178 research outputs found
Useful Circuit Analogies to Model THz Field Effect Transistors
The electron fluid model in plasmonic field effect transistor (FET) operation
is related to the behavior of a radio-frequency (RF) cavity. This new
understanding led to finding the relationships between physical device
parameters and equivalent circuit components in traditional parallel resistor,
inductor, and capacitor (RLC) and transmission models for cavity structures.
Verification of these models is performed using PSpice to simulate the
frequency dependent voltage output and compare with analytical equations for
the drain potential as a function of frequency
Simulation of beam-induced plasma in gas-filled rf cavities
Processes occurring in a radio-frequency (rf) cavity, filled with high
pressure gas and interacting with proton beams, have been studied via advanced
numerical simulations. Simulations support the experimental program on the
hydrogen gas-filled rf cavity in the Mucool Test Area (MTA) at Fermilab, and
broader research on the design of muon cooling devices. SPACE, a 3D
electromagnetic particle-in-cell (EM-PIC) code with atomic physics support, was
used in simulation studies. Plasma dynamics in the rf cavity, including the
process of neutral gas ionization by proton beams, plasma loading of the rf
cavity, and atomic processes in plasma such as electron-ion and ion-ion
recombination and electron attachment to dopant molecules, have been studied.
Through comparison with experiments in the MTA, simulations quantified several
uncertain values of plasma properties such as effective recombination rates and
the attachment time of electrons to dopant molecules. Simulations have achieved
very good agreement with experiments on plasma loading and related processes.
The experimentally validated code SPACE is capable of predictive simulations of
muon cooling devices.Comment: 10 pp. arXiv admin note: text overlap with arXiv:1709.0528
An atomic hydrogen beam to test ASACUSA's apparatus for antihydrogen spectroscopy
The ASACUSA collaboration aims to measure the ground state hyperfine
splitting (GS-HFS) of antihydrogen, the antimatter pendant to atomic hydrogen.
Comparisons of the corresponding transitions in those two systems will provide
sensitive tests of the CPT symmetry, the combination of the three discrete
symmetries charge conjugation, parity, and time reversal. For offline tests of
the GS-HFS spectroscopy apparatus we constructed a source of cold polarised
atomic hydrogen. In these proceedings we report the successful observation of
the hyperfine structure transitions of atomic hydrogen with our apparatus in
the earth's magnetic field.Comment: 8 pages, 4 figures, proceedings for conference EXA 2014 (Exotic Atoms
- Vienna
Observation of Coherently-Enhanced Tunable Narrow-Band Terahertz Transition Radiation from a Relativistic Sub-Picosecond Electron Bunch Train
We experimentally demonstrate the production of narrow-band (% at THz) THz transition radiation with tunable
frequency over [0.37, 0.86] THz. The radiation is produced as a train of
sub-picosecond relativistic electron bunches transits at the vacuum-aluminum
interface of an aluminum converter screen. We also show a possible application
of modulated beams to extend the dynamical range of a popular bunch length
diagnostic technique based on the spectral analysis of coherent radiation.Comment: 3 pages, 6 figure
Conversion of a transverse density modulation into a longitudinal phase space modulation using an emittance exchange technique
We report on an experiment to produce a train of sub-picosecond microbunches
using a transverse-to-longitudinal emittance exchange technique. The generation
of a modulation on the longitudinal phase space is done by converting an
initial horizontal modulation produced using a multislits mask. The preliminary
experimental data clearly demonstrate the conversion process. To date only the
final energy modulation has been measured. However numerical simulations, in
qualitative agreement with the measurements, indicate that the conversion
process should also introduce a temporal modulation.Comment: 4 pages, 6 figures. Submitted to the proceedings of the Physics and
Applications of High-Brightness Electron Beams (HBEB09), Nov. 16-19, 2009,
Maui H
Photoinjector-generation of a flat electron beam with transverse emittance ratio of 100
The generation of a flat electron beam directly from a photoinjector is an
attractive alternative to the electron damping ring as envisioned for linear
colliders. It also has potential applications to light sources such as the
generation of ultra-short x-ray pulses or Smith-Purcell free electron lasers.
In this Letter, we report on the experimental generation of a flat-beam with a
measured transverse emittance ratio of for a bunch charge of
nC; the smaller measured normalized root-mean-square emittance is
m and is limited by the resolution of our experimental setup.
The experimental data, obtained at the Fermilab/NICADD Photoinjector
Laboratory, are compared with numerical simulations and the expected scaling
laws.Comment: 5 pages, 3 figure
Electron Bunch Train Excited Higher-Order Modes in a Superconducting RF Cavity
Higher-order mode (HOM) based intra-cavity beam diagnostics has been proved
effectively and conveniently in superconducting radio-frequency (SRF)
accelerators. Our recent research shows that the beam harmonics in the bunch
train excited HOM spectrum, which have much higher signal-to-noise ratio than
the intrinsic HOM peaks, may also be useful for beam diagnostics. In this
paper, we will present our study on bunch train excited HOMs, including the
theoretic model and recent experiments carried out based on the DC-SRF
photoinjector and SRF linac at Peking University.Comment: Supported by National Natural Science Foundation of China (11275014
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