HYBRIS: R. Keller 041021 Page 1

A Hybrid Ion Source Conceptfor a Proton Driver Front-End

R. Keller, P. Luft, M. Regis, J. WalligM. Monroy, A. Ratti, and D. Syversrud

Lawrence Berkeley National Laboratory, Berkeley, CA, USA

and

R. Welton and D. AndersonSNS-Oak Ridge National Laboratory, Oak Ridge, TN, USA

Bensheim, Oct. 21, 2004

ICFA-HB 2004 Workshop

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Acknowledgments

John Staples LBNL 2 & 13-MHz rf matching

Richard Pardo ANL Microwave ECR ion source

Bob Scott ANL Microwave ECR ion source

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Background

Sources of intense H- beams are needed for future Proton Driversthat include Accumulator Rings

Specifically, the Spallation Neutron Source (SNS) needs to pursue cutting-edge technology in areas critical to accelerator operation

To ensure adequate performance Linac and Ring commissioning 1.44-MW production beam Future power upgrade towards 3 MW and higher

Ion source and beam-formation system constitute such an area H- beam production is particularly complex and challenging

R&D investment in this area is highly cost effective

Develop ion sources with highest levels of performance and reliability First phase of work aims at improving reliability and availability

of the plasma generator (the “ion source proper”) At least 500 hours of time-between-services

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Original SNS Ion Source and LEBTAreas for Improvement

Plasma Generation Beam Formation Electron Dumping LEBT

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HYBRIS Development Plan

Abandon standard SNS 2 & 13-MHz rf technology, including Internal, porcelain coated antenna 2-MHz amplifier and impedance matcher

Main-plasma generation by pulsed d.c. discharge Proven to work for H- production with filaments (e. g. KEK, JAERI)

Sustain main discharge by microwave-driven plasma cathode No need for thermionic filaments

No build-up of surface-poisoning deposits 2.45-GHz ECR plasma generators have proven extremely long lifetime and

reliability as proton sources (e. g. LANL-LEDA, CEA Saclay) Attempts to produce intense H- beams directly in ECR ion source were

moderately successful (~1mA beam current, e. g. TRIUMF, CEA Saclay) Controlling electron energy in main discharge vessel will be crucial

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Performance Parameters

Established SNS ion-source performance ~55 mA at about 0.1% duty factor

51 mA transported through LEBT, RFQ, and MEBT 2.5 weeks with 33 mA at 7.4% d. f. through LEBT

0.12 mm mrad normalized rms emittance 60 mA at 1.2 ms, 20 Hz through LEBT

Modified cesium collar/outlet aperture (see ICFA-HB 2002) 0.35 mm mrad normalized rms emittance

Ultimate HYBRIS performance goals 75 mA peak H- beam current 0.25 mm mrad normalized rms emittance 12% duty factor 2 months interval between services

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HYBRIS Layout

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HYBRIS Electrical Circuit

- + - + - + - + - +150 V 20 kV 150 V 6 kV 50 kV

1 A 0.1 A 5 A 0.4 A 0.2 A

Hot Deck

60 Hz1 ms1

0 - 20 sccm 0 - 100 sccm

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Envisaged Operational Parameters

H- collarH- beam currrent mA 50 Demonstration goalH- current density mA cm^-2 130 DerivedH- flux 1/s cm^2 8.E+17 DerivedH- outlet diameter mm 7 Given

Ion avg. energy eV 2 AssumedIon avg. speed cm/s 2.E+06 DerivedH- plasma density cm^-3 4.E+11 Derived

Main DischargeElectron plasma density cm^-3 4.E+12 Assumed

2.45-GHz ECR DischargeCritical density w/o ECR cm^-3 7.00E+10 GivenECR magnetic field mT 87.5 Given

Microwave power, max. kW 1.2 GivenHydrogen gas flow sccm 3 AssumedIon current density mA cm^-2 150 DemonstratedIon flux cm^-2 9.4.E+17 DerivedIon energy eV 20 AssumedIon avg. speed cm/s 6.E+06 DerivedIon plasma density cm^-3 1.5.E+11 DerivedElectron energy eV 20 AssumedElectron density cm^-3 1.5.E+11 DerivedElectron speed cm/s 2.65E+08 DerivedElectron current density mA cm^-2 6.4E+03 DerivedE-Outlet diameter mm 5 GivenElectron current mA 1262 Derived

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Status of HYBRIS Development

2.45-GHz ECRIS obtained on loan from Argonne Nat. Lab. Chalk River Nat. Lab. model

Test stand assembled Discharge pulser received from SNS and tested

Baseline test with rf-driven SNS prototype ion source performed

Capacitive rf impedance matcher worked very well ECR ion source operated

Immediately produced intense electron beam Electron beam current limited by uncooled extractor tube

So far, operated barely above ECR threshold for 2.45 GHz HYBRIS extraction chamber built and assembled

Modified, cooled, extractor tube First test imminent Still a low-budget effort

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HYBRIS

ECR Discharge Vessel Electron Extraction H- Discharge Vessel

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HYBRIS Test Stand

Tuner Directional Couplers HV Break Dummy Load Magnet Coils Vacuum Tank

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Future Developments

Optimize ECR discharge chamber as a plasma cathode Simplify magnetic field generation

Use one solenoid coil only - or permanent magnets Reduce electron extraction voltage Reduce distance between ECR and H- discharge chambers

Electron dumping mechanism

LEBT layout

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Summary

Hybrid Ion Source under development Aimed at producing high-current H- beams

at high duty factor with very high reliability Combining three well proven concepts

Pulsed d.c. main discharge Microwave-driven plasma cathode H- production chamber of existing SNS ion source

H- ion production still to be demonstrated Principal unproven issue is control of the electron

temperature in the H- production chamber

Areas of future developments identified