NLC 1 st and 2 nd IR performance and balancing the accelerator and detector issues

A.Seryi, 07/14/03, ALCW1

NLCNLC 11stst and 2 and 2ndnd IR IR performanceperformance

and balancingand balancing the accelerator and detector the accelerator and detector

issuesissues American Linear Collider WorkshopJuly 13-16, 2003

Andrei SeryiSLAC

for the NLC Accelerator Physics Group


A. Drozhdin, L. Keller, T. Markiewicz, T. Maruyama, N. Mokhov, Yu. Nosochkov, T. Raubenheimer, A. Seryi, P. Tenenbaum, M. Woodley


1st and 2nd IR design approach

• Would like to make 1st & 2nd IRs more equivalent, at least up to 1.3TeV CM– Require that Lumi of two IRs can be equal within 30%

• The two IRs will never be equal – 1st IR has higher potential (straight tunnel, => multi TeV)– 2nd IR needs big bend => BDS is shorter => lower energy

reach

• Luminosity loss in FF scales as dL/L~ 7/4 / 5/2. That means that though the required FF length scales only as ~ 7/10 , the luminosity loss can be significant when the FF length is decreased– => Want to make 1st and 2nd IR BDS as close in length as possible


1st and 2nd IR layout evolution

• Evolution of IR layout is driven by attempts to solve this contradiction:

– Need 2nd IR BDS to be as close to the “full length” as possible

– Need to limit the emittance growth in 2nd IR big bend

• This drives the big bend length up, and appear to contradict the previous …


NLC layoutevolution

e- e+

IP2

IP1

e- e+

1st IR : full length (1430m) BDS 2nd IR : 2/3 length (970m) BDS

Big Bend has to be long (600m) so that <30% @ 650 GeV/beam

2nd IR : 2/3 length one way bending BDS Big Bend shortened twice

Saved 125m in e- and 450m in e+ beamlines of 2nd IR

Lengthen the e+ 2nd IR BDS to full lengthThe e- 2nd IR BDS is still 2/3 length

June 03:

May 03:

July 03:


e+e-970m BDS

(will be 1100m)1400m BDS

1400m BDS 1400m BDS

Full length BDS (1430m) in 1st IR and in e+ side of 2nd IR

Only the e- side of 2nd IR has shorter BDS (presently 970m optics, but have space to lengthen it to 1100m)

IP1

IP2

Optics for July 03 layout

Picture is still June layout


BDS performance (July layout)1st and 2nd IR

Geometric luminosity (normalized) of NLC BDS. Include effect of aberration and synchrotron radiation. Beam-beam enhancement is not included. Same normalized emittances assumed for the entire range.

Th

e e-

2n

d I

R B

DS

can

sti

ll b

e le

ng

then

ed t

o i

mp

rove

per

form

ance

LO~E


BDS performance (July)in absolute units

Geometric luminosity for NLC BDS (optics only: include aberrations and synch.radiation; beam-beam luminosity enhancement is not included). Same normalized emittances assumed for the entire range.

len

gth

enin

g o

f 2n

d I

R e

- B

DS

to

110

0m w

ill

pu

ll i

t u

p s

om

ew

ha

t


FF upgrade means (1):

reduce bending angle in FFTo reduce synch.radiation in FF

magnets:

Reduce bending angle in FF twice, and increase bending angle in E-Collimation by ~15%.

Location of IP is fixed. BDS magnets need to be moved by ~20cm. Outgoing angle change by ~1.6 mrad

IP

FF bends: reduce

angle twice

E-Collimationbends:

Increase angle by 15%

One way bending BDS for 2nd IR

“Standard” (two way bending) BDS


FF upgrade means (2):use longer Final Doublet

Short FD

Short FD

Long FD

Long FD

Longer FD allow to reduce luminosity degradation due to synch.radiation in FD (Oide effect).

2nd IR FD optimized for 90-650 GeV CM range

2nd IR FD optimized for the energy upgrade


BDS performance (July)Benefits of the FF upgrade

Geometric luminosity (normalized). Thin curves show performance if upgrade (=layout & FD change) was not made, or if one goes back from 1TeV to Z

Whe

n lu

min

osity

loss

is s

o hi

gh a

t low

E,

it ca

n be

par

tly re

gain

ed b

y in

crea

sing *


Octupole Doublets

BetatronCollimation

EnergyCollimation

Entrance IP

Collimation in NLC BDS

Collimation system removes the beam halo. Losses of halo occur in dedicated places.No losses after last FF collimator.

Assumed halo is 0.1% of the beamK=1 corresponds to nominal collimation depth when SR from the halo do not touch the vertex detector

K=1

K>1

FD aperture

SR emitted by halo is lost only on dedicated masks, and do not touch vertex detector.


Collimation gaps

Collimation gaps are defined by requirement to protect Vertex Detector from synchrotron radiation emitted by beam halo

For a given optics design, gaps are proportional to the Vertex Radius (and are independent on beam energy)

Smallest spoiler gaps in NLC BDS are +-0.2mm (or +-0.6mm with tail folding octupoles)

collimator


Collimation gaps and wakes

Small gaps is an issue (TRC R3) because collimator wakes cause the IP beam jitter to increase

For NLC A~1.3 (or 0.7 with Octupoles) that means that Y-jitter increase by 64% (or 22% with Octupoles) at 500GeV CM

NLC spoiler is tapered to reduce wake-fields

Jitter amplification in y-plane (due to y’) is (1+ A

)0.5 times

Jitter amplification in y-plane (due to y’) is (1+ A

)0.5 times

Since Aalmost does not depend on optics, have only three choices:

–Solution 0: Ongoing studies will prove that the wake formula give an overestimate–Solution 1: Degrade * and Luminosity expectations at low E–Solution 2: Increase the vertex detector radius

The 22% number would be OK at 500 GeV CM, however, the effect scales as 1/Energy

At 90 GeV CM, will have A~ 7 (or A~ 3.9 with octupoles). Unacceptable.


Possible reduction of luminosity due to collimation

wakes

Assumed that for typical spoilers, A scales

as A ~ N / ( z1/2 gap3/2 ) or, equivalently, as

Assume that tolerable A is 0.7 (or 1.4), which gives 22% (or 72%) Y-jitter increase

Luminosity reduction at Z is 2.5 times (or 1.7 times)

For Rvx X 2, the reduction is 1.4 times (or none)

This assumes the tail folding Octupoles are ON (more optimistic case)

Ideal : Lumi ~

3/2VX

1/2z

*

2*

β Rσβγ

LNA


Vertex radius discussion*

Agreed that VX radius is, in certain extents, a free parameter that accelerator physicists can optimize

*) This discussion took place in a context of 500GeV CM. The low energy requirements need to be discussed again

From studies by Aaron Chou


Conclusion

• Performance of NLC BDS optics will allow almost equal luminosities in 1st and 2nd IR up to 1.3 TeV CM

• There are potential limitations at Z energy due to collimation wake fields, which need to be taken into account when detector parameters are to be chosen

Documents

NLC 1 st and 2 nd IR performance and balancing the accelerator and detector issues