1. Testing and installation of prototype diode insulation system in MB2950 Florian Meuter, 3rd Meeting on Diode Consolidation during LS2,

2. Outline Testing of insulation pieces in liquid nitrogen
Installation of insulation insert in MB2950
Installation of insulation plates in MB2950

3. Quenching of insulation insert in liquid nitrogen
Recent insulation insert design changes:
Reduced outer diameter to have more tolerances in case we find non circular diode containers (reviewer recommendation RT13)
Reduced surface area exposed to possible He pressure differences
Added ribs for improved mechanical properties
For testing its cryogenic compatibility the insulation insert is mounted with two M6 screws onto a stainless steel plate.
This assembly has been quenched five times in liquid nitrogen and afterwards warmed up in ambient air.

4. Formation of small cracks in insert made of ACCURA 25
After five quenching cycles in liquid nitrogen the insulation insert 3D printed from ACCURA 25 pure resin has small cracks.
The same insert geometry made of ULTEM 9085 is under production (expected delivery date ).
After five quenching cycles no cracks were found in an earlier version of an insulation insert made of ULTEM
cracks
Insulation insert made of ULTEM 9085 after quenching five times in liquid nitrogen.
Insulation insert made of ACCURA 25. After five times quenching in liquid nitrogen several small cracks are observed.

5. Setup for mechanical testing of the insulation insert
The setup for mechanical testing of insulation inserts in ambient air and in liquid nitrogen has been assembled and will be commissioned in the coming weeks.
The load is applied on the insulation insert using a M12 bolt and the force is monitored with the integrated load cell.
Photograph of the test setup with insulation insert.
CAD model of the test setup.

6. Insulation insert next steps
Define a procedure for the screw fixation (e.g. tightening torque, screw locking).
Develop alternative design that covers the diode venting hole (e.g. with grid that prevents metal chips to enter the diode venting hole or a “chicane”).
Design optimization by finite element simulations of relevant load cases.
Perform mechanical testing in ambient air and in liquid nitrogen.
Select material of choice for series production (e.g. ULTEM 1000 or Ryton) and order prototype pieces (ULTEM 9085 is used for first prototypes because we can get the pieces rather quickly).
Test final insulation insert geometry by mechanical testing in liquid nitrogen and in further magnet cold tests and mock-up tests.

7. Installation of insulation plates in MB2950
The diode busbars of MB2950 are severely deformed and misaligned in the T-tube.
The fibre glass insulation of the busbar is impregnated with epoxy resin which significantly increases the busbar cross-section.
The half moon insulation plates had to be strongly modified to allow installation on the half moon splices of MB2950.
An additional Kapton foil is placed under the insulation plates to fully cover the splice areas that are not covered by the plate.
Araldite 2011 epoxy will be applied to electrically insulate the metallic screws in MB2950. For future installations electrically insulating screws will be tested (reviewer recommendation RT11).
Insulation plates have to be modified to fit the significantly larger busbar cross section caused by the fiber glass insulation.

8. Different insulation plate types
In order to accommodate for the various bus bar cross sections and to enable installation, the original insulation plate cutout needs to be increased.
Alternative insulation plate geometries have been designed and are being tested.
(b)
(c)
(a)
(d)
(e)
(f)
(a) Original design of the insulation plate, (b) insulation plate with holes to accommodate for extending bolts, (c) insulation plate made of two parts and (d) three parts. (e) Insulation plate with enlarged busbar cutout to be installable on the left half-moon splice of MB2950 and (f) Kapton foil to be placed under the insulation plate as additional insulation to avoid remaining blank splice surfaces.