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Measurements of the emittance and current density profile of the beam produced by the ATA injector

Description: Measurements of the normalized emittance of the beam produced by the Advanced Test Accelerator (ATA) injector yielded values near 0.4 Radian-Centimeters at currents up to 10 kAmps. The instrument was also used to obtain beam-current-density profiles in two dimensions at the entrance mask of the instrument.
Date: June 27, 1983
Creator: Fessenden, T.J.
Partner: UNT Libraries Government Documents Department

Preliminary experiments with a carbon fiber tuft cathode

Description: This work reports initial tests of a carbon brush or tuft cathode intended for use by the Beam Research Program. It was found that electric fields of approximately 100 kV/cm were required to produce current densities above 20 A/sq cm. The beam extracted from the cathode consisted of many beamlets - one for each tuft. The beamlets were found to be quite uniform in peak current density and the cathode operation was microscopically repeatable. The turn-on time was estimated to be 200 ns.
Date: January 11, 1984
Creator: Fessenden, T.J.
Partner: UNT Libraries Government Documents Department

Research on ion induction linacs at Berkeley

Description: Since October 1983, most of the research in the US on heavy ion fusion (HIF) has been devoted to the physics and technology of the induction linac driver. The economic viability of the method was confirmed in the recent HIF Systems Assessment. Research at Berkeley comprises three experimental activities: the multiple-beam experiment, MBE-4, which accelerates four parallel, separately focused beams of cesium ions from 0.2 to 1 MeV; amplification of the beam power by a factor of nearly 40 is observed; development of a 16-beam, pulsed, 2-MV injector; and a single beam transport experiment (SBTE) for studying collective phenomena in ion beam transport. In addition, a major activity has been the development of a physics and engineering design for a larger experiment to test (in a scaled way) almost all of the manipulations needed in a full-scale driver. A complicating feature in the design is the combining of beams (in sets of four to one); the penalty in collectively enhanced emittance growth must be balanced against the cost savings gained in a driver. 12 refs., 6 figs., 1 tab.
Date: June 1, 1988
Creator: Fessenden, T.J.
Partner: UNT Libraries Government Documents Department

Diagnostics for induction accelerators

Description: The induction accelerator was conceived by N. C. Christofilos and first realized as the Astron accelerator that operated at LLNL from the early 1960`s to the end of 1975. This accelerator generated electron beams at energies near 6 MeV with typical currents of 600 Amperes in 400 ns pulses. The Advanced Test Accelerator (ATA) built at Livermore`s Site 300 produced 10,000 Ampere beams with pulse widths of 70 ns at energies approaching 50 MeV. Several other electron and ion induction accelerators have been fabricated at LLNL and LBNL. This paper reviews the principal diagnostics developed through efforts by scientists at both laboratories for measuring the current, position, energy, and emittance of beams generated by these high current, short pulse accelerators. Many of these diagnostics are closely related to those developed for other accelerators. However, the very fast and intense current pulses often require special diagnostic techniques and considerations. The physics and design of the more unique diagnostics developed for electron induction accelerators are presented and discussed in detail.
Date: April 1, 1996
Creator: Fessenden, T.J.
Partner: UNT Libraries Government Documents Department

MBE-4 experiments with bright Cesium+ beams

Description: Since 1985 the Heavy Ion Fusion Accelerator Research program at the Lawrence Berkeley Laboratory has been studying current amplification and emittance variations in MBE-4, a four-cesium-beam ion induction linac. This experiment models much of the accelerator physics of the electrostatically focused section of a fusion driver. Four space-charged Cs{sup +} beams, initially about one meter in length at currents of 5--10 mA, are focused by electrostatic quadrupoles and accelerated in parallel from approximately 200 keV up to one MeV by 24 accelerating gaps. Final currents of 20--40 mA per beam are typical. Recent experiments with extremely low emittance beams ({var epsilon}{sub n}=0.03 {pi}mm-mRad) have investigated variations of transverse and longitudinal normalized emittance for drifting and accelerating beams. Experiments show that very cold ({sigma}{sub o}=72{degrees},{sigma}=6{degrees}), off-axis or poorly matched beams increase transverse emittance when drifted or accelerated through these MBE-4 apparatus. Only by carefully centering and matching the beams can acceleration at constant normalized emittance be achieved. Warmer beams with less tune depression exhibit little to no emittance growth and show smaller emittance fluctuations when off axis or mis-matched. 10 refs., 10 figs.
Date: August 1, 1991
Creator: Fessenden, T.J.
Partner: UNT Libraries Government Documents Department

Emittance variations in current-amplifying ion induction linacs

Description: Since 1985 the Heavy Ion Fusion Accelerator Research program at the Lawrence Berkeley Laboratory has been studying current amplification and emittance variations in MBE-4, a four-cesium-beam induction linac. This experiment models much of the accelerator physics of the electrostatically focused section of a fusion driver. Four space-charge dominated Cs{sup +} beams, initially about one meter in length at currents of 5--10 mA, are focused by electrostatic quadrupoles and accelerated in parallel from approximately 200 keV up to one MeV by 24 accelerating gaps. Final currents of 20--40 mA per beam are typical. Recent experiments with extremely low emittance beams ({epsilon}{sub n} = 0.03 mm-mRad) have investigated variations of transverse and longitudinal normalized emittance for drifting and accelerating beams. These very strongly tune-depressed beams ({sigma}{sub o} = 72{degrees}, {sigma}{approx}6{degree}) are difficult to match the accelerator so as to avoid emittance growth during acceleration. During transport strong emittance fluctuations are observed in good qualitative agreement with simulations. Warmer beams with less tune depression exhibit little to no emittance growth, show smaller emittance fluctuations, and are much easier to match. A summary of findings from the MBE-4 studies is presented. 12 refs., 8 figs.
Date: April 1, 1991
Creator: Fessenden, T.J.
Partner: UNT Libraries Government Documents Department

Comparison of the initial ETA gas propagation experiments with theoretical models

Description: This report contains a description of the initial ETA propagation experiments in air at a beam current of 4.5 kA. The beam was observed to propagate at the pressures anticipated on the basis of previous theory and experiment. A comparison of measured net current waveforms with predictions of the PHOENIX code showed good agreement over the pressure range 0.1 to 200 torr. However, the beam was observed to expand with Z at a faster rate than theory predicts. Excessive transverse beam modulation at injection complicated the experiments and limited their comparison with theory.
Date: April 20, 1982
Creator: Chambers, F.W.; Clark, J.C. & Fessenden, T.J.
Partner: UNT Libraries Government Documents Department

Transportable charge in a periodic alternating gradient system

Description: A simple set of formulas is derived which relate emittance, line charge density, matched maximum and average envelope radii, occupancy factors, and the (space charge) depressed and vacuum values of tune. This formulation is an improvement on the smooth limit approximation; deviations from exact (numerically determined) relations are on the order of +-2%, while the smooth limit values are in error by up to +-30%. This transport formalism is used to determine the limits of transportable line charge density in an electrostatic quadrupole array, with specific application to the low energy portion of the High Temperature Experiment of Heavy Ion Fusion Accelerator Research. The line charge density limit is found to be essentially proportional to the voltage on the pole faces and the fraction of occupied aperture area. A finite injection energy (greater than or equal to 2 MeV) is required to realize this limit, independent of particle mass.
Date: May 1, 1985
Creator: Lee, E.P.; Fessenden, T.J. & Laslett, L.J.
Partner: UNT Libraries Government Documents Department

Diagnostics for the ATA beam propagation experiments

Description: This report contains a discussion of the diagnostics required for the beam propagation experiment to be done with the ATA accelerator. Included are a list of the diagnostics needed; a description of the ATA experimental environment; the status of beam diagnostics available at Livermore including recent developments, and a prioritized list of accelerator and propagation diagnostics under consideration or in various stages of development.
Date: November 1, 1981
Creator: Fessenden, T.J.; Atchison, W.L. & Barletta, W.A.
Partner: UNT Libraries Government Documents Department

Accelerator waveform synthesis and longitudinal beam dynamics in a small induction recirculator

Description: A recirculating induction accelerator requires accelerating waveforms that produce current amplification and provide bunch length control throughout the acceleration process. Current amplification occurs because of both an increase in the beam velocity and a shortening of the length of the beam bunch. The pulsed acceleration and control waveforms seen by the beam change in time as the pulse duration shortens. For one acceleration cycle of the small recirculator, each accelerating gap is driven by a burst of 15 pulses. As the beam gains velocity, the time interval between pulses shortens from approximately 20 to 10 {mu}sec. A zero-dimensional design code REC is used to develop the accelerator wave forms. An envelope/fluid code CIRCE and a 3-D particle code WARP3d are used to confirm the REC design and study the effects of errors. The authors find that acceleration errors can lead to space-charge waves launched at the bunch ends that strongly affect or even destroy the current pulse shape. The relation between the rate of longitudinal compression and the velocity of space charge waves is studied.
Date: April 1995
Creator: Fessenden, T.J.; Grote, D.P. & Sharp, W.M.
Partner: UNT Libraries Government Documents Department

Engineering study of a 10 MeV heavy ion linear accelerator

Description: LBL's Heavy Ion Fusion Accelerator Research group has completed the engineering study of the Induction Linac Systems Experiment (ILSE). ILSE will address nearly all accelerator physics issues of a scaled heavy ion induction linac inertial fusion pellet driver. Designed as a series of subsystem experiments, ILSE will accelerate 16 parallel carbon ion beams from a 2 MeV injector presently under development to 10 MeV at one ..mu..sec. This overview paper will present the physics and engineering requirements and describe conceptual design approaches for building ILSE. Major ILSE subsystems consist of electrostatic focusing quadrupole matching and accelerating sections, a 16 to 4 beam transverse combining section, a 4 beam magnetic focusing quadrupole accelerating section, a single beam 180 degree bend section, a drift compression section and a final focus and target chamber. These subsystems are the subject of accompanying papers. Also discussed are vacuum and alignment, diagnostics/data acquisition and controls, key conclusions and plans for further development. 10 refs., 4 figs., 1 tab.
Date: March 1, 1989
Creator: Fong, C.G.; Fessenden, T.J.; Fulton, R.L. & Keefe, D.
Partner: UNT Libraries Government Documents Department

Synthesis of MBE-4 accelerating waveforms

Description: An ion induction linac for HIF must operate near the space charge current limit along most of its length. Small errors in the voltages applied to the accelerating gaps can readily produce local unwanted beam bunching and consequent beam loss. Uncompensated space charge forces will generate current loss from longitudinal beam spreading. In the design of the MBE-4 ideal acceleration voltages were developed that assure self-similar amplifying current waveforms at each position along the accelerator. These were approximately synthesized by adding waveforms that can be obtained from realizable electrical pulsers. A code is used to study effects produced by the imperfect synthesis on the longitudinal ion dynamics and beam current waveforms in the presence of space-charge forces.
Date: May 1, 1985
Creator: Kim, C.H.; Brady, V.O.; Fessenden, T.J.; Judd, D.L. & Laslett, L.J.
Partner: UNT Libraries Government Documents Department

Time-resolved beam-profile measurements on the Experimental Test Accelerator (ETA)

Description: Examples are given of time-resolved beam profiles measured on ETA using several techniques. One method uses a Faraday cup that is remotely movable in two-transverse dimensions (x, y). In another method a small diameter wire or pellet target is moved across the beam and the bremsstrahlung x-ray intensity is plotted. Data for these methods are recorded using a Tektronix 7912 digitizer at 16 equally spaced times during 50 ns. Three other methods use a time gated (4 ns) microchannel plate television camera to record a two-dimensional image of the beam intensity on a single pulse. The light sources used for imaging are: Cherenkov light from a Kapton foil, prompt visible light from a titanium foil and radiated light from gas molecules excited by the beam. We are also testing an x-ray pinhole camera using K/sub ..cap alpha../ x-rays from tungsten.
Date: September 22, 1983
Creator: Chong, Y.P.; Lauer, E.J.; Clark, J.C.; Slaughter, D.R. & Fessenden, T.J.
Partner: UNT Libraries Government Documents Department

Transverse emittance studies of an induction accelerator of heavy ions

Description: Current amplification of heavy ion beams is an integral feature of the induction linac approach to heavy ion fusion. As part of the Heavy Ion Fusion Accelerator Research program at LBL we have been studying the evolution of the transverse emittance of ion beams while they are undergoing current amplification, achieved by longitudinal bunch compression and acceleration. Experiments are conducted on MBE-4, a four beam Cs{sup +} induction linac. The space-charge dominated beams of MBE-4 are focused by electrostatic quadrupoles while they are accelerated from nominally 200 keV up to {approximately} 1 MeV by 24 accelerating gaps. Initially the beams have currents of typically 4 mA to 10 mA per beam. Early experimental results showed a growth of the normalized emittance by a factor of 2 while the beam current was amplified by up to 9 times its initial value. We will discuss the results of recent experiments in which a mild bunch length compression rate, more typical of that required by a fusion driver, has shown that the normalized emittance can be maintained at its injection value (0.03 mm-mr) during acceleration. 4 refs., 4 figs., 1 tab.
Date: April 1, 1991
Creator: Garvey, T.; Eylon, S.; Fessenden, T.J.; Hahn, K. & Henestroza, E.
Partner: UNT Libraries Government Documents Department

Development of beam position monitors for heavy ion recirculators

Description: Work is underway at the Lawrence Livermore National Laboratory to design and build a small-scale, heavy ion recirculating induction accelerator. An essential part of this design work is the development of small nonintercepting diagnostics to measure beam current and position. This paper describes some of this work, with particular emphasis on the development of a small capacitive probe beam position monitor to resolve beam position to the 100 {mu}m level in a 6 cm diameter beam pipe. Initial measured results with an 80 keV potassium ion beam are presented.
Date: April 25, 1995
Creator: Deadrick, F.J.; Barnard, J.J.; Fessenden, T.J.; Meridith, J.W. & Rintamaki, J.
Partner: UNT Libraries Government Documents Department

Preliminary results from MBE-4: a four beam induction linac for heavy ion fusion research

Description: Preliminary results are presented from a scaled experimental multiple beam induction linac. This experiment is part of a program of accelerator research for heavy ion fusion. It is shown that multiple beams can be accelerated without significant mutual interaction. Measurements of the longitudinal dynamics of a current-amplifying induction linac are presented and compared to calculations. Coupling of transverse and longitudinal dynamics is discussed.
Date: May 1, 1986
Creator: Fessenden, T.J.; Judd, D.L.; Keefe, D.; Kim, C.; Laslett, L.J.; Smith, L. et al.
Partner: UNT Libraries Government Documents Department

Intense heavy-ion beam transport with electric and magnetic quadrupoles

Description: As part of the small induction recirculator development at LLNL, the authors are testing an injector and transport line that delivers 4 {micro}s beams of potassium with repetition rates up to 10 Hz at a nominal current of 2 mA. The normalized K-V equivalent emittance of the beams is near 0.02 {pi} mm-mrad and is mostly determined by the temperature of the source (0.1 eV). K{sup +} ions generated at 80 keV in a Pierce diode are matched to an alternating gradient transport line by seven electric quadrupoles. Two additional quads have been modified to serve as two-axis steerers. The matching section is followed by a transport section comprised of seven permanent magnet quadrupoles. Matching to this section is achieved by adjusting the voltages on the electric quadrupoles to voltages calculated by an envelope matching code. Measurements of beam envelope parameters are made at the matching section entrance and exit as well as at the end of the permanent magnet transport section. Beam current waveforms along the experiment are compared with results from a one-dimension longitudinal dynamics code. Initial experiments show particle loss occurring at the beam head as a result of overtaking. The apparatus is also being used for the development of non or minimally intercepting diagnostics for future recirculator experiments. These include capacitive monitors for determining beam line-charge density and position in the recirculator; flying wire scanners for beam position; and gated TV scanners for measuring beam profiles and emittance.
Date: August 1, 1995
Creator: Fessenden, T. J.; Barnard, J. J.; Cable, M. D.; Deadrick, F.J.; Eylon, S.; Nelson, M. B. et al.
Partner: UNT Libraries Government Documents Department

Preliminary design of a 10 MV ion accelerator

Description: At the low energy end of an induction linac HIF driver the beam current is limited by our ability to control space charge by a focusing system. As a consequence, HIF induction accelerator designs feature simultaneous acceleration of many beams in parallel within a single accelerator structure. As the speed of the beams increase, the focusing system changes from electrostatic to magnetic quadrupoles with a corresponding increase in the maximum allowable current. At that point the beams are merged thereby decreasing the cost of the subsequent accelerator structure. The LBL group is developing an experiment to study the physics of merging and of focusing ion beams. In the design, parallel beams of ions (C/sup +/, Al/sup +/, or Al/sup + +/) are accelerated to several MV and merged transversely. The merged beams are then further accelerated and the growth in transverse and longitudinal emittance is determined for comparison with theory. The apparatus will then be used to study the problems associated with focusing ion beams to a small spot. Details of the accelerator design and considerations of the physics of combining beams are presented.
Date: June 1, 1986
Creator: Fessenden, T.J.; Celata, C.M.; Faltens, A.; Henderson, T.; Judd, D.L.; Keefe, D. et al.
Partner: UNT Libraries Government Documents Department

MBE-4: an induction linac experiment for heavy ion fusion

Description: The multiple-beam induction linac approach to a heavy ion fusion driver features continuous current amplification along the accelerator and a minimum of transverse beam manipulation from source to pellet. Current amplification and bunch length control require careful shaping of the accelerating voltages. This driver approach exploits developments in electron induction linac technology that have occurred within the last 15 years at LBL, LLNL and NBS. MBE-4 is a four beam induction linac that models much of the accelerator physics of the electrostatically focused section of a considerably longer induction accelerator. Four parallel Cs/sup +/ beams are electrostatically focussed and will be accelerated from 200 keV to approximately one MeV when the experiment is complete in the spring of 1987. The current in each of the four beams will increase from 10 to 40 mA due to both increase in beam speed and shortening of the bunch length. Results of experiments with the injector and first eight accelerating gaps are presented.
Date: June 1, 1986
Creator: Fessenden, T.J.; Avery, R.T.; Brodzik, D.A.; Faltens, A.; Gough, D.E.; Henderson, T.F. et al.
Partner: UNT Libraries Government Documents Department

Advanced Test Accelerator (ATA) injector

Description: The ATA injector, developed from experience gained from the Experimental Test Accelerator (ETA) linac, has recently been completed. The injector consists of ten 0.25 MV cells that are used to develop 2.5 MV across a single diode gap. The 10 kA beam is extracted from a 500 cm/sup 2/ plasma cathode at average rates of up to 5 Hz and burst rates to 1 kHz. Pulsed power from 20 water filled blumleins is divided and introduced symmetrically through four ports on each cell. All major insulators are fabricated from filled epoxy castings. With these improvements, the ATA injector is smaller than the ETA injector; has a faster pulse response; has lower voltage stress on insulators and higher ultimate performance. Injector characterization tests began in October 1982. These tests include beam current, energy, and emittance measurements.
Date: March 9, 1983
Creator: Jackson, C.H.; Bubp, D.G.; Fessenden, T.J.; Hester, R.E.; Neil, V.K.; Paul, A.C. et al.
Partner: UNT Libraries Government Documents Department

Survey of initial experiments on ATA beam dynamics

Description: The Advanced Test Accelerator (ATA) is a linear induction electron accelerator whose design parameters are 50 MeV, 10 kA and 70 ns pulse duration. The key physics issues affecting performance of the accelerator involve beam dynamics during transport through the accelerator structure. In this report, we present experimental results describing the initial operating phases of ATA. These results illustrate the complexity of the beam transport phenomena but also indicate the means to stabilize beam dynamics. Improvements in beam transport, which result from deploying various stabilization techniques, are also presented.
Date: June 25, 1984
Creator: Prono, D.S.; Caporaso, G.J.; Chong, Y.P.; Fessenden, T.J.; Hester, R.E.; Lauer, E.J. et al.
Partner: UNT Libraries Government Documents Department