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

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

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

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

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)

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

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

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

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.

How we measure the resistive voltage Rq VA VB 𝑉 𝑟 = 𝑉 𝐴 − 𝑉 𝐵

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)

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

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

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

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 + 0.75 Ω), with the ground set in the middle

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