J. Kewisch

Secondary Emission Enhanced Photoinjector

We report a new approach to the generation of high-current, high-brightness electron beams. Primary electrons are produced by a photocathode (or other means) and are accelerated to a few thousand electron-volts, then strike a specially prepared diamond window. The large Secondary Electron Yield (SEY) provides a multiplication of the number of electrons by about two orders of magnitude. The secondary electrons drift through the diamond under an electric field and emerge into the accelerating proper of the “gun” through a Negative Electron Affinity surface of the diamond. The advantages of the new approach include the following: 1. Reduction of the number of primary electrons by the large SEY, i.e. a very low laser power in a photocathode producing the primaries. 2. Low thermal emittance due to the NEA surface and the rapid thermalization of the electrons.3. Protection of the cathode from possible contamination from the gun, allowing the use of large quantum efficiency but sensitive cathodes. 4. Protection of the gun from possible contamination by the cathode, allowing the use of superconducting gun cavities. 5. Production of high average currents, up to ampere class. 6. Encapsulated design, making the “load-lock” systems unnecessary. Section

Optics for High Brightness and High Current ERL Project at BNL

An energy recovery linac (ERL), under development at Brookhaven National Laboratory [1,2], will push ERLs further towards high current and high brightness beams. This R&D ERL will operate in two modes: a high current mode and a high charge mode. In this paper we present a lattice of the machine and PARMELA simulations from the cathode to the beam dump. We discuss the design considerations and present main parameters for various modes of operation.

Study of Secondary Emission Enhanced Photoinjector

The secondary emission enhanced photoinjector (SEEP) is a very promising new approach to the generation of high-current, high-brightness electron beams. Primary electrons with a few thousand electron-volts of energy strike a specially prepared diamond window. The large Secondary Electron Yield (SEY) provides a multiplication of the number of electrons by about two orders of magnitude. The secondary electrons drift through the diamond under an electric field and emerge into the accelerating proper of the “gun” through a Negative Electron Affinity (NEA) surface of the diamond (Hydrogen terminated). We present the calculation of heating power sources and the temperature distribution in detail. Some properties of the secondary electron beam related to beam dynamics are also reported. The results demonstrate the feasibility of this kind of cathode.

Layout and optics for the RHIC electron cooler

As part of a luminosity upgrade it is planned to add an electron cooling section to the RHIC accelerator. Existing electron coolers operate at low beam energies and use a continuous electron stream. The ion energy of 100 GeV/u in RHIC requires an electron energy of 55 MeV. Therefore the RHIC cooler uses a linac with energy recovery for the electron acceleration. Short bunches exiting the linac section are stretched longitudinally to reduce the momentum charge and space charge effects in the cooling section, and compressed afterwards for deceleration and energy recovery in the linac. This report describes the design of the electron beam transport and simulation results.

Diamond Amplifier For Photocathodes

We report a new approach to the generation of high‐current, high‐brightness electron beams. Primary electrons are produced by a photocathode (or other means) and are accelerated to a few thousand electron‐volts, then strike a specially prepared diamond window. The large Secondary Electron Yield (SEY) provides a multiplication of the number of electrons by about two orders of magnitude. The secondary electrons drift through the diamond under an electric field and emerge into the accelerating region proper of the “gun” through a Negative Electron Affinity surface of the diamond. The advantages of the new approach include the following: 1. Reduction of the required number of primary electrons by the large SEY, i.e. we can utilize a very low laser power in a photocathode producing the primaries. 2. Low thermal emittance due to the NEA surface and the rapid thermalization of the electrons.3. Protection of the cathode from possible contamination from the gun, allowing the use of large quantum efficiency but sen...

Low emittance electron beams for the RHIC electron cooler

An electron cooler, based on an energy recovery linac (ERL) is under development for the relativistic heavy ion collider (RHIC) at Brookhaven National Laboratory. This will be the first electron cooler operating at high energy with bunched beams. In order to achieve sufficient cooling of the ion beams the electron have to have a charge of 5 nC and a normalized emittance less than 4 mu. This paper presents the progress in optimizing the injector and the emittance improvements from shaping the charge distribution in the bunch.

Commissioning of a first-order transition jump in RHIC

When accelerating gold ions in the Relativistic Heavy Ion Collider (RHIC) the transition energy must be crossed. RHIC uses a set of special quadrupoles and power supplies which can reverse polarity in less than 40 milliseconds. These quadrupoles are used to produce dispersion bumps which increase the transition energy as the beam approaches transition. The change of polarity will then jump the transition energy across the beam energy. This paper describes the commissioning of the RHIC transition crossing system.

High average current low emittance beam employing CW normal conducting gun

CW normal conducting guns usually do not achieve very high field gradient and waste much RF power at high field gradient compared to superconducting cavities. But they have less trapped modes and wakefields compared to the superconducting cavities due to their low Q. The external bucking coil can also be applied very close to the cathode to improve the beam quality. By using a low frequency gun with a recessed cathode and a carefully designed beam line we can get a high average current and a high quality beam with acceptable RF power loss on the cavity wall. This paper shows that the CW normal conducting gun can be a backup solution for those projects which need high peak and average current, low emittance electron beams such as the relativistic heavy ion collider (RHIC) e-cooling project and energy recovery linac (ERL) project.

Electron Beam Generation and Transport for the RHIC Electron Cooler

An electron cooler, based on an Energy Recovery Linac (ERL) is under development for the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory. This will be the first electron cooler operating at high energy with bunched beams. A better understanding of the cooling process and more accurate measurements of Intra Beam Scattering in RHIC have imposed increased requirements on the electron accelerator: Besides a doubling of the bunch charge to 20 nC, the strength of the cooling solenoid was increased five-fold to 5 Tesla. The magnetic field on the cathode should be increased to 500 Gauss to match the magnetization required in the cooling solenoid. This paper reports the measures taken to minimize the electron beam emittance in the cooling section.

Half-Cell RF Gun Simulations with the Electromagnetic Particle-in-Cell Code VORPAL

We have simulated Brookhaven National Laboratory’s half‐cell superconducting RF gun design for a proposed high‐current ERL using the three‐dimensional, electromagnetic particle‐in‐cell code VORPAL. VORPAL computes the fully self‐consistent electromagnetic fields produced by the electron bunches, meaning that it accurately models space‐charge effects as well as bunch‐to‐bunch beam loading effects and the effects of higher‐order cavity modes, though these are beyond the scope of this paper. We compare results from VORPAL to the well‐established space‐charge code PARMELA, using RF fields produced by SUPERFISH, as a benchmarking exercise in which the two codes should agree well.