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Study of ferrite formation in neutron irradiated austenitic stainless steels. Progress report, June 1, 1973--February 28, 1974

Description: A vibrating reed magnetometer was constructed for measurements on small irradiated samples. It can be operated at 4 to 500 deg K and can detect a magnetic moment of 4 x 10/sup -5/ erg/O/sub e/, with a signal-to-noise ratio of 20. A simple calibration procedure was devised. The magnetometer was used to measure magnetization curves of an irradiated type 316 austenitic stainless steel specimen at two different temperatures. Results confirm that the specimen contains numerous small magnetic particles which are presumed to be ferrite. Transmission electron microscopy of the irradiated specimen was not conclusive for the presence or absence of ferrite. (5 figures) (DLC)
Date: January 1, 1974
Creator: Stanley, J.T. & Hendrickson, L.E.
Partner: UNT Libraries Government Documents Department

Study of ferrite formation in neutron irradiated austenitic stainless steels. Progress report, March 1, 1975--February 29, 1976

Description: Magnetization measurements were carried out on a number of neutron- irradiated austenitic stainless steel specimens. Variation of magnetization with field indicates that the magnetic phase particles are very small so that the particles show superparamagnetic behavior. The temperature dependence of the magnetization indicates that more than one ferromagnetic phase may be present in some of the specimens. Postirradiation annealing at 500$sup 0$C increased the quantity of magnetic phase in specimens that had been irradiated at 425$sup 0$C and annealing in a magnetic field of 33 kOe has the effect of increasing the total quantity of magnetic phase but reducing the average size of the magnetic particles. (auth)
Date: January 1, 1976
Creator: Stanley, J.T. & Hendrickson, L.E.
Partner: UNT Libraries Government Documents Department

Linac Coherent Light Source Longitudinal Feedback Model

Description: The Linac Coherent Light Source (LCLS) will be the world's first x-ray free-electron laser (FEL). To ensure the vitality of FEL lasing, it is critical to preserve the high quality of the electron beam during acceleration and compression. The peak current and final energy are very sensitive to system jitter. To minimize this sensitivity, a longitudinal feedback system on the bunch length and energy is required, together with other diagnostics and feedback systems (e.g., on transverse phase space). Here, we describe a simulation framework, which includes a realistic jitter model for the LCLS accelerator system, the RF acceleration, structure wakefield, and second order optics. Simulation results show that to meet the tight requirements set by the FEL, such a longitudinal feedback system is mandatory.
Date: June 15, 2005
Creator: Wu, Juhao; Emma, P.; Hendrickson, L. & /SLAC
Partner: UNT Libraries Government Documents Department

Recording PEP2 Ring Beam Losses at SLAC

Description: The PEP2 (e+)(e-) storage rings contain many complex interrelated systems. When the beam aborts, examining a record of the orbit from the time just before the abort can help identify the root cause. At the Stanford Linear Accelerator Center (SLAC) a system has been developed to continuously record beam orbits from Beam Position Monitors (BPMS) into a circular buffer. When the beam is aborted the buffers are frozen and their contents are stored for later analysis. BPM orbits are saved on a turn by turn basis for 2800 turns in both the high energy ring (HER) and the low energy ring (LER). Each BPM Processor (BPMP) can either monitor the HER or the LER, but not both as the readout of the two rings is multiplexed into a single readout channel. Tools exist as part of the SLAC Control Program (SCP) to collect, display, and save the data. A physicist or operator can choose a few BPMS in which to view all 2800 turns to identify the turn in which the beam went awry; then ask for that specific orbit from all of the BPMS in the storage ring to determine the root cause of the abort.
Date: September 30, 2005
Creator: Zelazny, M.; Gromme, T.; Himel, T.; Hendrickson, L.; Krauter, K. & /SLAC
Partner: UNT Libraries Government Documents Department

Limitations of interaction-point spot-size tuning at the SLC

Description: At the Stanford Linear Collider (SLC), the interaction-point spot size is minimized by repeatedly correcting, for both beams, various low-order optical aberrations, such as dispersion, waist position or coupling. These corrections are performed about every 8 hours, by minimizing the IP spot size while exciting different orthogonal combinations of final-focus magnets. The spot size itself is determined by measuring the beam deflection angle as a function of the beam-beam separation. Additional information is derived from the energy loss due to beamstrahlung and from luminosity-related signals. In the 1996 SLC run, the typical corrections were so large as to imply a 20-40% average luminosity loss due to residual uncompensated or fluctuating tunable aberrations. In this paper, the authors explore the origin of these large tuning corrections and study possible mitigations for the next SLC run.
Date: May 1, 1997
Creator: Emma, P.; Hendrickson, L.J.; Zimmermann, F. & Raimondi, P.
Partner: UNT Libraries Government Documents Department

Use of digital control theory state space formalism for feedback at SLC

Description: The algorithms used in the database-driven SLC fast-feedback system are based on the state space formalism of digital control theory. These are implemented as a set of matrix equations which use a Kalman filter to estimate a vector of states from a vector of measurements, and then apply a gain matrix to determine the actuator settings from the state vector. The matrices used in the calculation are derived offline using Linear Quadratic Gaussian minimization. For a given noise spectrum, this procedure minimizes the rms of the states (e.g., the position or energy of the beam). The offline program also allows simulation of the loop's response to arbitrary inputs, and calculates its frequency response. 3 refs., 3 figs.
Date: May 1, 1991
Creator: Himel, T.; Hendrickson, L.; Rouse, F. & Shoaee, H.
Partner: UNT Libraries Government Documents Department

Correlation plot facility in the SLC control system

Description: The Correlation Plot facility is a powerful interactive tool for data acquisition and analysis throughout the SLC. A generalized interface allows the user to perform a wide variety of machine physics experiments without the need for specialized software. It has been used extensively during SLC commissioning and operation. The user may step one or two independent parameters such as magnet or feedback setpoints while measuring or calculating up to 160 others. Measured variables include all analog signals available to the control system as well as a variety of derived parameters such as beam size or emittance. Various fitting algorithms and display options are provided for data analysis. A software-callable interface is also provided. Applications based on this facility are used to phase klystrons, measure emittance and dispersion, minimize beam size at the interaction point and maintain beam collisions. 4 refs., 3 figs.
Date: May 1, 1991
Creator: Hendrickson, L.; Phinney, N. & Sanchez-Chopitea, L.
Partner: UNT Libraries Government Documents Department

Correlation Plot facility in the SLC control system

Description: The Correlation Plot facility is a powerful interactive tool for data acquisition and analysis throughout the SLC. This generalized interface allows the user to perform a range of operations or machine physics experiments without the need for any specialized analysis software. The user may step one or more independent parameters, such as magnet or feedback setpoints, while measuring or calculating up to 160 other parameters. Measured variables include all analog signals available to the control system, as well as calculated parameters such as beam size, luminosity, or emittance. Various fitting algorithms and display options are provided. A software-callable interface has been provided so that a host of applications can call this package for analysis and display. Such applications regularly phase klystrons, measure emittance and dispersion, minimize beam size, and maintain beam collisions at the interaction point. 4 refs., 5 figs.
Date: November 1, 1991
Creator: Hendrickson, L.; Phinney, N.; Sanchez-Chopitea, L. & Clark, S.
Partner: UNT Libraries Government Documents Department

Experience with wire scanners at SLC

Description: Fifty wire scanners are in use at SLC for phase space and beam optics monitoring. A large number of failures of the 50 {mu}m wire used in the scanners have occurred. Studies of these show strong electro-magnetic fields produced by the beam to be the probable cause. The problem has been cured with the adoption of a ceramic mounting scheme. Other improvements including very high dynamic range scans and scans of non-gaussian beams are described.
Date: December 1, 1992
Creator: Ross, M. C.; Bong, E.; Hendrickson, L.; McCormick, D. & Zolotorev, M.
Partner: UNT Libraries Government Documents Department

Feedback performance at the Stanford Linear Collider

Description: Many feedback loops are used at the Stanford Linear Collider (SLC) to control the orbit and energy of particle beams. Problems with corrector magnet slew rates, actuator calibrations, and computation of the beam transport matrix between loops have resulted in operation of many SLC feedback loops at lower than design gain. The response of various feedback loops to these errors is measured and analyzed in an attempt to improve performance.
Date: June 1, 1995
Creator: Minty, M.G.; Adolphsen, C.; Hendrickson, L.J.; Sass, R.; Slaton, T. & Woodley, M.
Partner: UNT Libraries Government Documents Department

Wire scanners for beam size and emittance measurements at the SLC

Description: The SLC wire scanner beam profile monitors provide accurate beam size and emittance measurements for each bunch in the three bunch SLC beam. The beam size measurement error for typical 50GeV SLC linac beams (100{mu}m {sigma}({sub x,y})) is better than 5{mu}m. Beam profile measurements can be performed throughout much of the SLC with no interruption to normal machine operation and no adverse impact on interaction region detector backgrounds. The linac input and output emittance is determined using sets of four scanners spaced by {approximately}45{degrees} betatron phase advance. Each scanner contains three wires, x, y and u (45{degrees}), from which an estimate of the x-y coupling can be obtained. Advanced high level control software allows the use of wire scanner data in feedback and beam optimization procedures. Non-invasive scans are performed almost continually and the results are logged so that long term trends in emittance can be examined. In this paper we describe the design, construction, performance and uses of SLC wire scanners. 7 refs., 3 figs., 1 tab.
Date: May 1, 1991
Creator: Ross, M.C.; Seeman, J.T.; Bong, E.; Hendrickson, L.; McCormick, D. & Sanchez-Chopitea, L.
Partner: UNT Libraries Government Documents Department

Generalized fast feedback system in the SLC

Description: A generalized fast feedback system has been developed to stabilize beams at various locations in the SLC. The system is designed to perform measurements and change actuator settings to control beam states such as position, angle and energy on a pulse to pulse basis. The software design is based on the state space formalism of digital control theory. The system is database-driven, facilitating the addition of new loops without requiring additional software. A communications system, KISNet, provides fast communications links between microprocessors for feedback loops which involve multiple micros. Feedback loops have been installed in seventeen locations throughout the SLC and have proven to be invaluable in stabilizing the machine.
Date: November 1, 1991
Creator: Hendrickson, L.; Allison, S.; Gromme, T.; Himel, T.; Krauter, K.; Rouse, F. et al.
Partner: UNT Libraries Government Documents Department

Fast feedback for linear colliders

Description: A fast feedback system provides beam stabilization for the SLC. As the SLC is in some sense a prototype for future linear colliders, this system may be a prototype for future feedbacks. The SLC provides a good base of experience for feedback requirements and capabilities as well as a testing ground for performance characteristics. The feedback system controls a wide variety of machine parameters throughout the SLC and associated experiments, including regulation of beam position, angle, energy, intensity and timing parameters. The design and applications of the system are described, in addition to results of recent performance studies.
Date: May 1, 1995
Creator: Hendrickson, L.; Adolphsen, C.; Allison, S.; Gromme, T.; Grossberg, P.; Himel, T. et al.
Partner: UNT Libraries Government Documents Department

Beam-based monitoring of the SLC linac optics with a diagnostic pulse

Description: The beam optics in a linear accelerator may be changed significantly by variations in the energy and energy spread profile along the linac. In particular, diurnal temperature swings in the SLC klystron gallery perturb the phase and amplitude of the accelerating RF fields. If such changes are not correctly characterized, the resulting errors will cause phase advance differences in the beam optics. In addition RF phase errors also affect the amplitude growth of betatron oscillations. The authors present an automated, simple procedure to monitor the beam optics in the SLC linac routinely and non-invasively. The measured phase advance and oscillation amplitude is shown as a function of time and is compared to the nominal optics.
Date: July 1, 1997
Creator: Assmann, R.W.; Decker, F.J.; Hendrickson, L.J.; Phinney, N.; Siemann, R.H.; Underwood, K.K. et al.
Partner: UNT Libraries Government Documents Department

General, database-driven fast-feedback system for the Stanford Linear Collider

Description: A new feedback system has been developed for stabilizing the SLC beams at many locations. The feedback loops are designed to sample and correct at the 60 Hz repetition rate of the accelerator. Each loop can be distributed across several of the standard 80386 microprocessors which control the SLC hardware. A new communications system, KISNet, has been implemented to pass signals between the microprocessors at this rate. The software is written in a general fashion using the state space formalism of digital control theory. This allows a new loop to be implemented by just setting up the online database and perhaps installing a communications link. 3 refs., 4 figs.
Date: May 1, 1991
Creator: Rouse, F.; Allison, S.; Castillo, S.; Gromme, T.; Hall, B.; Hendrickson, L. et al.
Partner: UNT Libraries Government Documents Department

Tutorial on beam-based feedback systems for linacs

Description: A generalized fast feedback system stabilizes beams in the SLC. It performs measurements and modifies actuator settings to control beam states such as position, angle, energy and intensity on a pulse to pulse basis. An adaptive cascade feature allows communication between a series of linac loops, avoiding overcorrection problems. The system is based on the state space formalism of digital control theory. Due to the database-driven design, new loops are added without requiring software modifications. Recent enhancements support the monitoring and control of nonlinear states such as beam phase using excitation techniques. In over three years of operation, the feedback system has grown from its original eight loops to more than fifty loops, and it has been invaluable in stabilizing the machine.
Date: August 1994
Creator: Hendrickson, L.; Allison, S.; Gromme, T.; Grossberg, P.; Himel, T.; Krauter, K. et al.
Partner: UNT Libraries Government Documents Department

Using higher order modes in superconducting accelerating cavities for beam monitoring

Description: Dipole modes have been shown to be successful diagnostics for the beam position in superconducting accelerating cavities at the Free Electron Laser in Hamburg (FLASH) facility at DESY. By help of downmixing electronics the signals from the two higher order mode (HOM) couplers mounted on each cavity are monitored. The calibration, based on sigular value decomposition, is more complicated than in standard position monitors. Position like signals based on this calibration are currently being in the process of being included in the control system. A second setup based on digitizing the spectrum from the HOM couplers has been used for monitoring monopole modes. The beam phase with respect to the RF has been thus monitored. The position calibration measurements and phase monitoring made at the FLASH are presented.
Date: January 1, 2006
Creator: Molloy, S.; Baboi, N.; Eddy, N.; Frisch, J.; Hendrickson, L.; Hensler, O. et al.
Partner: UNT Libraries Government Documents Department

Using Higher Order Modes in Superconducting Accelerating Cavities for Beam Monitoring

Description: Dipole modes have been shown to be successful diagnostics for the beam position in superconducting accelerating cavities at the Free Electron Laser in Hamburg (FLASH) facility at DESY. By help of downmixing electronics the signals from the two higher order mode (HOM) couplers mounted on each cavity are monitored. The calibration, based on singular value decomposition, is more complicated than in standard position monitors. Position like signals based on this calibration are currently being in the process of being included in the control system. A second setup based on digitizing the spectrum from the HOM couplers has been used for monitoring monopole modes. The beam phase with respect to the RF has been thus monitored. The position calibration measurements and phase monitoring made at the FLASH are presented.
Date: March 7, 2008
Creator: Molloy, S.; Baboi, N.; Eddy, N.; Frisch, J.; Hendrickson, L.; Hensler, O. et al.
Partner: UNT Libraries Government Documents Department

Beam Position Monitoring with Cavity Higher Order Modes in the Superconducting Linac FLASH

Description: FLASH (Free Electron Laser in Hamburg) is a user facility for a high intensity VUV-light source [1]. The radiation wavelength is tunable in the range from about 40 to 13 nm by changing the electron beam energy from 450 to 700 MeV. The accelerator is also a test facility for the European XFEL (X-ray Free Electron Laser) to be built in Hamburg [2] and the project study ILC (International Linear Collider) [3]. The superconducting TESLA technology is tested at this facility, together with other accelerator components.
Date: March 20, 2007
Creator: Baboi, N.; Molloy, S.; Eddy, N.; Frisch, J.; Hendrickson, L.; Hensler, O. et al.
Partner: UNT Libraries Government Documents Department

Nanosecond-Timescale Intra-Bunch-Train Feedback for the Linear Collider: Results of the FONT2 Run

Description: We report on experimental results from the December 2003/January 2004 data run of the Feedback On Nanosecond Timescales (FONT) experiment at the Next Linear Collider Test Accelerator at SLAC. We built a second-generation prototype intra-train beam-based feedback system incorporating beam position monitors, fast analogue signal processors, a feedback circuit, fast-risetime amplifiers and stripline kickers. We applied a novel real-time charge-normalization scheme to account for beam current variations along the train. We used the system to correct the position of the 170-nanosecond-long bunchtrain at NLCTA. We achieved a latency of 53 nanoseconds, representing a significant improvement on FONT1 (2002), and providing a demonstration of intra-train feedback for the Linear Collider.
Date: May 11, 2005
Creator: Barlow, R.; Dufau, M.; Kalinin, A.; /Daresbury; Myatt, G.; Perry, C. et al.
Partner: UNT Libraries Government Documents Department