1. 1 “The Gatling Gun” A High Current Polarized Electron Gun System John Skaritka Collider-Accelerator Department Brookhaven National Laboratory

2. 2 Outline Overview Next generation scientists of the project Description of Gatling Gun system components and their operation Summary

3. 3 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.

4. 4 Training next generation scientists Eric Riehn, Post Doc Develop and measure performance of optimized photocathodes and manufacturing processes for the Gatling Gun. Erdong Wang, Post Doc Electro magnetic and beam dynamic codes and photocathode preparation and testing Omer Rahman, PhD Student VORPAL code modeling to study 3-D beam dynamics and cathode development and testing

5. 5 30 deg Combiner, 700 kHz rotating magnetic bending Bunching cavity (112 MHz) 3 rd harmonic cavity Ballistic compression Booster linac Gatling gun “Gatling Gun” concept 20 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

6. 6 Depressed Collector Diagnostic insertion Gatling gun chamber Combiner Gatling Fun Feasibility system with diagnostic section and Depressed Collector 6

7. 7 Gatling Gun System Layout Cathode Exchange Chamber Gatling-Gun Extreme vacuum chamber Gun Laser System table, (Laser Lab not Shown) Cathode Transport Line Cathode Prep.Chamber ( Grand Central ) Cathode Regeneration Forest Fresh Cathode Load Lock 300 KV Feed through

8. 8 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.

9. 9 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. Chamber 20 Cathode Shroud(Revolver) Inject able Cathode Magazine Cathode Module Manipulator Cathode Train Cathode Exchange Chamber(CEC) path of motion

10. 10 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

11. 11 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.

12. 12 The drive laser Laser 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.. Electro- optic modulato r Pulsar with Phase- locked loop Multi-stage EDFA 10 W 1560 nm Periodically – poled LiNbO 3 4W 780 nm CW DFB laser Accelerator RF ref Frequency doubling module

13. 13 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 l XHV manufacturing practices have been developed and implemented in Industry. l 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