BEAM PROFILE MEASUREMENT WITH OPTICAL FIBER SENSORS AT FLASH

Abstract The system is intended to determine the beam profile at the DESY-FLASH undulator section as well as measuring beam losses with high spatial resolution. The measurement setup is based on wire scanners, optical fibers which are symmetrically mounted around the beam line over the full length (30 m) of the undulator section, a signal conditioning unit and a data acquisition system. The optical fibers are used as beam loss sensors, and depending on the software configuration, the setup is working either as a beam loss position monito

Pore confinement effects and stabilization of carbon nitride oligomers in macroporous silica for photocatalytic hydrogen production

An ordered macroporous host (mac-SiO2) has been used to prevent aggregation of layered photocatalysts based on carbon nitride. Using typical carbon nitride synthesis conditions, cyanamide was condensed at 550 °C in the presence and absence of mac-SiO2. Condensation in the absence of mac-SiO2 results in materials with structural characteristics consistent with the carbon nitride, melon, accompanied by ca. 2 wt% carbonization. For mac-SiO2 supported materials, condensation occurs with greater carbonization (ca. 6 wt%). On addition of 3 wt% Pt cocatalyst photocatalytic hydrogen production under visible light is found to be up to 10 times greater for the supported composites. Time-resolved photoluminescence spectroscopy shows that excited state relaxation is more rapid for the mac-SiO2 supported materials suggesting faster electron-hole recombination and that supported carbon nitride does not exhibit improved charge separation. CO2 temperature programmed desorption indicates that enhanced photoactivity of supported carbon nitride is attributable to an increased surface area compared to bulk carbon nitride and an increase in the concentration of weakly basic catalytic sites, consistent with carbon nitride oligomers

Beam Loss Position Monitor using Cerenkov radiation in optical fibers

The VUV FEL in TESLA technology at DESY provides Giga Watt output power in laser pulses. The SASE single pass Free Electron Laser FEL has been developed for high brightness user applications. At the design parameters the average power of the electron beam is about 72 kW. To avoid vacuum breakdown and high radiation levels caused by electron losses a machine protection system is required. Collimators are installed upstream of the radiation sensitive undulators. How ever, the proper operation of the collimator system needs to be measured with a beam loss monitor. Conventional radiation sensor systems are not suited for the VUV FEL undulators, because of the restricted free space in the undulator gap. A Beam Loss Position Monitor BLPM based on Cerenkov light in optical fibers allows real time monitoring of loss location and loss intensity. Electrons with energies above 175 keV generate Cerenkov light during their penetration of the optical fiber. The fast response of the Cerenkov signal is detected with photomultipliers at the end of the irradiated fibers. The reconstruction of the particle loss trace in 3 space dimensions became possible with four sensor

Beam loss Monitors for FEL using optical Fiber

Beam losses and beam profiles at particle accelerators can be determined by measuring the ionizing radiation outside the vacuum chamber. The next generations of free elec tron lasers require novel solutions for beam loss monitor and radiation detection systems. A new concept at the Free Electron Laser Hamburg FLASH and Photo Injector Test Facility Zeuthen PITZ was developed and put into operation. The concept based on optical fibers used as radiation detection sensor. Slow beam loss monitors determine the total ionization dose at selected positions or along the beam line and undulator sections in a response time of a few milliseconds by measuring the radiation induced attenuation of the fiber. Fast beam loss monitors detect the Cerenkov light generated by relativistic electrons penetrating radiation hard fiber. The new beam loss position and beam profile monitor systems utilize this effect. The time response is below milliseconds with a time resolution of some nanoseconds. These monitors provide a technique to improve the beam performance and trace the stability of the over all setting parameters. This paper presents the new diagnostic methods and the operation experience of the systems with a focus on the fast beam loss monitor