Q4 2008


Vishay ESTA Supplies Filter Capacitor Banks for Particle Accelerator

In its quest for the mysterious Higgs particle, the European organization for particle physics (CERN) activated its new LHC particle accelerator, close to Geneva, Switzerland, in September 2008.  The LHC (Large Hadron Collider) is an accelerator for heavy particles, such as protons and heavy ions, also known as hadrons. With a tunnel length of 27 km, the LHC is the largest particle accelerator in the world.

The LHC’s tunnel is more than 100 m underground and is filled with magnets and high-tech devices. The superconducting magnets are cooled down to the temperature of outer space, and can thus produce very strong magnetic fields.

In the LHC, either protons or lead ions are accelerated and brought to collision. The collisions take place in four enormous underground halls, known as the ATLAS, ALICE, CMS and LHCb particle detectors, located approximately 100 m under the surface of the earth. The ATLAS and CMS halls are so-called general-purpose experiments, designed to prove the existence of yet undiscovered elementary particles.  Large expectations lie in proving the Higgs boson, the only unproven particle in the standard model of particle physics theory.

Besides the LHC accelerator, further large particle accelerators are also operated at CERN: The oldest is the Proton Synchrotron (PS, 628 m in length; constructed in 1959), followed by the Super Proton Synchrotron (SPS, 7 km in length; constructed in 1976) and lastly, the LHC, 27 km in length.   Each accelerator feeds the particles into the following larger ring.  To operate the LHC, both the PS and SPS are needed.

At the end of last year, Vishay ESTA supplied CERN with eight 18-kV filter capacitor banks for the SPS. The filter banks have an installed rating of 247 Mvar and consist of 420 capacitors. The filter banks serve as mains voltage stabilization and reactive power compensation for CERN’s super proton synchrotron (SPS) particle accelerator.

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The filter capacitor banks supplied by Vishay ESTA were required for one of the SPS’s two new reactive power compensation installations. The SPS serves mainly for the acceleration of protons and ions, as well as experiments with antimatter. It operates with a pulsating frequency of approximately 14 s, with power pulses of 0 to 230 MW and 200 Mvar, which are lined up non-stop every 14 seconds, for about nine months of the year. This pulse operation is achieved with 12-pulse and 6-pulse inverters. The Vishay ESTA filter capacitors banks are used to filter the harmonic waves generated by the inverters.

In order to accurately steer the particle beam into the pipe, which measures only a few centimeters, the current control in the static inverter and magnets must exhibit a fraction of a percentage precision. For this reason, unusually high quality standards are demanded from the mains supply, and tolerances for fast voltage transients and harmonics must be kept far lower than a percentage point, whereas the loads switched in a 1-second pulse rate draw on the supply network in ways found in steel mills and rolling mills. Compared with industrial networks, however, the network quality must be better by a factor of 10 in order to steer the particles on their course. Due to the large amplitudes and the short rise time of the SPS’s power pulses, particularly fast reactive power compensation is needed to stabilize the voltage.

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The SPS accelerator also makes very high demands on the power supply. The availability and life span of individual components is crucial, since loss of the compensation plant would bring to a stop the SPS and LHC accelerator particle experiments. As the utilization of the accelerators is determined by precise schedules, a failure in the compensation plant would result in enormous delays in the research programs.  CERN makes its installations available to the 20 member countries that run research programs by scientists, universities, and institutes.  Since some of these scientists take many years to prepare for a series of experiments, larger delays would have extensive consequences

The SPS is powered from a European 400-kV very- high-voltage grid by two 90 Mvar transformers 400/18 kV, with a third identical one in reserve. The two reactive power compensation installations are at the 18-kV level.

CERN has placed great emphasis on a very conservative capacitor design to guarantee the highest reliability in the compensation plant and to ensure sufficient reserve as well as long-lasting and trouble-free capacitor operation. This is also proven by our internal test statistics: Not a single capacitor has failed during quality testing.

During technical discussions with CERN’s technicians and engineers, a further, quite old reactive power compensation plant was addressed. Vishay had also supplied the capacitors for this in 1989. Since then, these capacitors have been operating almost non-stop under the demanding conditions of CERN’s medium voltage network. So far, CERN is very pleased with the capacitors’ operating conditions and has confirmed that during the entire period of operation, failure rates have been unusually low.

As the research operations of the new LHC accelerator begin, Vishay ESTA will have contributed a small but very important component to the CERN project.  There will, no doubt, be other power compensation projects in the future.

By Christian Mergenthaler
Sales, HV Capacitors, Vishay ESTA