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

望远镜阵列位于美国犹他州的沙漠中，利用空气荧光望远镜(FD)观测到空气中产生的极高能量宇宙射线的大范围空气骤雨。我们提出了一种非常独特的端到端绝对定标方法，通过观测小型电子直线加速器(TA-LINAC)在空中发射的电子束诱导的空气簇射来对望远镜进行绝对定标。其最大电子能量为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，在5%的精度内测量1μ秒宽度的160pc/脉冲的束流。柴田达夫和池田大介与我们合作进行了这项研究，我们用束流模拟的方法设计了TA-直线加速器，并研究了用TA-直线加速器进行绝对校准的方法。我们在高能加速器研究机构中建立了TA-LINAC。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。准确度在1%以内。测量了影响束流能量稳定性的磁场稳定性。因此，我们可以测量39.75 MeV的电子能量，精度大约在0.01%以内。我们用法拉第杯测量了3%的束流。在束流运行过程中，我们使用磁芯监测器来监测束流。我们确认了法拉第杯与岩心监测器之间的线性关系，准确度在5%以内。在确认演出后，我们将TA-LINAC送往美国。混凝土基础和辐射控制围栏的施工是在其中一个FD站附近的TA-LINAC现场进行的。

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.