Polarized Electron Source with 100% Polarization

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(1) Photocathode Development toward 100% Polarization The break-throughs against 50% limitation if electron polarization were achieved by two kinds of new semiconductor-cathode, strained GaAs and AlGaAs-Ga As superlattice, developed by our group. The relation between maximum polarization, residual strain and lattice-mismatch was studied for a strained GaAs cathode, and 0.1% quantum efficiency was achieved. A new-type of superlattice cathode made by InGaAs-GaAs was developed and 85% polarization was achieved.(2) Photocathode Development with High Quantum Efficiency In order to improve the quantum efficiency, we developed two of new devises. One is "Resonance-Absorption-Photocathode" which employs a Bragg reflector to enhance the photo-absorption-rate for strained GaAs, and the other is "Modulation-Doping-Photocathode" which has high doping density in a thin surface-layr. The quantum efficiencies more than 1% were achieved by both of these methods.(3) Investigation for High Peak-Current Polarized Beam The record of peak-current, 2.3*10^<11>e^-/2.5nsec was obserbed for the SLC (Stanford Linear Collider) polarized gun using our modulation-doping superlattice. It was impressive that this maximum value corresponds to the space-charge-limit, and no effect called "total charge limit" is observed.(4) Construction of Polarized Gun for High Energy Accelerators 100KeV Guns were constructed and photo-currents were already extracted. The reduction of "dark current" is being examined to improve the cathode life-time.(5)Fundamental Research to Check the Feasibility of Polarized RF Gun For the future polarized electron souce, the polatized RF gun seems most at tractive, and we started fundamental experiments to reduce the dark-current.