1. ECR on pole order of the HL-LHC IT circuit and resulting implications
H. Prin
Thursday 6th June 77th HL-LHC Technical Coordination Committee

2. ECR description LHC-LMQXFE-EC-0001 EDMS 2150746
To eliminate additional splices in the Q1/3 cold masses and to be able to perform vertical tests of MQXFA magnets at BNL, the pole order of the quadrupole magnets is proposed to be revised. To keep the field direction for the entire inner triplet as it was before this proposed change, the connection scheme on Q2 magnets as well as the main circuit and instrumentation leads connection to their power supply have to be revised.
Presented in the MCF in April the 16th

3. Reason for change
The leads (labelled as A and B) of the MQXFA magnets located on the lead end of the magnet relative to each other has been developed as part of the magnet design and it has been frozen after the AUP project passed the DOE review for starting the construction of the magnets. In parallel, the BNL Vertical Test Facility has been successfully developed and started testing these magnets: from the early experience, it was realized that in order to test magnets one needs to cut Lead A to a shorter length. For the current electrical scheme this is the lead that should be directly exiting from the cold mass to the interconnect. Consequently, this is the lead long enough to prevent making additional splices. Since the space between the end cover and the magnet is tight, making an additional splice in this area and at the same time keeping functional the expansion loop is very difficult. If the electrical scheme is changed as proposed, the longer lead (Lead B) will be exiting directly to the interconnect. Making the change at the magnet side or at the Vertical Magnet Test Facility side is possible but has significant schedule and cost impact compared to changing the electrical scheme.

4. Reason for change with pictures Pole sequence proposal for Q1 and Q3
Feb the 5th 2019, proposal to exchange the MQXFA lead A and B
Courtesy of S. Feher
In Q1 and Q3 the sequence becomes:
MQXFA.A MQXFA.B
iP3o-oP2i-oP4i-iP1o-oP1i-iP4o-iP2o-oP3i

5. Consequences for Q2
Inverting the current direction in the MQXFA magnets that are located in Q1/3 implies to reverse the current direction in the MQXFB magnets located in the Q2 magnets as well.
The leads of the MQXFB magnets have to be re-arranged to circulate the current in these magnets in the opposite direction. Lead A (from pole 1) has to be routed to the M2N interconnection nozzle and lead B (from pole 3) has be connected to the internal busbar.
The cold protection diodes (if there will be any) direction, shall be reversed.

6. Impact on Cost, Schedule & Performance
Except circuit drawings and scheme modification, no major cost is identified due to this change request.
The initial work on the busbars routing has to be revised, since it is very preliminary no major impact on the schedule is foreseen.
Introducing the proposed modifications of the electrical scheme allows to eliminate two additional splices per Cold Mass that are buried inside the Cold Mass of Q1/3 and one in the Q2. Besides lowering the heat load and improving the performance of the cryo-assembly the risk associated with making faulty splice joints is also significantly reduced.

7. Impact on other WPs
The 18kA and 2kA trim circuits polarities shall be reversed.
CLIQ and QH power supplies must be connected according to updated electrical scheme related to the IP side configuration.

8. Actions to be carried out if ECR is accepted
The Drawing LHCLMQXF_E0001 is updated, approval was launched in parallel in EDMS:
LHC-LMQXFE-DF-0001 v.2 ( ).
The HL-LHC Circuits Layouts and drawing shall also be updated in the Magnet Circuit Forum webpages.
The CLIQ and quench heaters polarities shall be checked according to the new baseline
Regarding the implications on the IT circuit failure scenarios, new simulations should be performed as the voltage-to-ground will change. These modifications imply that the electrical circuit shall be considered as new compared to the present one.

9. Summary Reasons for change clearly are identified
Impacts on the Q2 cold mass were considered and feasibility study completed
6 splices could be eliminated from the main circuit as well as 18 V-Taps
18kA main circuit are 2kA trim ones polarities shall be reversed
CLIQ and QH power supplies must be connected accordingly
Cold diodes direction shall be reversed
No major cost identified
Electrical schemes and drawings should be revised from both sides of the IP
Additional simulations needed to reflect the voltage to ground changes

10. Spare Slides

11. MQXFB connection box study according to the new pole sequence proposal (iP3o-oP2i-oP4i-iP1o)
Splice busbar/lead iP3 (fixed point)
Instrumentation barrel connection box
CLIQ leads routing
Connected busbar
Magnet lead P1o i o P1 P2 P4 P3
Passing through busbar