Speaker
Description
Summary
Since a few years coherent synchrotron radiation (CSR) generated by short electron bunches is provided at the ANKA light source. Electron bunches can be filled in up to 184 buckets with a distance between two adjacent bunches of 2 ns corresponding to the RF system frequency of 500 MHz. Arbitrary filling patterns can be used to study the interaction of adjacent bunches in CSR. To detect and study the THz emission characteristics of CSR over multiple revolutions a detector system based on thin YBa2Cu3O7−δ (YBCO) superconductor film detectors can be used. The intrinsic response time of YBCO thin films is only a few picoseconds and allows one to resolve the signal of individual bunches even within a multi-bunch environment. Response transients excited by CSR THz pulses as short as 17 ps has been determined as the FWHM at the output. A novel system for fast and continuous sampling of the individual ultra-short terahertz pulses has been developed. The setup is accomplished by real-time data processing based on high-end graphics processing units (GPUs). The data acquisition system consists of detector, low-noise amplifier, fast pulse sampling FMC board, readout board and the readout PC. The analog output of the low noise amplifier operating at ambient temperature is connected to the fast sampling board. Four samples are recorded in parallel for each terahertz pulse with programmable sampling times in the range of 3 to 100 ps. The readout board provides programmable logic (FPGA) and large memories for on-line data processing and temporary storage. The FPGA performs an on-line pulse reconstruction and calculates both the peak amplitude of each pulse and the time between consecutive bunches with a picosecond time resolution using fast waveform sampling technics. Finally, the data is transmitted to the readout computer. The readout interface is realized by a bus master DMA engine connected to PCI Express endpoint logic to ensure a high data throughput of up to 2 GByte/s. The fast pulse sampling board and the high data throughput board have been tested with terahertz YBCO detectors at ANKA. Multi-turn measurements of CSR have turned out to be an important diagnostic tool for storage rings with short bunch operation. With the DAQ system it is possible to resolve the bursting behavior of single bunches even in a multi-bunch environment to study the bunch-bunch-interactions.
