SLAC从高极化光电阴极中提取高电荷用于未来对撞机的最新进展
Recent Progress at SLAC Extracting High Charge from Highly-Polarized Photocathodes for Future-Collider Applications
摘要：
未来的对撞机，如NLC和JLC，将需要一个高度极化的宏脉冲，其电荷超过SLC所能产生的数量级。SLC均匀掺杂GaAs光电阴极的最大电荷量受到表面电荷极限（SCL）的限制。SCL效应可以通过使用极高（>1019 cm-3）的表面掺杂剂浓度来克服。当在活性层的大部分中与中等掺杂剂浓度结合时（以避免去极化），已经发现表面浓度在正常热清洗（在600 ℃下1小时）期间降低。与Zn或C掺杂剂相比，MBE生长的超晶格阴极中通常使用的Be掺杂剂特别容易受到这种影响。通过降低清洗温度可以得到一些缓解，但长期的一般解决方案似乎是原子氢清洗。
英文摘要：
Future colliders such as NLC and JLC will require a highly-polarized macropulse with charge that is more than an order of magnitude beyond that which could be produced for the SLC. The maximum charge from the SLC uniformly-doped GaAs photocathode was limited by the surface charge limit (SCL). The SCL effect can be overcome by using an extremely high (>1019 cm-3) surface dopant concentration. When combined with a medium dopant concentration in the majority of the active layer (to avoid depolarization), the surface concentration has been found to degrade during normal heat cleaning (1 hour at 600 C). The Be dopant as typically used in an MBE-grown superlattice cathode is especially susceptible to this effect compared to Zn or C dopant. Some relief can be found by lowering the cleaning temperature, but the long-term general solution appears to be atomic hydrogen cleaning.
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