AC losses of Rutherford MgB₂ cables made by powder-in-tube and internal magnesium diffusion processes

Abstract

Magnetization losses of Rutherford MgB 2 cables of different sheath materials (Cu, CuNi and Al+Al 2 O 3 ) made by powder-in-tube and internal magnesium diffusion processes were studied experimentally. Short cable samples consisting of 12 strands were measured in the temperature range from 18 K up to 40 K, external fields up to 70 mT and frequencies 72 Hz and 144 Hz. The effects of inter-strand resistance by soldering and external field orientation (perpendicular and parallel) were also tested. The impact of eddy current losses in the sheath material was determined by the loss measurement in cable samples without MgB 2 . It was found that very high eddy current losses of Cu sheathed strands overlap the hysteresis loss. The lowest AC losses at 20 K were measured for a Rutherford MgB 2 cable with an Al+Al 2 O 3 sheath, which makes it attractive for applications where low loss and also low coil mass are required (e.g. wind turbines or airborne engines).

MgB2 cables made of thin wires manufactured by IMD process

“…In the experiments, all voltages are always measured using the same polarity, left-right, in such a way that in the normal state all measured voltages are positive. AC losses in Rutherford MgB2 cable with and without Al2O3 insulating layer were measured by the system based on the calibration free method [20]. External magnetic field was oriented perpendicular to the plane of cable sample.…”

“…AC losses in Rutherford MgB 2 cable with and without Al 2 O 3 insulating layer were measured by the system based on the calibration free method [13]. External magnetic field was oriented perpendicular to the plane of cable sample.…”

“…Recently, Rutherford MgB2 cables were also made by using unreacted in-situ [12] and IMD wires [13]. AC losses in these cables can be suppressed effectively by increased inter-strand resistivity [14]. To avoid a strong degradation of the transport currents, better way is to made cables of thin wires with one ore small number of filaments.…”

“…Recently, Rutherford MgB 2 cables were also made by using unreacted in-situ [11] and IMD wires [12]. AC losses in these cables can be suppressed effectively by increased inter-strand resistivity [13].…”

Low‐purity Cu and Al sheathed multi‐core MgB2 wires made by IMD process

“…Another type of six filament IMD made MgB 2 wire with Al-Al 2 O 3 sheath has shown sufficient thermal stabilization and also promising electro-mechanical properties [15]. It was shown that MgB 2 cable stabilized by OFHC copper in AC regime is heated up by large eddy current losses induced in the high conductive Cu [16], see figure 1(a).…”