DC/RF: With the long-term goal of a table-top X(UV) laser in
mind, a project was started in 1998 at the University of Technology Eindhoven (TUE) to
produce an electron source capable of generating 100 pC bunches at 10 MeV with a
bunch length of 100 fs and an emittance below 1 pi mm mrad. These
high-quality, high-current, ultra-short pancake shaped bunches are ideal for subsequent
acceleration in an advanced accelerator, for example based on wake fields of a laser pulse
traveling through a plasma. This paves the way towards challenging future applications
such as X-ray free electron lasers.
Although the desired bunches can be
produced by a photo-excited rf-gun followed by longitudinal bunch
compression after acceleration to an energy of over 100 MeV we have
investigated a novel acceleration scheme. In addition to a state-of-the-art
rf-gun, we propose 1 GV/m DC pre-acceleration of laser excited
electrons across a 2 mm gap in a diode, following recent developments
at Brookhaven Nat. Lab. This extremely high diode field, positioned just
before the cathode area of the rf-gun, avoids the necessity of downstream
magnetic compression and associated problems due to coherent synchrotron
radiation.
With the diode scheme, a 100 pC bunch can be
accelerated to 2 MeV with a final bunch length of 70 fs FWHM and an emittance
well below 1 pi mm mrad. Using the General Particle Tracer (GPT) code, the beam dynamics
in the diode system has been studied. A 2.6-cell rf cavity will follow the 2 MeV
diode to increase the beam energy to 10 MeV. The combined diode and rf-booster set-up
can be used in a number of different modes, with emphasis on either short pulses or
emittance values, depending on external focusing with a solenoid.
The
set-up investigated is shown in the following figures.
Diode and booster geometry.
Booster geometry.
See also: Home
page of this project
Collaboration: This project is commissioned
by the Technical University of Eindhoven (TUE),
Department of Physics, The Netherlands.
