Transcript BABAR Drift Chamber Design and Construction Annecy, Carleton/CRPP, Colorado, Colorado State, LBNL, Maryland, McGill, MIT, Montreal, INFN Padova, INFN Pisa, Princeton, INFN Rome,

BABAR Drift Chamber
Design and Construction
Annecy, Carleton/CRPP, Colorado, Colorado State, LBNL, Maryland, McGill, MIT, Montreal, INFN Padova,
INFN Pisa, Princeton, INFN Rome, UC San Diego, UC Santa Cruz, SLAC, TRIUMF, UBC, and Victoria
Overhead view of
clean room showing
parallel operation
of two stringing
teams, each with
two human
operators and a
transport robot
Operators thread
wire on needles for
robot transport,
receive needle at far
end, and fasten
wire by crimping
Close-up of rear endplate after completion of 5
superlayers (above) showing dense pattern of
plastic and metal feedthroughs and crimp pin for
holding wire. Typical cell shown in cross section
below. Sense wires are at 1960V, requiring 6mmdiameter plastic insulator for feedthrough. Field
wires are at ground potential.
Partially installed wire field, showing one of two
industrial robots used to transport wire between
endplates. With no human traffic, inner clean room
between endplates maintained below class 1000.
The pattern of reflections in the photographs occur
due to the superlayer pattern with wires having the
same small-angle stereo direction.
24mm Al Endplate
Drift System Design
40-layer small-cell chamber
7104 drift cells formed from hexagonal field wire pattern
80 & 120 mm Aluminum field wires and 20 mm tungsten sense wires
Layers organized into superlayers
Wire directions in axial-u-v pattern
Allows fast Level 1 trigger based on segments
80:20 helium:isobutane gas mixture
After the
completion of
stringing, a small
number of wires
was replaced with
chamber swung to
vertical position
Low-mass gas to minimize multiple scattering
Small Lorentz angle results in simple t-to-d relation
Mechanical Structure
Thin aluminum endplates
30K precision holes locate feedthroughs with crimp pins
Forward endplate reduced to 12 mm thickness in acceptance region
Outer cylinder
installed in two
halves and load
transferred from
fixtures
Load-bearing cylindrical walls
1-mm thick beryllium inner wall (40% load)
Nomex-carbon fiber composite outer wall assembled in two halves
Beryllium
inner wall
Assembly of endplates in stringing fixtures.
Deflection studies under simulated full load
(above) and spider structure for holding wire
load during stringing (below)
Thin Al
forward
endplate
Precision drilling
of feedthrough
holes achieved
25mm RMS
position accuracy,
as determined by
quality assurance
measurements
Superlayer
grouping of
drift layers
Typical Drift Cell (1.2x1.8cm)
with 50 ns isochrones
Installation of
the chamber
into BABAR as
seen from the
forward (right)
and rear ends
of the detector
(below)
12mm Al Endplate