Search Results (13 total)

Presented are details of the staged electron laser acceleration (STELLA) experiment, which demonstrated high-trapping efficiency and narrow energy spread in a staged laser-driven accelerator. Trapping efficiencies of up to 80% and energy spreads down to 0.36% (1σ) were demonstrated. The experiment validated an approach that may be suitable for the basic design of a laser-driven accelerator system. In this approach, a laser-driven modulator together with a chicane creates a train of microbunches spaced apart by the laser wavelength. These microbunches are sent into a second laser-driven accelerator designed to efficiently trap the microbunches in the ponderomotive potential well of the laser electric field while maintaining a narrow energy spread. The STELLA scientific apparatus and procedures are described in detail. In-depth comparisons between the data and model are given including the predicted energy spectrum, energy-phase plot, and microbunch length profile. Data and model comparisons as a function of the phase delay between the microbunches and the accelerating wave are presented. The model is exercised to reveal how the high-trapping efficiency process evolves during the acceleration process.

Laser-driven electron accelerators (laser linacs) offer the potential for enabling much more economical and compact devices. However, the development of practical and efficient laser linacs requires accelerating a large ensemble of electrons together (“trapping”) while keeping their energy spread small. This has never been realized before for any laser acceleration system. We present here the first demonstration of high-trapping efficiency and narrow energy spread via laser acceleration. Trapping efficiencies of up to 80% and energy spreads down to 0.36% (1σ) were demonstrated.

We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact high-energy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.

Preservation of the femtosecond (fs) microbunches, created during laser acceleration, is a crucial step to enable staging of the laser acceleration process. This paper focuses on the optimization of the beam dynamics of fs microbunches transported through the staged electron laser acceleration (STELLA-II) experiment being carried out at the Brookhaven National Laboratory Accelerator Test Facility. STELLA-II consists of an inverse free electron laser (IFEL) untapered undulator, which acts as an electron beam energy modulator; a magnetic chicane, which acts as a buncher; a second IFEL tapered undulator, which acts as an accelerator; and a dipole, which serves as an energy spectrometer. When the energy-modulated macrobunch traverses through the chicane and a short drift space, microbunches of order fs in duration (i.e., ∼3  fs FWHM) are formed. The 3-fs microbunches are accelerated by interacting with a high-power CO₂ laser beam in the following tapered undulator. These extremely short microbunches may experience significant space charge and coherent synchrotron radiation effects when traversing the STELLA-II transport line. These effects are analyzed and the safe operating conditions are determined. With less than 0.5-pC microbunch charge, both microbunch debunching and emittance growth are negligible, and the energy-spread increase is less than 5%. These results are also useful for the laser electron acceleration project at SLAC and in possible future programs where the fs microbunches are employed for other purposes.

Detailed experimental results of staging two laser-driven, relativistic electron accelerators are presented. During the experiment called STELLA (staged electron laser acceleration), an inverse free-electron laser (IFEL) is used to modulate the electron energy, thereby, causing ∼3 fs microbunches to form separated by the laser wavelength at 10.6 μm (equivalent to a 35 fs period). A second IFEL accelerates the electrons depending upon the phase of the microbunches entering the second IFEL with respect to the laser beam driving the second IFEL. The data presented includes electron energy spectra as a function of the phase delay and laser power driving the first IFEL. Also shown is a comparison with the computer model, which includes space charge and misalignment effects.

Staging of two laser-driven, relativistic electron accelerators has been demonstrated for the first time in a proof-of-principle experiment, whereby two distinct and serial laser accelerators acted on an electron beam in a coherently cumulative manner. Output from a CO₂ laser was split into two beams to drive two inverse free electron lasers (IFEL) separated by 2.3 m. The first IFEL served to bunch the electrons into ∼3 fs microbunches, which were rephased with the laser wave in the second IFEL. This represents a crucial step towards the development of practical laser-driven electron accelerators.

The status of the research on muon colliders is discussed and plans are outlined for future theoretical and experimental studies. Besides work on the parameters of a 3–4 and 0.5 TeV center-of-mass (COM) energy collider, many studies are now concentrating on a machine near 0.1 TeV (COM) that could be a factory for the s-channel production of Higgs particles. We discuss the research on the various components in such muon colliders, starting from the proton accelerator needed to generate pions from a heavy-Z target and proceeding through the phase rotation and decay (π→μν_μ) channel, muon cooling, acceleration, storage in a collider ring, and the collider detector. We also present theoretical and experimental R&D plans for the next several years that should lead to a better understanding of the design and feasibility issues for all of the components. This report is an update of the progress on the research and development since the feasibility study of muon colliders presented at the Snowmass '96 Workshop [R. B. Palmer, A. Sessler, and A. Tollestrup, Proceedings of the 1996 DPF/DPB Summer Study on High-Energy Physics (Stanford Linear Accelerator Center, Menlo Park, CA, 1997)].

An electron beam microbunched on the optical wavelength scale of ≈2.5 μm by an inverse free electron laser accelerator was observed. The optimum bunching was achieved for a 1% energy modulation of a 32 MeV electron beam with 0.5 GW CO₂ laser power. The microbunching process was investigated by measuring the coherent transition radiation produced by the energy modulated electron beam. A quadratic dependence of the transition radiation signal on the electron beam charge was observed. The observed shortest wavelength of coherent transition radiation is less than 2.5 μm. The debunching process of the microbunched electron beam was experimentally investigated.

We discuss how proposed supernova neutrino detectors could measure masses for ν_μ or ν_τ neutrinos in the range of 15 to 50 eV. The range for measurable masses might be extended down to 5 eV, depending on our confidence in some of the predicted features of the supernova-neutrino-burst signal. We discuss the expected characteristics of supernova neutrino signals in proposed neutral-current-based detectors.

We report the first experimental test of the physics of plasma wake-field acceleration performed at the Argonne National Laboratory Advanced Accelerator Test Facility. Megavolt-per-meter plasma wake fields are excited by a intense 21-MeV, multipiscosecond bunch of electrons in a plasma of density n_e≃10¹³ cm^-3, and probed by a low-intensity 15-MeV witness pulse with a variable delay time behind the intense bunch. Accelerating and deflecting wake-field measurements are presented, and the results compared to theoretical predictions.

We have observed 16 events of the type μ⁺μ^-+(missing energy and momentum) from e⁺e^- annihilations at center-of-mass energies between 6.4 and 7.4 GeV. Taking into account QED backgrounds, we find an excess of 11 anomalous dimuon events. If these are attributed to the production and subsequent decay of a pair of heavy leptons L^±, we obtain the muonic braching ratio B((L⁺→μ⁺ν_μν̅ _L) / (L⁺→all))=0.22_-0.08^+0.07.

A search for the rare decay K⁺→π⁺e⁺e^- has been carried out at the Lawrence Berkeley Laboratory using a sparkostrictive wire-chamber spectrometer. Analysis programs identified events with three tracks or with two tracks of which one was an electron and the other a positron. Analysis of the three-track events yields a branching ratio Γ(K⁺→π⁺e⁺e^-) / Γ(K⁺→all)<1.7×10^-6 (90% confidence). The two-track events, analyzed by searching for sparks on a possible pion track, yield a limit of Γ(K⁺→π⁺e⁺e^-) / Γ(K⁺→all)<2.7×10^-7 (90% confidence). The latter value implies that the coupling constant for a vector neutral current must be about three orders of magnitude smaller than the coupling constant for the charged vector current.

Using the reaction π⁺d→pp(MM) at 2.13 GeV/c with photons from the final-state π⁰'s detected by tantalum plates in the 30-in. ANL bubble chamber, a 2π⁰ mass spectrum has been obtained in several ways. This spectrum is found to be in good agreement with phase-space expectations and presents no evidence for the production of a "narrow" ε (Γ<200 MeV). The 2π⁰ cross section for Δ²<15μ² is 386 ± 80 μb. ππ production and scattering angular distributions are presented. Good agreement with the one-pion-exchange model is noted. Assuming that the ratios of peripheral pion-production cross sections are equal to their pole values, a new method for extracting ππ scattering parameters is discussed. Using this method the I=0 s-wave phase shift is uniquely determined from threshold to 1 GeV/c² and found to be similar to the so-called UP-DOWN solutions of s-p wave interference analyses. In addition, the ratios of I=0 to I=2 s-wave scattering phase shifts and scattering lengths are found to be equal to -(3.2_-1.0^+1.5) near ππ threshold. Using a dispersion sum rule, the ππ scattering lengths are found to be a₀=+(0.15±0.08)μ^-1 and a₂=-(0.05±0.01)μ^-1.