Backgrounds in the NLC BDS

Backgrounds in the NLC BDS


ISG9

December 10
–

13 2002

Takashi Maruyama


SLAC

Background and collimation

•
Major source of detector background:


Halo particles hitting beamline components generate muons and
low energy particles.


Halo particles generate sync. radiations that hit VXD.


Beam
-
gas scattering generates low energy particles.

•
Collimate Halo particles:


Spoilers and Absorbers


Collimation depth
–

(
n
x
s

,
n
y
s
y
)


Reduce halo size using Octupoles

•
What is Halo, and How much:


Drozhdin’s 1/x
-
1/y model


Flat distribution with 50
s
x
,50
s
x
’,200
s
y
,200
s
y
’,3%
D
E/E


Pencil beam hitting SP1


Calculated halo ~10
-
6
, but design collimation for 10
-
3
.



2001 Collimation System & FF integrated design

New scheme of the Collimation Section and Final Focus with ODs

Energy

collimation

Betatron

collimation

Final Focus

IP FD IP FD IP

FD

S SA SA SA A

A

FD

A

Final Focus

collimation

A

IP

Octupole Doublets

NLC Beam Delivery Section in Geant 3

1480 m

295 cm

sp1

sp2

a2

sp3

a3

sp4

a4

sp5

a5

E
-
slit

FF Collimators

TRANSPORT lattice

Magnets (bands,quads,

sexts, octs)

location, orientation,

length, field strength,

aperture

Geant 3

Spoilers and Absorbers

IP

Muon Backgrounds from Halo Collimators

No Big Bend, Latest Collimation & Short FF

If Halo = 10
-
6
, no need to do anything

If Halo = 10
-
3

and experiment
requires

<1 muon per 10
12

e
-

add
magnetized tunnel filling shielding

Reality probably in between

18m & 9m
Magnetized
steel spoilers


Betatron

Betatron

Cleanup

Energy

FF

250 GeV/beam Muon Endcap Background

Engineer for
10
-
3

Halo

Bunch
Train
=10
12


Calculated
Halo is 10
-
6

Collimation

Efficiency 10
5


LCD Detector in GEANT3/FLUKA

GEANT3: e+/e
-

and
g
=
扡捫杲潵b摳
=
䙌F䭁:
=
=
乥畴牯rs
=

NLC Detector Masking

Plan View w 20mrad X
-
angle

LD

–

3 Tesla

SD

–

5 Tesla

32 mrad

30 mrad

R=1 cm

Apertures: 1 cm beampipe at the IP


1 cm at Z =
-
350 cm

VXD Hits from 250 GeV e
-

hitting QD0

250 GeV e
-

e
-
, e+

QD0

z

Synchrotron radiations

FF doublet aperture 1 cm

bends

quads

Photons from quads

Photons from bends

Sync. Radiation vs.
s
IP

n
y

n
x

cm

x
IP

y
IP



Track particle with n•
s

backward


from IP to AB10.




Track particle to IP and generate


sync. radiations
.



=
Find sync. radiation edge


as a function of (nx, ny).


nx = 18.5


x
+
, 17.2


x
-


ny = 50.9


y




Find AB10 and AB9 apertures


as a function of (nx, ny)


Sync. radiation at z =
-
350 cm

n
x

n
y

x

y

Apertures at AB10 & AB9

AB10

AB9

AB10

AB9

x

y

n
x

n
y

n
x

= 16.2


x+

nx

= 16.8


x
-

ny

= 41.6


y

Spoiler/Absorber Scattering

Spoilers/Absorbers Settings for NO OCT

Half apertures

X Y (um)


s
x

s
y

Sp1 ~ SP4 settings with OCT x2.5

ESP 0.5 X0 ~x5 beamloss

*

*

*

*
TRC


6500


3900


8000

Synchrotron Radiation and Collimation Depth

1) x’ < 570

rad =
19

x 30.3

rad y’ < 1420

rad =
52

x 27.3

牡r
=
=
2) x’ < 520

rad =
17

x 30.3

rad Y’ < 1120

rad =
41

x 27.3

牡r
=
䍲C瑥物愺t乯⁰桯N潮猠桩琠删㸠ㄠ捭=慴‱==z‽=〠捭=潲o㈩2z=㴠㌵〠捭
=
x

y

Halo Model

X’

X
(cm)

Y
(cm)

Y’

10
-
5

y
(cm)

x
(cm)


1/x and 1/y density over


A
x

= (6
–

16)
s
x

and


Ay = (24
–

73)
s
y




E/E = 1% (Gaussian)



Halo rate 10
-
3

Particle loss distribution

Z (m)

OCT
-
OFF

OCT
-
ON

42% to IP

82% to IP

ESP

EAB

AB10

AB7

DP2

Particle distributions at FF absorbers.

AB10

AB9

AB7

DP1

DP2

y is OK, but x is tight.

Integral Particle Loss Distribution

Sync. Radiations at IP

X (cm)

Y

X (cm)

Log10(E) (GeV)

Quad

Bend

Ng=7
.3 Ne
-

<E
g
>=4.8 MeV

Hit 1 cm

42% to IP

50
s
x
,50
s
x
’,200
s
y
,200
s
y
’,3%
D
E/E

OCT
-
OFF

1/x
–

1/y

FLAT

Z (m)

ESP

EAB

AB10

AB7

FLAT Halo

42% to IP

0.6% to IP

Integral Particle Loss Distribution

ESP

EAB

Transmission rate through E
-
slit and beam
-
loss in FF

OCT
-
OFF

OCT
-
ON

Pencil beam hitting SP1

Summary

•
NLC BDS and collimation system are studied using
Geant 3.

•
FF absorbers are set so that no sync. radiations
hit the detector apertures.

•
Assuming 10
-
3

halo, the particle loss is < 10
-
8

in FF
and the muon background is tolerable.

•
Octuples allow x2.5 looser spoiler settings.

•
OCT
-
OFF settings are well optimized, but OCT
-
ON settings need further optimization.