[en] The proceedings of Working Group 4 of the 2005 Energy Recovery Linac (ERL) workshop are summarized. Working Group 4 dealt with the challenging topic of beam diagnostics for ERL machines. Energy Recovery Linacs represent a challenge for beam diagnostics from several perspectives; invasive versus non-invasive diagnostics, longitudinal and transverse beam diagnostics, overall machine timing/synchronization and machine protection. Beam diagnostics for an ERL can benefit strongly from the experience at third generation light sources, recirculating linacs and presently operating ERLs. During the workshop there were presentations from all these communities, representing a large range operation experience in beam diagnostics. A brief summary Working Group 4 discussion is presented in this paper

[en] The hypernuclear physics program at Jefferson Lab [JLAB] requires a tight upper limit on the RMS beam energy spread of sigmaE over E < 3 x 10^-5. The energy spread is determined by measuring the beam width at a dispersive location (D ∼ 4 m) in the transport line to the experimental halls. Ignoring the intrinsic beam size, this low energy spread corresponds to an upper bound on the beam width of sigma_beam < 120 mu-m. Such small beam sizes cannot be measured using direct imaging of the synchrotron light due to diffraction limitations. Using interferometry of the synchrotron light the resolution of the optical system can be made very high. The non-invasive nature of this measurement is also very advantageous as it allows continuous energy spread monitoring. Two synchrotron light interferometers have been built and installed at Jefferson Lab, one each in the Hall-A and Hall-C transport lines. The two devices operate over a beam current range from 10 to 120 mu-A and have a spatial resolution better than 10 mu-m. The structure of the interferometer, the experience gained during its installation, beam measurements and energy spread stability are presented

[en] Beam halo formation in the beam transport design for the Jefferson Lab 12GeV upgrade was investigated using 12GeV beam transport models as well as data from 6GeV CEBAF operations. Various halo sources were considered; these covered both nuclear interactions with beam gas as well as optics-related effects such as non linearities in the magnetic fields of the transport elements. Halo due to beam gas scattering was found to be less of a problem at 12GeV compared to the 6GeV machine. Halo due to non linear effects of magnetic elements was characterized as a function of beam orbit and functional forms of the distribution were derived. These functional forms were used as inputs in subsequent detector optimizations studies

[en] A new method of beam position measurement suitable for monitoring high energy and high power charged particle beams in the vicinity of high power beam dumps is presented. We have found that a plate made of Chemical Vapor Deposition (CVD) Silicon Carbide (SiC) has physical properties that make it suitable for such an application. CVD SiC material is a chemically inert, extremely radiation-hard, thermo-resistive semiconductor capable of withstanding working temperatures over 1500 C. It has good thermal conductivity comparable to that of Aluminum, which makes it possible to use it in high-current particle beams. High electrical resistivity of the material, and its semiconductor properties allow characterization of the position of a particle beam crossing such a plate by measuring the balance of electrical currents at the plate ends. The design of a test device, and first results are presented in the report

[en] Proper transport of the electron beam with over 0.5MW of power to the beam dump is a prerequisite for operations at Jefferson Lab. Operations has relied on imaging the beam on a beam viewer located at the entrance to the beam dump. The large beam size at the dump entrance, due to beam scattering in the experimental target, sometimes results in no observable image on the view-screen. Chemical vapor deposited silicon carbide [CVD] material with its large thermal conductivity and high melting point is well suited for surviving the thermal effects of beam exposure with this power density. We are exploring the CVD properties and how it can be used as a robust beam position monitor. Results of some beam tests with 0.5MW beams will be presented

[en] The hyper-nuclear physics program at JLAB requires an upper limit on the RMS momentum spread of (delta)p/p < 3 x 10^-5. The momentum spread is determined by measuring the beam width at a dispersive location (D ∼ 4m) in the transport line to the experimental halls. Ignoring the epsilon-beta contribution to the intrinsic beam size, this momentum spread corresponds to an upper bound on the beam width of σ_beam < 120 (micro)m. Typical techniques to measure and monitor the beam size are either invasive or do not have the resolution to measure such small beam sizes. Using interferometry of the synchrotron light produced in the dispersive bend, the resolution of the optical system can be made very small. The non-invasive nature of this measurement allows continuous monitoring of the momentum spread. Two synchrotron light interferometers have been built and installed at JLAB, one each in the Hall-A and Hall-C transport lines. The devices operate over a beam current range from 20 (micro)A to 120 (micro)A and have a spatial resolution of 10um. The structure of the interferometers, the experience gained during its installation, beam measurements and momentum spread stability are presented. The dependence of the measured momentum spread on beam current will be presented

[en] The proposed HAPPEX experiment at CEBAF employs a three cavity monitor system for high precision (1um), high bandwidth (100 kHz) position measurements. This is performed using a cavity triplet consisting of two TM110-mode cavities (one each for X and Y planes) combined with a conventional TM010-mode cavity for a phase and magnitude reference. Traditional systems have used the TM010 cavity output to directly down convert the BPM cavity signals to base band. The multi-channel HAPPEX digital receiver simultaneously I/Q samples each cavity and extracts position using a CORDIC algorithm. The hardware design consists of a RF receiver daughter board and a digital processor motherboard that resides in a VXI crate. The daughter board down converts 1.497 GHz signals from the TM010 cavity and X and Y signals from the TM110 cavities to 3 MHz and extracts the quadrature digital signals. The motherboard processes this data and computes beam intensity and X-Y positions with resolution of 1um, 100 kHz output bandwidth, and overall latency of 1us. The results are available in both the analog and digital format

[en] The G0 parity violation experiment at Jefferson Lab is based on time-of-flight measurements, and is sensitive to timing effects between the two electron helicity states of the beam. Photon counters triggered by time-of-arrival at the target mandate that timing must be independent of delays associated with different orbits taken by the two helicity states. In addition, the standard 499 MHz beam structure is altered such that 1 of every 16 microbunches are filled, resulting in an arrival frequency of 31.1875 (31) MHz, and an average current of 40 (micro)A. Helicity correction involves identifying and tracking the 31 MHz subharmonic, applying a fast/fine phase correction, and finally producing a clean 31 MHz trigger and a 499 MHz clock train. These signals are phase-matched to the beam arrival at the target on the order of femtoseconds. The 10 kHz output bandwidth is sufficiently greater than the 30 Hz helicity flip settling time (500 (micro)s). This permits the system to correct each helicity bin for any orbit-induced timing inequalities. A sampling phase detection scheme is used in order to eliminate the unavoidable 2n/n phase shifts associated with frequency dividers. Conventional receiver architecture and DSP techniques are combined for maximum sensitivity, bandwidth, and flexibility. Results of bench tests, commissioning and production data will be presented

[en] Energy recovering a 1 GeV beam through CEBAF (Continuous Electron Beam Accelerator Facility) presents many operational challenges. As a result, it is important to have a quantitative understanding of the beam behavior throughout the machine. The emittance provides a figure of merit in this context inasmuch as it characterizes the extent to which beam quality is preserved during energy recovery. A solution to the problem of obtaining a high-resolution emittance measurement in the extraction region of the CEBAF-ER experiment (CEBAF with Energy Recovery) is presented. The method makes use of a single scanning quadrupole and a downstream wire scanner. In addition, by using multiple wire scans, a scheme for measuring the emittance and momentum spread of the first pass beam in the injector and Arcs 1 and 2 was implemented. And by using a novel technique employing wire scans in conjunction with PMTs (Photomultiplier Tubes) to accurately measure the beam profile at the dump, we can quantify . ..

[en] The future experimental program at Jefferson Lab requires an absolute current calibration of a 1 μA CW electron beam to better than 1% accuracy. This paper presents the mechanical and electrical design of a Tungsten calorimeter that is being constructed to provide an accurate measurement of the deposited energy. The energy is determined by measuring the change in temperature after beam exposure. Knowledge of the beam energy then yields number of electrons stopped by the calorimeter during the exposure. Simulations show that the energy lost due to electromagnetic and hadronic particle losses are the dominant uncertainty. Details of the precision thermometry and calibration, mechanical design, thermal simulations and simulations will be presented