DESY, Hamburg, Germany
Fermilab, Batavia, Illinois, USA
CERN, Geneva, Switzerland
Transverse Higher Order Modes (HOM) excited by electron beams in the 3.9 GHz accelerating cavities at FLASH may damage the beam quality. They can be reduced by extracting their energy through special couplers and by aligning the beam in the cavity. Electronics has been designed at FNAL for monitoring some of the potentially most damaging HOMs. This may be used for beam centering and therefore reducing the HOM effects. Moreover, the signals can be potentially calibrated into beam offset, so that they could be used as beam position monitors (HOM-BPM). The specifications of the monitors have been defined during an extensive study on the 4-cavity accelerating module installed at FLASH. Signals around 5.44 GHz have been chosen for higher precision measurements. However these signals propagate into the entire 1.2 m long module. Therefore in addition modes at about 9 GHz were selected for localized measurements in each cavity. The electronics has been recently installed at FLASH. The commissioning results will be presented in this paper. Instabilities previously observed in a test electronics as well as the HOM-BPMs in 1.3 GHz cavities will also be investigated*. This electronics will also serve as a prototype for the electronics developed for the 3.9 GHz cavities at the European XFEL**.
*L. Shi et al., this Conference
**T. Wamsat et al., this Conference
Fermilab, Batavia, Illinois, USA
The latest generation of IPM's installed in the Fermilab Main Injector and Recycler incorporate a 1 kG permanent magnet, a newly designed high-gain, rad-tolerant preamp, and a control grid to moderate the charge that is allowed to arrive on the anode pick-up strips. The control grid is intended to select a single Booster batch measurement per turn. Initially it is being used to allow for a faster turn-on of a single, high-intensity cycle in either machine. The expectation is that this will extend the Micro Channel Plate lifetime, which is the high-cost consumable in the measurement system. We discuss the new design and data acquired with this system.
