36 research outputs found
Aberration Corrected Emittance Exchange
Full exploitation of emittance exchange (EEX) requires aberration-free
performance of a complex imaging system including active radio-frequency (RF)
elements which can add temporal distortions. We investigate the performance of
an EEX line where the exchange occurs between two dimensions with normalized
emittances which differ by multiple orders of magnitude. The transverse
emittance is exchanged into the longitudinal dimension using a double dog-leg
emittance exchange setup with a five cell RF deflector cavity. Aberration
correction is performed on the four most dominant aberrations. These include
temporal aberrations that are corrected with higher order magnetic optical
elements located where longitudinal and transverse emittance are coupled. We
demonstrate aberration-free performance of an EEX line with emittances
differing by four orders of magnitude, \textit{i.e.} an initial transverse
emittance of 1~pm-rad is exchanged with a longitudinal emittance of 10~nm-rad
Nano-modulated electron beams via electron diffraction and emittance exchange for coherent x-ray generation
We present a new method for generation of relativistic electron beams with
current modulation on the nanometer scale and below. The current modulation is
produced by diffracting relativistic electrons in single crystal Si,
accelerating the diffracted beam and imaging the crystal structure, then
transferring the image into the temporal dimension via emittance exchange. The
modulation period can be tuned by adjusting electron optics after diffraction.
This tunable longitudinal modulation can have a period as short as a few
angstroms, enabling production of coherent hard x-rays from a source based on
inverse Compton scattering with total accelerator length of approximately ten
meters. Electron beam simulations from cathode emission through diffraction,
acceleration and image formation with variable magnification are presented
along with estimates of the coherent x-ray output properties
A 250 GHz photonic band gap gyrotron amplifier
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 191-206).This thesis reports the theoretical and experimental investigation of a novel gyrotron traveling-wave-tube (TWT) amplifier at 250 GHz. The gyrotron amplifier designed and tested in this thesis has achieved a peak small signal gain of 38 dB at 247.7 GHz, with a 32 kV, 0.35 A electron beam and a 8.9 T magnetic field. The instantaneous -3 dB bandwidth of the amplifier at peak gain is 0.4 GHz. A peak output power of 45 W has been measured. The output power is not saturated but is limited by the 7.5 mW of available input power. The amplifier can be tuned for operation from 245- 256 GHz. With a gain of 24 dB and centered at 253.25 GHz the widest instantaneous -3 dB bandwidth of 4.5 GHz was observed for a 19 kV, 0.305 A electron beam. To achieve stable operation at these high frequencies, the amplifier uses a novel photonic band gap (PBG) interaction circuit. The PBG interaction circuit confines the TE₀₃-like mode which couples strongly to the electron beam. The PBG circuit provides stability from oscillations by supporting the propagation of TE modes in a narrow range of frequencies, allowing for the confinement of the operating TE₀₃-like mode while rejecting the excitation of oscillations at lower frequencies. Experimental results taken over a wide range of parameters, 15-30 kV and 0.25-0.5 A, show good agreement with a theoretical model. The theoretical model incorporates cold test measurements for the transmission line, input coupler, PBG waveguide and mode converter. This experiment achieved the highest frequency of operation (250 GHz) for a gyrotron amplifier. At present, there are no other amplifiers in this frequency range that are capable of producing either high gain or high-output power. With 38 dB of gain and 45 W this is also the highest gain observed above 94 GHz and the highest output power achieved above 140 GHz by any conventional-voltage vacuum electron device based amplifier. The output power, output beam pattern, instantaneous bandwidth, spectral purity and shot-to-shot stability of the amplified pulse meet the basic requirements for the implementation of this device on a pulsed dynamic nuclear polarization (DNP) nuclear magnetic resonance (NMR) spectrometer.by Emilio A. Nanni.Ph.D
Direct laser acceleration of electrons in free-space
Compact laser-driven accelerators are versatile and powerful tools of
unarguable relevance on societal grounds for the diverse purposes of science,
health, security, and technology because they bring enormous practicality to
state-of-the-art achievements of conventional radio-frequency accelerators.
Current benchmarking laser-based technologies rely on a medium to assist the
light-matter interaction, which impose material limitations or strongly
inhomogeneous fields. The advent of few cycle ultra-intense radially polarized
lasers has materialized an extensively studied novel accelerator that adopts
the simplest form of laser acceleration and is unique in requiring no medium to
achieve strong longitudinal energy transfer directly from laser to particle.
Here we present the first observation of direct longitudinal laser acceleration
of non-relativistic electrons that undergo highly-directional multi-GeV/m
accelerating gradients. This demonstration opens a new frontier for direct
laser-driven particle acceleration capable of creating well collimated and
relativistic attosecond electron bunches and x-ray pulses
Report of the Snowmass 2021 ee-Collider Forum
A summary of the Snowmass 2021 ee-Collider Forum discussions, white
papers submitted to the Snowmass 2021 community study, submissions of the
Energy Frontier (EF) subgroups and the Accelerator Frontier (AF) Integrated
Task Force (ITF) are presented
Utilization of Additive Manufacturing for the Rapid Prototyping of C-Band RF Loads
Additive manufacturing is a versatile technique that shows promise in
providing quick and dynamic manufacturing for complex engineering problems.
Research has been ongoing into the use of additive manufacturing for potential
applications in radiofrequency (RF) component technologies. Here we present a
method for developing an effective prototype load produced out of 316L
stainless steel on a direct metal laser sintering machine. The model was tested
within simulation software to verify the validity of the design. The load
structure was manufactured utilizing an online digital manufacturing company,
showing the viability of using easily accessible tools to manufacture RF
structures. The produced load was able to produce an S value of -22.8 dB
at the C-band frequency of 5.712 GHz while under vacuum. In a high power test,
the load was able to terminate a peak power of 8.1 MW. Discussion includes
future applications of the present research and how it will help to improve the
implementation of future accelerator concepts
Toward a terahertz-driven electron gun
Femtosecond electron bunches with keV energies and eV energy spread are
needed by condensed matter physicists to resolve state transitions in carbon
nanotubes, molecular structures, organic salts, and charge density wave
materials. These semirelativistic electron sources are not only of interest for
ultrafast electron diffraction, but also for electron energy-loss spectroscopy
and as a seed for x-ray FELs. Thus far, the output energy spread (hence pulse
duration) of ultrafast electron guns has been limited by the achievable
electric field at the surface of the emitter, which is 10 MV/m for DC guns and
200 MV/m for RF guns. A single-cycle THz electron gun provides a unique
opportunity to not only achieve GV/m surface electric fields but also with
relatively low THz pulse energies, since a single-cycle transform-limited
waveform is the most efficient way to achieve intense electric fields. Here,
electron bunches of 50 fC from a flat copper photocathode are accelerated from
rest to tens of eV by a microjoule THz pulse with peak electric field of 72
MV/m at 1 kHz repetition rate. We show that scaling to the readily-available
GV/m THz field regime would translate to monoenergetic electron beams of ~100
keV.Comment: 16 pages, 4 figure
Terahertz-driven, all-optical electron gun
Ultrashort electron beams with narrow energy spread, high charge, and low
jitter are essential for resolving phase transitions in metals, semiconductors,
and molecular crystals. These semirelativistic beams, produced by
phototriggered electron guns, are also injected into accelerators for x-ray
light sources. The achievable resolution of these time-resolved electron
diffraction or x-ray experiments has been hindered by surface field and timing
jitter limitations in conventional RF guns, which thus far are <200 MV/m and
>96 fs, respectively. A gun driven by optically-generated single-cycle THz
pulses provides a practical solution to enable not only GV/m surface fields but
also absolute timing stability, since the pulses are generated by the same
laser as the phototrigger. Here, we demonstrate an all-optical THz gun yielding
peak electron energies approaching 1 keV, accelerated by 300 MV/m THz fields in
a novel micron-scale waveguide structure. We also achieve quasimonoenergetic,
sub-keV bunches with 32 fC of charge, which can already be used for
time-resolved low-energy electron diffraction. Such ultracompact, easy to
implement guns driven by intrinsically synchronized THz pulses that are pumped
by an amplified arm of the already present photoinjector laser provide a new
tool with potential to transform accelerator based science.Comment: 24 pages, 9 figure