Magnets and Helium: Partners in Superconductivity

The United States government currently provides approximately 30 percent of the world’s helium. Their involvement in the gas goes back to the beginning of World War I, when blimps were thought to be the next big thing in military aircraft. Although blimps have all but retired to the green pastures of professional football fields, MR imaging depends on liquid helium to keep the magnet cold and the electrical current superconductive. In 1925, the federal government established the Federal Helium Reserve out of an abandoned salt mine about a dozen miles northwest of Amarillo, Texas. The military significance of blimps quickly diminished but the Federal Helium Reserve continued to manufacture the gas, which is a byproduct of natural gas that can be pumped out of the ground.
By 1996, the helium reserve had accumulated $1.3 billion in debt, so Congress passed the Helium Privatization Act, which required the government to complete the sell off of its helium supply by 2015. As the deadline approached it became clear that it was not likely to happen. HCBN spoke to David Fisher, vice president of health policy and strategy at Siemens Healthcare, about the decisions that followed. Siemens was part of a coalition that set out to educate legislators on the economic risks associated with shutting down the helium reserve. “A law was passed to modify the 1996 law,” says Fisher. “It did two main things: allowed the helium reserve to remain open and sell helium, and established a new mechanism for selling helium through auction.” Fisher says the new law, H.R. 527, known as the Helium Stewardship Act, established the framework for those auctions, which would be conducted on a semi-annual basis. “The Government Accountability Office did a report in quarter two of this year where they gave an update on the status of the helium sale,” says Fisher. “My understanding is that the first auction was at the end of July and it sold helium at a price closer to the market price.” He says there are still some details that need to be worked out with regard to volume of sale and price of sale, but the government can now continue selling its helium supply in large volumes, and that was the intent of the law. The government will preserve a relatively small portion of the helium for strategic purposes. HCBN spoke to David Joyner, the president of Air Liquide, a company that supplies industrial gases, including helium. Joyner described his experience attending the first U.S. Helium Reserve auction as, “Very unique.” He says, “It was a one of a kind methodology of selling helium that hasn’t occurred in the marketplace before,” a live bid process between the private industry players and the helium industry. Joyner says that in recent years, the vast majority of federal crude helium has been sold to three companies that own refineries along the federal helium pipeline. By changing the method of selling, Congress has opened access to other purchasers, and is requiring those refineries along the pipeline to process that helium for those outside purchasers. “Most of the volume purchased by non-refiners has not reached the market-place yet because it hasn’t gone through that tolling (or refining) process,” says Joyner. “It’s important that the Bureau of Land Management tightens up that process and ensures that the tolling occurs.” Aside from their involvement in the U.S. helium auctions, Joyner says Air Liquide recently built the world’s largest liquefier in Qatar, and utilizes a diverse chain of suppliers including sources in Algeria. “The BLM posted price for helium is becoming more volatile and less reflective of private transactions in the marketplace,” says Joyner. He anticipates a trend of moving away from the BLM index to avoid distorting true market value. Dr. Boop, a pediatric neurosurgeon at Le Bonheur Children’s Hospital, recalls a time when a helium shortage affected his practice directly. “It was an issue where our magnet broke down and needed helium,” says Boop. “It took a while for us to get some so it delayed our ability to bring our scanner back up to a usable state because of the shortage.” Siemens and GE are two companies that have become mindful of ways they can reduce the amount of helium they lose at their factories. Richard Hausmann, president and CEO of MR global business at GE, describes a $17 million initiative to recapture the helium that is sometimes lost at the MR manufacturing site if a test quench is conducted, or a magnet cools down. That burn off can be thought of like steam from a tea kettle which, if collected, can be turned back into water. GE performs this reliquification process in their own factories. Craig Marshall, the managing director of Siemens magnet technology, discussed the nature of superconductivity with HCBN. “At room temperature, most metals conduct electricity very well. As the temperature is reduced, electrical conductivity continues to increase and conversely electrical resistivity continues to decrease,” says Marshall. “There is a point for certain metals where the resistance suddenly becomes zero, these metals are known as superconductors.” In its liquid state, helium is very cold, just four degrees Kelvin, at this temperature a magnet submerged in liquid helium will operate as a superconducting magnet. Marshall says once that magnet has been electrically energized it will operate in an electrical equivalent to perpetual motion. “Once energized, you can take away the power supply and the electrical current keeps going without any resistance and it remains there for years and years and years,” says Marshall. In deep space, a superconductive magnet would work without a source of power because it’s already cold enough. According to Marshall, some satellites exploit these properties on their journeys through the cosmos. Knowing the status of the helium in an MR scanner is essential for nmaintaining the system, avoiding downtime, and preventing costly situations. Remote monitoring is one solution to that dilemma. HCBN spoke to David Schuetz, director of service business management MR for Siemens Healthcare, about Siemens Remote Services. Schuetz and his colleagues monitor shield temperature, water temperature, helium levels, and chiller water flow rates over a secure network established between their service center and the facilities using their MR systems, (HCBN will provide extensive coverage of chillers in our November issue). “With regards to helium monitoring, we’re looking specifically at the cooling system parameters,” says Schuetz. “We’re looking at the health of the cold-head, we’re looking at pressures inside the magnet, and with those parameters, we can tell the overall health of the cooling system.” Historically, magnets were kept at 10 degrees Kelvin but today, most new MR magnets are 4 degrees Kelvin. That colder temperature means less helium is boiled off and doesn’t need to be topped-off as often. “The 4k systems operate within a very small tolerance of helium level fluctuation,” says Schuetz. “So if you have a 4k system that has been working perfectly for five years, and there’ve been no power interruptions, and the chilled water has been functioning right, and the system has been operating exactly the way it should be, you’ll notice zero boil off.” But, Schuetz says, environmental situations may result in minor boil off here and there, and remote monitoring can limit that impact. As an alternative to OEM remote monitoring, some end-users opt for independent monitoring services, such as that provided by Cool Pair Plus. HCBN spoke to Ron Schultz, the company’s field service manager, about the kind of problems one might have with magnets and helium. “In the majority of service calls received, the report is that the cold-head and compressor are not working,” says Schultz. “First question asked is if there have been any chiller or power issues at the site. If so, there is a list of questions to determine if it is indeed a cold-head or compressor issue or a site chiller issue,” says Shultz. Poor coolant flow and high temperature will cause issues with the helium compressor and cold-head. Another independent magnet monitor is Southwest Medical Resources. Don McCormack III, field service engineer, says their service gives end-users a unique opportunity to take remote monitoring into their own hands. “Our remote display unit (RDU) offers the option for the customer to [remote monitor their cryogens] themselves,” says McCormack. By linking in-house engineer and tech support cellphones to the RDU, McCormick says hospitals can become less dependent on outside assistance, including that of OEMs. He sees a trend of image outpatient centers being bought up by larger hospital chains. “These large chain hospitals are moving more and more towards in-house engineers and biomed programs,” says McCormick. Schuetz, with Siemens, describes the process of adding helium to an MR system. “We have helium fill kits that we stock in our depot in Memphis,” says Schuetz. “They are sealed in a vacuum casing, which means there is very little heat transfer from the outside to the inside.” The engineers receive the liquid helium in dewars of 250 to 500 liters. Helium push-gas is then used to pressurize the vessels and force the liquid helium out of the dewar, through a transfer line, and into the system’s fill port. While the day-to-day goal of remote monitoring is to ensure optimal performance from the MR system, it also ensures dangerous situations do not evolve over time. “Cold-head failures cause the shield to warm up, which increases the helium boil off,” says Schuetz. “If it’s not detected and corrected then the system may fall below the alarm threshold.” If nothing is done, then the system may fall to a critical level which may prevent the use of the system until entirely refilled. In such an extreme case there may be risk of a quench. A quench happens when the system goes resistive and the liquid helium converts into gas form. Marshall, the magnet expert from Siemens, says that one liter of liquid helium could warm up and become 770 liters of helium gas at room temperature. Today the vast majority of quenches are deliberate, although sometimes they happen when loading helium into the system. McCormick says a full quench recovery can typically take three days. “A quench is the result of instability in the actual magnet coil or a warm spot on the coil,” says Schuetz. “With a warm spot, if you think about oxygen getting sucked into a magnet vessel, it freezes that oxygen into ice. Even though that ice is exceptionally cold, if it falls off and lands on the coil, it’s actually much warmer than the liquid helium.” Quenches produce a noise Schuetz compares to a tornado or a freight train. Yet, with remote monitoring, issues can be detected long before they become critical. Regarding the benefits of OEM monitoring over independent service monitoring, Schuetz points to the proprietary nature of the system. “[Independent servicers] have limited access to the software and data. We have the experts who know exactly what to look for because we manufactured the magnets.” When asked the same question, Schultz, on behalf of Cool Pair Plus, says he believes their costs are lower than the OEMS and also cites 24/7 phone support and same day or expedited service availability. Schultz also says Cool Pair Plus uses a state of the art magnet monitoring system called daVinci, which continuously monitors key operating parameters and functions of the MR system. Remote monitoring was also discussed in the Cost Containment Corner of our August issue, where we interviewed Ed Sloan, an expert on the topic: When asked what the helium situation will look like ten years from now, Marshall says, “The BLM will only be around for a fraction of those years. As BLM subsidization goes away, the price is likely to increase.” Marshall expects some industries to move out of helium while others will find ways to be more efficient with it. GE is working on a low cryogen magnet which would require 10 liters of helium to cool the magnet, instead of 3,000 to 5,000 liters. “This will revolutionize magnet technology,” says Hausmann. Although still in the developmental stages, the system would be completely enclosed and not require the installation of a quench vent.

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