1. The Quench Detection-Wire-Feedthrough Plug-In of W7-X
Max-Planck-Institut für Plasmaphysik, EURATOM Association
The Quench Detection-Wire-Feedthrough Plug-In of W7-X
Kerstin Rummel, Detlef Rademann, Olaf Volzke
Max-Planck-Institut für Plasmaphysik, Euratom Association, Teilinstitut Greifswald, Wendelsteinstr. 1, D Greifswald, Germany
Introduction and requirements
Assembly
A test installation at the OV with a full-size prototype of a QD-Plug-in including making and testing the connection of QDD-wires to QD-wires was successfully carried out to qualify the assembly procedure and train the assembly team.
Special attention during this test was given to the support and handling of the 424 kg dome extension including QD-plug-in as well as the controlled overlap of MLI during alignment of the dome extension to the dome.
Now the assembly at W7-X has been started. Two QD-Plug-ins for the first module 5 are pre-assembled. The installation of these QD-Plug-ins on the QD-domes is underway.
For continuous on-line monitoring of the superconducting state 1624 Quench Detection-wires (QD-wires) are connected at the joints of the coils and the bus bars. The wires are bundled to wire cables and wire cables. The electrical potential of these wires must be fed through the Outer Vessel (OV) to the Quench Detection Units. Therefore, 10 QD-domes, i.e. two per module are provided on the OV. The QD-domes are differently located and oriented.
Several constraints require a complex feedthrough system design:
maximum allowed integral helium leak-rate of one QD-dome 10-8 mbar l/s.
maximum heat load to the thermal shield of the OV 140 W
electrical insulation of the electrical feedthroughs for a nominal voltage to ground of 6 kV DC and a related test voltage of 13 kV DC under conditions close to the Paschen minimum (Paschen test)
Pre-assembly procedure of the QD-plug-in
Assembly procedure of the QD-plug-in on the QD-dome
Mounting the sockets in the lid
Paschen test at 10kV and leak test of the sockets
Mounting of plug-in-tube , radiation shied and base plate (fig. 11, 12)
Wrapping of MLI around the plug-in-tube
Inserting the QD-plug-in in the dome extension
Leak-test of the flange connection between lid and dome extension
Fixing the QD-plug-in on the supports of the QD-dome (fig. 13, 14)
Mounting of QD-connectors (fig. 15)
Paschen test of each single connector at 5 kV
Installation of screen and strain relief at the connector
Thermal connection of base plate to the thermal shield of OV
Inserting the QD-plug-in in the dome extension
Leak-test of the flange connections
Design of the Quench Detection-Wire-Feedthrough Plug-in (QD-plug-in)
Fig. 1. QD-domes of module 1:
Inner diameter: 800 mm
Average height: 500 mm
Thermal Shield (70 K)
Outer vessel
MLI
31 (32) x
QDD-cable
Thermal
Connection
connector
Inside cryostat
31 (32) x assembled socket
Outside cryostat
Dome extension
QD-dome
Radiation shield
Plug-in-tube
4 ( 6)
Lid
Base plate
QD-cable tray
QD-cable
Strain relief
Flange connection
Bronze sheet
Copper plate
Electrical feedthroughs in the lid
Nineteen 6-wire cables and twelve 4-wire cables respectively thirteen 4-wire per dome
For commonly used weldable ceramic feedthroughs with 1 or 2 pins there is not enough available space on the lid
several commercial types of multi-pin feedthroughs were tested
7- and 4-pin female sockets from the company LEMO were chosen (fig. 3)
Fig QD-Plug-in installed on the QD-dome
Fig View on the lid
Fig Pre-assembled QD-plug-in without dome extension
Fig. 3. Electrical socket
Fig. 4. Cross section of a socket
Fig. 5. Sockets in the lid (view from vacuum side)
Design of QD-plug-in allows the replacement of O-rings
Sockets were assembled with 1.4 m long QDD-cables by the Lemo
To obtain the high voltage characteristics at different pressures the soldered pins to the wires are potted in Stycast (fig. 4)
Not connected seventh pin is connected to one of the other pins
After mounting the sockets in the lid Paschen tests and leak-tests are performed (fig. 5)
Fig QD-plug-in wrapped with MLI
Fig Installation of QD connectors
Electrical connectors
Fig. 2. QD-Plug-in
Electrical tests
Small, reliable, applicable for 4 and 6-wire cables
and easy to install
Consists of three pieces made of G10 and hoses
of polyethylene (fig. 6)
Hoses of PE protect the wires against too strong
bending at the edge of G10
For the 4-wire cables two holes in the center piece
will be closed by epoxy
Parts will be glued together and put over the wires (fig. 7-9)
Soldering point will be placed in the middle of the separator
Thermal losses
Filling Stycast in the seventh hole in the center (fig. 10)
Grooves in the center piece guarantee the flow of Stycast to the other holes
The level of Stycast in all seven holes and between the separator and sleeve rise uniformly
Numerous connectors were mechanically overstressed by bending the wires and then thermal cycled. All qualification samples have been passed successfully the Paschen test at 13 KV.
To proof the electrical characteristic small chambers were designed to make a Paschen-test for each single QD-connector (fig. 16)
They makes it possible to perform high voltage test under different air and Helium pressures on-site.
Test voltage of 5 kV, allowed leakage current 5 µA
During the Paschen test the work on the W7-X must be stopped
simultaneous tests of much as possible QD-connectors are required
simultaneous tests of
the QD connectors of one
electrical circuit for both
QD-Plug-ins
Only 7 tests compared to
64 tests with one chamber
The design of the QD-plug-in (fig. 2) was mainly driven by the thermal losses to the thermal shield of the cryostat.
Thermal radiation:
depends on the surfaces, emissivity and the temperature distribution along the plug-in-tube.
30 W
Thermal conduction:
depends on the cross section of conductor and shield of the 1.4 long QD-wires and on the 600 mm long stainless steel tube.
202 W
Copper of the conductor was replaced by constantan
Copper of the shield was replaced by stainless steel
Thermal contact to the base plate is minimized by using thermal insulated strain reliefs
134 W
groove
groove
center piece
separator
sleeve
Fig. 8. Assembly of QD-connector
Fig. 9. Soldering of wires
Fig Chamber for Paschen test
Fig. 7. QD-connector
Fig Filling of Stycast
Fig. 6. Parts of QD-connector
MT-22, Marseille, France, September 2011