Physics issues of storage ring . Gang XU IHEP, Apr. 26, 2006. contents. Beam-beam effects and luminosity Impedance and instabilities Optics issues commissioning softwares Summary. Tune survey with 11mrad crossing angle by Cai’s Code. Tune survey with 11mrad crossing angle
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IHEP, Apr. 26, 2006
by Cai’s Code
(by Zhang’s Code)
According to the formula of L0, decreasing β*y
and increasing kb can increase the L0
β Zhang’s code, the higher luminosity means closer to the half integer*y is by decreasing αp from 0.0235 to 0.0188,
The microwave instability threshold will decrease, HOM heating increase
Kb increase from 93 to 120 even 130
bunch spacing 6ns, e-cloud acceptable, parasitic beam-beam effect acceptable, RF power increase 30%, HOM heating increase
So L0 will increase by factor (1.5/1.2)*(120/93)=1.6
Lmax=1.6*0.6*L0~L0---1×1033 could be reached
Width 4mm，depth 2mm，step 6mm，number 27
Loss factor 2.25×10-4V/pC(1.78V/pC).
Loss factor 0.175V/pC.
It can not be used in BEPCII
Model in mafia
the shielding chamber with 1mm gap
Inducing part has been shielded
But the HOM heating is serious
The structure of shielding chamber must
The simulation of the electron cloud in the magnetic fields Zhang’s code, the higher luminosity means closer to the half integer
Because of the short circumference of the BEPC storage ring, most of the arc regions are occupied by magnets. So it is necessary to study the distribution and the motion of electron cloud in different magnetic fields. A two- dimensional code evoluted from the ECIC was used to simulate the motion, formation, distribution of the electron cloud in drift, dipole, quadrupole, sextupole and solenoid field regions.
In dipole magnetic field region without considering the fringe field, the magnetic field is only in vertical direction.
the electrons in the cloud are confined to move in tight vertical helices whose radius is typically a few microns, and whose cyclotron frequency is f=eB/2m, B=8000Gs, f=22.3GHz. The main consequence of the cyclotron motion of the electrons is the severe suppression of the horizontal component of the velocity of the electrons in the cloud.
For the quadrupole magnetic field, Zhang’s code, the higher luminosity means closer to the half integerB can be expressed by
For the sextupole magnetic field, B can be expressed by
In a uniform solenoid field, the magnetic field is only in longitudinal direction, i.e., B=Bz.
(left: antechamber chamber; right: elliptic chamber)
(a: field free region; b: dipole field; c: quadrupole field; d: sextupole field; e: solenoid field with Bz=10Gs )
(left: antechamber; right: elliptic chamber)
The uniform solenoid field is the most effective way to confine the photoelectrons. All of the photoelectrons are confined to the vicinity of the vacuum chamber wall. So in the design of the BEPCII, solenoids will be wound on the vacuum chamber of the straight sections with the magnetic field of 30Gs, which is enough to clear the electron cloud in the central region.
The drift length in BEPCII is much shorter than that in KEKB.
The occupation of all the drift region in BEPCII will profit to increase the luminosity.
before sorting 3~5mm COD
after sorting 0.3~0.5mm COD
Dynamic aperture with/without aliagnment errors for 6.51/5.58
Changing the polarity of the two magnets to connect SR ring, e+/e- ring
Orbit of the backup IR scheme
dot-dash: SR mode solid: e- ring dotline: e+ ring
backup IR scheme design field
Acceptable mini-gap : 11mm(15mm designed)
Potential issues: damage by heating, need more attentions
calculation (beta, tune, dispersion, emittance, bunch length, RF bucket-height)
match (beta, tune, dispersion)
dynamic aperture and Poincare phase-plot
main magnets (main bending, (de)focusing quadrupoles) setting
IR orbit feedback(in preparation)
Injection and collision conditions tuning in the horizontal plane
Collision conditions tuning in the vertical plane and some simulation results
during collision tuning in both horizontal and vertical plane
for the elimination of vertical crossing angle at the IP
in both horizontal and vertical plane
Control panel for Waist- plane y* scan
Control panel for the local coupling compensation in the IR. (Anti-solenoid system)
Control panel for the global coupling compensation. (Skew quadrupole system)
Orbit correction quadrupole system)
Beam response-matrix(windows-epics) good” BPMs.
Functions good” BPMs.