1. Quench protection of the MAGIX high-order correctors
Vittorio Marinozzi, Marco Statera, Massimo Sorbi
28/06/2017

2. Outline:
The correctors
Test results at LASA
Assumptions for quench simulations
Hot spot temperature
Peak voltages
Conclusions

3. 1.1 The MAGIX correctors Strand diameter Operation Current Length
Skew quadrupole
Sextupole
Octupole
Decapole
Dodecapole
Strand diameter
Operation
Current
Length
Yoke diameter
Quadrupole
0.7 mm
182 A
840 mm
460 mm
Sextupole
0.5 mm
132 A -> 105 A
123 mm
320 mm
Octupole
105 A
Decapole
83 mm
Dodecapole
464 mm

4. 1.2 Strands and MIITs Strand diameter Insulation thickness Cu/NCu
Quadrupole
0.7 mm
0.07 mm
2.3
Others
0.5 mm

5. Test successfully performed on: Sextupole (magnet and single coil)
2.1 Test at LASA
Test successfully performed on:
Sextupole (magnet and single coil)
Octupole (magnet and single coil)
Decapole (single coil)
Experimental data used to validate the simulation tool (QLASA) for the quench protection in the machine (with similar assumptions)

6. 2.2 Test at LASA Quench current Dump resistor Validation time
Voltage threshold
114 A
0.5 Ω
20 ms
200 mV

7. QLASA is a bit conservative
2.3 Test at LASA
(~10 %)
QLASA is a bit conservative

8. 3.1 Assumptions Simulation tool is QLASA,
a 3D pseudo analytical quench simulation software
Two scenarios for each magnet:
Protection without dump resistor
Protection with dump resistor (only if needed)
With dump
Without dump
Voltage threshold
10 V
Validation time
10 ms
180 ms
Switch delay time
Dump resistor
≤ 300V / I0
0 Ω
Quench heaters No
Quench current
108% of I0

9. 3.2 Assumptions Comments on the voltage threshold:
It has been proposed to protect the magnet with the current decay but:
We have assumed that the magnet is protected measuring the resistive voltage, and not the current decay. In fact, at LASA our protection system is not suitable for a similar study
Moreover, we do not know exactly the behavior of the power supply in the machine, therefore we cannot make any prediction in this scenario, which strongly depends on that.

10. How we measure the resistive voltageRq VA VB
𝑉 𝑟 = 𝑉 𝐴 − 𝑉 𝐵

11. 4.1 Hot spot temperature
The hot spot temperature is computed by QLASA using adiabatic methods, with the assumptions explained before
No dump scenario
Quadrupole
Sextupole
Octupole
Decapole
Dodecapole
Hot spot temperature
132 K
164 K
131 K
122 K
147 K
No issues are foreseen, and dump resistor seems not needed
Sextupole design to be updated (132 A -> 105 A)

12. 5.1 Peak voltage to ground How it is computed?
The voltage is evaluated as the sum of the voltage across each coil, computed by QLASA
The peak voltage is evaluated in the worst case (quenched coil is the first or the last in the series)
We neglect the voltage distribution inside the coil
The bulk coil is impregnated and well insulated, while the connections are weak points, which could suffer short-circuit Vp

13. We want to keep the voltage below 300 V Optimal ≤ 250 V
5.2 Peak voltage to ground
We want to keep the voltage below 300 V
Optimal ≤ 250 V
No dump scenario
Quadrupole
Sextupole
Octupole
Decapole
Dodecapole
Peak voltage to ground
633 V
135 V
70 V
36 V
251 V
Quadrupole is well beyond the maximum limit
Other magnets are ok
Quadrupole needs a protection study with dump resistor

14. 5.3 Peak voltage to ground - quadrupole
Three scenarios for the ground:
Magnet end set to ground
Ground in the middle of dump resistor
Ground in the middle of the quadrupole
𝑉 𝑝 = 𝑉 𝑟 + 𝑅 𝑑 𝐼
𝑉 𝑝 = 𝑉 𝑟 + 𝑅 𝑑 𝐼 2
𝑉 𝑝 =2 𝑉 𝑖

15. 5.4 Peak voltage to ground - quadrupole
Maximum dump is 300 V / I0 ≈ 1.5 Ω
Ground at magnet end
Ground at half dump
Ground at half magnet
0 Ω
633 V
422 V
0.5 Ω
474 V
447 V
316 V
1 Ω
407 V
357 V
271 V
1.5 Ω
358 V
287 V
238 V
The most realistic scenario for the quadrupole is protection with a 1.5 Ω dump resistor (0.75 Ω Ω), with the ground set in the middle

16. Conclusions:
A protection study for the MAGIX high-order correctors has been presented, under machine conditions
The tool used for simulations has been compared with experimental data obtained at LASA, with good results
The hot spot temperature of the magnet is under control without dump resistor
The peak voltage to ground of the magnets is ok, except the quadrupole, which needs a dump resistor to be protected
We propose:
To consider protecting the magnets measuring resistive voltage, instead current decay
To protect the quadrupole with 1.5 Ω dump resistor, with the ground set in the middle
To protect the other magnets without dump resistor