1 August 12, 2005 Running 2mrad IR in e-e- mode: BDS constraints A.Seryi August 12, 2005.
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1 August 12, 2005 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 August 12, 2005 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 August 12, 2005 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 August 12, 2005 e+e- 2mrad IR e-e- 2mrad IR y * = 9 mm x * = 30 mm y * = 0.3 mm x * = 30 mm Note also much larger dispersion in FD for e-e- FD for e+e- & e-e-
6 August 12, 2005 e+e- 2mrad IR e-e- 2mrad IR y * = 0.3 mm x * = 30 mm y * = 9 mm x * = 30 mm Optics for e+e- & e-e-
7 August 12, 2005 e-e- 2mrad IR e+e- 2mrad IR Chromaticity Note that chromaticity is larger and much less local in e-e-
8 August 12, 2005 Ideal e-e- luminosity For this optics, in ideal case, the GP calculated luminosity is 2.2E33 cm -2 s -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 August 12, 2005 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 -2 s -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)