Advanced Techniques in Collider Physics for Enhanced Luminosity

Explore cutting-edge research on beam-beam effects, crab waist colliders, and luminosity optimization in collider physics. Discover how innovative strategies like crab waist technology and bunch crabbing mitigation are revolutionizing particle collision studies. Dive into the complexities of achieving high luminosity in tau-charm factories through parameter optimization and collision scheme design.

• Collider Physics
• Luminosity Optimization
• Crab Waist Technology
• Particle Collision Studies
• Beam-Beam Effects

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1. Beam-Beam Effects and Crab Waist Collider Luminosity Dmitry Shatilov BINP, Novosibirsk Joint Workshop on Future Tau-Charm Factory LAL, Orsay, 4-7 December 2018

2. Outline Luminosity and collision scheme Requirements and limitations Problems specific to LPA collisions Parameter optimization Summary D. Shatilov Tau-charm Factory, Orsay, Dec. 2018 2

3. Luminosity and Collision Scheme x e- + e Li Luminosity for flat beams: x I tot y = L R z H * 2 er e y 2 x = tg z Collision scheme with large Piwinski angle: 2 x P. Raimondi, 2006 LPA and Crab Waist 1) Transverse separation at parasitic crossings is huge => bunch spacing is not limited by beam-beam. * y 2) The length of interaction area Li<< z => small << zwithout hourglass. 3) Crab waist suppresses betatron and synchro-betatron coupling resonances => y 0.2 D. Shatilov Tau-charm Factory, Orsay, Dec. 2018 3

4. Crab Waist at Work Crab Waist was successfully tested at DA NE -factory (INFN-LNF, Italy) providing a significant increase in luminosity. CW OFF CW ON Footprint (FMA) for DA NE with and without CW. Blue color corresponds to regular trajectories, red color stochastic. D. Shatilov Tau-charm Factory, Orsay, Dec. 2018 4

5. Requirements and Limitations We need at a "standard" bunch population Npto make >> 1, reduce increase yseveral-fold. This is possible only with a significant decrease in the transverse dimensions of the beam. (by about times), and * y + * y N r p = e y 2 2 (1 ) x y In CW collision, beam-beam interaction does not cause beam sizes blowup, long tails in the equilibrium distribution, etc. The main limitations are associated with obtaining the design values for lattice and beam parameters: Very small (FF design, DA, energy acceptance, etc.) Very small emittances with high populated bunches (intrabeam scattering, feedback noises, e-cloud, etc.) * y Besides, two limitations related to beam-beam interaction with LPA were found: Bunch crabbing Coherent X-Z instability Both are successfully mitigated by a proper choice of parameters. D. Shatilov Tau-charm Factory, Orsay, Dec. 2018 5

6. Bunch Crabbing Beam-beam interaction in collision with LPA leads to crabbing of bunches in X-Z plane. E. Perevedentsev, 2001 Bunch shape in X-Z plane (tracking) Bunch crabbing can destroy CW CP for head X/ x CP for tail Z/ z Collision Point for particles with Z 0 shifts away from the axis and also shifts longitudinally, away from the ywaist. * x ( ) ctg Tilt angle at IP: x * x Mitigation: x close to half-integer and small D. Shatilov Tau-charm Factory, Orsay, Dec. 2018 6

7. Coherent X-Z Instability Discovered by K. Ohmi in strong-strong simulations (BBSS). Reproduced in quasi-strong-strong simulations (Lifetrac). There is a good agreement between the two codes. Bunch shape in the horizontal plane at some turns Evolution of the horizontal emittance x(cm) x / x z / z Turns The effect is 2D, xincreases 5 15 times. Then betatron coupling leads to y growth in the same proportion, and luminosity falls several times. This instability cannot be mitigated by feedback. The only solution: find conditions under which it does not arise. D. Shatilov Tau-charm Factory, Orsay, Dec. 2018 7

8. Synchro-Betatron Resonances Coherent instability: xdependence on x and s. Quasi-strong-strong simulations. We need to reduce x/ s ratio and increase the order of resonances 2 x- 8 s= 1 near the working point. * x N 2 r for >> 1 p = e x 2 2 z 2 x- 10 s= 1 x( ) * x Small enough has a key role. We have x s /3, precisely because of this there are regions between 2 x- 12 s= 1 resonances free of instability. Good working points are located around x= 0.545 and 0.556. For smaller values the resonances are x The distance between resonances is s. The width depends on x and the order of resonance. too strong. D. Shatilov Tau-charm Factory, Orsay, Dec. 2018 8

9. Betatron Tunes Good area: red triangle in the bottom- left corner, xclose to half-integer. The bunch crabbing is small here. Luminosity vs. betatron tunes, simplified model, weak-strong simulations. Colors from zero (blue) to 1035cm-2c-1(red). 1.0 Only low-order resonances are visible, the others are suppressed by CW. High order synchrotron satellites of half-integer resonance are seen only in [quasi]-strong-strong model. y The range of permissible xfor large y is bounded on the right by 0.57 0.58. The tune shift yis far below the limit. We have margins for increasing either yor x. 0.5 x 0.5 1.0 (0.545, 0.580) D. Shatilov Tau-charm Factory, Orsay, Dec. 2018 9

10. Summary Crab Waist collision scheme can provide the highest possible luminosity for e+e- colliders. Beam-beam issues related to collision with LPA were found and mitigated by a proper choice of parameters. In the present design of Super -charm Factory, x,yare below the limits and no restrictions from beam-beam interaction are seen. Beam-beam simulations in a realistic nonlinear lattice were not yet performed, since the lattice is still under optimization (DA, energy acceptance, etc.). The main limitations are associated with obtaining the design values for the lattice and beam parameters. D. Shatilov Tau-charm Factory, Orsay, Dec. 2018 10