| Paper | Title | Page |
|---|---|---|
| TUPPH014 | Transverse Emittance of Diamond Field-Emitter Arrays | 262 |
|
||
| We present progress in transverse-emittance measurements of ungated diamond field-emitter arrays. Fine-pitch arrays are conditioned to provide uniform emission prior to emittance testing. The testing will be performed using a pepperpot technique with microlithographed silicon aperture arrays and a ZnO phosphor screen. Results will be compared to simulations performed in POISSON/GPT. | ||
| TUPPH016 | Fabrication of Diamond Field-Emitter-Array Cathodes for Free-Electron Lasers | 269 |
|
||
| Field-emitter arrays (FEAs) have several advantages as cathodes for free-electron lasers (FELs): they are rugged, require no laser driver, and generate little heat. We have developed two methods to fabricate diamond FEAs for FEL applications. In the first method, pyramids are formed on a Si substrate and sharpened by microlithography and then coated with CVD nanodiamond. The advantages of this approach are a rigid, planar Si substrate, and microelectronic type fabrication. Typically, tip radii on the order of hundreds of nanometers are formed on 20-μm pyramids. In the second method, all-diamond pyramids are formed by a mold-transfer process in which they become sharpened from an oxide layer in the mold process. The diamond array is then brazed to a Mo substrate and the Si mold removed. The advantage of this process is that the tips are sharper, with tip radii smaller than 10 nm formed on 10-μm pyramids. The fabrication techniques and the performance of these cathodes will be discussed and compared. | ||
| TUPPH028 | Uniformity Conditioning of Diamond Field-Emitter Arrays | 302 |
|
||
| We present results in the conditioning of diamond field-emitter arrays towards uniform emission. Post-fabrication conditioning procedures consisting of thermal annealing, gas exposure, and high field/emission operation have been examined. A high degree of emission uniformity was successfully achieved by thermal-assisted field evaporation of the diamond nanotips. This uniform emission was stable up to currents of 15 microamps per tip, at which point the phosphor anode began to degrade from the high input power density. | ||
| TUPPH034 | Toward Energy-Spread Measurements of Diamond Field-Emitter Arrays | 317 |
|
||
|
A high-resolution retardation energy analyzer is being developed to examine the energy spread of electron beams from diamond field-emitter arrays. Analyzer design was guided by previous work at UMER*, and simulations performed in SIMION. The anaylzer incorporates a cylindrical focusing electrode which, when properly tuned, gives millivolt resolution for multi-kilovolt beams. The analyzer is integrated into a low-energy cathode teststand, which allows arbitrary adjustment of the anode-cathode spacing and planarity during operation.
* Y. Cui, Y. Zou, A. Valfells, M. Reiser, M. Walter, I. Haber, R. A. Kishek, S. Bernal, and P. G. O’Shea, Rev. Sci. Instrum. 75, 8 (2004). |
||
| THAAU04 | Development of Diamond Field-Emitter Arrays for Free-Electron Lasers | 477 |
|
||
| We report recent advances in the development of diamond field-emitter arrays as a promising electron source for free-electron lasers. Both sparse and close-packed arrays have been produced using an inverse-mold transfer process. High-pitch arrays have been used in the development of conditioning techniques, which drive the emitters toward uniformity in a self-limiting fashion. Properties of these cathodes including I-V response, emitted energy spread, transverse emittance, temporal stability, and operational lifetime are being examined in two DC teststands. Highly uniform, stable emission current of 15 μA (DC) per tip has been achieved. The resulting high-input-power density destroyed the phosphor anode locally; therefore, higher currents could not be attempted. In an RF gun, pulsed picosecond operation will allow much higher peak currents, and back bombardment from sublimated anode material will not be present. The maximum DC-current densities observed scale to approximately 300 Amps per square centimeter for fine-pitch arrays, demonstrating great promise for use in free-electron lasers. |