Development of a new $^{48}$Ca enrichment method and the CANDLES experiment

CANDLES is a project to study double beta decay of $^{48}$Ca. CANDLES could become the most competitive experiment if we could have an efficient method to enrich $^{48}$Ca. We developed a new method for enrichment of large amount of calcium isotopes. The method is called Multi-Channel Counter-Current Electrophoresis (MCCCE) which can be found elsewhre.\footnote{T. Kishimoto et al., PTEP (2015) 033D03; doi:10.1093/ptep/ptv020} Essential point is the increase of the power density in the migration path. In MCCCE, ions migrate in multi-channels on a boron nitride (BN) plate by which substantial increase of the power density was achieved. We made a tiny prototype instrument with a 10 mm thick BN plate and obtained 3 for an enrichment factor for the ratio of abundance of $^{48}$Ca to $^{43}$Ca over that of natural abundance. It corresponds to 6 for the enrichment factor of $^{48}$Ca to $^{40}$Ca. Recently we obtained 10 for the enrichment factor by using 20 mm BN plate. This remarkably large enrichment factor demonstrates that the MCCCE is a realistic and promising method for the enrichment of large amount of ions. This method can be applied to many other elements and compounds. I will describe MCCCE and its effect on the study of double beta decay and other fields.