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Induction linacs for heavy ion fusion research

Description: The new features of employing an induction linac as a driver for inertial fusion involve (1) transport of high-current low-emittance heavy ion beams, (2) multiple independently-focussed beams threading the same accelerator structure, and (3) synthesis of voltage waveforms to accomplish beam current amplification. A research program is underway at LBL to develop accelerators that test all these features with the final goal of producing an ion beam capable of heating matter to approx. 70 eV. This paper presents a discussion of some properties of induction linacs and how they may be used for HIF research. Physics designs of the High Temperature Experiment (HTE) and the Multiple Beam Experiment (MBE) accelerators are presented along with initial concepts of the MBE induction units.
Date: May 1, 1984
Creator: Fessenden, T.J.
Partner: UNT Libraries Government Documents Department

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

Experimental test accelerator (ETA) II

Description: The Experimental Test Accelerator (ETA) is designed to produce a 10 kAmp electron beam at an energy of 4.5 MeV in 40 nsec pulses at an average rate of 2 pps. The accelerator also operates in bursts of 5 pulses spaced by as little as one millisec at an average rate of 5 pps. The machine is currently operating near 80% of its design values and has accumulated over 2.5 million pulses - mostly at a rate of one pps. The plasma cathode electron source, the remainder of the accelerator, and the operating characteristics of the machine are discussed.
Date: March 6, 1981
Creator: Fessenden, T.J.; Atchison, W.L. & Birx, D.L.
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

Emittance measurements on ETA and ATA

Description: Emittance measurements on beams produced by the ETA and ATA accelerators are discussed. Emittance and brightness are defined. The significance of emittance for a beam in an accelerator and in gas is discussed. Various measurement techniques and results are presented and contrasted. Implicit calculations of emittance are also reported. Finally, the measurement of the time variation of emittance is discussed and the techniques to be used on the upcoming ATA experiments are outlined.
Date: June 14, 1984
Creator: Chambers, F.W.; Prosnitz, D. & Fessenden, T.J.
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

Multiple beam induction linac research at LBL

Description: We present results of progress on the LBL multiple beam induction linac experiment (MBE-4). This machine models the accelerator physics of the electric-focused portion of a driver for heavy ion inertial confinement fusion. Four beams of cesium ions are accelerated in common through twenty four induction gaps while being separately focused in individual electrostatic AG focusing channels. Early experiments have demonstrated current amplification in the linac, from 10 mA to 90 mA per beam. This is achieved both by acceleration (from 200 keV to 1 MeV) and by carefully controlled bunch compression. Recent experiments have concentrated on studies of beams extracted from an ion source which produces 5 mA cesium beams at emittances near 0.03 {pi} mm-mrad (normalized). Experiments and theory show a growth of emittance (by about a factor of 2) as these beams are accelerated through the linac. Results of recent measurements of the transverse emittance behavior of these strongly space-charge-dominated ion beams are reviewed and compared with theory. 9 refs., 3 figs.
Date: June 1, 1990
Creator: Garvey, T.; Eylon, S.; Fessenden, T.J.; Hahn, K.; Henestroza, E. & Keefe, D.
Partner: UNT Libraries Government Documents Department

Transverse beam dynamics studies of a heavy ion induction linac

Description: The multiple beam induction linac experiment (MBE-4) was built to study the accelerator physics of the low energy, electrostatically focussed end of a driver for heavy ion inertial confinement fusion. In this machine four beams of Cs{sup +} ions are accelerated through 24 common induction gaps while being focussed in separate AG focussing channels. Each channel consists of a syncopated FODO lattice of 30 periods. We report results of the most recent studies of the transverse beam dynamics of a single drifting (180 keV) beam in this machine. The dependence of the emittance on the zero-current phase advance shows systematic variations which may be understood in the light of previous theoretical work on this topic. This result, unique to the beam parameters of a linac for heavy ion fusion, will be discussed in the context of its implications for a driver design. In addition we will discuss recent measurements of the motion of the beam centroid through the linac. These measurements, coupled with simulations, have proven to be a powerful tool in determining the presence of misalignment errors in the lattice of the accelerator. 6 refs., 3 figs.
Date: August 1, 1990
Creator: Garvey, T.; Eylon, S.; Fessenden, T.J.; Hahn, K.; Henestroza, E. & Keefe, D.
Partner: UNT Libraries Government Documents Department

Accelerator research on MBE-4, an experimental multi-beam induction linac

Description: The multiple beam accelerator MBE-4 is a device for research toward a heavy ion driver for inertial confinement fusion, based on the induction linac concept. Its main goal is proof of the principle of current amplification by acceleration and controlled self-similar beam pulse compression. Into the 16-m long device four beams, each with an initial current of 10 mA are injected from a Marx-driven diode at 200 keV. The current amplification is up to nine-fold, with a final beam energy of about 800 keV in the middle of the bunch. Now that all the apparatus' accelerator sections have been completed, installed and aligned, and its unaccelerated transport properties have been studied, our experimental research has reached the crucial phase of implementing appropriate accelerator schedules that approximate self-similar current-pulse compression. These schedules are established through a close interplay of computations using a one-dimensional simulation code and a manual empirical tuning procedure. In a first approach, with a rather vigorous schedule that uses most of the accelerator modules to their voltage limits, we have determined the limits of our capability for controlled pulse compression, mainly due to waveform shaping of the driving pulse-forming networks. We shall report on these results. In the future, we will also aim for gentler schedules that would model more closely an inertial confinement fusion scenario. 8 refs., 11 figs., 1 tab.
Date: June 1, 1988
Creator: Meuth, H.; Fessenden, T.J.; Keefe, D. & Warwick, A.I.
Partner: UNT Libraries Government Documents Department

Beam-dump/diagnostics box for a 10-kA 50-MeV, 50-ns electron beam

Description: We have developed a dump for the ATA beam that consists of a series of carbon plates whose collective thickness totals approximately 1.5 ranges at 50 MeV. The energy dissipated in the plates is radiated to a water-cooled wall. The dump is designed to dissipate up to 175 kW of average power. A small hole along the axis of the plates forms a beamlet that passes through an energy analyzer. The analyzer consists of a 60/sup 0/ bending magnet and two high-sensitivity beam-current/position monitors. The ratio of the beamlet current to full current is used to estimate the beam emittance.
Date: March 9, 1983
Creator: White, J.M.; Fessenden, T.J.; Fontaine, R.A.; Harvey, A.R. & Paul, A.C.
Partner: UNT Libraries Government Documents Department

Optical-emission studies in the ion-focused regime

Description: The utility of optical emissions for diagnostic purposes in the ion-focused regime is explored. Two possible uses of the emissions are examined: (1) the time delay of 337.1-nm emissions relative to 391.4-nm emissions is observed to scale with the beam-neutralization time, and (2) emissions at 391.4 nm may determine beam-current density at the front of the beam.
Date: January 5, 1983
Creator: Chong, Y.P.; Yu, S.S.; Masamitsu, J.A.; Fessenden, T.J. & Prono, D.S.
Partner: UNT Libraries Government Documents Department

The LBL (Lawrence Berkeley Laboratory) multiple beam experiments

Description: The multiple-beam induction linac approach to a heavy ion driver for inertial confinement, fusion features continuous current amplification along the accelerator and a minimum of beam manipulations from source to pellet. Current amplification and bunch length control require careful shaping of the accelerating voltages. MBE-4 is designed as a four-beam induction linac that models much of the accelerator physics of the electrostatically focused section of a significantly longer induction accelerator. Four space-charge-dominated Cs/sup +/ beams, initially about one meter in length at a current of 13 mA, are focused by electrostatic quadrupoles and accelerated in parallel from 200 to nearly 600 keV. The energy will reach approximately one MeV when the accelerator is complete. Experiments have proceeded in parallel with the construction of the apparatus which began in FY 85 and is now more than half complete. The results show a current amplification, so far, by a factor of 2.8 in good agreement with the longitudinal acceleration calculations.
Date: March 1, 1987
Creator: Fessenden, T.J.; Keefe, D.; Kim, C.; Meuth, H. & Warwick, A.
Partner: UNT Libraries Government Documents Department

TV-acquired optical diagnostics systems on ATA

Description: The purpose of this paper is to report on optical system developments on the ATA and their applications to ATA beam characterization. Television (TV)-acquired optical diagnostics data provide spatial and temporal properties of the ATA beam that complements recorded information from other types of sensors, such as, beam-wall current monitors, x-ray probes, and rf probes. The ATA beam operates: (1) in the normal mode at 50-MeV, 10-kA at a 1-Hz rate; and (2) in the 1-KHz burst mode (for 10-pulses) at a 0.5 Hz rate. The beam has a 70-ns pulse width in vacuum propagation; however, beam-head erosion will occur in atmospheric propagation, thus limiting the pulse width to less than 50-ns. Various optical systems are used for ATA diagnostics. Optical-imaging provides a convenient measurement in a single pulse of the 2-dimensional profile of the beam intensity. It can also provide multiple 2-D framing in a single pulse. In some studies it may be desirable to study optical events with temporal resolution less than 100-ps with 1-dimensional streak cameras. Spatially integrated data from phototube cameras can also be used for background measurement applications as well as for single pixel monitoring. The optical line-of-sight (LOS) configurations have been made versatile to accommodate a large number of options for the various optical systems.
Date: June 1, 1984
Creator: Kalibjian, R.; Chong, Y.P.; Cornish, J.P.; Jackson, C.H. & Fessenden, T.J.
Partner: UNT Libraries Government Documents Department

Performance of MBE-4: An experimental multiple beam induction linear accelerator for heavy ions

Description: An experimental induction linac, called MBE-4, has been constructed to demonstrate acceleration and current amplification of multiple heavy ion beams. This work is part of a program to study the use of such an accelerator as a driver for heavy ion inertial fusion. MBE-4 is 16m long and accelerates four space-charge-dominated beams of singly-charged cesium ions, in this case from 200 keV to 700 keV, amplifying the current in each beam from 10mA by a factor of nine. Construction of the experiment was completed late in 1987 and we present the results of detailed measurements of the longitudinal beam dynamics. Of particular interest is the contribution of acceleration errors to the growth of current fluctuations and to the longitudinal emittance. The effectiveness of the longitudinal focusing, accomplished by means of the controlled time dependence of the accelerating fields, is also discussed. 4 refs., 5 figs., 1 tab.
Date: June 1, 1988
Creator: Warwick, A.I.; Fessenden, T.J.; Keefe, D.; Kim, C.H. & Meuth, H.
Partner: UNT Libraries Government Documents Department