Bunch by bunch intensity control for the FCCee
Bunch by bunch intensity control for the FCC-ee injector K. Oide Oct. 30, 2020 126 th FCC-ee Optics Design Meeting Many thanks to D. Shatilov, F. Zimmermann
Bootstrap injection (D. Shatilov) ✤ The collider is filled with the maximum bunch intensity of the injector up to about a half of the design current. Then the injection bunch intensity is reduced up to 10% (Z) or 6% (W, H, tt) of the design intensity of the collider. ✤ Then a higher bunch intensity in the injector than the baseline does not shorten the injection time so much. ✤ If the imbalance of the colliding bunch pair once exceeds the limit, the balance cannot be recovered, by injecting to the weaker bunch. These bunches must be abandoned (never fill again). Oct. 30, 2020 K. Oide
Charge imbalance after the initial fill from scratch ✤ At the initial fill, which needs ∼ 10 cycles of injection, an imbalance in the bunch charge is inevitable. ✤ If the imbalance of bunch charge at each injection is , the stored imbalance will be. ✤ I guess a control to suppress less than 3% will be difficult (considering fluctuations of transmission in linac, damping ring, boosters, and colliders). ✤ Thus the collision starts with random bunch charge distribution by about 1% in both beams. Oct. 30, 2020 K. Oide
A crude simulation of the bunch decay & refill If there is no bunch-by-bunch charge control… ✤ Bunch-by-bunch injection intensity fluctuation: 3% ✤ Average injection intensity/bunch: 4% ✤ Intensity threshold: -2% ✤ Luminosity lifetime: 50% ✤ Relative intensity dependence of the lifetime: ± 3% for ± 1% intensity difference If the refill is constant over bunches, the charge imbalance quickly diverges! Oct. 30, 2020 K. Oide
Summary • • • According to the design of the FCC-ee collision, a “bootstrap” injection is necessary. The amount of charge must be controlled bunch-by-bunch, otherwise the balance of two colliding bunches will be lost quickly. A sort of AI may be needed to predict the necessary amount of each bunch charge for the next injection. Oct. 30, 2020 K. Oide
- Slides: 5