  Stacks of REBCO tapes can trap large amounts of magnetic fields and can stay
magnetized for long periods of times. This makes them an interesting option for
major engineering applications such as motors, generators and magnetic
bearings. When subjected to transverse alternating fields, superconducting
tapes face a reduction in the trapped field, and thus it is the goal of this
paper to understand the influence of all parameters in cross field
demagnetization of stacks of tapes. Major parameter dependencies considered for
the scope of this paper are ripple field amplitude, frequency, tape width, tape
thickness (from 1 to 20 $\mu$m), and number of tapes (up to 20). This article
also provides a systemic study of the relaxation time constant $\tau$, which
can be used to estimate the cross-field demagnetization decay for high number
of cycles. Modeling is based on the Minimum Electro-Magnetic Entropy Production
method, and it is shown that the 2D model gives very accurate results for long
samples when compared with 3D model. Analytical formulas for large number of
cycles have been devised. The results show that when the ripple field amplitude
is above the penetration field of one tape, the stack always fully
demagnetizes, roughly in exponential decay. Increasing the number of tapes only
increases the relaxation time. The formulas derived also hold when validated
against numerical results, and can be used for quick approximation of decay
constant. They also show that the cause of the decreases of cross-field
demagnetization with number of tapes is the increase in the self-inductance of
the magnetization currents. The trends and insights obtained for cross field
demagnetization for stacks are thus very beneficial for engineers and
scientists working with superconducting magnet design and applications.
