We report on the commissioning of a higher harmonic RF system designed to improve the Touschek lifetime of the Advanced Light Source. In our best results, we have achieved over a factor of two increase in the beam lifetime. Transient beam loading of the harmonic cavities by unequal fill patterns presents the greatest limitations on lifetime improvement. We also describe several interesting effects of the harmonic cavities on the operation of the longitudinal and transverse multibunch feedback systems.
The environmental and health effects of wildfires are discussed. The monitoring of wildfires from aircraft using remote sensing techniques is reviewed. A future autonomous aerial observing system for fire monitoring is described.
A modular programmable longitudinal feedback system has been developed as a component of the PEP-11 R+D program. This system is based on a family of VME and VXI packaged signal processing functions which implement a general purpose digital feedback controller for accelerators with bunch spacings of 2 ns. A complete PEP-11 prototype system has been configured and installed for use at the LBL Advanced Light Source. The system configuration used for tests at the ALS is described and results are presented showing the action of the feedback system. Open and closed loop results showing the detection and calculation of feedback signals from bunch motion are presented and the system is shown to damp coupled-bunch instabilities in the ALS. Use of the system for accelerator diagnostics is illustrated via measurement of grow-damp transients which quantify growth rates without feedback, damping rates with feedback, and identify unstable modes. PEP-11 Longitudinal PrototypeThe PEP-11 longitudinal prototype is a modular bunch-by-bunch processing system designed to implement longitudinal feedback signal processing [l]. The system is composed of several processing modules in VME and VXI formats. The analog-to-digital and digital-to-analog functions are implemented in a pair of VXI processing modules which are capable of sampling bunch motion and generating correction signals at a 500 MHz rate, which allows the system to operate with bunch spacings of 2 ns. The 500 MHz A/D functions are incorporated in the Downsampler module, which is a programmable sequencer capable of controlling the sampling of up to 2048 bunches with downsampling factors up to 32. The 500 MHz DIA is contained in the hold buffer VXI module, whose buffer memory contains the most recent kick value for each bunch in the system. A VXI packaged QPSK modulator (which generates a kicker carrier signal which spans 1 to 1.25 GHz) and a Timing module (which generates several ECL clock signals from the ring RF master oscillator} complete the digital signal processing VXI modules [2].The signal processing algorithms are implemented as programs coded on AT+T DSP 1610 microprocessors. These single-chip 16 bit processors are organized into groups of four, *Work supported by Department of Energy, contract DE-ACO3-76SFOO515with four processors on each V M E packaged DSP module. A system configuration for a particular accelerator requires 3 to 20 of the DSP modules, depending on the machine synchrotron frequency, revolution frequency and number of bunches. Each sampling interval the Downsampler module sends bunch data to a particular DSP board (based on the downsampler program) and the DSP board sends computed results to the Hold buffer module. Figure 1 is a photograph of the system configured for testing at the ALS, which uses 10 DSP modules total.The system is configured and downloaded via a set of control programs which specify the operating configuration of the system and generate coefficients for the DSP algorithms. An EPICS based user interface allows a single co...
Abstract.A bunch-by-bunch longitudinal feedback system has been used to control coupledbunch longitudinal motion and study the behavior of the beam at ALS, SPEAR, PEP-II, and DA Φ NE. Each of these machines presents unique challenges to feedback control of unstable motion and data analysis. Here we present techniques developed to adapt this feedback system to operating conditions at these accelerators. A diverse array of techniques has been developed to extract information on different aspects of beam behavior from the time-domain data captured by the feedback system. These include measurements of growth and damping rates of coupledbunch modes, bunch-by-bunch current monitoring, measurements of bunch-by-bunch synchronous phases and longitudinal tunes, and beam noise spectra. A technique is presented which uses the longitudinal feedback system to measure transverse growth and damping rates. Techniques are illustrated with data acquired at all of the four above-mentioned machines.
The operation of a longitudinal multi-bunch damping system using digital signal processing techniques is shown via measurements from the LBL Advanced Light Source. The feedback system (developed for use by PEP-11, ALS and DAcPNE) uses a parallel array of signal processors to implement a bunch by bunch feedback system for sampling rates up to 500 MHz. The programmable DSP system allows feedback control as well as accelerator diagnostics. A diagnostic technique is illustrated which uses the DSP system to excite and then damp the beam. The resulting 12 ms time domain transient is Fourier analyzed to provide the simultaneous measurement of growth rates and damping rates of all unstable coupled-bunch beam modes.
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