Absolute calibration of air fluorescence telescopes to detect the highest energy cosmic rays by a compact electron accelerator

位于美国犹他州沙漠中的望远镜阵列，利用空气荧光望远镜（FD）观测到极高能量宇宙射线在空气中产生的大范围空气簇射。我们提出了一个非常独特的方法，端到端的绝对校准望远镜观察空气簇射的电子束从一个紧凑的电子直线加速器（TA-LINAC）在空气中拍摄。最大电子能量为40 MeV，输出功率为6.4 mW。我们的目标是在1%的精度内测量40 MeV的能量和在5%的精度内测量160 pC/脉宽为1μsec的束流。本研究由柴田辰延柴田（研究员）和池田大辅（研究生）合作，利用束流模拟设计了TA-直线加速器，并研究了TA-直线加速器的绝对校准方法。我们在高能加速器研究所建造了TA直线加速器。它于2008年1月完成，我们成功地加速了光束。我们测量了决定束流能量的90度弯曲电磁铁的磁场值。1%的准确度。测量了影响束流能量稳定性的磁场稳定性。用法拉第杯测量了束流，测量精度为3%。在束流操作期间，我们使用堆芯监测器来监测束流。我们证实了法拉第杯和岩心监测器之间的线性关系，精度为5%。在确认性能后，我们将TA-LINAC发送到美国。混凝土基础和辐射控制围栏的施工在一个FD站附近的TA-LINAC现场进行。

The Telescope Array, located in the desert of Utah in USA, observes extensive air showers that extremely high energy cosmic rays generate in air by using air fluorescence telescopes (FD). We proposed a very unique method of end-to-end absolute calibration of telescopes by observing air shower induced by electron beams from a compact electron linear accelerator (TA-LINAC) shot in the air. It has the performance of maximum electron energy of 40 MeV and output power of 6.4 mW. We aimed at measuring the energy of40 MeV within 1% accuracy and the beam current of 160pC/pulse of 1μsec width within 5% accuracy. Tatsunobu Shibata (Researcher) and Daisuke Ikeda (Graduate student) cooperatec with us for this research.We designed TA-LINAC by using beam simulation, and investiaged the method of absolute calibration by using TA-LINAC. We constructed TA-LINAC in High Energy Accelerator Research Organization. It was completed in January, 2008, and we succeeded in accelerating beams. We measured the values of magnetic field of a 90-degree bending electromagnet that determines beam energy. within 1% accuracy. We measured the stability of magnetic field that affects the stability of beam energy. Thus we could measure electron energy of 39.75 MeV approximately within 0.01% accuracy.We measured beam current with an accuracy of 3% by a Faraday cup. During beam operation, we use a core monitor to monitor beam current. We confirmed linear relation between the Faraday cup and the core monitor within an accuracy of 5%. After confirming the performance, we sent TA-LINAC to USA. The construction of the concrete base and the fence of radiation control was performed at the site of TA-LINAC near one of the FD station.