1. DYNAMIC APERTURE OF JLEIC ELECTRON COLLIDER
RING WITH ERRORS AND CORRECTION*
Y. Nosochkov, Y. Cai, SLAC National Accelerator Laboratory, Menlo Park, CA, USA
F. Lin, V. S. Morozov, Y. Zhang, Jefferson Lab, Newport News, VA, USA
ABSTRACT
Design of the Jefferson Lab Electron-Ion Collider (JLEIC) includes low-beta Interaction Region (IR) and spin rotator optics for high luminosity and polarization. Magnet errors, especially in the high-beta final focus quadrupoles, result in optics perturbations which need to be corrected in order to attain sufficient dynamic aperture (DA). We present design of orbit correction system for the electron ring and evaluate its performance. The DA is then studied including misalignment, magnet strength errors, non-linear field errors, and corrections.
* Work supported by the U.S. Department of Energy, Office of Science, and Office of Nuclear Physics under Contracts DE-AC05-06OR23177, DE-AC02-06CH11357, and DE-AC02-76SF00515.
Layout of the JLEIC electron collider ring
RING PARAMETERS ERRORS AND ORBIT CORRECTION
Orbit response from quads near IP, offset by X,Y = 0.2 mm
Electron ring optics
Figure-8 layout
2.3-km e- and p rings
3 ‒ 12 GeV electrons
30 ‒ 200 GeV protons
Two 108° arcs in e-ring
IP * = 10 cm / 2 cm
e-ring e = GeV
e-ring tune = / 50.16
Misalignment, strength errors, and multipole field errors cause distortion of orbit, dispersion and b functions, coupling, chromaticity, tune shift, and non-linear effects. The most sensitivity is to errors in the final focus quadrupoles (FFQ), where b functions are large. Orbit correction system consisting of X,Y dipole correctors and BPMs is designed for the electron ring.
Dynamic APERTURE
X,Y correctors and BPMs in the e-ring IR
Dynamic aperture (DA) is calculated at 5 GeV in 2000-turn tracking using LEGO for 10 seeds of random errors generated within ±3 range.
Simulations include corrections of:
global orbit (using dipole correctors and BPMs)
betatron tune (2-family arc quadrupoles)
linear chromaticity (2-family arc sextupoles)
vertical dispersion (Y-correctors)
b functions (various quadrupoles)
X-Y coupling (sextupole vertical offsets)
SVD method is used to find the most efficient correctors. To avoid unstable optics due to large errors, the errors in the simulations are increased gradually, in small steps, while doing the corrections at each step, until the specified error values are reached.
PEP-II measured multipoles are used in tracking
Electron ring orbit after correction with Table 1 misalignment for 10 seeds of random errors
DA without errors vs Dp/p
DA = 15x × 45y
DA with misalignment and corrections for 10 seeds
DA = 14.5x × 44y
DA with misalignment and PEP-II multipole field errors for 10 seeds
DA = 10.1x × 41.5y
DA with misalignment, magnet strength errors, and multipole errors
DA = 9.4x × 40.6y
The used errors are conservative and can be considered as preliminary tolerances for most magnets. The resulting DA of 9.4x may be sufficient, but further improvement is desired. This is possible with more stringent tolerances for the FFQ magnets. The FFQ will be the new superconducting magnets, hence one can aim at a better field quality in these magnets. A factor of 2 reduction of the PEP-II multipole field in the FFQ increases the DA by ~1x to 10.4x.
DA with all errors vs FFQ multipole errors, scaled from PEP-II errors
CONCLUSION
Orbit correction system, designed for the electron collider ring, shows acceptable performance resulting in minimal DA degradation with conservative alignment errors. The DA with misalignment, magnet strength errors and PEP-II measured multipole field errors is almost 10 which may be sufficient. The DA could be increased by a better field quality in the new superconducting FFQ magnets, other optics improvements, and implementation of multipole field correctors in the FFQ.