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.
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