24nm
(4/1)x=24/29nm (6/14)
achieved scaled achieved scaled achieved scaled
# of bunches 51 1389 51 1389 100 1389
ILER
(mA)61 1661 75 2043 125 1736
IHER
(mA)34 924 30 817 74 1028
Luminosity
(/nb/sec) 0.594 16.5 0.611 17.0 1.03 14.3
Luminosity with/without crab cavityx=18/24nm
With Crab
x=18/24nm
No Crab (achieved)
achieved(2007/3/14)
scaled scaled acheived(2007/11/15)
achieved(2005/12/25)
# of bunches 51 1389 1585 1389 1585
ILER
(mA)61 1661 1933 1662 1800
IHER
(mA)34 924 1078 1340 1360
Luminosity
(/nb/sec) 0.594 16.5 18.8 17.1 15.2
Ecloud?Ecloud?
Specific Luminosity
L18 H24 (3/11, 4/3)
L18 H24(4/10, 4/19)
L24 H24 (3/29, 4/1)
L24 H29(6/14)
H. Koiso
No crab
What we expect crab cavity?• Establish symmetry of the collision
• Degree of freedom of the collision system is decreased to one for x->+0.5.
• Vertical motion is decoupled, therefore vertical emittance growth become weak.
• Motion in one degree of freedom is confined in KAM surface.
Symmetry breaking source• Optimization with a large number of parame
ters
• Offset x, y, x’, y’
• Twiss parameters, (waist), Ri=1,4, x,y, ’ x,y of each beam.
Tolerance for twiss parameters• Tolerance of all parameters are individually
in controllable range.
0.E+00
1.E+31
2.E+31
3.E+31
4.E+31
0 0.05 0.1 0.15 0.2 0.25
r4
L
LLgeo
1 unit for KEKB tuning: r4=0.021, =0.00016
0.E+00
1.E+31
2.E+31
3.E+31
4.E+31
0 0.0002 0.0004 0.0006 0.0008 0.001 0.0012
etay (m)
L
LLgeo
Difficulty for multi-parameters optimization
Crossing Angle and Horizontal Offset
The luminosity should be significantly degraded by small errors in the crab crossing mode. Therefore it is important to keep both the crossing angle and the horizontal offset between two beams sufficiently small. The crossing angle was optimized by adjusting the crab kick voltage. The horizontal offset must be less than 20 m. The offset was maintained by an orbit feedback to keep the canonical beam-beam kick constant. The target position was determined by the offset scan.
Lum
inosi
ty
Effect on the beam-beam performance of the phase jitter of RF’s
0
0.5
1
1.5
2
2.5
0 0.02 0.04 0.06 0.08 0.1 0.12
x/ σx
σx/σx0
e-
e+
e-
e+
• Luminosity and beam size as functions of x.
• Correlation time of the jitter, 1 or 10 turns, is important for the degradation.
• Since Q=200,000 and H=5120, the correlation time will be larger than 10 turns.
• Tolerance is 0.05 degree.
0
0.2
0.4
0.6
0.8
1
1.2
0 0.02 0.04 0.06 0.08 0.1 0.12
x/ σx
L/L0
Tcor=10
Tcor=1
LER HER
RF Phase Stability
Phase stability of the crab mode was better than the requirement with the rf feedback.
Slow stability below 1 Hz is shown above.
Independent measurement by a spectrum analyzer shows better than 0.01 deg for f > 2 kHz, 0.1 deg for 2 Hz < f < 2 kHz.
Backlash or friction exists in the coaxial tuner for the LER.
LER x, y tune dependence
x -x =integer
x +s =integer These resonances have to be eliminated.
Succeeded in some lattices, but not in some others.
Most serious issue in the crab operation • Asymmetry for the horizontal offset• Beam life time is very short in a region of a horizontal offset.• This asymmetry can not be reproduced by the simulation.
• We had a similar experience. Remember “egure”.• Banana shape of beam (D. Shatilov), or nonlinear?
Short life time
Long life time e+e-
Horizontal offset scan
• The (HER) beam current seems to be limited by the short life time of the LER beam.
• The (LER) beamlifetime is very asymmetric with respect to H offset.
Collision center given by the beam-beam kick
LER lifetime
Beam-beam halo in simulation• Long term simulation by Gaussian weak-strong model.
500x106 particle turn
Head-on 11 mrad
Life time can be improved due to the crab cavity.
Beam-Beam Simulation with lattice non-linearity
• Luminosity drops (beam loss) abruptly at threshold strengths.
• However, the threshold strengths are about 2 order higher than expected values.
Summary• Crab cavity operation starts from Feb. 2007.• High current operation was succeeded, 1.3 A
(e+) and 0.7 A(e-).• RF Phase fluctuation (20 sec period) was see
n at high current operation due to the backlash in the coaxial tuner. The fluctuation is seen only in collision mode. Related to beam-beam?
• Luminosity gain is not yet. • It seems to be essential for me to solve the as
ymmetry.