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“The Gatling Gun”

A High Current Polarized Electron Gun System

John SkaritkaCollider-Accelerator DepartmentBrookhaven National Laboratory

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Outline

•Overview•Next generation scientists of the project•Description of Gatling Gun system components and their operation•Summary

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Overview

• This is a Laboratory Directed Research and Development (LDRD) project.• The motivation is to develop a high-current polarized electron gun aimed

at eRHIC, where the requirement is 50 mA average current.• The specific approach is to use funneling of beams from multiple cathodes

in order to increase the (current * lifetime) product of the gun.• The goal of the LDRD project is to demonstrate that funneling works. To

be specific:• A reasonable current and lifetime achieved with one cathode.• The addition of a second cathode does not degrade the performance of

the first and thus doubles the current*lifetime product of the device.• A separate LDRD project is devoted to the development of the laser driver.• This program is complementary to high-current polarized gun R&D at

Jefferson Laboratory and at MIT, i.e. advances in each of the programs lead to a combined improvement in the eRHIC polarized injector.

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Training next generation scientistsEric Riehn, Post Doc

Develop and measure performance of optimized photocathodes and manufacturing processes for the Gatling Gun.

Erdong Wang, Post DocElectro magnetic and beam dynamic codes and

photocathode preparation and testing

Omer Rahman, PhD StudentVORPAL code modeling to study 3-D beam dynamics and cathode development and testing

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30 deg

Combiner, 700 kHz rotating magnetic bending

Bunching cavity (112 MHz)

3rd harmonic cavity

Ballistic compression

Booster linac

Gatling gun

“Gatling Gun” concept20 Photo-cathodes arranged in a ring

16 cm

Fixed magnetic bending

G-Gun Laser Systems

Target photo current to be 2.5 mA / cathode, beam current to be > 50 mA @ 200 kV

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Depressed Collector

Diagnostic insertion

Gatling gun chamber

Combiner

Gatling Fun Feasibility system with diagnostic section and Depressed Collector

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Functions of the Preparation Chamber

24 cathode train

Manipulator to move cathodes between train and prep trees

Atomic hydrogen gun

Cathode service flange assembly to heat, cool and

apply O2

System to deposit Cs on the cathode

cathode module

Cathodes Preparation Trees Assy.

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Sectioned View of the Gatling Gun Assembly shows, From left, the cathode train from the Cathode Prep. Chamber arrives in the Cathode Exchange Chamber lower right. A manipulator transfers the individual cathode

modules from the train to the cathode magazine to be is injected into the 20 Cathode Shroud (revolver assy.).

“Grand Central” Cathode Prep. Chamber20 Cathode Shroud(Revolver)Inject able Cathode MagazineCathode Module Manipulator

Cathode TrainCathode Exchange Chamber(CEC)

path of motion

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Cathode, Anode G-Gun Component design

“C” Style 1st Bend Dipole Copper Cathode Shroud < 250KV

Titanium Anode Focusing Solenoid

Gallium Arsenide Cathode

Molybdenum cathode base

Titanium conformer

Extreme Vacuum Cathode Ring NEG pump

Cathode Module

Cathode cooling ring

4W, 780 nm Laser Beam

2.5 mA. Electron Beam

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E-beam transport through the combiner

DC Dipoles bend the e-beams into a synchronized field rotating at 704KHz that bends the beam trajectory onto a common axis.

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The drive laserLaser undergoing final testing at Optilab LLC of Phoenix AZ, and Covesion Ltd,

of Hampshire, UK. Delivery expected shortly

A 1560 nm laser (CW DFB) is modulated synchronously with a subharmonic of the accelerating RF. After amplification in an Erbium-doped fiber amplifier chain (EDFA), the light is frequency doubled in periodically poled Lithium Niobate.

The output will be 4 Watts at 704 kHz (5.4 uJ/pulse), with an adjustable pulse width of 1.2-1.7 nsec.

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Electro-optic

modulator

Pulsar with Phase-locked loop Multi-stage EDFA

10 W1560 nm

Periodically – poled LiNbO3

4W780 nm

CW DFB laser

Accelerator RF ref

Frequency doubling module

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Summary• A brief overview of the conceptual design and operation of the Prototype

Gatling Gun and Cathode Prep system was presented. • Progress is being made on the Gatling Gun components in industry

XHV manufacturing practices have been developed and implemented in Industry. Detailed designs of Gatling Gun components are underway, some components

are being manufactured while others are being tested.• Schedule milestones that define the program have been presented that if

funded will fully demonstrate and categorize the Gatling Gun for use as a practical source for an ERL by the Fall of 2015