The Effect of Transverse Pressure on the Inter-Strand Coupling Loss of Rutherford Type of Cables

The Nb 3 Sn cables being developed under the LARP program will need to have suitable, reproducible, and uniform interstrand contact resistances (ICR) in the interests of acceleratorfield quality (low coupling magnetization) and stability (currentsharing between strands). In the first of a pair of studies ICR was measured in response to variation of strand surface condition. As a sequel to this the present set of measurements explores the influence of cable preparation conditions on ICR, determined as before using calorimetric and magnetic AC-loss measurement techniques in face-on and edge-on applied AC fields. Uncored Rutherford cables were wound at Fermilab from OST MJR-type strand and wrapped with S-glass tape impregnated in most cases with a ceramic binder (applied before reaction HT). The HT/pressurization sequence of the cables was made to mimic as closely as possible the expected LARP magnet-fabrication schedules. Derived from maxima in the loss-vs-frequency curves was an ICR "inhomogeneity"-two ICRs for each cable pack each associated with a particular fraction of the strands. Furthermore, both of the ICRs, at 0.4 and 4 , would in a magnet be too small to satisfy the generally accepted magnetization requirements.

Section: Methodsmentioning

confidence: 99%

Interstrand Contact Resistance in ${\rm Nb}_{3}{\rm Sn}$ Cables Under LARP-Type Preparation Conditions

Collings

Sumption

Ambrosio

et al. 2007

“…Magnetic measurements of the total AC loss per cycle were made using the inductive-or pick-up-coil method on cable samples installed in a cryostat that was also equipped for He-boil-off calorimetry [8]. In most of the experiments the loss was generated by an alternating dipolar field with amplitude, , of 400 mT and frequencies, , of 5 to 90 mHz in the presence of fixed background dipolar fields, , of 0 and 1 T. The magnetic loss was calibrated against the calorimetrically measured loss in the same cables, which was in turn calibrated against ohmic loss in a 100 calibration resistor.…”

Section: B the Critical-frequency Methodsmentioning

confidence: 99%

Magnetic Measurements of Interstrand Contact Resistance in<tex>$rm Nb_3rm Sn$</tex>Cables in Response to Variation of Pre-Heat-Treatment Condition

Collings

Sumption

Dietderich

et al. 2006

Inductive (pickup-coil) magnetometry was used to measure AC loss in uncored Nb 3 Sn Rutherford cables in the perpendicular and parallel orientations of the applied field. The four cables selected for study had widths of 8, and 13 mm and strand counts of 20 and 30, respectively. Under various surface conditions they were reaction heat treated (RHT) then vacuum impregnated with resin in preparation for measurement. The magnetic measurements were made at 4.2 K in sinusoidal fields of amplitude 400 mT and frequencies of 5 to 90 mHz, The total per-cycle loss so obtained was used to deduce the "crossover" interstrand contact resistance (ICR). Attention is focused on the ICRs of one particular 8-mm/20-strand cable measured in this and previous studies under several pre-RHT conditions: (i) as-received, (ii) acetone-degreased, and (iii) acetone-degreased then HCl-deoxidized then acetone rinsed. A comparison is also made to the ICR of a sub-size cored Nb 3 Sn cable.

“…7, currents in the diamond pattern flow on the bottom face from A to B and the top face from B to C. At C they cross over to the bottom face and flow to D and then to A, where they again cross over to the bottom face. By integrating over all possible diamond shapes, the magnetization due these coupling currents may be shown to be [8]:…”

Section: Couplingmentioning

confidence: 99%

Rutherford cables with anisotropic transverse resistance

Adam

Leroy

Oberli

et al. 1997

Putting a resistive core into the center of a Rutherford cable increases resistance between strands in the crossover direction, which greatly reduces the coupling currents, even when the resistance to adjacent turns remains small. This allows one to improve stability by soldering strands together or using porous metal, without incurring a penalty of increased coupling. We describe our manufacturing methods and an experimental measurement of coupling. Abstract -Putting a resistive core into the center of a Rutherford cable increases resistance between strands in the crossover direction, which greatly reduces the coupling currents, even when the resistance to adjacent turns remains small. This allows one to improve stability by soldering strands together or using porous metal, without incurring a penalty of increased coupling. We describe our manufacturing methods and an experimental measurement of coupling.