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Running 2mrad IR in e-e- mode: BDS constraints

Detailed overview of optimal optics constraints for the 2mrad IR e-e- mode, highlighting the crucial factors and adjustments needed for proper beam extraction and disruption management.

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Running 2mrad IR in e-e- mode: BDS constraints

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  1. Running 2mrad IR in e-e- mode: BDS constraints A.Seryi August 12, 2005

  2. BDS constraints on e-e- • In 2mrad IR, the kick by the first quad on the outgoing beam is essential for extraction of the disrupted beam • The strength of FD (quads and sextupoles) is optimized to extract the disrupted beam properly, and this is optimized for e+e- • It means that, in e-e-, the FD strength has to stay the same as in e+e-, but with reversed sign of QD0, QF1, SD0, SF1 to provide exactly the same conditions for the extracted beam

  3. BDS constraints on e-e- • Thus, the sign of FD is reversed for the incoming beam, and the last quad is defocusing in Y for the incoming beam • Thus, in order to keep reasonable collimation depth, we have to increase the vertical beta function at the IP, as we will see, by about factor of 30 • The corresponding increase of Y beam size by factor of 5.5 is actually consistent with the desire to have reasonably wide deflection curve, for IP feedback • Thus, increasing betaY* may also be needed for 20mrad IR • The horizontal beta-function at IP is kept the same as in e+e-, to keep the beamstrahlung reasonable, but in principle betaX* can be somewhat decreased

  4. Tuning FF for e-e- • FD strength reversed • betaY* increased 30 times • Used only upstream quads to retune the optics, to keep the same geometry • The optics shown on the next pages is a draft version, its bandwidth is not good and there are geometrical aberrations left. But it can be further improved.

  5. FD for e+e- & e-e- by* = 9 mm bx* = 30 mm e-e- 2mrad IR Note also much larger dispersion in FD for e-e- e+e- 2mrad IR by* = 0.3 mm bx* = 30 mm

  6. Optics for e+e- & e-e- by* = 9 mm bx* = 30 mm e-e- 2mrad IR by* = 0.3 mm bx* = 30 mm e+e- 2mrad IR

  7. Chromaticity e-e- 2mrad IR Note that chromaticity is larger and much less local in e-e- e+e- 2mrad IR

  8. Ideal e-e- luminosity • For this optics, in ideal case, the GP calculated luminosity is 2.2E33 cm-2s-1 • This is 8% of the e+e- luminosity (2.8E34) • Spectrum of disrupted beam for e-e- is very similar as e+e- • May decrease sigma_x, but only slightly – to keep low E tail acceptable • GP parameters: • energy = 500 GeV • particles = 2.0 E10 • sigma_x = 554 nm • sigma_z = 300 um • emitt_x = 10 E-6m • emitt_y = 0.04 E-6m • beta_x = 30 mm • e-e- beta_y = 9 mm • e-e- sigma_y = 19.2 nm • e+e- beta_y = 0.3 mm • e+e- sigma_y = 3.5 nm

  9. Discussion • From the incoming and extraction optics point of view, e-e- in 2mrad IR is feasible • Optics constraints require reversing polarity of FD and thus increasing betaY* by about factor of 30 • The incoming FF optics is quite different than e+e- and would require retuning for e-e- option • The ideal e-e- luminosity is 2.2E33 cm-2s-1 (about 8% of e+e-) • The increased Y size also decreases the disruption of e-e- collisions • Keep X size similar as in e+e-, to minimize energy tail for extraction • Increasing betaY* (=> increasing Y size) is good for feedback and should also be done in 20mrad IR (where the in/out beamlines are independent and there are no such optics constraints)

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