SRF GUN DEVELOPMENT

BNL’S MANY INTERESTS

Andrew Burrill on behalf of the electron cooling group

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Andrew Burrill on behalf of the electron cooling group

Brookhaven National Laboratory

Agenda

� Review past SRF gun testing at BNL

� Look at programs that have grown from this

work

� Discuss novel cathode insertion design

� Application for high average current

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� Application for high average current

� New Low Frequency SRF gun

� Photocathode transport

� Vacuum requirements, cleanliness, contamination

703 MHz SRF Gun for ERL

(AES Fabrication)

112 MHz Quarter wave Gun

(Niowave SBIR)

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1.3 GHz Bare Nb injector

(AES SBIR/CRADA)

Plug Gun

Choke joint Gun

(AES Fabrication)

(JLAB modification)

1.3 GHz Injectors

Our First Foray into SRF Gun Work

Goal: To use bare Nb as a cathode

QE 2e-4 at 266 nm in lab

2e-5 in Gun

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Testing courtesy of P.

Kneisel (JLAB)

Nb probesAl probes

1.3 GHz Plug Gun – GaAs Test System

� Gun modified to accept a

simple Nb plug

� Goal: Measure QE and beam

properties of GaAs in SRF gun

� Baseline cavity tests carried out

� Several interesting observation

with the plug inserted and with

GaAs on the plug

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Quarter wave choke jointCavity modified by adding a quarter wavelength choke

Joint for a demountable photocathode

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BNL_gun1 no cathode

First Pass

Second test after FE event

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Epeak (MV/m)

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Qo

Epk (MV/m)

Cathode installed

Barrier

Multipacting barrier at low field in choke region

Mitigation plans

1. High Temperature bake – reduced SEY

2. Bias cathode stalk

SRF Photoinjector at 703.75 MHz

� ½ Cell SRF injector� Demountable cathode

stalk

� High Temperature superconducting Solenoid

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Solenoid

� UHV cathode transporter carts� 2 fabricated and

delivered

� Testing underway

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High Temperature Superconducting

Solenoid already fabricated

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FPC schematic for ½ cell gun

Injector Fabrication and Cryomodule

Status� Injector fabrication underway at Advanced Energy Systems

� Significant delays caused by ASME pressure vessel code requirements, weld and braze sample preparation

� Choke joint machining finished� Nb VTA cathode fabricated

� Final weld development underway

� Cavity completion data 7/09

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� Cavity completion data 7/09

� Tentative plan to clean and test cavity at JLAB

� Tooling for string assembly being designed and fabricated in-house

� Cryomodule design complete, based on top loading, ballast tank system, similar to Linac cryomodule, going out for bid now.

VTF Injector Test Plan

� Test injector without cathode stalk� Determine operating conditions for cavity geometry

� Test with VTF cathode stalk inserted� Determine impact of cathode stalk on cavity performance

� Parallel development project with 1.3 GHz choke joint gun, working on high temperature bake of gun and biasing system

� Weld He vessel to gun and re-test

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� Weld He vessel to gun and re-test

� Final chemistry and HPR pass, build into hermetic string in cleanroom

� Transfer to BNL to complete cryomodule assembly� Same group responsible for Linac cryomodule

� Transfer to ERL building for horizontal testing and cathode transporter cart integration

Injector Fundamental Power Couplers

� 2X 500 kW CW coaxial couplers

with “Pringle tip” designed and

fabricated at CPI

� In house, awaiting completion of

resonant waveguide for conditioning

� BNL will condition FPCs with our 1

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� BNL will condition FPCs with our 1

MW Klystron

� Additional project with AES to test

legacy couplers to failure

Fundamental Power Coupler conditioning

� 2X 500 kW RF couplers

built for 703 MHz injector

� Plan to condition couplers at

BNL using 1 MW klystron

� Will also test spare AES Mark

II couplers to performance

limit

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limit

� Designed for 350 kW

operation, will push to failure

112 MHz Injector

SBIR proof of principle design

Applications for low energy electron cooling

Demonstration of 4K gun technology

Frequency (MHz) 112.5978

Vo (MeV, beta=<0.98>) 2.7

Ecathode (MV/m) 19.67

Eo (MV/m) 28.28

Epeak (MV/m) 51.29

Bpeak (mT) 97.83

Bp/Ep (mT/(MV/m)) 1.91

Pd (W) 16.55

T (K) 4.5

Q 3.48e9

G (Ohm) 38.25

R/Q (Ohm) 126.77

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R/Q (Ohm) 126.77

TTF 0.99

� Beer can laser size: R=5.5mm, L=11.0 deg(270ps, 8.14cm full length)

� 5nC/bunch

� Energy at gun exit and linac exit: 2.69MeV, 19.1MeV

112MHz

Gun

112MHz

Cavity

20cm 30cm 70cm 80cm5cm 160cm

Solenoids

0.455 nC Case

Work by X. Chang

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5 nC Case2nC Case

CsK2Sb Photocathode

� Deposition System in

house� 2 transporter carts delivered

� Base pressure 1x10-10 Torr

� System designed to eliminate

cross contamination of sources

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cross contamination of sources

� Provides for quicker source

exchange

� Transporter cart

� 2 UHV systems with LN2 cooling

capability

� Awaiting replacement

thermocouple prior to re-bake

Laser System

� Lumera built a 5 W, 355 nm, 10 ps, 9.38 MHz

laser system

� Designed for BNL needs for generation of 50 mA current

� We had discussions with vendor about upgrading to

system for 500 mA if funding is available

� Will be operated at 532nm, 355nm, and 266nm

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� Will be operated at 532nm, 355nm, and 266nm

� Active program for generation of spatial and temporal flat

top beams underway with good progress

� System arrived 2 weeks ago, and installation and field

testing is complete and met most expectation.

Contact: Triveni Rao