(Color online) (a) Schematic cross-section of all metal FEA. (b) SEM image of a 5-μm-pitch FEA used in the experiment.
(Color online) (Left) Schematic diagram of the picosecond electrical switching circuit of all metal FEAs by the bipolar current pulse method. FEA is mounted on a low-inductance FEA holder that is compatible with the acceleration field well above 30 MV/m, cf. Figs. 3 and 4 . (Right) Concept of the bipolar current pulse switching method. The field emission current pulse (bottom) with the pulse duration of T c is generated by modulating the gate-emitter potential with the duration of T s. T s can be in picosecond range by applying bipolar current pulse.
(Color online) 3D CAD drawing of the low-inductance FEA holder. The right panel shows the enlarged view around FEA.
(Color online) (a) Cross-section of the cathode–anode gap of the dc-gun teststand when the cathode is biased at −50 kV and the cathode–anode gap is ∼7 mm. The color scale indicates the electrical potential distribution. (b) The electric field distribution along the axis of the gun. (c) The electric field distribution at the FEA surface.
(Color online) Schematic diagram of the DC gun teststand. The cathode is insulated from the gun chamber and biased by a DC voltage source together with the FEA switching instruments housed in the high voltage cabinet. The FEA beam that propagates through the anode can be focused by the solenoid, which is integrated in the anode block, on the phosphor screen, or on the Faraday cup when it is inserted. The slit assembly allows us to make the emittance measurement (cf. Ref. 6 ). The cathode–anode gap, the transverse displacement between FEA and the anode iris, as well as the position of the phosphor screen in the gun-axis direction, can be adjusted in situ. The anode is connected to either ground or a voltage supply via an electrical feedthrough.
(Color online) (a) Relation between the DC gate-emitter potential V ge and the emission current collected at anode, when the cathode was connected to ground and the anode potential was 1 kV. I 1 was obtained after 4 days of conditioning in UHV with the background pressure P 1 below 7 × 10−9 millibars. I 2 was measured after 150 min conditioning in neon gas environment with the pressure of 10−4 millibars. (b) The evolution of the Fowler–Nordheim (FN) fitting parameter during the neon gas conditioning. (c) The beam image observed after the UHV conditioning. The FEA current pulse with 20 μA amplitude and 200 ns duration was generated by applying 20 V DC and 30 V pulse potential under −20 kV cathode potential. Solenoid current of 0.57 A was applied to image the beam distribution on the phosphor screen. (d) The beam image observed after the neon gas conditioning. The FEA current pulse was 20 μA and 200 ns duration, generated by applying 20 DC and 37 V pulse potential under the cathode potential of −50 kV (solenoid current was equal to 0.895 A).
(Color online) (a) Field emission pulse waveform generated by applying the bipolar current pulse on top of the DC bias (−32 V) with cathode potential of −40 kV. (b) Peak current amplitude of 0.2 ns pulses and 200 ns pulses, and DC emission in function of gate-emitter potential compared to the Fowler-Nordheim fitting (FN fit).
(Color online) (a) Time evolution of the gate-emitter potential generated by super imposing a 3-μs-long pulsed bias and picosecond switching pulse. (b) The current pulse (1 mA) generated by applying the gate-emitter potential depicted in (a). While Gaussian fitting of the entire current waveform (fit-2) gives pulse duration of 420 ps FWHM, the fitting around the pulse peak (fit-1) gives pulse duration of 280 ps FWHM.
(Color online) (a) Propagation of the gate-emitter potential pulse (top) and the induced field emission pulse (bottom) over the FEA excited by bipolar current pulse separated by 40 ps at r equal to 4 mm. The array is below r equal to 1.1 mm. (b) Calculated total emission current (top), average pulse V ge (p) over the FEA (V ge,FEA, in the middle panel), and the pulse V ge (p) at the edge of the gate (r = 2 mm) excited by the bipolar current pulse injected at the edge of the gate (r = 2 mm) shown in the bottom panel. DC offset of 40 V was assumed.
(Color online) Same as Fig. 9 in the case of FEA with the diameter of 0.5 mm: (a) Propagation of the gate-emitter potential (top) and the induced field emission pulse (bottom) excited by bipolar current pulse separated by 15 ps. (b) Calculated total emission current (top), average pulse V ge (p) over the FEA (V ge,FEA, in the middle panel), and the pulse V ge (p) at the edge of the gate (r = 2 mm) excited by the bipolar current pulse injected at the edge of the gate (r = 2 mm) shown in the bottom panel.
Summary of the Fowler–Nordheim fitting of the current–voltage characteristics before and after the neon gas conditioning (Fig. 5 ).
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