1. S. Feher MICE Magnet Readiness Review RAL, June 28th, 2016
SS QPS
S. Feher
MICE Magnet Readiness Review
RAL, June 28th, 2016

2. Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)
Outline
Status of SS electrical circuits
Operational Requirements
Modified magnet protection scheme and operation of the Power Supplies
Conclusions
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

3. Status of SS Electrical Circuit
SSD
Known Damage:
LTS lead between the HTS lead and the M1 coil is open
Internal diode pack connection is open for M1
At one side of the M1 LTS lead is shorted to ground
The two LTS leads for M1 are connected to each other; finite resistance
M2 coil is connected to M1 coil therefore connected to ground with ~ 1.3 kΩ resistance
Possible Future Degradations:
M2 ground connection becomes more solid; less resistance
Physical damage to M2 is worse than we currently believe
He-to-Vacuum leak occurs at M1/M2 feedthrough (between the cold mass and insulating vacuum)
SSU
No Known Issues
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

4. Status of SSD Electrical Circuit
Cold Mass Shell
LTSd
LTSa
LTSb
HTS R1
LTSc
LTS/N
PSU
External Diode
Pack
Internal Diode
Pack M1 R1 R2
Energy Absorber
LTSc
LTS/N
HTS
LTSa
LTSb
LTSd
Feedthroughs
LTSd
LTSa
LTSb
HTS R1
LTSc
LTS/N
PSU
External Diode
Pack
Internal Diode
Pack M2 R1 R2
Energy Absorber
LTSc
LTS/N
HTS
LTSa
LTSb
LTSd
Vacuum Shell
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

5. Operational Requirements
By design:
Powering
Current measurement accuracy 2x10-4 (new transductors being installed)
Fail safe powering; no harm to equipment (Magnet, leads, PS itself) and personnel
Magnet circuit protection
Coils are self protected; if the coil quenches it is sufficient to turn off the PS
HTS and LTS leads during quench: keep the hot spot temperature below 300 K
Coils hot spot temperature during quench less then 120 K
Magnet peak voltage relative to ground below 1600 V; for ECE circuit internal diode pack is needed to fulfill this requirement
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

6. Operational Requirements
Practical reasons:
Safe cold HV withstand to ground values measured for SSU and SSD were ~ 150 V ( breaks down ~ 200 V)
Localized at the feedthrough (air-to-vacuum) region
HTS lead voltage less than 3 mV
QPS HTS lead quench detection threshold value is set at 1 mV
Keep the LTS lead voltages during quench as low as possible
Apply low detection threshold values to keep the hot spot temperature as low as possible
No clear understanding (as built) what are the lead dimensions and/or cooling conditions, consequently quench integral value limits are not known.
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

7. Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)
QP Modifications
Existing QPS was reconfigured:
Introduced dI/dt signals for all the magnet currents
Every magnet current is measured with transductors
The dI/dt signal is obtained with digital signal processing of the magnet current signal
Quench detection of the M1 and M2 magnets are using Wcoil – const * dI/dt signals with low threshold values; the goal is to be at least less than 100 mV
Separate protection processor is used for LTS and HTS leads/magnet circuit
Second FPGA card provides additional trigger to open the external diode packs for each magnet circuit separately
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

8. Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)
Coil Protection
SSU
M1 and M2 is using Wcoil – const * dI/dt signals
E1-C-E2 is using Half – Half bucked half coil signals
SSD
M2 is using Wcoil – const * dI/dt signals
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

9. PS system Modifications
Redundant contactors were implemented for the main switches that open when quench is detected
External diode packs, dump resistors and additional contactors were procured and installed
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

10. Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

11. Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

12. Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)
END
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

13. Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)
Protection Issues
Cold Mass Shell
LTSd
LTSa
LTSb
HTS R1
LTSc
LTS/N
PSU
External Diode
Pack
Internal Diode
Pack
Feedthroughs R1 R2
Energy Absorber
LTSc
LTS/N
HTS
LTSa
LTSb
LTSd
Vacuum Shell
Direct protection of LTSa and LTSb segments with V-taps
LTSd is only protected with the magnet; low threshold settings are required to lower the hot spot temperature
LTS/N easily can be overheated
Internal diode/resistor pack does not extract enough energy
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

14. Proposed Operational Configuration
Cold Mass Shell
LTSd
LTSa
LTSb
HTS R1
LTSc
LTS/N
PSU
External Diode
Pack
Internal Diode
Pack
Feedthroughs R1 R2
Energy Absorber
LTSc
LTS/N
HTS
LTSa
LTSb
LTSd
Vacuum Shell
Carefully selected External diode pack (M1 and M2 ~ 5 V, for ECE ~ 10 V), and R2 (0.5 Ω)
Contactor for the External diode pack is open; not to interfere with PS operation
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

15. Different Quench and Failure Scenarios
Cold Mass Shell
LTSd
LTSa
LTSb
HTS R1
LTSc
LTS/N
PSU
External Diode
Pack
Internal Diode
Pack
Feedthroughs R1 R2
Energy Absorber
LTSc
LTS/N
HTS
LTSa
LTSb
LTSd
Vacuum Shell
Magnet quench
HTS lead quench
LTSa or LTSb quench
LTSd quench
Ground fault
PS malfunction
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

16. Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)
Magnet Quench
Cold Mass Shell
LTSd
LTSa
LTSb
HTS R1
LTSc
LTS/N
PSU
External Diode
Pack
Internal Diode
Pack
Feedthroughs R1 R2
Energy Absorber
LTSc
LTS/N
HTS
LTSa
LTSb
LTSd
Vacuum Shell
Magnet quench is detected
PS Contactors open for all circuits: M1 (for SSD M1 is floating), M2, ECE
External diode pack contactors close
Diode Pack is sized to keep the internal diode pack open (M1 and M2 ~ 5 V, for ECE ~ 10 V); current is circulated through the external diode pack
During magnet quench HTS or LTSa or LTSb quench occurs
External diode pack contactor opens for the particular circuit
R2 resistor is sized (0.5 Ω) to keep the max voltage below 150 V in a case LTSc or LTS/N opens
Ground fault occurs during quench
No additional action – no influence on maximum external voltage
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

17. HTS or LTSa or LTSb Quenches
Cold Mass Shell
LTSd
LTSa
LTSb
HTS R1
LTSc
LTS/N
PSU
External Diode
Pack
Internal Diode
Pack
Feedthroughs R1 R2
Energy Absorber
LTSc
LTS/N
HTS
LTSa
LTSb
LTSd
Vacuum Shell
HTS or LTSa or LTSb quench is detected
PS Contactors open for all circuits: M1 (for SSD M1 is floating), M2, ECE
External diode pack contactor remain open for the quenching circuit the rest of them will be closed – this requires major modifications of the QPS; more channels needed
R2 resistor is sized to keep the max voltage below 150 V in case LTSc or LTS/N opens
During HTS or LTSa or LTSb quench the magnet also quenches
No additional action – the current decay will be faster
Ground fault occurs during quench
No additional action – no influence on maximum external voltage
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

18. Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)
LTSd Quenches
Cold Mass Shell
LTSd
LTSa
LTSb
HTS R1
LTSc
LTS/N
PSU
External Diode
Pack
Internal Diode
Pack
Feedthroughs R1 R2
Energy Absorber
LTSc
LTS/N
HTS
LTSa
LTSb
LTSd
Vacuum Shell
LTSd quench is detected
This quench can not be separated from a magnet quench – very low quench detection threshold is required; dI/dt based quench detection system for M1 & M2 and significantly lower threshold for the ECE half coil based detection system (more filtering) are needed
PS Contactors open for all circuits: M1 (for SSD M1 is floating), M2, ECE
External diode pack contactor remain open for the quenching circuit the rest of them will be closed – R2 resistor is sized to keep the max voltage below 150 V in case LTSc or LTS/N opens
During LTSd quench the magnet also quenches
No additional action – the current decay will be faster
Ground fault occurs during quench
No additional action – no influence on the maximum external voltage
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

19. Ground Fault or PS Malfunction
Cold Mass Shell
LTSd
LTSa
LTSb
HTS R1
LTSc
LTS/N
PSU
External Diode
Pack
Internal Diode
Pack
Feedthroughs R1 R2
Energy Absorber
LTSc
LTS/N
HTS
LTSa
LTSb
LTSd
Vacuum Shell
Ground fault or PS malfunction
PS Contactors open for all circuits: M1 (for SSD M1 is floating), M2, ECE
External diode pack contactors close
Diode Pack is sized to keep the internal diode pack closed (M1 and M2 ~ 5 V, for ECE ~ 10 V); current is circulated through the external diode pack
During ground fault or PS malfunction HTS or LTSa or LTSb or LTSd quench occurs
External diode pack contactor opens for the particular circuit
R2 resistor is sized (0.5 Ω) to keep the max voltage below 150 V in a case LTSc or LTS/N opens
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

20. New SSD QPS Configuration
For the newly designed SSD cold mass we will implement several changes:
Every coil will have two center V-taps (one primary and one redundant)
All coils detection circuit will utilize Half Coil 1 – Half coil 2 signal with low threshold values
There will be separate V-taps for the LTS and HTS segments
At every V-tap locations will be two V-taps (one primary and one redundant)
External dump system will be used
Dump resistor will be adjusted to the HV withstand values
Every coil will have two heaters (one primary and one redundant)
Once LTS, HTS or magnet quench is detected the heaters will be energized to initiate a magnet quench
For ground fault and PS failure cases slow ramp down will be initiated
External diode pack will be used
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)

21. Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)
Conclusions
The proposed PS and QPS configuration will minimize the risk of loosing the magnet circuits
Requires major modifications of the QPS
June 28, 2016
Sandor Feher | MICE Magnet Rediness Review (Ral, June 28, 2016)