52 research outputs found
Fast Switching Ferroelectric Materials for Accelerator Applications
Fast switching (< 10 nsec) measurement results on the recently developed
BST(M) (barium strontium titanium oxide composition with magnesium-based
additions) ferroelectric materials are presented. These materials can be used
as the basis for new advanced technology components suitable for high-gradient
accelerators. A ferroelectric ceramic has an electric field-dependent
dielectric permittivity that can be altered by applying a bias voltage.
Ferroelectric materials offer significant benefits for linear collider
applications, in particular, for switching and control elements where a very
short response time of <10 nsec is required. The measurement results presented
here show that the new BST(M) ceramic exhibits a high tunability factor: a bias
field of 40-50 kV/cm reduces the permittivity by a factor of 1.3-1.5. The
recently developed technology of gold biasing contact deposition on large
diameter (110 cm) thin wall ferroelectric rings allowed ~few nsec switching
times in witness sample experiments. The ferroelectric rings can be used at
high pulsed power (tens of megawatts) for X-band components as well as at high
average power in the range of a few kilowatts for the L-band phase-shifter,
under development for optimization of the ILC rf coupling. Accelerator
applications include fast active X-band and Ka-band high-power ferroelectric
switches, high-power X-band and L-band phase shifters, and tunable
dielectric-loaded accelerating structures.Comment: 7 pages, 6 figures, submitted to Proceedings of 2006 Advanced
Accelerator Concepts Worksho
Double Cell Notch Filter for SRF Gun Investigations
Some projects of SRF guns apply the design where the cathode can be easily and quickly removed. One of the disadvantages of this design is the RF power leakage from the accelerating gun cavity cells to the cathode housing that result in the excessive cathode heating. To minimize the RF power leak different kinds of choke filters are used to protect the cathode structure. These choke filters represent resonant circuits with zero input impedance and installed at the entrance of the cathode structure that shunt the cathode housing. Still, since the choke filter frequency shift under working conditions is bigger than its bandwidth a filter tuning during assembly only in the warm stage seems insufficient and requires also fine tuning during operation. To eliminate the problems of the choke filter finetuning and hence ensure its stability during operation, a combination of the resonance choke elements can be implemented. In the paper we demonstrate advantages of the double cell notch filter using BERLinPro SRF gun cavity as an example with its simple design modification
Observation of Enhanced Transformer Ratio in Collinear Wakefield Acceleration
One approach to future high energy particle accelerators is based on the
wakefield principle: a leading high-charge drive bunch is used to excite fields
in an accelerating structure or plasma that in turn accelerates a trailing
low-charge witness bunch. The transformer ratio R is defined as the ratio of
the maximum energy gain of the witness bunch to the maximum energy loss of the
drive bunch. In general, for configurations in which the two beams traverse the
accelerator along the same trajectory (collinear wakefield acceleration). A
number of techniques have been proposed to overcome the transformer ratio
limitation. We report here the first experimental study of the ramped bunch
train (RBT) technique in which a dielectric loaded waveguide was used as the
accelerating structure. A single drive bunch was replaced by two bunches with
charge ratio of 1:2.5 and a separation of 10.5 wavelengths of the fundamental
mode. An average measured transformer ratio enhancement by a factor of 1.31
over the single drive bunch case was obtained in this experiment.Comment: 14 pages, 4 figs, accepted by Phys Rev Let
Experimental Observation of Energy Modulation in Electron Beams Passing Through Terahertz Dielectric Wakefield Structures
We report observation of a strong wakefield induced energy modulation in an
energy-chirped electron bunch passing through a dielectric-lined waveguide.
This modulation can be effectively converted into a spatial modulation forming
micro-bunches with a periodicity of 0.5 - 1 picosecond, hence capable of
driving coherent THz radiation. The experimental results agree well with
theoretical predictions.Comment: v3. Reviewers' suggestions incorporated. Accepted by PR
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Progress towards of a superconducting traveling wave accelerating structure
In the ILC project the required accelerating gradient is higher than 30 MeV/m. For current technology the maximum acceleration gradient in SC structures is determined mainly by the value of the surface RF magnetic field. In order to increase the gradient, the RF magnetic field is distributed homogeneously over the cavity surface (low-loss structure), and coupling to the beam is improved by introducing aperture 'noses' (reentrant structure). These features allow gradients in excess of 50 MeV/m to be obtained for a singe-cell cavity. Further improvement of the coupling to the beam may be achieved by using a TW SC structure with small phase advance per cell. We have demonstrated that an additional gradient increase by up to 46% may be possible if a {pi}/2 TW SC structure is employed. However, a TW SC structure requires a SC feedback waveguide to return the few GW of circulating RF power from the structure output back to the structure input. The test cavity with the feedback is designed to demonstrate the possibility of achieving a significantly higher gradient than existing SC structures
Experimental demonstration of wakefield effects in a THz planar diamond accelerating structure
We have directly measured THz wakefields induced by a subpicosecond, intense
relativistic electron bunch in a diamond loaded accelerating structure via the
wakefield acceleration method. We present here the beam test results from the
first diamond based structure. Diamond has been chosen for its high breakdown
threshold and unique thermoconductive properties. Fields produced by a leading
(drive) beam were used to accelerate a trailing (witness) electron bunch which
followed the drive bunch at a variable distance. The energy gain of a witness
bunch as a function of its separation from the drive bunch describes the time
structure of the generated wakefield.Comment: v3, accepted by APL. Updated to reflect reviewers' comment
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