• M.J. Hagmann
  NewPath, Salt Lake City, Utah

We have shown that a group of sinusoidally-wound coaxial toroids can be used to determine the transverse distribution of a time-dependent current that passes through their common aperture. The current is expressed in a basis of chapeau (pulse) functions over an array of pixels, and matrix methods are used to determine the current in each pixel from measurements of the voltages that are induced on the toroids. Optimum configurations of pixels are used, for which the condition number of the matrix is bounded by the number of pixels. For example, with a resolution of 50 pixels, the fractional errors in determining the current at each pixel are approximately 50 times the fractional errors in the measurements of the induced voltages as well as imperfections in the fabrication of the toroids and their placement. Our algorithms were tested numerically by specifying the currents, calculating the voltages that would be induced on the toroids, adding Gaussian noise to these voltages, and then using the algorithms to calculate the currents from the simulated voltage measurements. These simulations confirm that the condition number of the matrix is bounded by the number of pixels.

• M.M. Dehler, G.J. Behrmann
  PSI, Villigen
• M. Siemens, S. Vilcins
  DESY, Hamburg

Currently, a prototype fast intra bunch train feedback system is under development which is to be tested at FLASH. For pickups as well as kickers, stripline devices have been developed. The new pickup is based on the earlier designs used in the transfer lines of the swiss light source as well as in the proton cyclotron PROSCAN at PSI; in particular, the stripline electrode output coupling is intentionally mismatched in order to increase the shunt impedance seen by the beam. Two versions have been designed for a center frequency of 1.65 GHz and a loaded Q of 35. Prototypes have been fabricated and built into FLASH. The stripline kicker consists of four main elements (all in-vacuum): two stripline electrodes fabricated from extruded aluminum and two metallic ground planes, held in place by ceramic spacers. The latter reduce the mutual inductance between the electrodes and optimize the RF match for asymmetries in the RF feed. Prototypes have been built, measured in the lab, and are now in the process of being inserted into FLASH.

• W.X. Cheng, W.J. Corbett, A.S. Fisher
  SLAC, Menlo Park, California

A dual-axis, synchroscan streak camera was used to measure temporal bunch profiles in three storage rings at SLAC: the PEP-II low-energy and high-energy rings, and SPEAR3. At high currents, both PEP rings exhibit a transient shift in synchronous phase along the bunch train due to RF-cavity loading. Bunch length and profile asymmetry were measured along the train for a range of beam currents. To avoid the noise of a dual-axis sweep, we accumulated a single-axis synchroscan image over multiple turns while applying a 50-ns gate to the microchannel plate. To improve the extinction ratio, we synchronized this 2-kHz gate with an upstream mirror pivoting at 1 kHz to deflect light from other bunches off the axis. At SPEAR3 we compared the bunch length as a function of current for several lattices: achromatic, low-emittance and low momentum compaction. In the first two cases, resistive and reactive impedance components were extracted from the longitudinal bunch profiles. In the low-alpha configurations, we observed natural bunch lengths approaching the camera resolution, requiring special care to remove instrumental effects, and saw evidence of instability and periodic bursting.

• J.F. Power, J.D. Gilpatrick, D. Martinez
  LANL, Los Alamos, New Mexico

Beam position monitors planned for the LANSCE diagnostics upgrade will be required to measure beam position and phase of the 201.25-MHz bunched beam in the proton linac. One method to do this is direct down conversion to in-phase and quadrature-phase data of the BPM signals using either commercial digitizers or custom designed hardware. We are evaluating selected hardware for systems with emphasis on COTS hardware to the extent practical. Basic system requirements include a beam current range of 26 db, position resolution of 0.05% of beam aperture and relative phase measurement with 0.25 degree resolution. We present our results to date on three approaches including ZTEC Instruments ZT-410 digitizers, a custom four-channel ADC analog front end board combined with National instruments, Inc. digital I/O and some limited data taken with the Instrumentation Technologies Libera system. The Libera system is a stand-alone BPM system. The other two systems use PCI cards in a standard PC running Windows XP. Our primary points of comparison include measured position resolution, phase resolution, phase linearity, minimum cycle rate and approximate cost for these portions of a BPM system.

• M. Tobiyama, J.W. Flanagan, T. Obina, M. Tadano
  KEK, Ibaraki

Button electrodes with good time response are essential for the bunch-by-bunch feedback / diagnostic systems needed for future short-bunch-spacing accelerators, such as energy recovery linacs (ERL) or a super B-factory. The impedance matching and time-domain response of electrodes, particularly around the vacuum seal, have been studied using 3-D electromagnetic codes (HFSS, MAFIA and GdfidL). Several candidates have been fabricated to examine the tolerance for mechanical pressures and heat stress due to the welding process. The real beam response from a short bunch has also been studied using a test-beam line at the KEK-PF injector beam transport section.

• J.C. Dooling, L. Donley, M.K. Lien, C. Yao
  ANL, Argonne

A cw tune measurement system for the IPNS RCS is described. The pinger magnets are energized by a solid-state, transformer-coupled power supply operating at 30 Hz. In its present configuration, the power supply provides a 160-A pulse to a pair of series-connected, single-turn ferrite magnets. The magnet pair drive separately x- and y-plane orbit bumps in the h=1 beam. The dipole oscillations generated in the beam are sensed with pairs of split-can, "pie" electrodes. Raw signals from the H and V electrodes are carried on matched coax-cables to 0/180-degree combiners. The output difference signals are recorded with gated spectrum analyzers. Bunch circulation frequency varies from 2.21 MHz at injection to 5.14 MHz at extraction. With a fixed frequency span of 24 MHz, between 4 and 10 bunch harmonics and sidebands (SBs) are present in the difference spectra. Software has been developed to use the multi-harmonic SBs present over the span to improve the accuracy of the tune measurements. The software first identifies and then fits the multiple SBs to determine the tune. Sweeping the beam across the momentum aperture provides a method for measuring the chromaticity.