13 research outputs found
Experimental Study of Diamond Like Carbon (DLC) Coated Electrodes for Pulsed High Gradient Electron Gun
For the SwissFEL Free Electron Laser project at the Paul Scherrer Institute,
a pulsed High Gradient (HG) electron gun was used to study low emittance
electron sources. Different metals and surface treatments for the cathode and
anode were studied for their HG suitability. Diamond Like Carbon (DLC) coatings
are found to perform exceptionally well for vacuum gap insulation. A set of DLC
coated electrodes with different coating parameters were tested for both vacuum
breakdown and photo electron emission. Surface electric fields over 250MV/m
(350 - 400kV, pulsed) were achieved without breakdown. From the same surface,
it was possible to photo-emit an electron beam at gradients up to 150MV/m. The
test setup and the experimental results are presentedComment: 4 pages, 14 figures, IPMHVC 2010 : IEEE International Power Modulator
and High Voltage Conferenc
Empirical comparison of high gradient achievement for different metals in DC and pulsed mode
For the SwissFEL project, an advanced high gradient low emittance gun is
under development. Reliable operation with an electric field, preferably above
125 MV/m at a 4 mm gap, in the presence of an UV laser beam, has to be achieved
in a diode configuration in order to minimize the emittance dilution due to
space charge effects. In the first phase, a DC breakdown test stand was used to
test different metals with different preparation methods at voltages up to 100
kV. In addition high gradient stability tests were also carried out over
several days in order to prove reliable spark-free operation with a minimum
dark current. In the second phase, electrodes with selected materials were
installed in the 250 ns FWHM, 500 kV electron gun and tested for high gradient
breakdown and for quantum efficiency using an ultra-violet laser.Comment: 25 pages, 13 figures, 5 tables. Follow up from FEL 2008 conference
(Geyongju Korea 2008) New Title in JVST A (2010) : Vacuum breakdown limit and
quantum efficiency obtained for various technical metals using DC and pulsed
voltage source
A compact and cost-effective hard X-ray free-electron laser driven by a high-brightness and low-energy electron beam
We present the first lasing results of SwissFEL, a hard X-ray free-electron laser (FEL) that recently came into operation at the Paul Scherrer Institute in Switzerland. SwissFEL is a very stable, compact and cost-effective X-ray FEL facility driven by a low-energy and ultra-low-emittance electron beam travelling through short-period undulators. It delivers stable hard X-ray FEL radiation at 1-Ă… wavelength with pulse energies of more than 500 ÎĽJ, pulse durations of ~30 fs (root mean square) and spectral bandwidth below the per-mil level. Using special configurations, we have produced pulses shorter than 1 fs and, in a different set-up, broadband radiation with an unprecedented bandwidth of ~2%. The extremely small emittance demonstrated at SwissFEL paves the way for even more compact and affordable hard X-ray FELs, potentially boosting the number of facilities worldwide and thereby expanding the population of the scientific community that has access to X-ray FEL radiation
Beam Dynamics And Diagnostics For The High Energy Beam Transport Line of Minerva Project At Sck-Cen
Wavelength-tunable UV laser for electron beam generation with low intrinsic emittance
We developed a powerful UV laser at a central wavelength varying from 260-283 nm. The laser system based on a frequency-trippled Ti:sapphire amplifier delivers mJ pulse energy within a duration of 1-10 ps (fwhm) with 1.5 nm spectral width (fwhm). The system is used to explore thermal emittance and quantum efficiency dependence on photon energy from metallic photocathodes. With pepperpot and solenoid scan technique we have measured the predicted theoretical limit for thermal emittance at room temperature (0.4 mm.mrad/mm rms laser spot size at 283 nm) for metallic photocathodes
Electron beam characterization of a combined diode rf electron gun
Experimental and simulation results of an electron gun test facility, based on pulsed diode acceleration followed by a two-cell rf cavity at 1.5 GHz, are presented here. The main features of this diode-rf combination are: a high peak gradient in the diode (up to 100MV/m) obtained without breakdown conditioning, a cathode shape providing an electrostatic focusing, and an in-vacuum pulsed solenoid to focus the electron beam between the diode and the rf cavity. Although the test stand was initially developed for testing field emitter arrays cathodes, it became also interesting to explore the limits of this electron gun with metallic photocathodes illuminated by laser pulses. The ultimate goal of this test facility is to fulfill the requirements of the SwissFEL project of Paul Scherrer Institute; a projected normalized emittance below 0.4μm for a charge of 200 pC and a bunch length of less than 10 ps (rms). A normalized projected emittance of 0.23μm with 13 pC has been measured at 5 MeV using a Gaussian laser longitudinal intensity distribution on the photocathode. Good agreements with simulations have been obtained for different electron bunch charge and diode geometries. Emittance measurements at a bunch charge below 1 pC were performed for different laser spot sizes in agreement with intrinsic emittance theory [e.g. 0.54μm/mm of laser spot size (rms) for Cu at 274 nm]. Finally, a projected emittance of 1.25+/-0.2μm was measured with 200 pC and 100MV/m diode gradient. © 2010 The American Physical Society