BNL-52379 CAP-94-93R ACCELERATOR PHYSICS AND MODELING ZOHREH PARSA, EDITOR PROCEEDINGS OF THE SYMPOSIUM ON ACCELERATOR PHYSICS AND MODELING Brookhaven National Laboratory UPTON, NEW YORK 11973 ASSOCIATED UNIVERSITIES, INC. UNDER CONTRACT NO. DE-AC02-76CH00016 WITH THE UNITED STATES DEPARTMENT OF ENERGY DISCLAIMER This report was prepared as an account of work sponsored by an agency of the Unite1 States Government Neither the United States Government nor any agency thereof, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, doea not necessarily constitute or imply its endorsement, recomm.ndation, or favoring by the UnitedStates Government or any agency, contractor or subcontractor thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency, contractor or subcontractor thereof- Printed in the United States of America Available from National Technical Information Service U.S. Department of Commerce 5285 Port Royal Road Springfieid, VA 22161 NTIS price codes: Am&mffi TABLE OF CONTENTS Topic, Author Page no. Forward, Z . Parsa, Brookhaven National Lab. i Physics of High Brightness Beams , 1 M. Reiser, University of Maryland . Radio Frequency Beam Conditioner For Fast-Wave 45 Free-Electron Generators of Coherent Radiation Li-Hua NSLS Dept., Brookhaven National Lab, and A. M. Sessler, D. H. Whittum, Lawrence Berkeley Lab. Wake-Field and Space-Charge Effects on High Brightness 63 Beams. Calculations and Measured results for BNL-ATF Z. Parsa, Physics Dept., Brookhaven National Lab. Non-Linear Orbit Theory and Accelerator Design 165 A. J. Dragt, University of Maryland. General Problems of Modeling for Accelerators 189 A. Luccio, AGS Dept., Brookhaven National Lab. Development and Application of Dispersive Soft Ferrite 217 Models For Time-Domain Simulation J. F. Deford, G. Kamin, G. D. Craig, Lawrence Livermore National Lab and L. Walling S. S. C. Laboratory. Bunch Lengthening in the SLC Damping Rings 235 K. L. Bane Stanford Linear Accelerator Center Appendix— List of Registrants "FORWARD" The Symposium on Accelerator Physics and Modeling was held at Berkner Hall, Brookhaven National Laboratory on September 17, 1991. The purpose of this Symposium was to review and learn about "new" ideas and methods in Accelerator and Beam Physics. These proceedings reflects some of the presentations given at the Sympo- sium. We acknowledge the support and encouragement of Bill Willis and Bob Palmer, the enthusiastic pre-registration response, attendance and participation of members of various Departments. We also ac- knowledge the interest and large number of requests by physicists from outside of the Laboratory that regretfully we could not accom- modate due to lack of space. I was very pleased with the full attendance and the overwhelming success of the symposium. In that, I would like to thank the speakers for their informative presentations, their participation throughout the symposium and for providing copies of their contributions for inclu- sion in this proceedings. In the appendix we have included only the name of those who registered (pre or) at the symposium. Names of participants who did not register were not included in the appendix, since we do not have a list of their names. I would also like to acknowledge and thank R. Fernow (Physics), L. Ratner (AGS), S. Krinsky (NSLS) for chairing the sessions II, III and IV respectively; P. Tuttle's for Assisting with the registration at the Symposium and K. Tuohy for arranging for the refreshments. Zohreh Parsa, Editor Symposium Organizer: Z. Parsa. E-mail can be sent to PARSA@BNL PHYSICS OF HIGH BRIGHTNESS BEAMS Martin Reiser University of Maryland Chapter 1 Accelerator Physics and Modeling Symposium @ BNL Physics of High Brightness Beams M. Reiser University of Maryland Abstract Many advanced accelerator applications require high-intensity particle beams with very low emittance (i.e. high brightness) in which the beam physics is dominated by space charge effects. At the Univer- sity of Maryland, experiments have been in progress for several years to study space-charge induced intensity limits and emittance growth-in such beams. Different configurations of high-perveance 5 kV electron beams are transported through a long periodic channel consisting of 38 solenoid lenses. The most recent experiments with mismatched beams will be discussed. Experimental observations are compared with theory and particle simulation, and excellent agreement is found. Symposium on Accelerator Physics and Modeling Brookhaven National Laboratory September 17, 1991 -1 - Co-workers at Univ. of Maryland Assistant Research Scientists: S. Guharray J.G. Wang Graduate Research Assistants: C. Allen W. Guo D. Kehne D. Wang Others: J. Li and typically 1 or 2 undergraduate students Engineering/Technical Staff Outside Collaboration I. Haber (NRL) - Simulation H. Rudd (NRL) - Simulation J.D. Lawson (Rutherford Lab., U.K.) T. Wangler (LANL) GSI Darmstadt (Germany) - 1982-83 Sabbatical Research Support DOE (High Energy Physics), TASK A of "Accelerator Research" Con- tract: "Study of Transport and Longitudinal Compression of In- tense High Brightness Beams" ONR: "Low Energy Transport of high Brightness H~ Beams1' - 2 - 1. INTRODUCTION • Definition of Emittance and Brightness • Advanced Accelerator Applications • High Brightness Beam Sources • Causes of Emittance Growth 2. THEORY • Beam Transport in Linear Focusing Channels • Space-Charge Current Limit • Focusing Limit (Envelope Instabilities) • Emittance Growth in Space-Charge Dominated Beams 3. EXPERIMENTS, COMPARISON WITH THEORY AND SIMULATION • Focusing by a Single Solenoid Lens • Single-Beam Transport through a Periodic Solenoid Channel • Multiple Beam Transport Experiments 4. CONCLUSIONS - 3 - 1. Definitions of Emittance and Brightness Emittance = Beam Width x Divergence [m-rad] Divergence a ~ vx/v = dx/dz == x' Trace space plot of beam ellipse at waist: > x r Area of ellipse = emittance en = xmaxx maxn - 4 - NOTE: Emittance decreases with acceleration of beam since vx/v decreases with increasing velocity v. Normalized emittance en = fi^e is a better figure of merit since it remains constant through acceleration process if forces acting on beam are linear. Brightness: B = 2I/ir2e2 Normalized Brightness: 21 A/(m-rad)2 A/(d) Advanced accelerator requirements: 12 2 BnZl0 A/(m-rad) e.g. 7 = 1 kA, €„ = 10~5m-rad for an FEL. In practice, one achieves for electron beams from thermionic cathodes 1Q 2 Bn~10 A/(m-rad) - 5 - 2. Advanced Accelerator Applications A. Linear Collider (SLAC) Requires high brightness electron gun and "cool- ing" rings for both electrons and positrons to reduce beam emittance by radiation damping. B. Superconducting Supercollider (SSC) Requires high-brightness H" beam for the injector linac. (Bottleneck: Matching the H~ beam from source into RFQ accelerator). C. Neutral Particle Beams for Space Defense Requires H~ beam (for acceleration before neutral- ization) with brightness 10 times higher than SSC. D. Heavv Ion Inertial Fusion Requires kiloamperes of heavy ion beams (at several GeV energy) with exceedingly low emittance. E. Free Electron Laser (FEL) Emittance is proportional to wavelength A. High- power FELs require beam brightness exceeding state of the art. Need new electron sources, e.g. photo- cathode (;;rf gun"), and "cooling" (but how?) - 7 - F. High Power Linac for Transmuting Nuclear Waste 1 A 1.6 GeV, 250 mA proton beam incident on lead or lead-bismuth target produces high-flux thermal neu- trons which are used to "burn" or transmute long- lived radioisotopes (actinides) and fission products in nuclear waste through capture and fission pro- cesses. \ The very high average power (400 MW) of the pro- ton beam requires exceedingly precise beam control to avoid particle loss and nuclear activation of ac- celerator components. Hence, emittance growth and halo formation must be avoided, i.e. careful beam matching between ev- ery accelerator section is required. 3. High Brightness Beam Sources A. Electrons Thermionic cathodes: 11 2 Effective emittance en = 4era.r7TW = 2rc{kT/mcr) ' 21 Intrinsic brightness Bn = —r-r- = (Jc/2ir)(mc~/kT) kT = 0.1 eV 2 11 2 Jc = 20 A/cm —* Bn ~ 1.6 x 10 A/(m - rad) 10 2 Achieved experimentally Bn ~ 10 A/(m-rad) 2 Photocathodes: kT ~ 1 eV, Jc = 600 A/cm u 2 Intrinsic brightness Bn ~ 5 x 10 A/(m-rad) i0 2 Achieved experimentally Sn ~ 10 A/(m-rad) Pseudospark electron beam (Univ. of Maryland): Achieved experimentally 12 2 (charge neutralized beam) Bn ~ 10 A/(m-rad) B. H" Sources 6 Achieved experimentally (60 mA. en -- 0.5 x 10~ m-rad) 11 2 Bn ~ 10 A/(m-rad) - 9 - 4_. -Causes of Emittance Growth Nonlinear external focusing forces (spherical, chro- matic aberrations, etc.) Mismatch, misalignment, beam off-centering, and nonlinear external forces RF phase-dependent focusing forces Longitudinal-transverse coupling Single-particle resonances/instabilities • Space-charge induced emittance growth: Instabilities (e.g. CTQ > 90° in periodic channel, longitudinal instability, etc.) Nonuniform charge density, rms matched