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CAT-KEK SOKENDAI School on Spallation Neutron Source: Accelerator Physics ＆Technological Aspects February 2 – 8, 2004, Centre for Advanced Technology, Indore, India ION SOURCES Akira Takagi KEK (High Energy Accelerator Organization), Japan ION SOURCES(1) • • • • • • • • Early History of the Particle Accelerator Production Methods of Negative Ion Types of Negative Hydrogen Ion Source KEK-PS H- Ion Source LaB6 Filament Beam Chopping Secondary Electron by Ion Impact Heavy/Metal Negative Ion Early History • The First artificially induced nuclear transmutation. (Rutherford,1919) 16N + 4He 17O + 1H a-particles (7 MeV, 2x107 m/s) from radium • The results as a whole suggest that if a-particles –or similuar projectiles- of still greater energy were available for experiment, we might expect to break down the nuclear structure of many of the lighter atoms. Rutherford, Phil. Mag. 37, 578 (1919) Cockcroft-Walton’s Voltage Multiplier • The first nuclear disintegration by nuclear projectiles artificially produced in a man-made accelerator.(1932) 7Li + 1H 4He + 4He (+17.3MeV) Cockcroft, Walton, Proc. Roy. Soc. A137, 229(1932) Charge Transfer Processes (H+ -> H-) Charge Exchange (D-) Electron Affinities for atoms and molecules H- Ions from Duoplasmatron H- from Duoplasmatron Potential distribution at the metal surface PIG (Penning Ion Gauge) Type Magnetron H- Production (Surface Production) Magnetron Type Multicusp Surface H- Ion Source Multicusp Volume Production H- Ion Source Multi-Cusp Negative Hydrogen Ion Source (Surface Production Type) BLAKE-I KEK-PS Ion Source just before Installation Electron Suppression LaB6 & Tungsten LaB6 : W=2.67 eV 9 A/cm2 :1900 K W : W=4.55 eV 1.6 A/cm2 : 2700 K LaB6 Filament (15 mm dia.) Surfase Analysis of LaB6 Filament After 1000 hrs operation LaB6 Filament ＆ Cathode Flange After 3000 hrs Operation LaB6 Filament (20 mm dia.) LaB6 Filament＆Cathode Flange (Volume Source) Empty Cs Ampoules & Cs-Glass Reactants 750 keV Pre-Injector for 12 GeV PS Ratio Ratio of Negative Hydrogen Ions 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 CM2/CM1 CM3/CM2 0 20 40 Time (hr) 60 Operating Parameters Multicusp Surface production Negative Hydrogen Ion Source BLAKE-I • • • • • • ARC Current 83 A ARC Voltage 109 V ARC Pulse Width 180 msec Converter Voltage 650 V Gas Flow Rate 7.7 cc/min Filament Current & Voltage » FIL-1 72A x 8.0 V(1400 C) » FIL-2 73A x 8.1V (1390 C) • Cockroft-Walton Generator Voltage 749.5 kV • Beam Current 39.1 mA Beam Pulse : Ion Source Extraction & Linac Entrance U : Voltage drop of the terminal voltage M : Ion source output (H-) L : Linac Input (H-) Production of Direct-Chopped H- Ion Beam Fast chopped H- beam (2 MHz) by the direct modulation of converter voltage Radio Frequency Discharge Radio Frequency Skin Depth (Xe) Secondary Electron Emission • In the case of electron impact : The energy of the primary electron must be higher than the energy determined by the work function of the metal surface. • In the case of positive ion impact,: The secondary electron can be induced only if the sum of the potential energy E and the kinetic energy Ei is higher than twice the value of the work function f. E + Ei > 2f Secondary Electron Emission by Ion Impact Faraday Cup Signals by H-/+/o Beam (Without Secondary Suppression) Secondary electron Coefficients by H-/+/o Beam No Conclusion • Tomorrow’s my lecture: • Volume Production Negative Hydrogen Source • Early results in KEK • Recent results for J-PARC • H- diagnostics (with laser)