QUENCH AND MECHANICAL PERFORMANCE OF 1-M MODELMAGNETS FOR THE LHC LOW BETA QUADRUPOLES
T. Nakamoto, T. Ogitsu, Y. Ajima, E. Burkhardt, N. Higashi, H. Hirano,M. Iida, N. Kimura, H. Ohhata, N. Ohuchi, T. Shintomi, K. Sugita, K. Tanaka,A. Terashima, K. Tsuchiya, A. Yamamoto, KEK, Tsukuba, Japan
S. Murai, O. Oosaki, T. Orikasa, Toshiba, Yokohama, Japan
Abstract
Two 1-m model magnets for the LHC low-betainsertion quadrupole have been developed. One wasfabricated by KEK to confirm the magnet performancewith the final cross section. Another model that wasidentically designed was built at Toshiba to confirm thetechnical transfer. In the curing process, the coil size wascontrolled by the optimised curing shim thickness. Thesemagnets were connected in series and simultaneously
tested at 1.9 K. Quench history of the present models
showed better performance than the previous model andthe magnets were verified to reach the LHC operational
current without a quench after a thermal cycle. The R&D
phase of the LHC insertion quadrupole will move todevelopment of 6-m long prototype.

1 INTRODUCTION
Development of 70 mm aperture superconducting
quadrupole magnets for the LHC low-beta insertion, so
called as MQXA, is under way at KEK. The development
is a part of the collaboration between KEK and CERN for
the LHC, and sixteen 6-m long magnets will be installed
in low-beta beam insertion regions of the LHC together
with other 16 magnets by FNAL.
After the R&D of the two 1-m long model magnets,
the third 1-m model (Model #03) was fabricated with a
new coil design and the magnet performance was tested [1].
The fourth model (Model #04) was produced so that thequench performance and the field quality were comparedwith model #03. The fifth, identically designed, modelmagnet (Model #05) was built at Toshiba Keihin Product,that is the fabricator of the 6-m long prototypes and theproduction magnets, to confirm the technical transfer from
KEK to the company. These magnets were tested at KEKwith a new vertical cryostat [2] made for the 6-m longproduction magnet. To compromise with the test schedule,
the magnets were connected in series and excited
simultaneously. This paper reports the quench
performance and the mechanical behavior of models #04
and #05. Detailed report on the field quality is separately
presented at this conference [3].

2 DESIGN AND FABRICATION
Main design parameters of the new magnets are listed
in Table 1, and progress of the design study and R&D
works have been reported in [4]-[7].

Table 1: Main design parameters of low-beta
insertion quadrupoles for LHC
Models #04 and #05
Field Gradient (T/m)
Design (Operation)
240 (215)
Current (A)Design (Operation)
8057 (7150)
Peak Field (T)9.62
Load Line Ratio (%)
Inner Cable; IC91
Outer Cable; OC88
Number of Turns per Pole
1st Layer Coil
8 (IC)+4 (IC)with wedge
2nd Layer Coil
12(OC)+4 (IC)with wedge
3rd Layer Coil
15 (OC)
4th Layer Coil18 (OC)Stored Energy (kJ/m)
442
Inductance (mH/m)
13.6
Magnetic Forces per Octant
Fx (MN/m)
1.45
Fy (MN/m)-1.72
Table 2: Relative coil thickness and Young’s modulus of
inner- and outer- coils at 50 MPa
Relative coilYoung’s modulus
Magnetthickness (µm)(GPa)
Inner coil Outer coil Inner coil Outer coil
Model #03 89 (16) 145 (28) 6.5 (0.2) 7.1 (0.3)
Model #04 33 (18) 100 (19) 8.4 (0.3) 8.1 (0.4)
Model #05
4 (13)
9 (15)
7.5 (0.2) 9.2 (0.6)
Inner coil: 1st and 2nd layers, Outer coil: 3rd and 4thlayers.
Numbers in parenthesis indicate statistical errors (1σ).
Models #03, #04 and #05 were identically designed andfabricated except for the curing process: different shimthickness was adopted to each magnet to adjust the coilsize. Table 2 summarizes the relative coil thickness to theoriginal design value and the Young’s modulus of thefirst- and the second- layer (inner) coils and the third- andthe fourth layer (outer) coils. Numbers in parenthesis
indicate statistical errors (1σ). The mechanicalmeasurement was performed right after the first curing
process: each inner and outer coil was separately cured. Bychoosing the appropriate shim thickness, the coil size
gradually approached to the design value. Smaller coil

10Model #03
Model #04
Model #05

4003008Model #03
Model #04
Model #05

200

64100
20.00
-1000

Original Design
1020304050
Stress (MPa)6070Coil Young's Modulus (GPa)

Relative Coil Thickness (µm)

500080Figure 1: Relative coil thickness and Young’s modulus of4-layer coils. Bars indicate statistical errors (1σ).
Table 3: Azimuthal coil pre-stressduring assembly process (MPa)
#03
#04
#05
Process
Inner Outer Inner Outer Inner Outer
Collaring<5<5<5<5<5<5Yoking
40
53
3758
4147

3 EXCITATION TESTS
3.1 Quench History
Models #04 and #05 were simultaneously excited at 1.9
K with a ramp-rate of 10 A/sec in series connection, andapproximately half of the stored energy was extracted fromthe magnet by using a 50 mΩ dump resistor with firing
the quench protection heaters (QPHs). The excitation tests
were performed in the vertical cryostat newly constructed
for the 6-m long production magnets. A 3-m longstainless steel cylindrical vacuum chamber was suspended
below the model magnets as a dummy void so that theamount of superfluid helium coolant was saved and thecool-down time was minimized. The both models
experienced a full thermal cycle to room temperature toobserve the training memory. Further quench studies suchas fast ramp tests, AC loss tests, temperature dependence
tests or heater tests were not performed on these magnets.
Quench history of models #04 and #05 is shown in Fig.
2. The first quench occurred at 7326 A which exceeded theLHC operational current of 7150 A (G=215 T/m). The
following quench currents went up rapidly and themagnets only needed four quenches to reach the field
gradient of 230 T/m: a guide line to judge the quench
performance of MQXA at the magnet test in KEK. Afterreaching to 230 T/m, however, the quench curve seemed
to be saturated.
8500
8000
Quench Current (A)thickness generally traded off the higher Young’s modulus.
Both of the thickness and the Young’s modulus of models#04 and #05 distributed within small deviation and themedian plane shift was expected to be small enough.
Figure 1 plots the relative coil thickness and theYoung’s modulus of the 4-layer coils as a function of thestress. The measurement was made right after the second
curing process that gathered the inner- and the outer- coils
to be the 4-layer coil. The left hand vertical axis is therelative thickness to the original design value which thepre-stress of 50 MPa will be obtained after the magnet
assembly. Error bars indicate statistical errors (1σ). As
shown in the figure, each coil size was shifted andcontrolled in all stress range by varying the shimthickness. Model #05 was cured to be about 150 µm
smaller than model #03 and the coil size was fairly
adjusted to the original design value at 50 MPa.
Table 3 lists the azimuthal coil pre-stress during themagnet assembly. The pre-stress was determined by thecapacitive transducers installed between the coil and thestainless collar. Although the thickness of models #04
and #05 became smaller, the pre-stresses were almost
same as model #03. This might be due to the dimensional
problem of the brass shoes where the transducers weremounted. The unbalance of the pre-stress between theinner- and the outer- coils was reduced in model #05 byadjusting the coil size.

1st seriesof tests

2nd seriesof tests
240 T/m

7500

230 T/m

7000

215 T/m

6500
6000
55000

Model #03
Model #04
Model #05
No Quench at 220 T/m
Quench at ramp-down(Model #04)
510Run Number

Thermalcycle
1520Figure 2: Quench history of models #04 and #05.
After the first series of tests, the magnets experienced athermal cycle to room temperature. Since a technicalproblem took place with the power supply, the series ofquench tests were stopped. The magnets were once
energized up to the field gradient of 220 T/m to prove thetraining memory after the thermal cycle. The magnets, as
shown in Fig. 2, successfully reached to 220 T/m (I=7330A) without a quench although they quenched during thefollowing ramp-down process. This unexpected quench
was not understood.
Table 4 lists the quench locations of models #04 and#05. Quench locations could not be precisely localized dueto the lack of digitizers for the voltage taps and thequenched layer-coils are only listed in this table.
According to this table, the quench locations weredistributed in all poles, but concentrated in the secondlayer coils. Recent training results of the first 6-m
prototype also indicated that the most quenches initiatedin the second layer coils. It can be concluded that theMQXA designed magnets have weak regions in the second

layer coils except for model #03 which mostly quenchedin the fourth layer coils possibly due to the misalignmentof the insulating films.
Table 4: Quench locations of models #04 and #05.
Quench MIITs
QuenchCurrent (MA2s)
Quench Location
Number(A)
1st test 17326
9.26 #05, Pole2, 2nd layer
27369
8.90 #05, Pole3, 2nd layer
37520
9.58
#04, Pole4, 2nd layer
47725
8.50 #04, Pole2, 2nd layer
57688
8.58 #05, Pole3, 2nd layer
67763
9.56#05, Pole4, 2nd layer
2nd test 76725
8.80 #04, Pole3, 2nd layer

4 SUMMARY AND FURTHER PLAN

3.2 Mechanical Behaviour during Excitation
Figures 3(a) and (b) show azimuthal pre-stress changeof model #04 during excitation before and after the firsttraining quench, respectively. Pre-stress changes wereplotted as a function of square of the current andnormalized to be zero at the initial pre-stress right after
the cool-down.
In Fig. 3(a), the pre-stress curves of the inner coil were
gradually shifted to lower values as the magnet wasrepeatedly energized with increasing the ramp-up current
5#04: Inner Coil-5.00-10-5-15-10

1st Ramp: 3100A
3rd Ramp: 5100A
5th Ramp: 6000A
7th Ramp: 6500A
9th Ramp: 7050A-20010∆ Pre-stress: Outer Coil (MPa)∆ Pre-stress: Inner Coil (MPa)0.0#04: Outer Coil

-15

203040
Square of current (M A2 )50(a)5#04: Inner Coil
-5.0

0-10-5-15

14th Ramp: 7300 A
15th Ramp: 7300 A
16th Ramp: 7300 A
17th Ramp: 7300 A
18th Ramp: 7300 A-20010#04: Outer Coil203040
2
Square of current (M A )∆ Pre-stress: Outer Coil (MPa)∆ Pre-stress: Inner Coil (MPa)0.0

before the first training quench. The curves became
stabilised after the seventh excitation up to 6500 A, andthe pre-stress was about 3 MPa lower than the initialvalue right after the cool-down. The pre-stress changes
after the first quench in Fig. 3(b) precisely trace this curve.
The pre-stress change curves were saturated at the current
region above 5000 A. The lower pre-stress of the innercoil, however, did not affect the training characteristics
because the first quench took place over 7300 A and thetraining successfully went on.
For the outer coil, the pre-stress curves were distributed
within 1 MPa and decreased linearly: no saturation wasobserved. These mechanical behaviours were consistently
observed in model #05.

-10-1550(b)Figure 3: Azimuthal pre-stress change of model #04
during excitation (a) before and (b) after first training
quench.

Models #04 and #05 exceeded the operational field
gradient of 215 T/m without a quench and reached to230T/m after 4 quenches. The acceptable training memory
after the full thermal cycle was confirmed.
The R&D program of 1-m model magnets for theLHC-MQXA was completed. The 6-m long prototype
was fabricated at Toshiba and the excitation test is inprogress at KEK.

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[3] N. Ohuchi et al., “Field quality of the LHC-IRQ 1-m
model quadrupole magnets developed at KEK,” to bepresented at this conference, P2hc02.
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