Discussion of ILC high luminosity parameters

1
Discussion of ILC high luminosity parameters

• Andrei Seryi
• with suggestions from Tor Raubenheimerand
  critical comments by Peter Tenenbaum and Andy
  Wolski

2
Design challenges and 1 TeV high lumi case

• Extraction of the disrupted beam is one of ILC
  challenges
• Energy acceptance of extraction beamline is not
  unlimited
• so far achieved acceptance of approximately 35
  to 100
• Need to treat E acceptance in a similar way as
  other limits
• like emittance growth in the linac, or
• DR emittance due to coupling or collective
  effects
• Below, a very tentative set of parameters is
  suggested for discussion for 1 TeV high lumi case
• It is designed to relax extraction line problems,
  but it certainly push other parts of the design

3
Version of parameters February 28,
2005 http//www-project.slac.stanford.edu/ilc/acce
ldev/beamparameters.html Extraction line
challenge low energy tail
500GeV CM, high lumi
500GeV CM, nominal
1TeV CM, high lumi
1TeV CM, nominal
4

• For quick optimization used analytical expression
  for spectrum after collision
• Shape reproduced nicely, but the relative energy
  is somewhat lower in GP simulations
• Used as a criteria the energy, below which there
  is less than 10W of tail

Beam-beam simulations with Guinea-Pig
500GeV CM nominal ---Input energy250 particles
2 sigma_x655 sigma_y5.7 sigma_z300 emitt_x10 e
mitt_y0.04 beta_x0.021 beta_y0.0004 frepnb141
00
----Output (analytical numbers) P_b11280000 Dx
0.16 Dy18.4 Hd1.69 LumG1.20e038 Lum2.03e038
P_beamstrh243670 Upsilon0.045 nG1.26 delB0.021
6 inc. pairs/bc total206900 Elower10W136 GeV
( 54.5)
Analytical shape P.Chen, K.Yokoya
5

• For High Lumi 500 GeV CM, the 10W limit occur at
  30 of the nominal energy (analytical number)
• This case is barely works (or not) with 20mrad
  extraction
• Lets consider this 30 as the limit

----Output P_b11280000 Dx0.168 Dy21.71 Hd1.7
33 LumG2.837e038 Lum4.916e038 P_beamstrh78010
4 Upsilon0.13 nG1.73 delB0.069 inc. pairs/bc
total507646 Elower10W75 ( 30)
---Input energy250 particles2 sigma_x452 sigm
a_y3.5 sigma_z150 emitt_x10 emitt_y0.03 beta_x
0.01 beta_y0.0002 frepnb14100
6

• For High Lumi 1 TeV CM, the 10W limit presently
  occur at 13.3 of E0
• With present extraction design, with downstream
  diagnostics, this set does not appear to work
• Lets modify parameters so that 10W limit
  increase at least to 30 of E0

----Output P_b18048000 Dx0.167 Dy21.46 Hd1.7
4 LumG4.488e038 Lum7.812e038 P_beamstrh317698
9 Upsilon0.369 nG2.22 delB0.176 inc. pairs/bc
total1084825 Elower10W66.5 ( 13.3)
---Input energy500 particles2 sigma_x320 sigm
a_y2.5 sigma_z150 emitt_x10 emitt_y0.03 beta_x
0.01 beta_y0.0002 frepnb11280
7

• For new 1TeV high lumi case, basically need to
  decrease ? more than twice, while keeping L
  almost same and keeping Dy below 28
• aim for "high L" 2nominal, not higher
  (presently high/nom2.8)
• aim that disrupted beam tail has lt 10W below 30
  of E0
• Remind scaling
• Reduction of ? twice seem to possible only with
  twice longer bunch
• Further reduce ? by increasing sx faster then N
  (also helps to keep Dy lt 28)
• Same sy with 2long bunch (twice by) require
  smaller ey , gt slight increase of sy , so that
  required ey is more feasible
• In summary, the suggested 1TeV high L parameter
  set has
• twice longer bunch (300um, not 150um as in
  present 1TeV high L set)
• somewhat lower y emittance (0.023 , not 0.030)
• somewhat higher charge (2.4 , not 2.0)
• larger beam at IP (5502.7 , not 3202.5)
• higher y disruption ( 27 , not 21)

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• Suggested new 1 TeV High Lumi case
• If the higher charge is not possible, one can
  reoptimize with somewhat lower luminosity

Suggested 1TeV high L ----Input
energy500 particles2.4 sigma_x550 sigma_y2.7
sigma_z300 emitt_x10 emitt_y0.023 beta_x0.029
6 beta_y0.00031 frepnb11280
----Output P_b21657600 Dx0.136 Dy27.75 Hd1.6
4 LumG3.48e038 Lum5.718e038 P_beamstrh1450127
Upsilon0.128 nG1.697 delB0.0669 inc. pairs/bc
total786246 Elower10W146.5 ( 29.3)
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February 28, 2005
Suggested for discussion
10
Discussion

• The new 1TeV high L set need to be further
  discussed
• The biggest push is of course for DR performance
  and LET performance
• E.g. DR extracted emittance 18nm
• LET emittance dilution budget 5nm
• Other sets, e.g. high Lumi 500 GeV CM, need to be
  considered from the same assumptions