In the nineteen years since EGS4 was released, it has been used in a wide variety of applications, particularly in medical physics, radiation measurement studies, and industrial development. Every new user and every new application bring new challenges for Monte Carlo code designers, and code refinements and bug fixes eventually result in a code that becomes difficult to maintain. Several of the code modifications represented significant advances in electron and photon transport physics, and required a more substantial invocation than code patching. Moreover, the arcane MORTRAN3[48] computer language of EGS4, was highest on the complaint list of the users of EGS4. The size of the EGS4 user base is difficult to measure, as there never existed a formal user registration process. However, some idea of the numbers may be gleaned from the number of EGS4 manuals that were produced and distributed at SLAC: almost three thousand. Consequently, the EGS5 project was undertaken. It was decided to employ the FORTRAN 77 compiler, yet include as much as possible, the structural beauty and power of MORTRAN3. This report consists of four chapters and several appendices. Chapter 1 is an introduction to EGS5 and to this report in general. We suggest that youmore » read it. Chapter 2 is a major update of similar chapters in the old EGS4 report[126] (SLAC-265) and the old EGS3 report[61] (SLAC-210), in which all the details of the old physics (i.e., models which were carried over from EGS4) and the new physics are gathered together. The descriptions of the new physics are extensive, and not for the faint of heart. Detailed knowledge of the contents of Chapter 2 is not essential in order to use EGS, but sophisticated users should be aware of its contents. In particular, details of the restrictions on the range of applicability of EGS are dispersed throughout the chapter. First-time users of EGS should skip Chapter 2 and come back to it later if necessary. With the release of the EGS4 version, a deliberate attempt was made to present example problems in order to help the user ''get started'', and we follow that spirit in this report. A series of elementary tutorial user codes are presented in Chapter 3, with more sophisticated sample user codes described in Chapter 4. Novice EGS users will find it helpful to read through the initial sections of the EGS5 User Manual (provided in Appendix B of this report), proceeding then to work through the tutorials in Chapter 3. The User Manuals and other materials found in the appendices contain detailed flow charts, variable lists, and subprogram descriptions of EGS5 and PEGS. Included are step-by-step instructions for developing basic EGS5 user codes and for accessing all of the physics options available in EGS5 and PEGS. Once acquainted with the basic structure of EGS5, users should find the appendices the most frequently consulted sections of this report.« less

The EGS5 code system

ILC-REPORT-2007-01 CHEP A07-001 (CHEP/KNU) Cockcroft-07-04 DESY 07-046 FERMILAB-TM-2382-AD-CD-DO-E-FESS-TD JAI-2007-001 JINR Dubna-E9-2007-39 JLAB-R-2007-01 KEK Report 2007-1 LNF-07/9(NT) SLAC-R-857 I NTERNATIONAL L INEAR C OLLIDER R EFERENCE D ESIGN R EPORT DR AF T A PRIL, 2007

/pdf/international-linear-collider-reference-design-report-4mwt031i87.pdf

International linear collider reference design report

We present a comprehensive survey of the dynamics of spin-polarized beams in high-energy particle accelerators. A major theme of this review is to clarify the distinction between the properties of an individual particle—a spin—and that of a beam—the polarization. We include work from a number of institutions, including high- and medium-energy facilities, synchrotron light sources and muon storage rings (including a proposal to measure the muon electric dipole moment) and, briefly, linear accelerators and recirculating linacs. High-precision tests of the Standard Model using spin-polarized beams are reviewed; also innovative studies using spin dynamics as a tool for accelerator physics per se. We include important historical works as well as modern developments in the field. The fundamental theory is derived in detail, starting from the basic principles of quantum mechanics, electrodynamics and statistical mechanics, as well as 'accelerator physics'. The principal theoretical formulae in the field (Froissart–Stora, Sokolov–Ternov and Derbenev–Kondratenko) are presented, with in-depth attention to the quantum-statistical mechanics, as opposed to purely 'accelerator physics'. Publisher's note. A related review article by the same authors, Siberian Snakes in high-energy accelerators, has been published in Journal of Physics G: Nuclear and Particle Physics, volume 31, page R151

https://iopscience.iop.org/article/10.1088/0034-4885/68/9/R01/pdf

Spin-polarized charged particle beams in high-energy accelerators

The present work describes the source of polarized electrons that is run at the 855 MeV race track microtron MAMI at the Johannes Gutenberg Universitat in Mainz. The source is based on photoelectron emission from (III–V)-semiconductors. Presently strained layer InGaP- or GaAsP-cathodes are used, which are processed to negative electron affinity by coverage of the surface with a submonolayer of caesium and oxygen. Electron beams spin-polarized up to a degree of P = 55% at a quantum efficiency of QE = 2% or P = 75% at QE = 0.4%, respectively, are obtained. The well-known but hitherto unsolved problem of limited cathode lifetime has been sidestepped by the attachment of an UHV load lock system to the source electron gun. It allows quick replacement of cathodes without breaking the gun vacuum. Availabilities in excess of 85% are obtained regularly in beamtimes longer than 100h. The source was mainly applied in measurements of nucleon form factors via the reactions 1H(ē, e′ p), 2D(ē, e′ p), 2D(ē, e′ n), and 3He(ē, e′ n). More than 1600 h beamtime have been accomplished in physics experiments with polarized electron beams at MAMI up to now.

The mami source of polarized electrons

We review recent progress in the physics and technology of cold cathode electron emitters. The characteristics of emission from field emitter arrays, photocathodes, and ferroelectrics are presented, together with a summary of the understanding of the physics involved. The paper concludes with a description of L-band micropulse gun, based on secondary emission in an RF cavity. Emphasis is placed on cathode development for electron guns to drive microwave tubes and RF accelerators.

/pdf/advances-in-cold-cathode-physics-and-technology-5cjwzz5zbb.pdf

Advances in cold cathode physics and technology

The Stanford 3-km linear accelerator at SLAC has operated exclusively since early 1992 using a polarized electron beam for its high-energy physics programs. The polarized electron source now consists of a diode-type gun with a strained-lattice GaAs photocathode DC biased at high voltage and excited with circularly polarized photons generated by a pulsed, Ti:sapphire laser system. The electron polarization at the source is > 80%. To date the source has met all the beam requirements of the SLC and fixed target programs with < 5% downtime.

The Stanford linear accelerator polarized electron source

https://www.slac.stanford.edu/grp/rd/pprc/publications/PLA282_309.pdf

Photovoltage effects in photoemission from thin GaAs layers

The transverse emittance from optimized RF photoinjectors is limited by the thermal emittance. The thermal emittance can be lowered by a factor >2 by using a semiconductor photocathode.

/pdf/reduction-of-thermal-emittance-of-rf-guns-86eoj3e8ms.pdf

Reduction of thermal emittance of RF guns

The Stanford Linear Collider injector requires two 2 ns pulses of 4.5–5.5 × 10 10 electrons, separated by 61 ns at 120 Hz, from its source. Since 1992, these currents have been provided by a polarized electron source based on GaAs photocathodes. A beam polarization of 76 ± 4% has been measured at the end of the 50 GeV linac. At low photocathode quantum efficiencies, and for excitation near threshold, the maximum current delivered by the source is constrained, not by the space charge limit of the gun, but by a “charge limit” of the photocathode. The charge limited current is proportional to the photocathode quantum efficiency, but the proportionality varies for different photocathode types. Experience with high polarization strained GaAs photocathodes on a test beamline and on the SLC is presented.

https://www.slac.stanford.edu/pubs/slacpubs/6250/slac-pub-6275.pdf

The high peak current polarized electron source of the Stanford Linear Collider

The design of the Linac Coherent Light Source assumes that a low-emittance, 1 nC, 10 ps beam will be available for injection into the 15 GeV linac. The proposed rf photocathode injector that will meet this requirement is based on a 1.6-cell S-band rf gun equipped with an emittance-compensating solenoid. The booster accelerator with a gradient of 25 MV/m is positioned at the beam waist coinciding with the first emittance maximum, i.e., the “new working point.” The uv pulses required for cathode excitation will be generated by tripling the output of a Ti:sapphire laser system. Details of the design and the supporting simulations are presented.

/pdf/photoinjector-design-for-the-lcls-2ncogpzjqq.pdf

G. Mulhollan

Papers

The Stanford linear accelerator polarized electron source

Photovoltage effects in photoemission from thin GaAs layers

Reduction of thermal emittance of RF guns

The high peak current polarized electron source of the Stanford Linear Collider

Photoinjector design for the LCLs