Fastest Ramping Rates for Superconducting Accelerator Magnet

Physicists, engineers and technicians at the U.S. Department of Energy’s Fermi National Particle Accelerator Laboratory, led by Henryk Piekarz, just demonstrated the world’s fastest magnetic ramping rates for particle accelerator magnets. They achieved this record by using magnets made with energy-efficient, high-temperature superconducting material.

The superconducting accelerator test magnet is taking the ramping rate lead as Fermilab’s high-temperature superconductor test magnet has yielded rates of up to 290 T/s, while achieving a peak magnetic field strength of about 0.5 tesla. Piekarz and his team designed a magnet and operated it at temperatures between 6 and 20 K and up to 1,000 amps of electrical current.

Arxiv – Record High Ramping Rates in HTS Based Superconducting Accelerator Magnet

Fermilab’s Tevatron accelerator was the first machine based on superconducting steering magnets. The ramping of the 4.4 tesla magnets to full magnetic strength took more than a minute and a half, while electric fields increased the energy of the particles to 1 TeV. Today, the world’s most powerful accelerator, the Large Hadron Collider at CERN, uses superconducting steering magnets that ramp up to almost 8 tesla in approximately 20 minutes, while the accelerator propels particles to 6.5 TeV. This corresponds to a ramping rate of about 0.006 T/s and is much slower than the ramping rate of conventional accelerator magnets operating at room temperature.

The test magnet conductor operational current is 6 kA at 30 K. By increasing the cold pipe diameter to 10 mm, and by adding a second layer of the HTS strands the magnet operational current can be increased 12-fold, or up to 72 kA-turn.

A 12-fold increase in the number of strands, however, will likely make strand’s hysteresis and eddy losses to become dominant for the overall cable
power loss.

The plan for future work includes as accurately as possible measurements of the test magnet cable cryogenic power losses. They also will upgrade the magnet power supply to double the discharge voltage of the capacitor bank. This will allow to increase operating current to 2 kA, and the B-field in magnet gaps up to 0.8 T. With such upgrade the dB/dt ramping rates of up to 600 T/s should be achievable allowing to determine cryogenic power losses with higher precision and make projection of required cryogenic support for the future large accelerators more reliable.

Abstract

We report results of experimental test of the High Temperature Superconductor (HTS) based fast-cycling prototype accelerator magnet capable to operate up to about 300 T/s field ramping rate with some 0.5 T B-field in the magnet gap. The measured upper limit for the cryogenic cooling power required to support magnet conductor operation at high ramping rates indicates great potential for such type of magnets in rapid cycling synchrotrons for neutrino research or muon acceleration. The test magnet design, construction and supporting cryogenic and power systems are briefly described. The magnet’s power test results are discussed in terms of a possible upgrade of this magnet design to 2 T B-field, a maximum feasible with super-ferric magnet.

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