Niobium superconducting radio frequency cavities (SRF) are required for the International Linear Collider as well as other high energy physics projects. In order for these cavities to achieve the required particle acceleration gradients, electropolishing is conducted as a final surface finishing operation. Conventional electropolishing of SRF cavities is based on the well-established viscous salt film paradigm [
] and utilizes a viscous electrolyte consisting of a mixture of sulfuric acid (95-98%) and hydrofluoric acid (49%) in a 9:1 volume ratio [
]. The concentrated is included to establish a thick, viscous boundary layer to result in surface brightening or smoothing [
]. The hydrofluoric acid is included to remove the niobium oxide film formed during electropolishing [
]. Previously we described efforts directed towards demonstrating an innovative electropolishing process for niobium coupons in low concentration (5%) aqueous sulfuric acid without hydrofluoric acid enabled by pulse reverse voltage waveforms electrolyte [
]. The advantages of pulse reverse voltage electropolishing are summarized in in Figure 1. Specifically, the forward (anodic) pulse on-time and peak voltage are tuned to eliminate the need for concentrated sulfuric acid; the off-time is adjusted to dissipate heat, and the reverse (cathodic) pulse on-time and peak voltage are tuned to eliminate the need for hydrofluoric acid. In this contribution, we review and describe continuing efforts leading to the scale-up of the electropolishing process to single-cell and three-cell niobium SRF cavities [
]. Finally, we present a first order economic comparison of the pulse reverse voltage low concentration aqueous sulfuric acid process compared to baseline concentrated sulfuric acid-hydrofluoric acid process [
The financial support of Faraday corporate, DOE P.O. No. 594128 and DOE Contract No. DE-SC0004588 is acknowledged.
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