1. MQXFS1e – PH-to-Coil hipot tests
S. Stoynev and G. Chlachidze.
AUP
20 March 2019

2. MQXFS1 at FNAL
MQXFS1 - the first 150 mm aperture, 1.5 m long Nb3Sn quadrupole within the CERN and LARP collaboration
Coils fabricated by CERN (#103 and #104) and LARP (#3 and #5)
Five tests performed since 2016
MQXFS1a: Training, mag. measurements, PH tests,
energy extraction
MQXFS1b: (high azimuthal pre-stress) Training,
mag. measurements, CLIQ and heater tests
MQXFS1c: (high axial pre-stress) Training,
MQXFS1d: (welded SS shell test ) Training,
mag. measurements
MQXFS1e: (Through busbar test) Magnet training,
mag. measurements, spot heater tests
MQXFS1d test preparations

3. MQXFS1 quench/trip history
119 spontaneous quenches
230 provoked quenches and trips (above or equal to 1 kA)
48 unintended trips (above or equal to 1 kA)
Total of 8 thermal cycles (not counting the latest one for the hi-potting tests).
Training history (20 A/s ramps)

4. MQXFS1 Outer Layer Heaters
Heaters were fired in about 397 quenches and trips
Only in some of them (~30) heaters were delayed up to 1 s
Due to limited number of HFUs (power) not all heater strips were included in the magnet protection
Peak power density in OL heaters varied between up to 200 W/cm2
PH to coil Insulation: 50 um of Polyimide, plus Cable insulation um of fiber glass, all impregnated in CTD-101k
CERN coils
LARP coils

5. Goals of the hi-pot test
Verify heater to coil insulation soundness after the series of cold tests
OL PH-to-coil hi-potting tests at 75 K, 150 K and room temperature in the helium gas
Gradually decreasing the breakdown voltage in GHe
Providing different safety margins (see V. Marinozzi’s presentation)
If the polyimide insulation (Kapton layer) under the heater is cracked, the minimum distance between the coil and heaters could be as low as 0.2 mm
75K GHe 1 bar
104
275K GHe 1 bar
103
102
102

6. Test Preparations/Connections
Hi-potting tests in GHe never have been done above 1 kV at VMTF
All “weak” points identified, main concern was the
current limiting resistors
All voltage tap/SG/heater wirings were disconnected
Eliminating the current limiting resistors
All connectors, terminals were insulated
Magnet leads also were disconnected from
the main power leads
Condensation on copper flags makes hi-potting difficult
CLIQ leads (3) allow to bypass the resistor boards
Part of the feedthrough in the dewar not potted
CLIQ leads used for heater and coil connections
The CLIQ lead from the magnet connected to CL2
OL heaters (8 strips) in coils 3 & 103 connected to CL3
OL heaters (8 strips) in coils 5 & 104 connected to CL1

7. Hi-pot Tests Cool-down to 1.9 K Warm up to room temperature
Cold capacitance measurements (coil-heater and both to ground)
Warm up to room temperature
Heater-coil hi-pot at 75 K up to 800 V OK*
Heater-coil hi-pot at 150 K up to 800 V OK
Heater-coil hi-pot at 300 K up to 800 V OK
Heater-coil hi-pot up to 2300 V OK
Coil-ground hi-pot up to 1800 V FAILED at 1250 V
Heater-coil hi-pot at 75 K up to 1500 V OK
Heater-coil hi-pot at 150 K up to 1500 V CL1** OK, CL3 reached 1.5 kV but failed on arc at flattop
Heater-coil hi-pot at 300 K up to 1200 V CL1 OK, CL3 failed at 970 V
Heater-coil hi-pot at 300 K up to 1500 V CL1 failed at 1360 V
* HipotUltra 7804, threshold was 10 uA, flattop 5-30 s
**CL1: PH in coils 5/104, CL3: PH in 3/103

8. Backup Slides

9. 1.9 K Measurements Capacitance measurements at 1.9 K
Coil-to-heater at 1 kHz and 100 Hz: consistently 20.0 nF for CL1 and 20.5 nF for CL3
Coil-to-ground at 2 kHz: 13 nF with few nF fluctuations (worse for lower frequency)
Heater-to-ground at 2 kHz: 10 nF with few nF fluctuations (worse for lower frequency)