Download Vacuum chamber stress analysis

Tagger and Vacuum Chamber
Design
Outline.
• Design considerations.
• Stresses and deformations.
• Mechanical assembly.
Design Considerations.
The basic tagger parameters are:
•Main beam energy = 12 GeV.
•Magnetic field = 1.5 T – 12 GeV radius of curvature = 26.7 m.
•Momentum range of analysed electrons = 0.6 to 9.0 GeV/c.
•Intrinsic average focal plane momentum resolution = 0.05% E 0 .
•Decision to use an iron based magnet of reasonable size
imposes a limit on the main beam bend angle of around 15
degrees.
Adopted design.
•Total main beam bend angle = 13.4 degrees.
•Total length of focal plane (25% to 90% of E o ) ~ 9 m.
The focal plane detector package is divided into two parts.
Set of 141 fixed scintillators spanning the full energy range with 0.5 % resolution.
Movable microscope of finely segmented counters with 0.1% resolution spanning the
coherent peak – tagged photon energies between 8.5 and 9 GeV for GlueX.
•Magnet configuration of two identical rectangular dipoles in series, in front of
which there is a quadrupole to optimise the focal plane vertical focussing – the
photon energies of interest to GlueX are analysed in the first magnet.
For each: Gap width = 3.0 cm.
Pole length = 3.1 m.
Weight = 36 tonnes – heaviest single yoke piece ~13 tonnes.
Coil power = 30 kW.
•A straight focal plane with optics which are not inferior to those for a single dipole
tagger.
Reasons for adopting a two rather than a single dipole
design.
•Single dipole is ~ twice the length ( 6.2 m) and twice the weight (~75 tonnes) of the
individual magnets in the two magnet configuration.
•Difficult to find suppliers of ~ 6.5 m lengths of high quality iron at a reasonable cost.
•Top and bottom yokes for the single magnet tagger each weigh ~26 tonnes which will
require heavy duty lifting equipment to assemble the magnet or undertake future
repairs or modifications.
•The long structure of a single dipole tagger will be awkward to manoeuvre during
installation.
•The smaller magnets can be made by more manufacturers and will probably be
cheaper.
•Budget prices from a magnet supplier for the dipoles/vacuum chamber/dipole support
stand are 13% less for the 2 magnet design.
•Building costs will be less for the two magnet option – cheaper crane or rigging costs,
smaller access doors etc.
Vacuum chamber design.
•Since the tagger is broad-band it analyses electron energies from 25% to 90% of Eo
which are focussed along a focal plane ~ 9 m in length.
•The structure of the vacuum chamber should not intercept any of the analysed
electrons, and the chamber should extend to within a few cm of the focal plane.
•The vacuum chamber should also allow the main electron beam to exit cleanly
from the spectrometer.
•A long (~12.5 m) relatively narrow (~0.8 m) chamber with no internal supports is
required.
•The design adopted uses the pole shoes of the dipole magnets as part of the vacuum
system. The vacuum chamber fits around the pole shoes. Vacuum seals are made
between a lip around each pole shoe and the top or bottom surfaces of the vacuum
chamber. Compressed rubber O-rings form the vacuum seals.
The two identical magnets tagger
Vacuum chamber
Magnet 2
Magnet 1
The vacuum force is around 70
tonnes, so the vacuum chamber
needs external support.
General view of the tagger showing the lay-out of the dipole
magnets, focal plane and a selection of electron trajectories.
1
1
1
The electron entrance angle :5.9 degrees
Main beam exit angle: 6.608 degrees
Main beam bending angle 13.4 degrees
The angle between the photon exit beam and the focal plane: 9.94
degrees
Vertical section through one of the dipole magnets
showing pole profile and coil geometry
1
•
•
•
•
•
•
•
•
Length: 3.09 m.
Width: 1.09 m.
Height:1.41m.
Weight: ~38 Tons
for one magnet.
Conductor area:
135 cm2.
Current: 144 A.
Magnetic field:
1.5 T.
Pole gap: 3 cm
Vacuum chamber
Top view
Right hand
side view
looking along
output flange
Pumping
port
Front 1view
1
Vacuum chamber sections AA` and BB`
Weld
O-ring
Groove
Compression
pad
Enlarged view of output flange
(The electron direction is out of the plane of the figure)
For compression pad screws
For compression fitting screws
Vacuum window compression pad
Bevelled edge
To manufacture the vacuum chamber:
a. Weld together complete assembly.
b. Skim those parts of the top and bottom surfaces used for the
vacuum seals to make them flat and parallel.
Main flange bolt hole
Stresses and Deformations.
For each magnet:
magnetic force between the poles is ~ 150 tonnes,
weight ~ 36 tonnes.
Magnet 2
Magnet 1
Vacuum Forces.
Total force on chamber~ 70 tonnes.
This is supported by:
Honeycomb strengthening of ~40 tonnes,
4 vertical struts from manet 2 of ~15 tonnes,
3 vertical struts from magnet 1 of ~ 10 tonnes.
Magnet stress calculation with magnetic, vacuum and weight
forces - (3 point support defines boundary condition).
3 point
supports
Magnet deformation calculation with magnetic, vacuum and weight forces.
(Maximum deformation in the pole gap is less than 0.21mm which is much
smaller than the O-ring compression of ~6mm for the two O-rings – the
uncompressed diam. of each o-ring is 10 mm)
3 point
supports
Vacuum chamber stress analysis - (for complete chamber).
1.
Stainless steel – walls 15mm, ribs 20mm*160mm.
Vacuum chamber stress analysis – (for complete chamber).
1. Stainless steel – walls 15mm, ribs 20mm*160mm .
Boundary condition:
gap between pole
shoes and vacuum
chamber side walls
allowed to vary by
0.1 mm.
Vacuum chamber stress analysis – (for complete chamber).
2. Aluminium – walls 15mm, ribs 20mm*160mm.
Stresses on both the
SS and Al chambers
approximately the
same.
Vacuum chamber stress analysis – (for complete chamber).
2. Aluminium.
Deformation of Al
chamber ~3 times
that for SS chamber.
Mechanical Assembly.
Vertical section showing the arrangement
for compressing the vacuum O-rings.
Rods connected between yoke and vacuum chamber used to apply
compression to the O-rings.
Rubber O-ring.
*
Vertical sections showing how O-ring compression is defined.
Back of vacuum chamber
Spacer
Compressed
O-ring
Bottom pole shoe
Vertical section showing how coils are
supported against magnetic forces.
Vertical sections showing brackets which
counteract the magnetic forces on lower coils.
Pads
.
Vertical section showing how the weights of the lower coils are supported.
(Upper coil weights supported by magnetic force brackets.)
Vertical sections showing lower coil weight support brackets.
Brackets
O-ring compression
along exit face.
Magnetic force and
weight of coils.
O-ring compression
along the back and
side walls of vacuum
chamber.
Sequence of brackets– outwith exit face.
Top pole shoe
Vacuum
chamber
Bottom
pole shoe
Bottom
yoke
Sequence of brackets– along an exit face for a top yoke.
Top yoke
Vertical rods are
equispaced.
Pole
shoe
Top surface of vacuum
chamber
View with coils added.
Support
arms
Top yoke
Vacuum
chamber
Top
coil
Top pole
shoe
Exit
flange
Bottom
coil
The Tagger and vacuum
chamber assembly procedure
will be described in one of the
following presentations.