First Experimental Demonstration of Beam Storage by Three-Dimensional Spiral Injection Scheme for Ultra-Compact Storage Rings

Three-dimensional spiral injection scheme enables storage in ultra-compact rings with nanosecond revolution period. We report the first successful storage of a $297\,\mathrm{keV/}c$ electron beam in a $22\,\mathrm{cm}$ weak-focusing storage ring with a $4.7\,\mathrm{ns}$ revolution period using multi-turn vertical kick with a $140\,\mathrm{ns}$ kicker pulse. Using a scintillating-fiber detector, we observe a signal exceeding $5σ$ of the pre-injection rms noise for $\geq 1\,\mathrm{μs}$, confirming beam storage. By varying the weak-focusing field configuration and measuring the stored beam distribution, we show that the storage beam resides within the predicted region by Monte Carlo simulations. This result is a key proof-of-principle for realizing ultra-compact storage rings for next-generation precision measurements including the muon experiments at J-PARC and PSI.