SLAC, Menlo Park, California
Stanford University, Stanford, Califormia
The LCLS accelerator produces a 14GeV beam with a normalized emittance on the order of one micron RMS, and peak current exceeding 1000 Amps. The design of the beam measurement system relied heavily on optical transition radiation profile monitors, in conjunction with transverse cavities, and conventional energy spectrometers. It has been found that the high peak currents, and small longitudinal phase space of the beam generate strong coherent optical emission that prevents the use of OTR or other prompt optical diagnostics, requiring the use of wire scanners or fluorescent screen based measurements. We present the results of the beam measurements, measurements of the coherent optical effects, and future plans for diagnostics.
GSI, Darmstadt
Scintillation screens are widely used for qualitative beam profile monitoring, but precise profile measurements yields ambivalent results for high beam currents. Moreover, these screens are an essential part of a pepper-pot emittance system requiring a quantitative profile evaluation. Therefore, we investigated the optical properties of 14 scintillating materials with different beams in the energy range 5.5 to 11.4 MeV/u as delivered by the heavy ion linac at GSI. Beside sensitive scintillators like YAG we focus on ceramic materials with lower light yield, like BN, ZrO2, Al2O3 and Al2O3+Cr. Their properties (light yield, beam width, high statistical moments etc.) are compared to different quartz glasses. The image of each macro-pulse is recorded by a digital CCD camera and individually evaluated by a high performance data acquisition system. For some materials, a decay of the light yield and an increase of the imaged beam width were observed. Moreover, the light yield depends on the screen temperature, which is significantly increased by the beam impact. A quantitative comparison under different beam conditions is presented.
ORNL, Oak Ridge, Tennessee
Taking Advantage of recent successes with the Laser Profile monitor, a new protottype is being built to use the laser wire as both a profile monitor and a slit for an emittance measuring device. This improved system takes advantage of the steering dipole magnet prior to ring injection of SNS such that only the recently stripped H0 protons continue forward to the emmitance device. In this way we hope to make an emittance device that is both parasitic to neutron production, and capable of accurate measurements during full power applications.
KIP, Heidelberg
CERN, Geneva
GSI, Darmstadt
Synchrotron radiation has proven to be a flexible and effective tool for measuring a wide range of beam parameters in storage rings, in particular information about the longitudinal beam profile. It is today an established and widely used diagnostic method providing online measurements and thus allowing for continuous optimization of the machine performance. At the CLIC Test Facility (CTF3), synchrotron radiation is routinely used at a number of diagnostic stations, in particular in the Delay Loop and the Combiner Ring. Measurements with both standard CCDs and a streak camera showed the wide range of possible applications of this method, including determination of inter-bunch spacing, charge per pulse and monitoring of the manipulation of the effective path length by an undulator. This contribution first addresses the critical points during the design phase of long optical lines with lengths of more than 30 meters as they had to be realized at CTF3. Second, a summary of the present installations is given and results from measurements are shown.
INFN/LNF, Frascati (Roma)
INFN-Roma, Roma
The DAΦNE Beam Test Facility (BTF), initially optimized to produce single electrons and positrons in the 25-750 MeV energy range, can now provide beam in a wider range of intensity, up to 1010 electrons/pulse. The facility has been also equipped with a system for the production of tagged photons, and the possibility of photo-production of neutron is under study. Different diagnostic tools have been developed and are available for high-energy users and accelerator community to monitor and check beam and device under test performance. The main results obtained, the performance and the most significant characteristics of the facility diagnostics and operation are presented, as well as the users experience collected during these years of operation.
SLAC, Menlo Park, California
The Linac Coherent Light Source (LCLS) must deliver a high quality electron beam to the undulator. High resolution beam position monitoring is required to accomplish this task. Critical specifications are a dynamic range of 0.08-8.0 nC with a 5 microns resolution at 200 pC. New processor electronics was designed, processing is based on filtering the signals and direct digitization of the resulting pulse train. The processor consists of an Analog Front-End (AFE) and Analog-to-Digital Converter (ADC) boards, all are packed into 19-in rack mount chassis, 1U high. AFE board has a very low input noise, approximately 3 microV rms in a 7 MHz bandwidth centered at 140 or 200 MHz. The maximum gain is 34 dB with attenuation of up to 46 dB in 1 dB step. An on-board pulser sends the short CW burst to the striplines to perform between pulse calibration. The ADC board has four 16-bit digitizers, the sampling frequency is 120 MHz. The low-jitter clock is on a separate board in the same chassis. For the LCLS injector 22 prototypes of the processors were built and installed in 2007. Measured resolution at 200 pC is typically 3-5 microns. The 53 improved and modified processors are in production
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.
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.
I-Tech, Solkan
Libera Brilliance has proved successful in the field of beam diagnostics. High performance, system reliability and its high level of integration into accelerator control systems makes Libera a very accurate, robust and powerful measuring system. Although Libera Brilliance has been developed mainly for applications involving frequency domain processing, the flexibility makes it a good time domain measuring system for single pass applications. Moreover, there are other applications dealing with pulses, where a modified version of Libera Brilliance can be used. This is the case of beam phase and position measurements in accelerators, like Spiral2 (Ganil) and LANSCE (Los Alamos), dealing with heavy particles (protons, deuterons and heavy ions). The phase information extracted by the measurement in such systems is used to control the acceleration process of such heavy particles. This paper shows the approach adopted in processing the signals produced by such bunch trains. A modified Libera Brilliance unit, configured for the LANSCE bunch trains, has been tested by means of extensive laboratory measurements. Performance has been evaluated by applying different digital signal processing.
ORNL, Oak Ridge, Tennessee
The original wire-scanner software was written by one of the Spallation Neutron Source (SNS) partners, Los Alamos National Laboratory. This software was designed for the types of wire-scanners initially planned and their planned usage at that time. New variations in the wire-scanner hardware added gearing, different position read-back methods, and a timing card. The new software handles these additional hardware variations in a flexible manner through configuration files. The software upgrade allows the user to synchronize the stepping of the fork with external applications, such as loss monitors to study the losses caused by the wire. Another new functionality allows you to change what part of the beam pulse is used to determine the transverse profile after the data has been taken. This avoids having to do time consuming rescans if the timing was not perfectly setup. The new software, also a LabVIEW program, is structured around a state-machine with sequence capability to manage the complexities of stepping through a scan and interacting with the user. This paper discusses the features of the new software, the implementation, and the obtained results.
Fermilab, Batavia
INFN/LNF, Frascati (Roma)
Università di Roma II Tor Vergata, Roma
ANL, Argonne
We have previously experimentally observed and modeled the near-field optical diffraction radiation (ODR) generated by a 3-nC micropulse of a 7-GeV electron beam at the Advanced Photon Source (APS). Due to the high gamma of ~14,000, the scaling factor of γλ/2π was about 1.4 mm for 0.628 um radiation. Thus, a standard CCD camera was sufficient for imaging at an impact parameter of 1.25 mm. The extension of this technique to γ 1000 is challenged by the ·1014 reduction in visible light photon production compared to the APS case. We discuss the feasibility of monitoring at a new Fermilab facility a high average current linac beam of 3000 times more charge in a video frame time and with a more sensitive 12- to 16-bit camera. Numerical integrations of our base model show beam size sensitivity for ±20% level changes at 200- and 400-um base beam sizes. We also evaluated impact parameters of 5 σy and 12 σy for both 800-nm and 10-um observation wavelengths. The latter examples are also related to a proposal to apply the technique to an ~ 0.94 TeV proton beam, but there are trades on photon intensity and beam size sensitivity to be considered at such gammas.
Fermilab, Batavia
ANL, Argonne
During the commissioning of the LCLS injector in 2007, unexpected enhancements of the signals in the visible light optical transition radiation (OTR) monitors occurred after compression in a chicane bunch compressor. These were attributed to a microbunching effect of some kind. Explorations of such effects have now been performed on the Advanced Photon Source (APS) linac. The APS injector complex includes an option for photocathode (PC) gun beam injection into the 450-MeV S-band linac. At the 150-MeV point, a 4-dipole chicane was used to compress the micropulse bunch length from a few ps to sub-0.5 ps (FWHM). Noticeable enhancements of the OTR signal sampled after the APS chicane were observed. A FIR CTR detector and interferometer were used to monitor the bunch compression process and correlate the appearance of localized spikes of OTR signal (5-10 times brighter than adjacent areas) within the beam image footprint. We have done spectral dependency measurements at 375 MeV with a series of band pass filters centered from 400 to 700 nm and observed a broad-band enhancement in these spikes. Discussions of the possible mechanisms will be presented.
CERN, Geneva
Built at CERN by an international collaboration, the CLIC Test Facility 3 (CTF3) aims at demonstrating the feasibility of a high luminosity 3 TeV e+-e- collider by the year 2010. The CLIC project is based on the so called ?two-beam acceleration scheme? where the RF accelerating power is provided by a high current high frequency electron beam. The required performances put high demands on the diagnostic equipment and innovative monitors have been developed during the past years. This paper gives an overview of the instrumentation developed at CTF3 with a special emphasis on short bunch length measurements, high precision beam position monitors, high dynamic range beam imaging system and high precision beam phase measurements.