The Alpha Magnetic Spectrometer

1
Magnet Test Rig
In April we reported that the magnet had been
suspended inside the MATR
2
and that hydraulic, electronic, and
superconducting connections were being made.
3
Fixing the instrumentation wiring took longer
than anticipated
4
although we had additional help from colleagues
from Beijing.
5
Extensometers were mounted in the bore of the
magnet
6
to measure structural deformations.
7
The magnet test rig (MATR) was completed by

• Finishing the inner vacuum chamber (IVC)
• Finishing the 80 K radiation shield
• Finishing the 5 K radiation shield
• Finishing the outer vacuum case (OVC).

8
Operation of the MATR.
9
Cool down to 100 K.
10
Cool down to 20 K.
11
Cool down to 4.2 K.
12
Operation at 1.8 K.
13
Details of the IVC.
14
External leak test showed the IVC was leak
tight. But on assembly, the IVC was leaking to
the OVC. The system therefore had to be
disassembled to try to find the leak.
15
Internal leak test on the IVC revealed a small
leak on the flange. This was improved by
overloading the bolts
16
then the cryostat was reassembled.
17
Cool down started on 18 June when the liquid
nitrogen tank was filled.
18
Initial cool down by radiation from the 80 K
shield only.
19
Cool down to 100 K using the liquid nitrogen heat
exchanger (MATR sensors).
20
Cool down to 100 K using the liquid nitrogen heat
exchanger (magnet sensors).
21
Cool down of the IVC to 20 K by direct injection
of liquid helium.
22
Cool down of the magnet to 4.2 K by filling the
liquid helium vessel.
23
Persistent switch test.
24
Cool down of the magnet to 1.8 K by pumping on
the liquid helium vessel.
25
Dipole quench heater test pulse (zero current).
26
Charging to 100 A (persistent switch).
27
Charging to 100 A (magnet temperatures).
28
Deliberate quench from 100 A.
29
Re-cool after the 100 A quench.
30
Charging to 230 A (persistent switch).
31
Charging to 230 A (stray field measurement).
32
Charging to 230 A (extensometer measurement).
33
Deliberate quench from 230 A.
34
Deliberate quench from 230 A.
35
Deliberate quench from 230 A (helium level).
36
After the quench from 230 A, a number of the
voltage taps on the magnet were open circuit.
Without these taps the quench detector is
inoperable, so it is not possible to charge the
magnet to high currents without risk of damage
until the high voltage wiring is repaired. To
check that the magnet was NOT damaged, a further
charge to 50 A was carried out.
37
Re-cool to 4.2 K with liquid helium.
38
Charge to 50 A at 4.2 K. No change in the magnet
behaviour.
39
Warming up to room temperature to repair the
high-voltage wiring.
40
Summary (1) The helium tank has been cleaned to
the level necessary for flight. All the
components required to continue with the leak
testing have been installed.
41
Summary (2) The procedures for covering the
helium tank with Cryocoat have been fully
developed. The Cryocoat material is in stock at
Culham.
42
Summary (3) The magnet has been tested to 50 of
its nominal field, and set persistent (at a lower
current). Repairs are required to the high
voltage wiring in the test rig, then testing at
higher fields will continue.