53998460
High-power beam-based coherently enhanced THz radiation source
We propose a compact Smith-Purcell radiation device that can potentially generate high average power THz radiation with high conversion efficiency. The source is based on a train of short electron bunches from an rf photoemission gun at an energy of a few MeV. Particle tracking simulation and analysis show that, with a beam current of 1 mA, it is feasible to generate hundreds of watts of narrow-band THz radiation at a repetition rate of 1 MHz.
7518066
First observation of the exchange of transverse and longitudinal emittances.
An experimental program to demonstrate a novel phase-space manipulation in which the horizontal and longitudinal emittances of a particle beam are exchanged has been completed at the Fermilab A0 Photoinjector. A new beam line, consisting of a TM(110) deflecting mode cavity flanked by two horizontally dispersive doglegs has been installed. We report on the first direct observation of transverse and longitudinal emittance exchange.
73558089
INITIAL BEAM-PROFILING TESTS WITH THE NML PROTOTYPE STATION AT THE FERMILAB A0 PHOTOINJECTOR*
The beam-profile diagnostics station prototype for the superconducting rf electron linac being constructed at Fermilab at the New Muon Lab has been tested. The station uses intercepting radiation converter screens for the low-power beam mode: either a 100-{micro}m thick YAG:Ce single crystal scintillator or a 1-{micro}m thin Al optical transition radiation (OTR) foil. The screens are oriented with the surface perpendicular to the beam direction. A downstream mirror with its surface at 45 degrees to the beam direction is used to direct the radiation into the optical transport. The optical system has better than 20 (10) {micro}m rms spatial resolution when covering a vertical field of view of 18 (5) mm. The initial tests were performed at the A0 Photoinjector at a beam energy of {approx}15 MeV and with micropulse charges from 25 to 500 pC for beam sizes of 45 to 250 microns. Example results will be presented.
54683815
The optimization of a DC injector for the Energy Recovery Linac upgrade to APS
An energy recovery linac based light source is a potential revolutionary upgrade to the Advanced Photon Source (APS) at Argonne National Laboratory. The concept relies on several key research areas, one of which is the generation of ultra-low emittance, high-average-current electron beams. In this paper, we present our investigation of a dc-gun-based system for ultra-low emittance bunches in the 20 pC range. A parallel multi-objective numerical optimization is performed in multi-parameter space. Parameters varied include experimentally feasible drive-laser shapes, the DC gun voltage, the thermal energy of the emitted photo-electrons and other electric or magnetic field strengths, RF cavity phase etc. Our goal is to deliver a {approx}10 MeV, 20 pC bunch at the entrance of the linac with an emittance of 0.1 {micro}m or lower, rms bunch length of 2 {approx} 3 ps, and energy spread no larger than 140 keV. We present the machine parameters needed to generate such an injector beam, albeit without a merger.
111318901
Potential performance and challenges of an energy recovery linac upgrade to the Advanced Photon Source
The Advanced Photon Source (APS) is a third-generation synchrotron radiation source operating at 7 GeV that has been in operation for over 10 years. In that time, the emittance has been improved from 8 to 3.1 nm, which is close to the practical minimum. Recently, APS undertook an intensive exploration of potential upgrades, including options for a replacement storage ring or Energy Recovery Linac (ERL) injector. Our conclusion was that only the ERL would provide a dramatically new capability. This paper discusses the potential performance available from an ERL upgrade to the APS and reviews the challenges of delivering this performance.
116149099
Angular-momentum-dominated electron beams and flat-beam generation
In the absence of external forces, if the dynamics within an electron beam is dominated by its angular momentum rather than other effects such as random thermal motion or self Coulomb-repulsive force (i.e., space-charge force), the beam is said to be angular-momentum-dominated. Such a beam can be directly applied to the field of electron-cooling of heavy ions; or it can be manipulated into an electron beam with large transverse emittance ratio, i.e., a flat beam. A flat beam is of interest for high-energy electron-positron colliders or accelerator-based light sources. An angular-momentum-dominated beam is generated at the Fermilab/NICADD photoinjector Laboratory (FNPL) and is accelerated to an energy of 16 MeV. The properties of such a beam is investigated systematically in experiment. The experimental results are in very good agreement with analytical expectations and simulation results. This lays a good foundation for the transformation of an angular-momentum-dominated beam into a flat beam. The round-to-flat beam transformer is composed of three skew quadrupoles. Based on a good knowledge of the angular-momentum-dominated beam, the quadrupoles are set to the proper strengths in order to apply a total torque which removes the angular momentum, resulting in a flat beam. For bunch charge around 0.5 nC,more » an emittance ratio of 100 {+-} 5 was measured, with the smaller normalized root-mean-square emittance around 0.4 mm-mrad. Effects limiting the flat-beam emittance ratio are investigated, such as the chromatic effects in the round-to-flat beam transformer, asymmetry in the initial angular-momentum-dominated beam, and space-charge effects. The most important limiting factor turns out to be the uncorrelated emittance growth caused by space charge when the beam energy is low, for example, in the rf gun area. As a result of such emittance growth prior to the round-to-flat beam transformer, the emittance ratio achievable in simulation decreases from orders of thousands to hundreds. Finally, factors that might spoil the smaller transverse emittance such as beamline misalignments and dispersions caused by magnetic elements are discussed. The limit of the emittance measurement system, such as camera resolution, is also studied.« less
64370202
Observing the origin of superconductivity in quantum critical metals
Despite intense efforts during the last 25 years, the physics of unconventional superconductors, including the cuprates with a very high transition temperature, is still a controversial subject. It is believed that superconductivity in many of these strongly correlated metallic systems originates in the physics of quantum phase transitions, but quite diverse perspectives have emerged on the fundamentals of the electron-pairing physics, ranging from Hertz style critical spin fluctuation glue to the holographic superconductivity of string theory. Here we demonstrate that the gross energy scaling differences that are behind these various pairing mechanisms are directly encoded in the frequency and temperature dependence of the dynamical pair susceptibility. This quantity can be measured directly via the second order Josephson effect and it should be possible employing modern experimental techniques to build a `pairing telescope' that gives a direct view on the origin of quantum critical superconductivity.
55751567
Designs for a Linac-Ring LHeC
We consider three scenarios for the recirculating electron linear accelerator (RLA) of a linac-ring type electron-proton collider based on the LHC (LHeC): (i) a pulsed linac with a final beam energy of 60 GeV ['p-60'], (ii) a higher luminosity configuration with two cw linacs and energy-recovery (ERL) also at 60 GeV ['erl'], and (iii) a high energy option using a pulsed linac with 140-GeV final energy ['p-140']. We discuss parameters, synchrotron radiation, footprints, and performance for the three scenarios.
118458267
Lattice potentials and fermions in holographic non Fermi-liquids: hybridizing local quantum criticality
A bstractWe study lattice effects in strongly coupled systems of fermions at a finite density described by a holographic dual consisting of fermions in Anti-de-Sitter space in the presence of a Reissner-Nordström black hole. The lattice effect is encoded by a periodic modulation of the chemical potential with a wavelength of order of the intrinsic length scales of the system. This corresponds with a highly complicated “band structure” problem in AdS, which we only manage to solve in the weak potential limit. The “domain wall” fermions in AdS encoding for the Fermi surfaces in the boundary field theory diffract as usually against the periodic lattice, giving rise to band gaps. However, the deep infrared of the field theory as encoded by the near horizon AdS2 geometry in the bulk reacts in a surprising way to the weak potential. The hybridization of the fermions bulk dualizes into a linear combination of CFT1 “local quantum critical” propagators in the bulk, characterized by momentum dependent exponents displaced by lattice Umklapp vectors. This has the consequence that the metals showing quasi-Fermi surfaces cannot be localized in band insulators. In the AdS2 metal regime, where the conformal dimension of the fermionic operator is large and no Fermi surfaces are present at low T/μ, the lattice gives rise to a characteristic dependence of the energy scaling as a function of momentum. We predict crossovers from a high energy standard momentum AdS2 scaling to a low energy regime where exponents found associated with momenta “backscattered” to a lower Brillioun zone in the extended zone scheme. We comment on how these findings can be used as a unique fingerprint for the detection of AdS2 like “pseudogap metals” in the laboratory.
108668588
FODO-Supercell Based Compact Ring Design with Tunable Momentum Compaction and Optimized Dynamic Aperture
A storage ring with tunable momentum compaction has the advantage in achieving different RMS bunch length with similar RF capacity, which is potentially useful for many applications, such as linear collider damping ring and pre-damping ring where injected beam has a large energy spread and a large transverse emittance. A tunable bunch length also makes the commissioning and fine tuning easier in manipulating the single bunch instabilities. In this paper, a compact ring design based on a supercell is presented, which achieves a tunable momentum compaction while maintaining a large dynamic aperture.
17403659
On the z=4 Horava-Lifshitz Gravity
We consider z = 4 Horava-Lifshitz gravity in both 3+1 and 4+1 dimensions. We find black hole solutions in the IR region for a kind of z = 4 Horava-Lifshitz gravity which is inherited from the new massive gravity in three dimensions and an analog of the new massive gravity in four dimensions through the quantum inheritance principle. We analyze thermodynamic properties for the black hole solutions for z = 4 Horava-Lifshitz gravity. We also write out the Friedmann equation in 3+1 dimensions for cosmological solutions.