CHARACTERIZATION OF NBTI BUSBAR FOR HL-LHC …...CHARACTERIZATION OF NBTI BUSBAR FOR HL-LHC INTERACTION REGION QUADRUPOLES M. Baldini, G. Ambrosio, R. C. Bossert, G. Chlachidze, S.

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]