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CHARACTERIZATION OF NBTI BUSBAR FOR HL-LHC INTERACTION REGION QUADRUPOLESM. Baldini, G. Ambrosio, R. C. Bossert, G. Chlachidze, S. Feher, P. Ferracin, V. Marinozzi, D. F Orris, H. Pan, S. Stoynev
GOALS
▪ Validate the bus assembly design for the interaction region triplet of
the HL-LHC.
▪ Characterize the bus thermo electrical properties: quench propagation
velocities, quench integral and hot spot temperature
▪ Demonstrate that the bus is well protected up to ultimate current
according to Hi-Lumi LHC project requirements.
DESIGN
BUS ORIENTATION
975 mm3.9 mm
19.2 mm
18.2 mm
9.78 mm
▪ The bus consists in two slabs of NbTi flat cable
soldered together and wrapped in polyimide
▪ A positive and negative bus terminals carry the
current.
▪ The bus was connected to a short Nb3Sn MQXF magnet (MQXFS1e)
and tested at 1.9 K at FNAL.
▪ Orientation: the two bus terminals are parallel to magnetic flux
lines to minimize Lorentz forces.
▪ Polarity: the current of each bus terminal flows in opposite
direction with respect of the adjacent coil block.
TEMPERATURE MARGIN DETERMINATION
QUENCH PROPAGATION VELOCITIES
QUENCH INTEGRAL
CONCLUSIONS
▪ The two straight sections of the bus terminals were
instrumented with spot heater, a temperature sensor and
28 voltage taps.
▪ Temperature margins were determined at 15.5, 16.5 and
17.5 kA to extrapolate the quench temperature value at
ultimate current.
▪ The margin value is above the requirements established
in the Hi-Lumi projects (5K).
Current levels and Voltage detection thresholds
Current (kA) Voltage Threshold
(mV)
Voltage Threshold
(mV)
Voltage Threshold
(mV)
Voltage Threshold
(mV)
5.0 50 200
8.2 50
9.9 50
11.5 50
13.1 50
14.8 50
16.5 50 200 500 800
17.8 50
▪ Quench transverse propagation has been observed at the
lowest current values (5.0 kA and 8.2 kA). A 1.8s delay was
observed between the longitudinal and the transversal
quench fronts at 8.2 kA and, a 4.6s delay at 5.0 kA.
▪ Transverse velocity is two order of magnitude smaller than
the longitudinal one at 8.2 kA and three order of magnitude
smaller at 5.0 kA.
▪ Quench propagation velocities were computed in adiabatic
conditions at several current levels.
▪ Tests in the MQXFS1e magnet were carried out for the same current
levels at several voltage detection thresholds.
▪ Quench propagation velocities were estimated experimentally using
time of flight method.
NBTI CABLE AND STRAND SPECIFICATION
CoatingStrand diameter after coating
Number of strandsCopper to superconductor ratio
Twist pitch after cablingCable widthCable height
Cable RRRCritical current at 10 T, 1.9 K
Sn5Wt%Ag1.065 + 0.0025 mm
3411.06 = 0.05 mm
18+1.518.15 mm1.92 mm
>150515 A
CROSS SECTION AREA OF THE BUS ASSEMBLY ELEMENTS
Entire bus
CuPolyimide
NbTiAg0.94Sn0.06
93.88 mm2
37.55 mm227.07 mm2 23.01 mm26.246 mm2
▪ Quench integral and hot spot temperatures were obtained from
experimental data.
▪ The hot spot temperatures are well below 100 K at each current and
threshold level.
+
__
+Bus polarity with respect
to coil blocksBus bar orientation in the MQXFS1e magnet
Conceptual layout of Hl-LHC triplet: two 4.2 m long MQXFA magnets are installed in each Q1 or Q3 cold masses and a
single unit MQXFB ~7.5-m-long magnet in the Q2 a+b element.
Bus Terminal
1
Bus Terminal 2
Voltage taps (orange lines), spot heaters (yellow rectangular shape) and
temperature sensor (green dots) positions on the buses.
Top: panel: Current ramp
(green curve, left y axes) and
temperature increase
(purple curve, right y axes)
up to quench. The arrows
indicate which axes each
curve belongs to. Bottom
panel: current dependence
of temperature margins.
Inset: Current dependence
of quench temperatures. A
parabolic fit (red line) was
used to extrapolate the
quench temperature at
ultimate current.
Current dependence of the quench velocities for several segments placed on the left (top panel)
and on the right (bottom panel) of the quench heater. Results are compared with QLASA
simulations (red line empty symbols)
Comparison between
quench propagation
fronts at 8.0 kA.
The black line is the
voltage rise observed
in the segment where
the quench is started.
Blue and light blue
lines are the voltage
onsets observed after
the quench propagates
transversally.
Summary of all the quench
integral data. Symbols
refers to experimental data
obtained at different current
values and detection
thresholds. Curves of the
same color refers to quench
integrals obtained from
calculations. Simulations are
in good agreement with the
experimental results.
Acknowledgments: This work was supported by the U.S. Department of Energy, Office of Science, Office of High Energy
Physics, through the US LHC Accelerator Research Program (LARP) and by the High Luminosity LHC project at CERN. The U.S. Government
retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a non-exclusive, paid-
up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, o/r allow others to do so, for U.S.
Government purposes.
• The bus bar assembly was tested together with the
MQXFSe magnet.
• The test demonstrated that bus design is adequate since
no spontaneous quench took place up to ultimate current.
• The bus design was validated with a temperature margin
of 6 K which is above the one required for the Hi-Lumi
triplet bus.
• The obtained quench integrals and hot spot temperatures
(< 100 K) guarantee that the bus is well protected up to
ultimate current.
• The design guarantees the protection of the bus for the
quench detection voltage threshold (100 mV) established
for the Hi-Lumi LHC interaction region.
Mon-Mo-Po1.03-09 [29]