Background and collimator study in CEPC double ring

Background and collimator study in CEPC double ring Sha Bai, Chenghui Yu, Yuan Zhang, Yiwei Wang, Jie Gao CEPC AP meeting 2017 -09 -15

Radiative Bhabha scattering events • βx*=0. 36 m的energy acceptance~1. 5%. • Generate 100000 particles~ energy spread

Lost particles statistic βx*=0. 36 m p Lattice version： cepc. lat. bx 036. 242. 9. sad p Gaussian distribution energy spread adding to the 100000 particles generated by RBB generator p Set aperture according to beampipe p RBB generated at IP 1, tracking in SAD p The number of particle lost in the downstream and upstream of 1 st turn is: 3192/223 p The number of particle lost in downstream and upstream of 2 nd turn is: 18/32 p The number of particle lost in downstream and upstream of 3 rd turn is: 0/5

Loss particles due to RBB in turns Lost particles due to RBB in turns(bx=0. 36 m) 3500 3192 3000 2500 Counts 2000 1500 1186 1000 427 500 223 0 203 1832 05 1 2 downstream 3192 18 upstream 223 32 23 112 102 73 42 28 23 2497 28 18 17 254 23 5 12 115 0 3 4 5 6 0 1186 23 1 5 427 203 15 7 0 73 8 5 42 9 12 28 10 23 18 11 12 13 14 24 28 17 2 97 112 102 54 15 2 3 10 76 77 92 68 29 5 1 1 11 013 034 140 13 9 99 218 15 011 04 00 00 62 39 84 43 1 028 2 0 0 16 1 0 17 0 13 26 0 11 30 0 11 32 0 0 33 0 0 34 0 0 35 0 0 36 0 28 18 0 34 19 1 40 20 13 76 21 9 77 turns 22 5 92 23 1 68 24 1 29 25 1 1 27 0 99 28 2 18 29 1 5 31 0 4 37 2 62 38 1 39 39 0 84 40 0 43

Beamstrahlung events • βx*=0. 36 m的energy acceptance~1. 5%. • 与RBB输出的粒子的能散相比，beamstrahlung效应随能散呈指数增加，所以绝大 多数的粒子的能散都分布在略大于1. 5%的区域里。 • Generate 100000 particles~ energy spread

Lost particles statistic βx*=0. 36 m p. Lattice version：cepc. lat. bx 036. 242. 9. sad p Gaussian distribution energy spread adding to the 100000 particles generated by BS generator p Set aperture according to beampipe p BS generated at IP 1, tracking in SAD p The number of particle lost in downstream and upstream of 1 st turn is: 0/84 p The number of particle lost in the downstream and upstream of 2 nd turn is: 2/17 p The number of particle lost in downstream and upstream of 3 rd turn is: 0/10 p The number of particle lost in downstream and upstream of 4 th turn is: 5504/566

Loss particles due to BS in turns Lost particles due to BS in turns(bx=0. 36 m) 6000 5504 5000 Counts 4000 3000 2000 1504 1416 1243 925 1000 0 566 084 217 010 1 downstream 0 upstream 84 2 2 17 262 129 517 087 2736 1437 3146 3 4 5 6 0 5504 129 5 10 566 262 17 7 0 87 8 27 36 9 14 37 169 202 404 77 41 1136 951 957 825 1440 17 10 11 12 13 14 15 31 169 202 77 41 14 46 925 1504 1243 825 40 16 1 7 174 1 511 22 167 157 724 367 40 1 4 99 814 0 2 17 18 19 20 21 22 23 24 25 1 1 22 167 157 40 1 4 8 74 404 511 957 1416 849 367 14 turns 1012 849 246 103 183 56 8 10 2 1 13 26 27 28 29 30 31 0 2 8 10 2 1 99 1136 246 103 183 56 32 1 3 435 678 628 00 03 035 3 33 0 0 34 0 3 35 36 37 38 39 40 0 3 28 14 2 0 35 435 724 628 1012 678 28 14 2 0

Preliminary Design of Collimators • There are two kinds of collimator aperture, round and rectangular. l Upper Limit: l TMCI: l Injection:

Preliminary design of collimators ~βx*=0. 36 m Since the low gradient of final doublet in IR, the beta function are much larger than in the single ring. In this case, the upper limit are much high, and there seems no space for collimators to choose for both horizontal and vertical.

Collimator design in ARC Phase BSC/2/m Range of half width allowed/m m 0. 24 349. 16 0. 010242 1~10 104. 65 0. 24 350. 91 0. 010117 1~10 1953. 13 116. 82 0. 12 349. 85 0. 003752 1~3. 5 1742. 15 125. 21 0. 16 350. 60 0. 003778 1~3. 5 Horizontal Beta Dispersion/ function/m m name Position Distance to IP/m APTX 1 D 1 I. 1884 2203. 06 108. 36 APTX 2 D 1 I. 1909 1710. 79 APTY 1 D 1 I. 1897 APTY 2 D 1 I. 1908

Beam loss with collimators RBB loss upstream vs horizontal collimator half width BS loss upstream vs horizontal collimator half width 180 2500 160 2000 140 100 BS loss RBB loss 120 80 1500 1000 60 40 500 20 0 y=3 mm y=2 mm 10 167 9 147 19 8 112 7 7 63 3 x(mm) 6 35 2 5 0 0 y=3 mm y=2 mm 10 2197 9 1911 197 8 1563 129 7 917 79 x(mm) 6 440 31 5 9

RBB loss with collimators Ø horizontal collimator half width 1 cm, vertical collimator half width 3 mm Lost particles due to RBB in turns with collimators x 1 cmy 3 mm 3500 3192 3000 Counts 2500 2000 1500 1000 500 0 0 00 1 2 downstream 3192 0 upstream 0 0 00 630 11 00 00 01 029 332 024 03 01 00 00 00 01 08 00 00 00 016 010 03 02 00 00 01 04 3 0 0 5 1 1 6 0 0 7 0 0 8 0 0 9 0 0 1 11 0 29 15 0 1 16 0 0 17 0 0 18 0 0 19 0 0 20 0 0 21 0 0 22 0 1 23 0 8 24 0 0 25 0 0 26 0 0 27 0 16 30 0 2 31 0 0 32 0 0 33 0 0 34 0 0 35 0 0 36 0 0 37 0 0 38 0 0 39 0 1 40 0 4 4 63 0 12 3 32 13 0 24 14 0 3 turns 28 0 10 29 0 3

RBB loss with collimators Ø horizontal collimator half width 6 mm, vertical collimator half width 2 mm Lost particles due to RBB in turns with collimators x 6 mmy 2 mm 3500 3192 3000 Counts 2500 2000 1500 1000 500 00 00 00 00 00 00 01 00 00 00 1 2 downstream 3192 0 upstream 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 10 0 0 11 0 0 12 0 0 13 0 0 14 0 0 15 0 0 16 0 0 17 0 0 18 0 0 19 0 0 20 0 0 21 0 0 22 0 0 23 0 0 24 0 0 25 0 0 26 0 0 27 0 1 28 0 0 29 0 1 30 0 0 31 0 0 32 0 0 33 0 0 34 0 0 35 0 0 36 0 0 37 0 0 38 0 0 39 0 0 40 0 0 turns

RBB loss with collimators Ø horizontal collimator half width 5 mm, vertical collimator half width 2 mm Lost particles due to RBB in turns with collimators x 5 mmy 2 mm 3500 3192 3000 Counts 2500 2000 1500 1000 500 00 00 00 00 00 00 00 00 00 1 2 downstream 3192 0 upstream 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 9 0 0 10 0 0 11 0 0 12 0 0 13 0 0 14 0 0 15 0 0 16 0 0 17 0 0 18 0 0 19 0 0 20 0 0 21 0 0 22 0 0 23 0 0 24 0 0 25 0 0 26 0 0 27 0 0 28 0 0 29 0 0 30 0 0 31 0 0 32 0 0 33 0 0 34 0 0 35 0 0 36 0 0 37 0 0 38 0 0 39 0 0 40 0 0 turns

Conclusions and Prospects • Radiative Bhabha scattering and Beamstrahlung events are generated and lost particles information got after tracking in SAD. • Beam loss background in βx*=0. 36 m lattice seems serious, especially in the upstream of multi-turn tracking. • With two pairs of horizontal and vertical collimators in ARC(half width 5 mm and 2 mm), beam loss reduced significantly.