CERN Courier July/August 2017 Advertising feature Mineral PET WEKA Hybrid HTS Current Leads Introduction be cooled either by heat conduction or also by means Discovering Superconducting magnets create very high magnetic of a cooling gas flow. An adoption of the design for fields for research projects in nuclear fusion as well HTS 2nd generation can be implemented. as for accelerator systems. To establish such magnetic fields huge electrical currents are required. Performance Tests These currents are in the range of several 10,000 The 10kA prototypes were tested by EPFL CRPP at amperes and must be conducted from ambient PSI in Villingen, Switzerland both in standard and diamonds temperature, at which they are generated, to the critical extreme situations. The expected operating temperature of the magnets which is performance could successfully be verified extremely low, typically around 4.4K. The connection In a follow-up project, WEKA customized, between these two temperature levels is done with manufactured and delivered a pair of 25.7kA current current leads. Together with EPFL CRPP, WEKA has leads to CEA Saclay, where they were installed in a developed hybrid current leads for fields of JT-60SA test rig for magnet testing. Also these applications in the range of around 3 to 30kA. current leads fulfilled the specified performance parameters. The required cooling fluid between the Outstanding achievements 300K and the 50K level of 1.8g/s at 50K and 27.5kA The focus of the development was set on optimizing could successfully be verified and the contact the efficiency of the current leads to achieve a resistance between the current leads and the significant reduction of the refrigerant consumption. feeders at the cold end was not higher than the As a result, operating costs can be reduced by more specified 7nΩ. than 10% compared to other solutions, while also having high functional reliability. Conclusion WEKA hybrid HTS current leads have an excellent WEKA current leads are based on a hybrid design performance compared to traditional designs. They with a copper heat exchanger on the warm side and a offer a high degree of customization for each High Temperature Superconductor (HTS) section on individual application and are industrially the cold side. The transition region is cooled by manufactured with stable processes and extensive another upstream heat exchanger. Due to the testing. With the launch of current leads, WEKA will ingenious design of these heat exchangers, highest continue to be a competent partner in the market of A new technique for sorting diamond from a few decades, and it costs around $10–26 to process each tonne heat transfer ratio can be achieved at lowest cryogenic engineering and manufacturing of of rock. With the number of new, economically viable diamond pressure drop. In contrast to metal-resistive cryogenic components. rock based on technology developed for sources declining – combined with high rates of diamonds being structures, this design undergoes far less heat input extracted, ageing mines and increasing costs – most forecasts and thus requires significantly less cooling power. Product range high-energy physics detectors is poised to WEKA current leads consist of the following main predict a decline in rough diamond production compared to Key features components: make mines more efficient. demand, starting as soon as 2020. The upper resistive part of the current leads contains A new diamond-discovery technology called MinPET (mineral an integrated heat exchanger made out of copper, • warm end connection positron emission tomography) could help to ensure that precious which is cooled by means of a cooling gas flow. • heat exchanger with vacuum flange While typically Helium at 50K input temperature is • transition zone sources of natural diamonds last for much longer. Inspired by the used, any other customer specific refrigerant in the • superconducting zone Natural diamonds are old, almost as old as the planet itself. They same principles adapted in modern, high-rate, high-granularity range between 4 and 80K is possible as well. The • cold end connection at 4.4K mostly originated in the Earth’s mantle around 1 to 3.5 billion years detectors commonly found in high-energy physics experiments, heat exchanger is one of the core elements of a ago and typically were brought to the surface during deep and vio- MinPET uses a high-energy photon beam and PET imaging to current lead. The geometry of the cooling channels The present design of WEKA current leads covers a must be designed so that a high degree of heat range from 3 to 30kA. Typically it is cooled with lent volcanic eruptions some tens of millions of years ago. Dia- scan mined kimberlite for large diamonds, before the rocks are exchange is combined with a low pressure drop. This Helium gas at 50K, but a customer specific monds have been sought after for millennia and still hold status. smashed to pieces. goal is achieved by geometry of parallel walls at low adaptation to other refrigerants in the range of 4 to They are also one of our best windows into our planet’s dynamics distance. In this way, deep and narrow channels are 80K is possible as well. The cooling fluid and can, in what is essentially a galactic narrative, convey a rich From eagle eyes to camera vision consumption as well as the transfer resistance at the directly incorporated into the surface of the copper story of planetary science. Each diamond is unique in its chemical Over millennia, humans have invented numerous ways to look for cylinder, which spiral around the solid core. The cold end is very low and the warm and cold design principle allows for variation in depth and mechanical contact connections or the detailed and crystallographic detail, with micro-inclusions and impurities diamonds. Early techniques to recover loose diamonds used the number of channels and wall width of the cooling design can be customized to the specific application. within them having been protected over vast timescales. principle that diamonds are hydrophobic, so resist water but stick ribs. The channel widths are continuously enlarged Several options like voltage and temperature Diamonds are usually found in or near the volcanic pipe that readily to grease or fat. Some stories even tell of eagles recover- towards the warm end to reduce potential pressure measurement points, voltage breaker for the cooling brought them to the surface. It was at one of these, in 1871 near ing diamonds from deep, inaccessible valleys, when fatty meat drop. The heat exchanger may be extended from a gas connection or Paschen insulation are possible as single coil to a double or event triple helix to ensure well. The WEKA current lead design is especially Kimberley, South Africa, where the diamond rush first began – thrown onto a valley floor might stick to a gem: a bird would fly higher volumetric flow into the warm part. With both the specific selection of the material and lightweight and slim, but still very robust in sense of and where the mineral that hosts most diamonds got its name: down, devour the meat, and return to its nest, where the diamond the sophisticated design of the two heat exchangers mechanical decoupling at the warm end connection. kimberlite. Many diamond sources have since been discovered could be recovered from its droppings. Today, technology hasn’t Special focus was put on the transition zone the required cooling flow can be reduced, which and there are now more than 6000 known kimberlite pipes (fig- evolved much. Grease tables are still used to sort diamond from between the copper unit and the superconducting leads to a significant reduction of the operating cost. part of the current lead. Through the integration of Contact: ure 1 overleaf). However, with current mining extraction tech- rock, and the current most popular technique for recovering dia- another heat exchanger in a conical helix form, the The superconducting part consists of a stainless Pascal Erni, WEKA AG nology, which generally involves breaking up raw kimberlite to monds (a process called dense media separation) relies on the contact temperature at the warm end of the HTS steel support with incorporated longitudinal Schuerlistrasse 8, see what’s inside, diamonds are often damaged and are steadily principle that kimberlite particles float in a special slurry while s stack could be reduced with the temperature of the grooves. HTS stacks of BSCCO2223 type are soldered 8344 Baeretswil, becoming mined out. Today, a diamond mine typically lasts for diamonds sink. The excessive processing required with these cooling fluid remaining unchanged. into the grooves. This part of the current leads may Switzerland 29 CCJul17Ad_Weka_FP_Advertorial.indd 1 26/06/2017 11:10 CCJulAug17_DIAMONDS.indd 29 28/06/2017 16:49 CERNCOURIER www. V OLUME 5 7 N UMBER 6 J ULY /A UGUST 2 0 1 7 CERN Courier July/August 2017 CERN Courier July/August 2017 Mineral PET Mineral PET All image credits on this page: S Connell older technologies wastes water, takes up huge amounts of land, releases dust into the surrounding atmosphere, and also leads to severe diamond breakage. Just 1% of the world’s diamond sources have economically viable grades of diamond and are worth mining. At most sites the gem- stones are hidden within the kimberlite, so diamond-recovery tech- niques must first cr ush each rock into gravel. The more bar ren rock there is compared to diamonds, the more sorting has to be done. This varies from mine to mine, but typically is under one carat per tonne – more dilute than gold ores. Global production was around 127 million carats in 2015, meaning that mines are wasting mil- Fig. 3. PET image (right) of a 5 cm-wide kimberlite rock spiked lions of dollars crushing and processing about 100 million tonnes with a diamond.