DESY, Hamburg
To control the beam position at the entrance of the FLASH dump a position monitor is required outside of the vacuum. When a charged particle travels through a gas it will ionize the atoms. Therefore the signal from a capacitive button monitor is caused not only by the electric field of the beam but also by the ionized atoms which add high background to the usable signal. To avoid the ionization signal a magnetic coupled monitor is designed. The monitor consists of four longitudinal loops symmetrically arranged at the tube wall. An analytical expression of the signal for this monitor is derived and compared with simulation. Raw data are compared with the expectation.
DESY, Hamburg
DESY Zeuthen, Zeuthen
Additional beam diagnostics has been installed in the dump line at FLASH in 2009. Its purpose is to prevent damage by long high current electron beam pulses, as happened in autumn 2008, when a vacuum leak occurred near the dump vacuum window. Beam position monitors (BPM), scintillator-based loss monitors and temperature sensors have been installed thus far in the dump area. Additional BPMs and loss monitors have meanwhile been installed. These include a magnetic BPM placed after the vacuum window. Magnetic loops are used in order to prevent the influence of the ions on the pick-up signals. Four ionization chambers, consisting of air-filled tubes, and 4 glass fibers have been installed parallel to the vacuum pipe, along the last 2 m of beam pipe. Beam halo monitors were installed next to the magnetic BPM. These consist of 4 diamond and 4 sapphire sensors operating as solid state ionization chambers. The halo monitors are sensitive to very small losses. These additional diagnostic monitors were commissioned in autumn 2009, and have contributed to the successful run of long pulses with 3-9 mA current and up to 800 microsecond length. Their performance will be summarized in this paper.