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ARDA/Groups/Lattice Dynamics/Projects
Current projects.
- Lattice design for PEP-II
Over the past year, we worked extensively to improve the performance of the PEP-II. For optics, we started the investigation of possibility of running both the High Energy Ring and the Low Energy Ring near the half integer resonance so that the dynamic b effect from the beam-beam interaction is enhanced to further increase the luminosity. We designed new lattices. These lattices were successfully implemented into the machines during the machine development. The closeness of the tune to the half integer resonance caused much increase of b beating in the machines. We upgraded the object-oriented library: LEGO to correct this b beating. The simulation of the correction has been carried out successfully. The scheme will be used to correct the b beating in the machines soon.
- Beam-Beam Simulation
A highly accurate self-consistent particle code to simulate the beam-beam collision in e+e- storage rings has been developed. It adopts a method of solving the Poisson equation with an open boundary. The method consists of two steps: assigning the potential on a finite boundary using the Green's function, and then solving the potential inside the boundary with a fast Poisson solver. Since the solution of the Poisson's equation is unique, our solution is exactly the same as the one obtained by simply using the Green's function. The method allows us to select much smaller region of mesh and therefore increase the resolution of the solver. The better resolution makes more accurate the calculation of the dynamics in the core of the beams. The luminosity simulated with this method agrees quantitatively with the measurement for the PEP-II B-factory ring in the linear and nonlinear beam current regimes.
In order to make more reliable prediction of a better working point for the PEP-II, the two-dimensional code for the beam-beam simulation has been extended to the three-dimensional one on single-processor computer. To achieve the required accuracy of the calculation, we have to run the code on parallel supercomputers. Currently, the parallel version of the three-dimensional code is under the development.
We have simulated the additional beam-beam collision from the linac for PEP-N. The result of the simulation has quantified the degradation of the luminosity.
- Model Independent Analysis (MIA) technique applied to PEP-II
The principal goal is to use these high-precision tools to measure and analyze the transverse orbits in storage rings so as to accurately estimate the linear machine parameters for checking the machine quality and guiding the machine correction. Currently, these techniques are being applied to the PEP-II rings.
After obtaining about 2000-turn BPM buffer data of the resonantly excited beam for the horizontal and vertical tunes, two pairs of conjugate linear transverse orbits are obtained with a high resolution (2-orders-of-magnitude enhancement) through FFT filtering. The resolution can be further enhanced, if needed, by taking more sets of "same condition" data. The two pairs of the conjugate linear orbits allow for immediate calculation of the phase advancement and betatron motion amplitude at each BPM.
These two pairs of conjugate linear transverse orbits can also be used for calculating the Green's functions (R12, R34, R14, R32) between BPMs. Hence the actual machine optics can be compared with that of the ideal lattice model. Taking all BPM gains and couplings, Quadrupole's normal and skew components, and sextupole misalignments as variables, we use SVD enhanced least square fitting to determine the difference between the machine and the model lattice. We can also obtain the actual machine linear map for calculating the betatron functions and the coupling parameters (global coupling angle for example) at each BPM. These fitted and calculated parameters are used for checking the accelerator machine quality and guiding the machine correction.
Last modified on Thursday, 14-Oct-2004 15:13:54 PDT
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