Technology to market - HTS wire helps CERN circulate first LHC beam
The European Organisation for Nuclear Research (CERN), the world's largest research
organisation devoted to studying particle physics, constructed a 27km accelerator in a circular tunnel to examine the fundamental characteristics of matter. Electrical Review takes a closer look at the project
The Large Hadron Collider (LHC) is the world's largest particle accelerator complex, intended to collide opposing beams of protons to explore the validity and limitations of the Standard Model, the current theoretical picture for particle physics. The LHC utilizes thousands of superconductor magnets to create immense magnetic fields along the precisely engineered ring running 100m below ground.
Subatomic particles are accelerated in this environment of nearly 100,000 times the strength of earth's natural magnetic field, and investigators observe their behavior to better understand their nature. Since 1954, Geneva-based CERN (Conseil Européen pour la Recherche Nucléaire) has conducted groundbreaking efforts in both theoretical and applied science. Among the results of CERN's work are new cancer therapies; medical and industrial imaging; electronics; new manufacturing processes and materials; and the world wide web. With approximately 7,000 employees, a total investment of four billion euros and 24 years of planning, development and construction, the LHC is the world's largest research projects ever undertaken.
The specialized electromagnets that generate the LHC's colossal magnetic field operate at cryogenic temperatures: 1.9 degrees Kelvin or 456 degrees below zero on the Fahrenheit scale. These electromagnets needed to be connected to a power source.
Solution
High temperature superconductor (HTS) wires allow electric current to flow without resistance. In contrast to connecting CERN's superconducting electromagnets with their room temperature power source over conventional copper wires, HTS wires block thermal leaks more effectively and so reduce the refrigeration required to maintain required cryogenic temperatures.
After conducting a number of years of experiments and reliability studies, CERN engineers designed and developed specialized current leads that employ HTS wire to connect the electromagnets to their power source. The HTS component of the current lead reduces the amount of heat leaking into the magnets' cryogenic environment, despite carrying up to 13,000 Amperes of electric current. (By comparison, typical homes today are built with 200 Amp service.)
At the heart of CERN's design are specially prepared bundles of HTS wire. Seven lengths of wire, conforming to precise fabrication requirements, were vacuum-soldered together to form a ‘stack. This critical portion of the manufacturing process required HTS wires with highly uniform electrical performance and exceptionally consistent surface conditions.
Outcome
The LHC project includes a total of approximately 1,000 HTS leads. CERN selected American Superconductor (AMSC) to provide HTS wire for 50% of the current leads designed and developed by CERN. Just six months after receiving CERN's order, AMSC delivered 14,000 meters (over eight-and-a-half miles) of advanced wire from its manufacturing plant in Devens, Massachusetts. CERN specialists fabricated the wire into 1,600 stacks; then, 36 stacks at a time, they fitted them into custom-made cylinders. In final assembly, this component serves as the HTS element of a single completed current lead.
CERN's design calls for current leads ranging in power from 600-13,000 Amps. The total amount of current they transport to the superconductor magnets exceeds 3 million Amps. CERN circulated its first beam on September 10. Once stable circulating beams have been established, they will be brought into collision. Following the successful completion of this benchmark, CERN will then commission the LHC's acceleration system to boost the energy to 7 TeV, taking particle physics research to a new frontier.
Dr Amalia Ballarino, CERN's lead scientist on the current leads project, said the high quality of AMSC's wire and the firm's experience in meeting challenging HTS specifications helped her team ensure the reliability and performance of the thousands of superconductor magnets that make up the heart of the Large Hadron Collider.
"Not only did American Superconductor deliver 14 kilometers of HTS wire ahead of schedule," Dr Ballarino said, "but the wire performance exceeded our specifications by a large margin." She added the "success rate of these stacks to date has been 100%." Of equal importance to CERN is the economic benefit. Because HTS current leads significantly reduce the heat associated with conventional copper leads.
HTS current leads based on American Superconductor's Cryoblock wire are used commercially today to overcome similar cryogenic problems in other settings. Applications include magnetic resonance imaging (MRI) systems for medical diagnostics, and ultra-sensitive measuring equipment for physicists or medical researchers (called superconducting quantum interference devices, or SQUIDs).
For more information on American Superconductor's projects visit www.amsc.com
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