Production of Far-infrared Coherent Synchrotron Radiation on Electron Storage Ring

通常，同步加速器辐射强度与参与辐射的电子数量成正比。然而，当电子被束成一个短脉冲，其长度小于辐射波长时，单个电子的辐射是相干发射的，辐射强度与电子数的平方成正比。这种现象称为相干同步辐射（CSR）。由于存储环中的典型电子数为10^<10>，因此CSR的强度可以比普通同步辐射大许多数量级。我们一直在尝试在存储环中循环的电子束上产生CSR。我们的方法是创建一个密度调制，其典型长度短于辐射波长，而不是缩短电子脉冲的长度。结果，我们探测到非常强烈的太赫兹辐射爆发，其峰值强度比正常辐射大4个数量级。这些脉冲仅在单束填充模式下观察到，光束电流高于某一阈值电流。我们假设电子束的不稳定性在电子束上产生了典型尺度在毫米范围内的密度调制。这种调制迫使电子束发出如此强烈的爆发。这些爆发的典型持续时间为100微秒。脉冲的间隔通常为10毫秒，并随波束电流的变化而变化。这种现象本质上是不稳定和混乱的。为了利用这种强烈的辐射，我们必须控制爆发的发生。我们正试图利用电子和激光脉冲之间的相互作用，在电子束上产生密度调制。我们已经成功地制造出由外部触发器控制的强烈爆发。

Normally, synchrotron radiation intensity is proportional to number of electrons which contribute to the radiation. However, when the electrons are bunched into a short pulse whose length is shorter than the radiation wave length, the radiation from individual electrons is emitted coherently and the radiation intensity is proportional to the square of the number of the electrons. This phenomenon is called coherent synchrotron radiation(CSR). Since the typical number of the electrons in a storage ring is 10^<10>, the intensity of CSR can be larger than the normal synchrotron radiation by many orders of magnitudes.We have been trying to produce CSR on the electron beam circulating in a storage ring. Our approach is to create a density modulation whose typical length is shorter than the radiation wavelength, in stead of shortening the electron pulse length. As a result, we have detected very intense bursts of terahertz radiation, whose peak intensity is larger than normal radiation by 4 orders of magnitudes. These bursts were observed only in single bunch filling mode with the beam current higher than a certain threshold current. We suppose that a density modulation whose typical scale is in millimeter range, is created on an electron beam as a result of beam instability. This modulation forces the electron beam to emit such intense bursts. The typical duration of these bursts are 100 micro-seconds. The interval of the bursts is typically 10 milliseconds and varied on the beam current. This phenomenon is essentially unstable and chaotic. To utilize this intense radiation, we must control the occurrence of the bursts. We are trying to produce density modulation on an electron beam by utilizing the interaction between the electrons and laser pulses. We have already succeeded in producing intense bursts whose occurrence is controlled by an external trigger.