Preliminary Report on Single and Multi-Crystal Diamond Electron Cathodes

Transcription

1 Preliminary Report on Single and Multi-Crystal Diamond Electron Cathodes Eisuke. J. Minehara FEL Laboratory at Tokai, APRC, Kansai, JAERI, 2-4 Tokai, Naka, Ibaraki, JAPAN The next generation high brightness and high current electron source like a photo cathode, a thermionic cathode, a crystal Diamond electron cathode and others would be expected to realize the next generation ERL (energy recovery linac) based light source and SASE X-Ray free-electron laser. The JAERI FEL group has recently started to develop a new crystal Diamond electron cathode technology for high current, high brightness, and long life electron source. In the presentation, we plan to explain and to discuss our strategy and a preliminary experimental work of the crystal Diamond cathode, and related extreme high vacuum evacuation system.

2 Diamond Cathode Trials in Thermionic Gun and GaAsPC Gun JAERI ERL-FEL Diamond Cathode Guns Natural Single Crystal Sheet SEM GaAs NEA Photocathode Gun Academic Applications Synthetic enhancement Single and Evaluation of poly-crystal Secondary Themionic Industrial Emission Gun Applications Industrial produced P-doped CVD DLC Energy Dependence Measurement and Other kinds of Evaluations

3 Diamond and Diamond Like Carbon SEM Material Evaluation Material Evaluation by using SEM brightness. fig.1, 0.3mm thick CVD DLC film. fig.2, H-terminated and B doped Dark because of No NEA Layer hot W preparation. Bright and No P-doped. because of NEA Layer.. fig.3, H-terminated and B doped RF plasma preparation. Bright because of NEA Layer.

4 Diamond secondary emission cathode will be discussed here as Diamond electron cathode using primary electron as the exciting quanta to produce many electron hole pairs instead of the laser photon. In the scheme, we can expect very high quantum efficiency, say 10% quantum efficiency means 10 photons need to produce one electron, on the other hand, 2.6keV primary electron can produce about 200 electrons in principle. N: Mutliplication Factor( is proportional to E.) N=E/ E eh =E/(2.2 Nr E phonon ) E : Primary Electron Kinetic Energy E eh :Energy needed for producing single electron hole pair=~13ev : Gap Energy of Diamond=~5.5eV, Nr: Averaged Number of Primary Electron Excited Phonon E phonon : Dissipated Phonon Energy ~several tens mev

5 Forward Angle Extracted secondary electrons Diamond Source Excited by Photoelectron 1 Laser Primary Electron Generating Photo Cathode, 2. High Energy Quanta for Exciting Secondary Electrons, 3. Diamond Semiconductor and Insulator Multiplying Film, 4.Many Excited Electron Hole Pairs, 5. Negative Electron Affinity Surface, 6.Secondary Electrons Extraction to Vacuum,

6 Right Angle Extracted secondary electrons Diamond Source Excited by Photoelectron 1 2 Laser Primary Electron Generating Photo Cathode, 2. High Energy Quanta for Exciting Secondary Electrons, 3. Diamond Semiconductor and InsulatorMultiplying Film, 4.Many Excited Electron Hole Pairs, 5. Negative Electron Affinity Surface, 6.Secondary Electrons Extraction to Vacuum,

7 Reflected Secondary Electrons Diamond Source Excited by Photoelectron 1 2 Laser

8 Band Structures of NEA Layered Secondary Electron Diamond Cathode and Primary Electron Photo Cathode 6Forbidden Band Electric 6 Electrons Electric 5Conduction Band Electron Field 5 Electrons Field 4Forbidden Band 8Vacuum Level 7 NEA 4 8Vacuum Level 7 NEA 3Valence Band Hole Layer Holes Layer 3 2Forbidden Band 2 1Inner Shell Electrons 1 Primary Electron Secondary Electron Photo Cathode Diamond Cathode

9 Multiplication Process in the Band Structure of NEA Layered Secondary Electron Diamond Cathode and Primary Electron Photo Cathode Sencondary Electrons Laser Photon Primary Electron 6Forbidden Band 6 Electron 5 Conduction Band Electric Field 5 Electric Field 4Forbidden Band Hole 3Valence Band 7 NEA Layer NEA Layer 2Forbidden Band 2 Hole 1Inner Shell Electrons Primary Electron Photo Cathode 1 Secondary Electron Diamond Cathode

10 30kV E-Gun XYsteerer, Focus Lens, Several tens microns diameter beam spot

11 Natural highest quality Diamond IIa Crystal Sample Holder Side

12 Natual Diamond IIa Crystal Sample, Electrode and Holder

13 KS120 Ti-Alloy Test Chamber for Future JAERI-EGUN 5x10-13 Torr Achieved

14 Summary 1. Current Status of JAERI Diamond Electron Cathode Development was discussed. #Thermionic Gun and GaAs NEA Gun as the primary electron source are planned to realize the JAERI Diamond Electron Cathode for ERL-LS and ERL-FEL. #A Simple and Emperical Multiplication factor is estimated to be proportional to primary electron kinetic energy in ideal case. #Diamond Material Evaluation by SEM, Multiplication Factor and Others Now under way. 2. XHV(Extreme High Vacuum) Ti alloy chamber as a future Gun chamber candidate is shown as one of our Gun activities.