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Atomic data needs for beam transport in gas

Description: Determination of the parameters Z/sub eff/, electrical conductivity, plasma density, and the plasma temperature is essential in the study of heavy ion beam transport in gas. The calculation of these parameters require input from atomic physics. This note is an attempt to make these needs known to atomic physicists.
Date: November 3, 1977
Creator: Yu, S.S.
Partner: UNT Libraries Government Documents Department

Intense electron beams

Description: This paper is concerned with intense electron beams, typically of the order of a few kA in current and up to tens of MeV in beam energy. A beam of this kind can be produced from induction machines, examples of which are the ERA (4 MeV, 1 kA) at Lawrence Berkeley Laboratory and the ASTRON (5 MeV, 500A), ETA (5 MeV, 10 kA), and ATA (50 MeV, 10 kA) at Lawrence Livermore National Laboratory (LLNL). The emphasis of the paper is on the characteristics of these beams and some applications. 13 refs., 2 figs. (LSP)
Date: October 20, 1987
Creator: Yu, S.S.
Partner: UNT Libraries Government Documents Department

Is the two-term expansion valid for highly anisotropic systems. The Townsend ionization coefficient in strong runaway as a test case

Description: The Townsend ionization coefficient in the strong runaway regime is calculated within the framework of the two-term expansion. Results are compared to the 1-D model. General features of the two models are qualitatively similar, but quantitative differences by factors of approx. 2 are observed.
Date: July 15, 1982
Creator: Yu, S.S. & Melendez, R.E.
Partner: UNT Libraries Government Documents Department

Model of current enhancement at high pressure

Description: A model is proposed to account for the phenomenon of net current enhancement at high pressures recently observed on the Experimental Test Accelerator. The proposed mechanism involves energetic secondary electrons (delta rays) which are pushed forward by the self-magnetic field of the electron beam. For high current beams, the forward delta ray current can build up to a significant fraction of the beam current. Analytic calculations of the steady-state solution as well as the rate of buildup of the delta ray current are presented in this paper. In addition, numerical results from a nonlocal Boltzmann code, NUTS, are presented. The analytic and numerical results have many features which are in qualitative agreement with the experiments, but quantitative discrepancies still exist.
Date: April 5, 1983
Creator: Yu, S.S. & Melendez, R.E.
Partner: UNT Libraries Government Documents Department

Model of emittance growth in a self-pinched beam

Description: A semi-phenomenological formula is proposed for the change of emittance of a self-pinched beam which is not matched to its equilibrium radius. Near equilibrium this formula, coupled with an envelope equation, yields the damped sausage oscillations observed in simulation and experiments. For a beam which is injected cold (no transverse velocity spread), the formula coincides with the analytically calculated initial growth of emittance. The basic theory is developed here and used to compute the linear damping rate for several current profiles. The resultant non-linear increase in equilibrium quantities is also calculated in lowest order of the degree of mismatch.
Date: December 3, 1979
Creator: Lee, E.P. & Yu, S.S.
Partner: UNT Libraries Government Documents Department

Focal spot size predictions for beam transport through a gas-filled reactor

Description: Results from calculations of focal spot size for beam transport through a gas-filled reactor are summarized. In the converging beam mode, we find an enlargement of the focal spot due to multiple scattering and zeroth order self-field effects. This enlargement can be minimized by maintaining small reactors together with a careful choice of the gaseous medium. The self-focused mode, on the other hand, is relatively insensitive to the reactor environment, but is critically dependent upon initial beam quality. This requirement on beam quality can be significantly eased by the injection of an electron beam of modest current from the opposite wall.
Date: January 23, 1980
Creator: Yu, S.S.; Lee, E.P. & Buchanan, H.L.
Partner: UNT Libraries Government Documents Department

Aspects of three field approximations: Darwin, frozen, EMPULSE

Description: The traditional approach used to study high energy beam propagation relies on the frozen field approximation. A minor modification of the frozen field approximation yields the set of equations applied to the analysis of the hose instability. These models are constrasted with the Darwin field approximation. A statement is made of the Darwin model equations relevant to the analysis of the hose instability.
Date: May 25, 1985
Creator: Boyd, J.K.; Lee, E.P. & Yu, S.S.
Partner: UNT Libraries Government Documents Department

The stability of free-electron lasers against filamentation

Description: In inertial confinement fusion (ICF) experiments, the high electromagnetic fields propagating through a relatively dense plasma can result in a transverse instability, causing the matter and light to form filaments oriented parallel to the light beam. We examine whether a similar instability exists in the electron beam of a free-electron laser, where such an instability could interfere with the transfer of beam kinetic energy into optical wave energy. We heuristically examine the instability in a relativistic beam through which an intense laser beam is propagating. We ignore the FEL effects. We estimate how the altered index of refraction in an FEL affects the dispersion relation. Finally, we estimate the effect that the instability could have on the phase coherence of a particle as it transits an FEL. 10 refs., 2 tabs.
Date: September 15, 1987
Creator: Barnard, J.J.; Scharlemann, E.T. & Yu, S.S.
Partner: UNT Libraries Government Documents Department

Time-dependent field equations for paraxial relativistic electron beams: Beam Research Program

Description: A simplified set of field equations for a paraxial relativistic electron beam is presented. These equations for the beam electrostatic potential phi and pinch potential Phi identical to A/sub z/ - phi retain previously neglected time-dependent terms and for axisymmetric beams reduce exactly to Maxwell's equations.
Date: July 20, 1987
Creator: Sharp, W.M.; Yu, S.S. & Lee, E.P.
Partner: UNT Libraries Government Documents Department

Ion Motion inthe Adiabatic Focuser

Description: In this paper we numerically study the effect of ion motion in an adiabatic focuser, motivated by a recent suggestion that ion motion in an adiabatic focuser might be significant and even preclude operation of the focuser as previously envisioned. It is shown that despite ion motion the adiabatic focuser should work as well as originally envisioned.
Date: June 10, 2006
Creator: Henestroza, E.; Sessler, A.M. & Yu, S.S.
Partner: UNT Libraries Government Documents Department

Beam dynamics studies of the Heavy Ion Fusion Accelerator injector

Description: A driver-scale injector for the Heavy Ion Fusion Accelerator project has been built at LBL. This machine has exceeded the design goals of high voltage (> 2 MV), high current (> 0.8 A of K{sup +}) and low normalized emittance (< 1 {pi} mm-mr). The injector consists of a 750 keV diode pre-injector followed by an electrostatic quadrupole accelerator (ESQ) which provides strong (alternating gradient) focusing for the space-charge dominated beam and simultaneously accelerates the ions to 2 MeV. The fully 3-D PIC code WARP together with EGUN and POISSON were used to design the machine and analyze measurements of voltage, current and phase space distributions. A comparison between beam dynamics characteristics as measured for the injector and corresponding computer calculations will be presented.
Date: April 1, 1995
Creator: Henestroza, E.; Yu, S.S.; Eylon, S. & Grote, D.P.
Partner: UNT Libraries Government Documents Department

Ion sources for heavy ion fusion

Description: The development of ion sources for heavy ion fusion will be reported with particular emphasis on a recently built 2 MV injector. The new injector is based on an electrostatic quadrupole configuration, and has produced pulsed K{sup +} ions of 950 mA peak from a 6.7 inch curved alumino silicate source. The ion beam has reached 2.3 MV with an energy flatness of {+-}0.2% over 1 {micro}s. The measured normalized edge emittance of less than 1 {pi} mm-mr is close to the source temperature limit. The design, construction, performance, and comparisons with three-dimensional particle-in-cell simulations will be described.
Date: September 1, 1995
Creator: Yu, S.S.; Eylon, S. & Chupp, W.
Partner: UNT Libraries Government Documents Department

Simulations of ion beam neutralization in support of theneutralized transport experiment

Description: Heavy ion fusion (HIF) requires the acceleration, transport, and focusing of many individual ion beams. Drift compression and beam combining prior to focusing result in {approx}100 individual ion beams with line-charge densities of order 10{sup -5} C/m. A focusing force is applied to the individual ion beams outside of the chamber. For neutralized ballistic chamber transport (NBT), these beams enter the chamber with a large radius (relative to the target spot size) and must overlap inside the chamber at small radius (roughly 3-mm radius) prior to striking the target. The physics of NBT, in particular the feasibility of achieving the required small spot size, is being examined in the Neutralized Transport Experiment (NTX) at Lawrence Berkeley National Laboratory. Interpreted by detailed particle-in-cell simulations of beam neutralization, experimental results are being used to validate theoretical and simulation models for driver scale beam transport. In the NTX experiment, a low-emittance 300-keV, 25-mA K{sup +} beam is focused 1 m downstream into a 4-cm radius pipe containing one or more plasma regions. The beam passes through the first 10-cm-long plasma, produced by an Al plasma arc source, just after the final focus magnet and propagates with the entrained electrons. A second, 10-cm-long plasma (produced with a cyclotron resonance plasma source) is created near focus to simulate the effects of a photo-ionized plasma created by the heated target in a fusion chamber. Given a 0.1-{pi}-mm-mrad beam emittance, two and three-dimensional particle-in-cell (PIC) LSP simulations of the beam neutralization predict a &lt; 2-mm beam rms radius at focus with only the first plasma. The beam radius can be further improved with the addition of the second plasma located further downstream.
Date: September 7, 2003
Creator: Welch, D. R.; Rose, D. V.; Yu, S. S. & Henestroza, E.
Partner: UNT Libraries Government Documents Department

Design of inductively detuned RF extraction cavities for the Relativistic Klystron Two Beam Accelerator

Description: An inductively detuned traveling wave cavity for the Relativistic Klystron Two Beam Accelerator expected to extract high RF power at 11. 424 GHz for the 1 TeV Center of Mass Next Linear Collider has been designed. Longitudinal beam dynamics studies led to the following requirements on cavity design: (a) Extraction of 360 MW of RF power with RF component of the current being 1.15 kAmps at 11.424 GHz, (b) Inductively detuned traveling wave cavity with wave phase velocity equal to 4/3 the speed of light, (c) Output cavity with appropriate Q{sub ext} and eigenfrequency for proper matching. Furthermore, transverse beam dynamics require low shunt impedances to avoid the beam break-up instability. We describe the design effort to meet these criteria based on frequency-domain and time-domain computations using 2D- and 3D- electromagnetic codes.
Date: April 1, 1995
Creator: Henestroza, E.; Yu, S.S. & Li, H.
Partner: UNT Libraries Government Documents Department

Stable propagation of an electron beam in gas

Description: Conditions for the stable propagation of a pinched electron beam in low pressure gas (p approximately 0.1 to 100 torr) are described. The observed window of good propagation around p approximately 2 torr air is interpreted as the quenching of the two-stream mode by sufficiently high plasma density and collision frequency, and the simultaneous suppression of the resistive hose mode by sufficiently rapid generation of electrical conductivity from breakdown ionization.
Date: September 30, 1977
Creator: Lee, E.P.; Chambers, F.W.; Lodestro, L.L. & Yu, S.S.
Partner: UNT Libraries Government Documents Department

Prospects for a soft x-ray FEL powered by a relativistic-klystron high-gradient accelerator (RK-HGA)

Description: We present here the concept of x-ray FELs using high gain, single-pass amplifiers with electron beams accelerated in high gradient structures powered by relativistic klystrons. Other authors have also considered x-ray FELs; the unique aspect of this paper is the use of high gradient acceleration. One of the authors has previously presented preliminary studies on this concept. The intent in this paper is to display the results of a top level design study on a high gain FEL, to present its sensitivity to a variety of fabrication and tuning errors, to discuss several mechanisms for increasing gain yet more, and to present explicitly the output characteristics of such an FEL. The philosophy of the design study is to find a plausible operating point which employs existing or nearly existing state-of-the-art technologies while minimizing the accelerator and wiggler lengths. The notion is to distribute the technical risk as evenly as possible over the several technologies so that each must advance only slightly in order to make this design feasible. This study entailed no systematic investigation of possible costs so that, for example, the sole criterion for balancing the trade-off between beam energy and wiggler length is that the two components have comparable lengths. 20 refs., 10 figs., 1 tab.
Date: September 28, 1989
Creator: Shay, H.D.; Barletta, W.A.; Yu, S.S.; Schlueter, R. & Deis, G.A.
Partner: UNT Libraries Government Documents Department

Comparisons of hydrodynamic beam models with kinetic treatments

Description: Hydrodynamic models have been derived by Mark and Yu and by others to describe energetic self-pinched beams, such as those used in ion-beam fusion. The closure of the Mark-Yu model is obtained with adiabatic assumptions mathematically analogous to those of Chew, Goldberger, and Low for MHD. The other models treated here use an ideal gas closure and a closure by Newcomb based on an expansion in V/sub th//V/sub z/. Features of these hydrodynamic beam models are compared with a kinetic treatment.
Date: October 6, 1983
Creator: Boyd, J.K.; Mark, J.W.; Sharp, W.M. & Yu, S.S.
Partner: UNT Libraries Government Documents Department

Novel accelerators employing high-current electron beams numerical simulations

Description: Numerical simulations codes are described which can be used to study the physical phenomena of high-current electron beams employed in some novel accelerator schemes. Examples are given of the study of transverse effects in the free electron laser part of a Two-Beam Accelerator, the study of ion guiding in a Relativistic Klystron, and a study of the acceleration phase of a Collective implosion Accelerator.
Date: January 1, 1986
Creator: Fawley, W.M.; Teague, M.R.; Caporaso, G.J.; Yu, S.S. & Sessler, A.M.
Partner: UNT Libraries Government Documents Department

Comparisons of hydrodynamic beam models with kinetic treatments. Revision 1

Description: Hydrodynamic models have been derived by Mark and Yu and by others to described energetic self-pinch beams, such as those used in ion-beam fusion. The closure of the Mark-Yu model is obtained with adiabatic assumptions mathematically analogous to those of Chew, Goldberger, and Low for MHD. The other models treated here use an ideal gas closure and a closure by Newcomb based on an expansion in V/sub th//V/sub z/. Features of these hydrodynamic beam models are compared with a kinetic treatment.
Date: December 21, 1983
Creator: Boyd, J.K.; Mark, J.W.; Sharp, W.M. & Yu, S.S.
Partner: UNT Libraries Government Documents Department

Transport and error sensitivity in a heavy-ion recirculator

Description: An envelope code has been developed to facilitate the design of a recirculating accelerator for a heavy-ion fusion reactor. A novel feature of the model is the treatment of the beam charge density as a Lagrangian fluid in the axial direction. Transport results for a preliminary recirculator design are presented, and sensitivity of the transport to errors in the magnet strength is discussed. 4 refs., 4 figs.
Date: May 1, 1991
Creator: Sharp, W.M.; Barnard, J.J. & Yu, S.S.
Partner: UNT Libraries Government Documents Department

Engineering systems designs for a recirculating heavy ion induction accelerator

Description: Recirculating heavy ion induction accelerators are being investigated as possible drivers for heavy ion fusion. Part of this investigation has included the generation of a conceptual design for a recirculator system. This paper will describe the overall engineering conceptual design of this recirculator, including discussions of the dipole magnet system, the superconducting quadrupole system and the beam acceleration system. Major engineering issues, evaluation of feasibility, and cost tradeoffs of the complete recirculator system will be presented and discussed. 5 refs., 4 figs.
Date: May 1, 1991
Creator: Newton, M.A.; Barnard, J.J.; Reginato, L.L. & Yu, S.S.
Partner: UNT Libraries Government Documents Department