10487498
Advances In The SLAC RDDS : Modeling Manifold Damping And Its Effect On The Wakefield For The Next Linear Collider
The RDDS (Rounded Damped Detuned Structure) accelerator damps the transverse wakefield excited by bunches of electrons traversing thousands of linear accelerator structures. Errors in the fabrication of the cells which constitute each structure can result in a wakefield which is resonantly driven by the bunches, leading to BBU (Beam Break Up) and to a substantial growth in the beam emittance. One means to avoid these deleterious effects is to provide additional damping of the manifold, via plating the walls of the manifold with an electrically lossy material such as canthol or by fabricating the wall with stainless steel rather than copper. Results are presented on the wakefield and emittance growth in structures with a moderately lossy manifold.
17815790
Polarized electron sources for linear colliders
Linear colliders require high peak current beams with low duty factors. Several methods to produce polarized e{sup {minus}} beams for accelerators have been developed. The SLC, the first linear collider, utilizes a photocathode gun with a GaAs cathode. Although photocathode sources are probably the only practical alternative for the next generation of linear colliders, several problems remain to be solved, including high voltage breakdown which poisons the cathode, charge limitations that are associated with the condition of the semiconductor cathode, and a relatively low polarization of {le}5O%. Methods to solve or at least greatly reduce the impact of each of these problems are at hand.
117399426
A Resonant Cavity Approach to Non-Invasive, Pulse-to-Pulse EmittanceMeasurement
We present a resonant cavity approach for non-invasive, pulse-to-pulse, beam emittance measurements of non-circular multi-bunch beams. In a resonant cavity, desired field components can be enhanced up to Q{sub L{lambda}}/{pi}, where Q{sub L{lambda}} is the loaded quality factor of the resonant mode {lambda}, when the cavity resonant mode matches the bunch frequency of a bunch-train beam pulse. In particular, a quad-cavity, with its quadrupole mode (TM{sub 220} for rectangular cavities) at beam operating frequency, rotated 45{sup o} with respect to the beamline, extracts the beam quadrupole moment exclusively, utilizing the symmetry of the cavity and some simple networks to suppress common modes. Six successive beam quadrupole moment measurements, performed at different betatron phases in a linear transport system determine the beam emittance, i.e. the beam size and shape in the beam's phase space, if the beam current and position at these points are known. In the presence of x-y beam coupling, ten measurements are required. One measurement alone provides the rms-beam size of a large aspect ratio beam. The resolution for such a measurement of rms-beam size with the rectangular quad-cavity monitor presented in this article is estimated to be on the order of ten microns. A prototype quad-cavity was fabricated and preliminary beam tests were performed at the Next Linear Collider Test Accelerator (NLCTA) at the Stanford Linear Accelerator Center (SLAC). Results were mainly limited by beam jitter and uncertainty in the beam position measurement at the cavity location. This motivated the development of a position-emittance integrated monitor.
15840236
Effects of alternating cell misalignments on the DDS
The authors study some effects of cell misalignments in accelerator structures in which each cell is displaced the same amount and direction but with sign which alternates from cell to cell. In particular they study the manifold radiation in a damped detuned structure (DDS1) and wakefield effects in a uniform constant impedance structure. A synchronous wave aliasing phenomenon is observed. In previous treatments the effect of cell misalignment has been modeled by replacing it by beam displacement. Here they compare finite difference simulation of cell misalignment with the beam displacement model. They conclude with discussions about the relevance of the results for general misalignment profiles.
36965886
A traveling wave accelerator with HOM outcouplers for FELs
The application to FELs (free-electron lasers) of RF electron guns with laser-driven photocathodes has opened the door to developing efficient optical FELs. The next task is to develop accelerator structures which can transport such beams with a minimum of beam degradation. A low-cost approach to this using four 1.26-m constant gradient (CG) TW sections driven in parallel by a SLAC 5045 klystron is suggested. Using CG sections makes the higher order modes incoherent due to the linearly decreasing group velocity along the structure. Together with incorporating higher-order-mode outcouplers, this system is predicted to accelerate 1 nC per micropulse, 0.4 A per macropulse to 75 MeV from an injection energy of 5 MeV. Emittance growth is predicted to be 5 mm-mr.<<ETX>>
18642583
Application of a Mapping Function Technique to the Design of Damped Detuned Structures and to the Rapid Calculation of Their Wakefields
In order to reduce the dipole wake encountered by the first few bunches accelerated in a multi-bunch NLC scenario the DDS (damped detuned structure) was redesigned such that a much improved Gaussian fall-off occurs in the initial wake-function. From the 9 parameterized model of DDS1 the authors use a mapping function to allow DDS 3 and 4 to be modeled and hence avoid additional and prohibitively time consuming MAFIA runs. The equivalent circuit parameters and geometrical parameters are treated as functions of the synchronous frequency and are readily mapped onto the new synchronous frequencies. The new geometrical parameters form a family where each is associated with the iris diameter.
116422220
A Measurement of K0(L) --> pi+ pi- pi0 Decay Parameters
The decay ${K}_{L}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ has been studied in an experiment using the Argonne 12-ft hydrogen bubble chamber exposed to a ${K}_{L}^{0}$ beam of momentum 550 \ifmmode\pm\else\textpm\fi{} 35 MeV/c. After radiative corrections to the data, a fit using a matrix element of the form ${|M|}^{2}\ensuremath{\propto}1+\frac{g({s}_{3}\ensuremath{-}{s}_{0})}{{{m}_{{\ensuremath{\pi}}^{+}}}^{2}}+h{[\frac{({s}_{3} \ensuremath{-} {s}_{0})}{{{m}_{{\ensuremath{\pi}}^{+}}}^{2}}]}^{2} + k{[\frac{({s}_{1} \ensuremath{-} {s}_{2})}{{{m}_{{\ensuremath{\pi}}^{+}}}^{2}}]}^{2}$ gives $g = 0.681\ifmmode\pm\else\textpm\fi{}0.24$, $h = 0.095\ifmmode\pm\else\textpm\fi{}0.032$, and $k = 0.024\ifmmode\pm\else\textpm\fi{}0.010$. The branching ratio $\frac{\ensuremath{\Gamma}({K}_{L}^{0}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0})}{\ensuremath{\Gamma}({K}_{L}^{0}\ensuremath{\rightarrow}\mathrm{charged})}$ was measured to be 0.163 \ifmmode\pm\else\textpm\fi{} 0.003. These results, when compared to those obtained in other ${K}_{L}^{0}$ and ${K}^{\ifmmode\pm\else\textpm\fi{}}$ decay experiments, indicate a substantial $\ensuremath{\Delta}g\frac{1}{2}$ contribution to the ${K}_{L}^{0}$ decay amplitude.
187201784
An Assembly Procedure for Drift Tube Chambers
125417837
New Geometry of Muon Walls in October 1997 Tilecal Beam Test
Computer controlled positioning system of muon walls is described. Suitable setting for the leakage detection during the extended barrel module 0 beam test is explained in details.
17568135
Topology Types of Adinkras and the Corresponding Representations of N -Extended Supersymmetry
We present further progress toward a complete classification scheme for describing supermultiplets of N-extended worldline supersymmetry, which relies on graph-theoretic topological invariants. In particular, we demonstrate a relationship between Adinkra diagrams and quotients of N-dimensional cubes, where the quotient groups are subgroups of $(Z_2)^N$. We explain how these quotient groups correspond precisely to doubly even binary linear error-correcting codes, so that the classification of such codes provides a means for describing equivalence classes of Adinkras and therefore supermultiplets. Using results from coding theory we exhibit the enumeration of these equivalence classes for all cases up to 26 supercharges, as well as the maximal codes, corresponding to minimal supermultiplets, for up to 32 supercharges.
17714212
The NLC positron source
A baseline design for the NLC positron source based on the existing SLC positron system is described. The proposed NLC source consists of a dedicated S-band electron accelerator, a conventional positron production and capture system utilizing a high-Z target and an adiabatic matching device, and an L-band positron linac. The invariant transverse acceptance of the capture system is 0.06 m/spl middot/rad, ensuring an adequate positron beam intensity for the NLC.