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Maximum efficiency of a conventional klystron output cavity

Description: By using a photocathode instead of a thermionic cathode in a klystron, the possibility exists to make very short low energy spread bunches of high efficiency. However, there is a fundamental limit to the efficiency of a conventional output cavity, such as the one used in the SLAC XK-5 klystron. The fringing electric field in the drift tube acts on the beam as it leaves the output cavity and results in a net acceleration. All electrons which eventually reach the collector emerge from the drift tube with a substantial kinetic energy and as a result, the highest practical efficiency is about 80% for a 400 kV single output cavity tube. The behavior of these very short low energy spread bunches was calculated using MASK, a 2D field and particle program as well a much simpler 1D program. Using multiple output cavities, it may be possible to extract energy from the electrons more efficiently.
Date: May 1, 1986
Creator: Welch, J.J.
Partner: UNT Libraries Government Documents Department

Low energy cyclotron for radiocarbon dating

Description: The measurement of naturally occurring radioisotopes whose half lives are less than a few hundred million years but more than a few years provides information about the temporal behavior of geologic and climatic processes, the temporal history of meteoritic bodies as well as the production mechanisms of these radioisotopes. A new extremely sensitive technique for measuring these radioisotopes at tandem Van de Graaff and cyclotron facilities has been very successful though the high cost and limited availability have been discouraging. We have built and tested a low energy cyclotron for radiocarbon dating similar in size to a conventional mass spectrometer. These tests clearly show that with the addition of a conventional ion source, the low energy cyclotron can perform the extremely high sensitivity /sup 14/C measurements that are now done at accelerator facilities. We found that no significant background is present when the cyclotron is tuned to accelerate /sup 14/C negative ions and the transmission efficiency is adequate to perform radiocarbon dating on milligram samples of carbon. The internal ion source used did not produce sufficient current to detect /sup 14/C directly at modern concentrations. We show how a conventional carbon negative ion source, located outside the cyclotron magnet, would produce sufficient beam and provide for quick sampling to make radiocarbon dating milligram samples with a modest laboratory instrument feasible.
Date: December 1, 1984
Creator: Welch, J.J.
Partner: UNT Libraries Government Documents Department

Beam dynamics, efficiency and power of the SLAC lasertron: simulation results

Description: Results are described for the computer simulation of the SLAC proof of principle lasertron device with a conventional single gap output cavity, using the 2D relativistic field and particle code called MASK. The rf to beam power efficiency is calculated for different power levels, dc voltages and optical pulse lengths. The calculated efficiency at the initial operating point of 50 MW beam power, 400 kV, and with 60 picosecond optical pulse duration, is 66%. The maximum rf power at 400 kV is about 50 MW. At 600 kV the maximum power increases to about 110 MW, but the efficiency at low power is not much changed from what it was at 400 kV. The simulation calculation does not take into account loss of rf power due to backscattered electrons nor the full effects of the impedance of the accelerating gap. A calculation of the efficiency of the lasertron with a double output cavity has been carried out, and generally yields efficiencies about 10 percentage points higher than the single cavity simulation.
Date: May 1, 1986
Creator: Welch, J.J.
Partner: UNT Libraries Government Documents Department

Estimate of Undulator Magnet Damage Due to Beam Finder Wire Measurements

Description: Beam Finder Wire (BFW) devices will be installed at each break in the Undulator magnet line. These devices will scan small wires across the beam causing some electrons to lose energy through bremsstrahlung. The degraded electrons are subsequently detected downstream of a set of vertical dipole magnets after they pass through the vacuum chamber. This signal can then be used to accurately determine the beam position with respect to the BFW wire. The choice of the wire diameter, scan speed, and operating parameters, depends on the trade-off between the signal size and the radiation damage to the undulator magnets. In this note I estimate the rate of undulator magnet damage that results from scanning as a function of, wire size, scan speed, and average beam current. A separate analysis of the signal size was carried out by Wu. The damage estimate is primarily based on two sources: the first, Fasso, is used to estimate the amount of radiation generated and then absorbed by the magnets; the second, Alderman et. al., is used to estimate the amount of damage the magnet undergoes as a result of the absorbed radiation. Fasso performed a detailed calculation of the radiation, including neutron fluence, that results from a the electron beam passing through a 100 micron diamond foil inserted just in front of the undulator line. Fasso discussed the signficance of various types of radiation and stated that photoneutrons probably play a major role. The estimate in this paper assumes the neutron fluence is the only significant cause of radiation-induced demagnetization. The specific results I use from Fasso's paper are reproduced here in Figure 1, which shows the radial distribution of the integrated neutron fluence per day in the undulator magnets, and Figure 2, which shows the absorbed radiation dose all along the undulator line. ...
Date: December 3, 2010
Creator: Welch, J.
Partner: UNT Libraries Government Documents Department

Electromelt furnace evaluation

Description: An electromelt furnace was designed, built, and operated at the Idaho National Engineering Laboratory to demonstrate the suitability of this equipment for large-scale processing of radioactive wastes in iron-enriched basalt. Several typical waste compositions were melted and cast. The furnace was disassembled and the components evaluated. Calcines and fluorides attacked the furnace lining, unoxidized metals accumulated under the slag, and electrode attrition was high.
Date: September 1, 1981
Creator: Reimann, G.A. & Welch, J.M.
Partner: UNT Libraries Government Documents Department

BXS Re-calibration

Description: Early in the commissioning it was noticed by Cecile Limborg that the calibration of the BXS spectrometer magnet seemed to be different from the strength of the BX01/BX02 magnets. First the BX01/BX02 currents were adjusted to 135 MeV and the beam energy was adjusted to make the horizontal orbit flat. Then BX01/BX02 magnets were switched off and BXS was adjusted to make the horizontal orbit in the spectrometer line flat, without changing the energy of the beam. The result was that about 140-141 MeV were required on the BXS magnet. This measurement was repeated several times by others with the same results. It was not clear what was causing the error: magnet strength or layout. A position error of about 19 mm of the BXS magnet could explain the difference. Because there was a significant misalignment of the vacuum chamber in the BXS line, the alignment of the whole spectrometer line was checked. The vacuum chamber was corrected, but the magnets were found to be in the proper alignment. So we were left with one (or conceivably two) magnet calibration errors. Because BXS is a wedged shaped magnet, the bend angle depends on the horizontal position of the incoming beam. As mentioned, an offset of the beam position of 19 mm would increase or decrease the bend angle roughly by the ratio of 135/141. The figure of 19 mm is special and caused a considerable confusion during the design and measurement of the BXS magnet. This is best illustrated in Figure 1 which was taken out of the BXS Traveler document. The distance between the horizontal midplanes of the poles and the apex of the beam path was chosen to be 19 mm so the beam is close to the good field region throughout its entire path. Thus it seemed ...
Date: November 24, 2010
Creator: Welch, J.
Partner: UNT Libraries Government Documents Department

Undulator Hall Air Temperature Fault Scenarios

Description: Recent experience indicates that the LCLS undulator segments must not, at any time following tuning, be allowed to change temperature by more than about {+-}2.5 C or the magnetic center will irreversibly shift outside of acceptable tolerances. This vulnerability raises a concern that under fault conditions the ambient temperature in the Undulator Hall might go outside of the safe range and potentially could require removal and retuning of all the segments. In this note we estimate changes that can be expected in the Undulator Hall air temperature for three fault scenarios: (1) System-wide power failure; (2) Heating Ventilation and Air Conditioning (HVAC) system shutdown; and (3) HVAC system temperature regulation fault. We find that for either a system-wide power failure or an HVAC system shutdown (with the technical equipment left on), the short-term temperature changes of the air would be modest due to the ability of the walls and floor to act as a heat ballast. No action would be needed to protect the undulator system in the event of a system-wide power failure. Some action to adjust the heat balance, in the case of the HVAC power failure with the equipment left on, might be desirable but is not required. On the other hand, a temperature regulation failure of the HVAC system can quickly cause large excursions in air temperature and prompt action would be required to avoid damage to the undulator system.
Date: November 17, 2010
Creator: Sevilla, J. & Welch, J.
Partner: UNT Libraries Government Documents Department

On the Kinematics of Undulator Girder Motion

Description: The theory of rigid body kinematics is used to derive equations that govern the control and measurement of the position and orientation of undulator girders. The equations form the basis of the girder matlab software on the LCLS control system. The equations are linear for small motion and easily inverted as desired. For reference, some relevant girder geometrical data is also given. Equations 6-8 relate the linear potentiometer readings to the motion of the girder. Equations 9-11 relate the cam shaft angles to the motion of the girder. Both sets are easily inverted to either obtain the girder motion from the angles or readings, or, to find the angles and readings that would give a desired motion. The motion of any point on the girder can be calculated by applying either sets of equations to the two cam-planes and extrapolating in the z coordinate using equation 19. The formulation of the equations is quite general and easily coded via matrix and vector methods. They form the basis of the girder matlab software on the LCLS control system.
Date: August 18, 2011
Creator: Welch, J
Partner: UNT Libraries Government Documents Department

QM02 Strength Measurement

Description: In late April, Paul Emma reported that his orbit fitting program could find a reasonably good fit only if the strength of QM02 was changed from design value of -5.83 kG to -6.25 kG - a strength change of 7.3%. In late May, we made a focal length measurement of QM02 by turning off all focusing optics between YC07 and BPMS1 (in the spectrometer line) except for QM02 and adjusted the strength of QM02 so that vertical kicks by YC07 did not produce any displacements at BPMS1 (see Figure 1). The result was quoted in the LCLS elog was that QM02 appeared to 6% too weak, and approximately agreed with Paul's observation. The analysis used for the entry in the log book was based on the thin lens approximation and used the following numbers: Distance YC07 to QM02 - 5.128 m; Distance QM02 to BPMS1 - 1.778 m; and Energy - 135 MeV. These distances were computed from the X,Z coordinates given the on the large plot of the Injector on the wall of the control room. On review of the MAD output file coordinates, it seems that the distance used for QM02 to BPMS1 is not 1.778 m. The correct value is Distance, center of QM02 to BPMS1 - 1.845 m. There may be a typo on the wall chart values for the coordinates of BPMS1, or perhaps there was a misinterpretation of edge versus center of QM02. In any case, the effect of this change is that the thin lens estimate changes from 6% too weak to 9% too weak. At John Galayda's suggestion, we looked into the thin lens versus thick lens approximation. A Mathematica program was written to solve for the K value of the QM02, in the thick lens approximation, that provides point to point ...
Date: November 24, 2010
Creator: Welch, J; Wu, J.; /SLAC & ,
Partner: UNT Libraries Government Documents Department

Technical results of Y-12/IAEA field trial of remote monitoring system

Description: A Remote Monitoring System (RMS) field trial has been conducted with the International Atomic Energy Agency (IAEA) on highly enriched uranium materials in a vault at the Oak Ridge Y-12 Plant. The RMS included a variety of Sandia, Oak Ridge, and Aquila sensor technologies which provide containment seals, video monitoring, radiation asset measurements, and container identification data to the on-site DAS (Data Acquisition System) by way of radio-frequency and Echelon LonWorks networks. The accumulated safeguards information was transmitted to the IAEA via satellite (COMSAT/RSI) and international telephone lines. The technologies tested in the remote monitoring environment are the RadCouple, RadSiP, and SmartShelf sensors from the ORSENS (Oak Ridge Sensors for Enhancing Nuclear Safeguards) technologies; the AIMS (Authenticated Item Monitoring System) motion sensor (AMS), AIMS fiber-optic seal (AFOS), ICAM (Image Compression and Authentication Module) video surveillance system, DAS (Data Acquisition System), and DIRS (Data and Image Review Station) from Sandia; and the AssetLAN identification tag, VACOSS-S seal, and Gemini digital surveillance system from Aquila. The field trial was conducted from October 1996 through May 1997. Tests were conducted during the monthly IAEA Interim Inventory Verification (IIV) inspections for evaluation of the equipment. Experience gained through the field trials will allow the technologies to be applied to various monitoring scenarios.
Date: August 1, 1997
Creator: Corbell, B.H.; Whitaker, J.M. & Welch, J.
Partner: UNT Libraries Government Documents Department

Status of the Berkeley small cyclotron AMS (accelerator mass spectrometry) project

Description: A small, low-energy cyclotron has been designed and built at Berkeley for direct detection dating of /sup 14/C. The system combines the use of a negative ion source to reject /sup 14/N with the high resolution of a cyclotron to reject other background ions. In order to allow the dating of old and small samples, the present system incorporates a high-current external ion source and injection beamline. The system is expected to be operational by mid-1987.
Date: April 1, 1987
Creator: Bertsche, K.J.; Friedman, P.G.; Morris, D.E.; Muller, R.A. & Welch, J.J.
Partner: UNT Libraries Government Documents Department

Advanced accelerator methods: The cyclotrino

Description: Several new and unusual, advanced techniques in the small cyclotron are described. The cyclotron is run at low energy, using negative ions and at high harmonics. Electrostatic focusing is used exclusively. The ion source and injection system is in the center, which unfortunately does not provide enough current, but the new system design should solve this problem. An electrostatic extractor that runs at low voltage, under 5 kV, and a microchannel plate detector which is able to discriminate low energy ions from the /sup 14/C are used. The resolution is sufficient for /sup 14/C dating and a higher intensity source should allow dating of a milligram size sample of 30,000 year old material with less than 10% uncertainty.
Date: April 1, 1987
Creator: Welch, J.J.; Bertsche, K.J.; Friedman, P.G.; Morris, D.E. & Muller, R.A.
Partner: UNT Libraries Government Documents Department

Characterization of iron-enriched synthetic basalt for transuranic containment

Description: In the slagging pyrolytic incineration process, combustibles are burned and noncombustibles, including metals, are oxidized into a molten , an electromelter, where the molten slag, with further processing conducted in a heated tundish, e.g. is allowed to homogenize (within a reasonable time period) and then cast into large, cylindrical metal containers. Analyses of Idaho National Engineering Laboratory waste slags show them similar in composition and appearance to natural basalts, but rich in iron. The electromelt process and the resulting iron-rich castings offer great promise for rendering nuclear waste into a stable form. The process offers great flexibility with regard to both compositional variation of the incoming waste and the high rates at which the waste can be introduced and cast. The cast product, a fine-grained basalt-like material, shows excellent homogeneity with little or no reaction to the steel containment. The preliminary mechanical and chemical durability data show the form to have adequate containment properties for TRU waste. However, work presently underway to improve these properties through additives and controlled cooling cycles has greatly enhanced the durability of the waste form. Furthermore, recent evidence indicates that divalent iron (Fe/sup 2 +/) included in the crystalline phases of granites and basalts imparts a resistance to leaching of uranium and other actinide ions.
Date: October 17, 1980
Creator: Flinn, J.E.; Henslee, S.P.; Kelsey, P.V.; Tallman, R.L. & Welch, J.M.
Partner: UNT Libraries Government Documents Department

Absolute beam flux measurement at NDCX-I using gold-melting calorimetry technique

Description: We report on an alternative way to measure the absolute beam flux at the NDCX-I, LBNL linear accelerator. Up to date, the beam flux is determined from the analysis of the beam-induced optical emission from a ceramic scintilator (Al-Si). The new approach is based on calorimetric technique, where energy flux is deduced from the melting dynamics of a gold foil. We estimate an average 260 kW/cm2 beam flux over 5 {micro}s, which is consistent with values provided by the other methods. Described technique can be applied to various ion species and energies.
Date: April 1, 2011
Creator: Ni, P. A.; Bieniosek, F. M.; Lidia, S. M. & Welch, J.
Partner: UNT Libraries Government Documents Department

Computation of the Longitudinal Space Charge Effect in Photoinjectors

Description: The LCLS Photoinjector produces a 100A, 10 ps long electron bunch which is later compressed down to 230 fs to produce the peak current required for generating SASE radiation. SASE saturation will be reached in the LCLS only if the emittance and uncorrelated energy spread remain respectively below 1.2 mm.mrad and 5.10{sup -4}. This high beam quality will not be met if the Longitudinal Space Charge (LSC) instability develops in the injector and gets amplified in the compressors. The LSC instability originates in the injector beamline, from an initial modulation on top of the photoelectron pulse leaving the cathode. Numerical computations, performed with Multiparticle Space Charge tracking codes, showing the evolution of the longitudinal phase space along the LCLS injector beamline, are discussed. Their results are compared with those deduced from theoretical models in different regimes of energy and acceleration and for different modulation wavelengths. This study justifies the necessity to insert a ''laser heater'' in the LCLS Photoinjector beamline.
Date: May 9, 2005
Creator: Emma, P.; Huang, Z.; Limborg-Deprey, C.; Welch, J.J.; Wu, J. & /SLAC
Partner: UNT Libraries Government Documents Department

Software Based Controls Module Development

Description: A project was initiated at the Oak Ridge Y-12 Plant to implement software geometric error compensation within a PC-based machine tool controller from Manufacturing Data Systems, Inc. This project may be the first in which this type of compensation system was implemented in a commercially available machine tool controller totally in software. Previous implementations typically required using an external computer and hardware to interface through the position feedback loop of the controller because direct access to the controller software was not available. The test-bed machine for this project was a 2-axis Excello 921 T-base lathe. A mathematical error model of the lathe was created using homogeneous transformation matrices to relate the positions of the machine's slides to each other and to a world reference system. Equations describing the effects of the geometric errors were derived from the model. A software architecture was developed to support geometric error compensation for machine tools with up to 3 linear axes. Rotary axes were not supported in this implementation, but the developed architecture would not preclude their support in the future. Specific implementations will be dependent upon the configuration of the machine tool. A laser measuring system from Automated Precision, Inc. was used to characterize the lathe's geometric errors as functions of axis position and direction of motion. Multiple data files generated by the laser system were combined into a single Error File that was read at system startup and used by the compensation system to provide real-time position adjustments to the axis servos. A Renishaw Ballbar was used to evaluate the compensation system. Static positioning tests were conducted in an attempt to observe improved positioning accuracy with the compensation system enabled. These tests gave inconsistent results due to the lathe's inability to position the tool repeatably. The development of the architecture and compensation ...
Date: December 10, 1999
Creator: Graves, V. B.; Kelley, G. & Welch, J. C.
Partner: UNT Libraries Government Documents Department

Experimental program to build a multimegawatt lasertron for super linear colliders

Description: A lasertron (a microwave ''triode'' with an RF output cavity and an RF modulated laser to illuminate a photocathode) is a possible high power RF amplifier for TeV linear colliders. As the first step toward building a 35 MW, S-band lasertron for a proof of principle demonstration, a 400 kV dc diode is being designed with a GaAs photocathode, a drift-tube and a collector. After some cathode life tests are made in the diode, an RF output cavity will replace the drift tube and a mode-locked, frequency-doubled, Nd:YAG laser, modulated to produce a 1 us-long comb of 60 ps pulses at a 2856 MHz rate, will be used to illuminate the photocathode to make an RF power source out of the device. This paper discusses the plans for the project and includes some results of numerical simulation studies of the lasertron as well as some of the ultra-high vacuum and mechanical design requirements for incorporating a photocathode.
Date: April 1, 1985
Creator: Garwin, E.L.; Herrmannsfeldt, W.B.; Sinclair, C.; Weaver, J.N.; Welch, J.J. & Wilson, P.B.
Partner: UNT Libraries Government Documents Department

Interface between computational fluid dynamics (CFD) and plant analysis computer codes

Description: Computational fluid dynamics (CFD) can provide valuable input to the development of advanced plant analysis computer codes. The types of interfacing discussed in this paper will directly contribute to modeling and accuracy improvements throughout the plant system and should result in significant reduction of design conservatisms that have been applied to such analyses in the past.
Date: November 1, 1993
Creator: Coffield, R. D.; Dunckhorst, F. F.; Tomlinson, E. T. & Welch, J. W.
Partner: UNT Libraries Government Documents Department

Inverse Free Electron Laser Heater for the LCLS

Description: The Linac Coherent Light Source (LCLS) free electron laser employs an RF photocathode gun that yields a 1nC bunch a few picoseconds long, which must be further compressed to yield the high current required for Self Amplified Spontaneous Emission (SASE) gain. The electron beam from the RF photocathode gun is quite sensitive to microbunching instabilities such as coherent synchrotron radiation (CSR) in the compressor chicanes and longitudinal space charge (LSC) in the linac. These effects can be Landau damped by adding energy spread to the electron bunch prior to compression. They propose to do this by co-propagating an infrared laser beam with the electron bunch in an undulator in the LCLS injector beamline. The undulator is placed in a four bend magnet chicane to allow the Ir laser beam to propagate colinearly with the e-beam while it oscillates in the undulator. The IR laser beam is derived from the photocathode gun drive laser, so the two beams are synchronized. Simulations presented elsewhere in these proceedings show that the laser interaction damps the microbunching instabilities to a very great extent. This paper is a description of the design of the laser heater.
Date: May 11, 2005
Creator: Bentson, L.D.; Bolton, P.; Carr, R.; Dowell, D.; Emma, P.; Gilevich, S. et al.
Partner: UNT Libraries Government Documents Department