32 research outputs found
High field hybrid photoinjector electron source for advanced light source applications
The production of high spectral brilliance radiation from electron beam sources depends critically on the electron beam qualities. One must obtain very high electron beam brightness, implying simultaneous high peak current and low emittance. These attributes are enabled through the use of very high field acceleration in a radio-frequency (rf) photoinjector source. Despite the high fields currently utilized, there is a limit on the achievable peak current in high brightness operation, in the range of tens of Ampere. This limitation can be overcome by the use of a hybrid standing wave/traveling wave structure; the standing wave portion provides acceleration at a high field from the photocathode, while the traveling wave part yields strong velocity bunching. This approach is explored here in a C-band scenario, at field strengths (>100 MV/m) at the current state-of-the-art. It is found that one may arrive at an electron beam with many hundreds of Amperes with well-sub-micron normalized emittance. This extremely compact injector system also possesses attractive simplification of the rf distribution system by eliminating the need for an rf circulator. We explore the use of this device in a compact 400 MeV-class source, driving both inverse Compton scattering and free-electron laser radiation sources with unique, attractive properties
An Ultra-Compact X-Ray Free-Electron Laser
In the field of beam physics, two frontier topics have taken center stage due
to their potential to enable new approaches to discovery in a wide swath of
science. These areas are: advanced, high gradient acceleration techniques, and
x-ray free electron lasers (XFELs). Further, there is intense interest in the
marriage of these two fields, with the goal of producing a very compact XFEL.
In this context, recent advances in high gradient radio-frequency cryogenic
copper structure research have opened the door to the use of surface electric
fields between 250 and 500 MV/m. Such an approach is foreseen to enable a new
generation of photoinjectors with six-dimensional beam brightness beyond the
current state-of-the-art by well over an order of magnitude. This advance is an
essential ingredient enabling an ultra-compact XFEL (UC-XFEL). In addition, one
may accelerate these bright beams to GeV scale in less than 10 meters. Such an
injector, when combined with inverse free electron laser-based bunching
techniques can produce multi-kA beams with unprecedented beam quality,
quantified by ~50 nm-rad normalized emittances. These beams, when injected into
innovative, short-period (1-10 mm) undulators uniquely enable UC-XFELs having
footprints consistent with university-scale laboratories. We describe the
architecture and predicted performance of this novel light source, which
promises photon production per pulse of a few percent of existing XFEL sources.
We review implementation issues including collective beam effects, compact
x-ray optics systems, and other relevant technical challenges. To illustrate
the potential of such a light source to fundamentally change the current
paradigm of XFELs with their limited access, we examine possible applications
in biology, chemistry, materials, atomic physics, industry, and medicine which
may profit from this new model of performing XFEL science.Comment: 80 pages, 24 figure
Generation and acceleration of electron bunches from a plasma photocathode
Plasma waves generated in the wake of intense, relativistic laser1,2 or particle beams3,4 can accelerate electron bunches to gigaelectronvolt energies in centimetre-scale distances. This allows the realization of compact accelerators with emerging applications ranging from modern light sources such as the free-electron laser to energy frontier lepton colliders. In a plasma wakefield accelerator, such multi-gigavolt-per-metre wakefields can accelerate witness electron bunches that are either externally injected5,6 or captured from the background plasma7,8. Here we demonstrate optically triggered injection9–11 and acceleration of electron bunches, generated in a multi-component hydrogen and helium plasma employing a spatially aligned and synchronized laser pulse. This ‘plasma photocathode’ decouples injection from wake excitation by liberating tunnel-ionized helium electrons directly inside the plasma cavity, where these cold electrons are then rapidly boosted to relativistic velocities. The injection regime can be accessed via optical11 density down-ramp injection12–16 and is an important step towards the generation of electron beams with unprecedented low transverse emittance, high current and 6D-brightness17. This experimental path opens numerous prospects for transformative plasma wakefield accelerator applications based on ultrahigh-brightness beams
Improved magnetization in sputtered dysprosium thin films
50nm thick nanogranular polycrystalline dysprosium thin films have been
prepared via ultra-high vacuum DC sputtering on SiO2 and Si wafers. The maximum
in-plane spontaneous magnetization at T = 4K was found to be MS4K = 3.28T for
samples deposited on wafers heated to 350C with a Neel point of TN = 173K and a
ferromagnetic transition at TC = 80K, measured via zero field cooled field
cooled magnetization measurements, close to single crystal values. The slightly
reduced magnetization is explained in the light of a metastable face centered
cubic crystal phase which occurred at the seed interface and granularity
related effects, that are still noticeably influential despite an in-plane
magnetic easy axis. As deposited samples showed reduced magnetization of MS4K =
2.26T, however their ferromagnetic transition shifted to a much higher
temperature of TC = 172K and the antiferromagnetic phase was completely
suppressed probably as a result of strain.Comment: 16 pages, 3 figure
Experimental characterization of the transverse phase space of a 60-MeV electron beam through a compressor chicane
Space charge and coherent synchrotron radiation may deteriorate electron beam quality when the beam passes through a magnetic bunch compressor. This paper presents the transverse phase-space tomographic measurements for a compressed beam at 60Â MeV, around which energy the first stage of magnetic bunch compression takes place in most advanced linacs. Transverse phase-space bifurcation of a compressed beam is observed at that energy, but the degree of the space charge-induced bifurcation is appreciably lower than the one observed at 12Â MeV
REMOVAL OF RESIDUAL CHIRP IN COMPRESSED BEAMS USING A PASSIVE WAKEFIELD TECHNIQUE
Abstract The removal of residual chirp in XFELs is of paramount importance for efficient lasing. Although current S-band XFELs remove the unwanted residual chirp using off-crest acceleration after the final bunch compressor, this technique is not possible for XFELs with soft X-ray lines as there are no further accelerating structures. The off-crest dechirping technique is also expensive for future superconducting XFELs. In response, RadiaBeam Systems presents its work, building upon the theoretical work of Bane and Stupakov [1], in RF-free residual chirp mitigation using only passive techniques. Beam-induced longitudinal wakefields are produced with opposing corrugated plates which allow for an entirely RF-free chirp removal. Theory, engineering, and experimental results are presented