1993 Fiscal Year Final Research Report Summary
Development of Polarized Electron Source for Linear Colliders by Using Superlattice Photocathhode
| Project/Area Number |
04640315
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
核・宇宙線・素粒子
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| Research Institution | National Laboratory for High Energy Physics (KEK) |
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Principal Investigator |
OMORI Tsunehiko National Laboratory for High Energy Physics (KEK), Physics Division, Research Associate, 物理部, 助手 (80185389)
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| Co-Investigator(Kenkyū-buntansha) |
NAKANISHI Tsutomu Nagoya Univ., Faculty of Science, Associate Professor, 理学部, 助教授 (40022735)
KURIHARA Yoshimasa National Laboratory for High Energy Physics (KEK), Physics Division, Research As, 物理部, 助手 (50195559)
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| Project Period (FY) |
1992 – 1993
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| Keywords | Linear Collider / JLC / Superlattice / Polarized Electron / Photocathode / Modulation Doping / Charge Limit |
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| Research Abstract |
We achieved 715 polarization of photoemission from the ALGA-As-GaAs superlattice in early 1991. The study described below has been performed to proceed the fruits further aimed to apply the superlattice in future linear colliders (JLC for example).
We have studied the spin depolarization during the diffusion of electrons in the conduction band. The superlattice is p-doped to achieve negative-electron-affinity, which is necessary to use the superlattice for a photocathode. We applied lower acceptor concentration in most part of a superlattice, on the other hand normal(5x10^<18>/cm^3), or even higher, concentration near the surface. We have found this type of modulation doping improves both polarization and quantum efficiency of a photocathode.
We have studied that how polarization depends on the total thickness of the superlattice. The extrapolation to zero thickness gave a polarization of -75%. We tested sample which has various surface conditions. Non of them showed significant improvement of the polarization. We have concluded there was no source of large depolarization near the surface. Therefore the polarization of electrons exited in the conduction band was -75%.
We have tested large charge-extraction from a superlattice. This test was performed at SLAC as a part of the Japan-SLAC collaboration. The result was successful ; 2.3x10^<11>electrons were extracted in 2.5nsec. No charge Limit of the photochatode material was observed. The resultant number of electrons was limited by Space Charge Limit of the gun. This result is very encouraging becaouse the charge Limit phenomenon is supposed to be the most serious problem of a photocathode gun in a future linear collider.
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