Detector for coherent synchrotron radiation measurements from separate electron bunches in a millimeter wavelength region

Room-temperature detector, manufactured by the company ‘‘SPINOR’’ (Tomsk Russia) was tested for the investigations of the coherent synchrotron radiation characteristics at the bent electron beam of FLASH (Hamburg) in the wavelength region 0.5–3mm. Detector is based on a low-threshold diode and a broadband antenna with a built-in preamplifier. The detector characteristics allowed us to measure a radiation pulse from separate electron bunches from electron train. The measured coherent synchrotron radiation spectral characteristics in comparison with ones, measured using the cryogenic bolometer show a good homogeneity of the spectral sensitivity of our detector for wavelengths longer than 1.5mm. The comparison of temporal characteristics with the well-established pyro-electric detectors shows a response time around 1.5 ns. The measured detector sensitivity was about 100MV/J. & 2008 Elsevier B.V. All rights reserved. 1. Design of detector DPU-1 The room-temperature detector DPU-1 is intended for measurement of the radiation in a millimeter wavelength region. Detector was manufactured by the company ‘‘SPINOR’’ (Tomsk, Russia). Main elements of the detector are the low-threshold diode, broadband antenna and fast preamplifier. Standard power supply of 12V is provided in a complete set with detector. The main applicability of detector is a measurement of different types of coherent radiation from a single submillimeter length bunch of charged particles for a purpose of beam diagnostics. The detector has a sensitive area of 4mm and registers radiation without any horn. 2. Detector response Test was performed using the coherent synchrotron radiation (CSR) beam, which is generated from the edge of bending magnet placed downstream to the first bunch compressor in line of injector of FLASH (Hamburg, Germany). CSR beam is extracted from accelerator vacuum chamber through the vacuum window of the beamline of CF63-type with the outcoupling area of 60mm wide and 8mm high, converted to ll rights reserved. +73822423934. nko). the parallel beam and transported by the optical tract to the TOSYLAB laboratory [1]. Main electron beam characteristics are shown in Table 1. Fig. 1 shows the sample of detector response on the CSR from a single bunch. The pulse consists of two components. The main component has the amplitude 20–30mV and the width 1.5ns (FWHM). The area under the peak is E35mVns. Besides the main peak there is slow component with an average amplitude E2.5mV, which reaches the duration E150ns. The area under the shape is E380mVns. Both are a response of the radiation and are proportional to the radiation energy. As the temporal window of analog-digital converter (ADC) is about 8ns, we can provide the measurement using the main peak component with the good accuracy. Nevertheless, the shape limits the temporal resolving possibility if an incoming bunches period is less than 150ns. As shown in Fig. 1, the peak/noise ratio for observed signal is ZDPU 1E40. This is the important criterion of detector sensitivity. For comparison, the value of the peak/noise ratio for pyro-electric detector DTGS (see Ref. [2]) is ZDTGSE3.3. Usually the detector responsivity criterion is defined as the relation of a detector response peak voltage to a radiation pulse energy Er (if the response duration is much larger than radiation pulse duration). However, such criterion does not define unambiguously the detector responsivity characteristics, because it strongly depends on a preamplifier and additional amplifier properties. In this case, the more correct criterion of detector sensitivity is the relation w=Z/Er. The inverse value of w is the