The quench simulation for ATLAS central solenoid is preformed with a detailed simulation model including the effect of pure aluminum strips. The simulation agrees with the measurement data with the estimated uncertainty of±20 K. It is difficult to predict the quench for ATLAS central solenoid since the magnetic field and thermal conductivity of
0 10 20 30 40 50 60 Time [sec]
0 1000 2000 3000 4000 5000 6000 7000 8000
Current [A]
0 20 40 60 80 100 120 140
Temperature [K]
Measurement B = 2.6 Tesla B = 1.0 Tesla B = 0.5 Tesla
0 10 20 30 40 50 60
Time [sec]
0 1000 2000 3000 4000 5000 6000 7000 8000
Current [A]
0 20 40 60 80 100 120
Temperature [K]
Measurement Polyimide GFRP-G10
Figure C.4: Predicted current decay and temperature rise at hot spot for a scan of magnetic field (left) and various of insulation thermal conductivity (right).
insulation cause the large uncertainty. Conversely, the thermal conductivity of insulation is a one of the important parameter that affects the quench propagation for a large aluminum-stabilized solenoid. Using the insulation with good thermal conductivity could help the quench protection.
As for the PCS magnets, the magnetic field distribution does not affect the quench so much due to the multi-layer coils. Also, the uncertainties are well studied in the chapter 5, and the impact of thermal conductivity and other parameters are not significant since the coil is mush smaller than the ATLAS central solenoid.
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Appendix D
Studies on Mineral Insulated HTS Tape
As discussed in Chapter 6, the insulation is an issue to develop the HTS-based coil in the high radiation environment, since the radiation breaks the chemical bonds and prevent the recombination of bonds. The radiation will cause the permanent degradation in insulation so that it cannot be recovered by thermal cycle like metals. Thus the lifetime is determined by the radiation resistance of the insulation for a superconducting magnet operated in the high radiation environment. In this chapter, a ceramic-coated insulation on the HTS tape is studied.
D.1 Investigation of the Heat Treatment
In order to fabricate the solenoid with a coated HTS tape and the ceramic-impregnation, the coil or HTS tape will be cured at high temperature. However, the heat treatment can degrade the HTS tape due to the presence or absence of oxygen deficiency in the YBCO crystal structure [121]. In this work, the heating tolerance on the critical current of HTS tape is investigated.
D.1.1 Experiment
Experimental Setup
In this experiment, the critical current of HTS tape (SuperPower, SCS4050-AP) at liquid nitrogen temperature is measured before and after the heat treatment on each test sample. Figure D.1 shows the experimental setup for the critical current measurement. The critical current is measured by four-wire configuration, in which the voltage is monitored with a nanovoltmeter (Keithley, Model 2182A), and current is obtained by measuring the voltage of known shunt resistor with a multimeter (Keithley, Model 2000). A resistor with a resistance of 0.25 mΩ (Yokogawa, 2215) is employed as the shunt resistor. A DC power supply (Hewlett-Packard, 6680A) provides the current of 500 A at maximum.
The test sample of HTS tape is settled on the G10 plate, in which both ends are attached to the copper holder, and fixed by bolting a copper plate on the copper holder.
The cables of power supply are also bolted on the copper holder. To avoid the degradation of critical current for HTS tape due to the high temperature of soldering, the voltage of HTS is measured with a pair of contact probes attached on the test sample with a distance of 5 cm. Additionally, to protect the HTS tape against the burnout, a pair of voltage tape is attached to the copper plate to send a shut-down signal to power supply when the voltage of whole HTS tape is higher than a given threshold voltage.
Multimeter Shunt Resistor
Power Supply Nanovoltmeter
Vh
Vp
5 cm
Voltage tap HTS tape
Power supply
Contact probe
Vh
Figure D.1: The experimental setup for the critical current measurement at liquid nitrogen temperature.
Heat Treatment
The effect of heat treatment is investigated with various the treatment time at 180◦C and 200◦C. The heat treatment is preformed with a drying furnace (ETTAS, 50NW-600S) in which the HTS tape is placed on the aluminum foil, and two K-type temperature sensors are attached to the both ends of aluminum foil to measure the sample temperature.
Figure D.2 shows the measured temperature during the curing. The temperatures of the aluminum foil are given in channel 1 and channel 2, and the channel 3 is the temperature in drying furnace. During the heat treatment, the temperature is stable, while the measured temperature on the aluminum foil has the temperature difference of ±10◦C. In the heat treatment, the shortest duration to ramp up the temperature is 36 min. Since the critical current of HTS is sensitive with the treatment time, the test sample cured only in a time of ramp-up an ramp-down is also measured.
Appendix D. Studies on Mineral Insulated HTS Tape
0 5 10 15 20 25 30 35 40
Time [hours]
0 50 100 150 200
Temperature [◦ C]
channel 1 channel 2 channel 3
Figure D.2: Measured temperature during the heat treatment. The temperature of blue and red line are measured on test sample, and the one of green line is the temperature in the furnace.
D.1.2 Result
The critical current is determined with a conventional way, power fit for the voltage-current (V-I) curve [122] as following function:
E =Ec·(I
Ic)n+a (D.1)
where Ic is the critical current, n is the n-value, Ec is the reference electric field of 0.1 µV/cm, and a is the offset of the measurement in the unit of µV/cm, respectively.
Figure D.3 shows the V-I characteristics fitted with the power law before and after the heat treatment. Compared with the critical current of 117 A before the curing, the critical current of HTS decreases until 70 A after the heat treatment of 180◦C with 30 h. The critical current before and after the heat treatment is listed in Table D.1 and plotted in Fig. D.4, in which the error indicates the derivation of the number of measurement (one point of critical current is measured over 20 times). Compared with the heating time, the degradation of critical current is more sensitive with the heating temperature. Also, the degradation of n-value is observed in this measurement, however, the degradation is not significant. According to the conceptual design in chapter 6, the operating current of 105 A can produce the magnetic field of 3 Tesla on target. To avoid the degradation on the critical current, the heating temperature and time must be kept below 200◦C and 2 hours during the curing.