22303829
RF Phase Focusing in Portable X-Band, Linear Accelerators
In order to minimize the size and weight of the x-ray or neutron source for a series of portable radiographic linear accelerators, the x-ray head was packaged separately from the rest of the system and consists of only the linac accelerating structure, electron gun, built-in target, collimator, ion pump and an RF window. All the driving electronics and cooling are connected to the x-ray head through flexible waveguide, cables, and waterlines. The x-ray head has been kept small and light weight by using the RF fields for radial focusing, as well as for longitudinal bunching and accelerating the beam. Thus, no external, bulky magnetic focusing devices are required. The RF focusing is accomplished by alternating the sign of the phase difference between the RF and the beam and by tapering from cavity to cavity the magnitude of the buncher field levels. The former requires choosing the right phase velocity taper (mix of less than vp=c cavities) and the latter requires the right sizing of the cavity to cavity coupling smiles (irises).
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>>
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.
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.
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.
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.
118734978
High resolution magnetic spectrometer for antiproton physics at rest and low energies
A spectrometer is being installed in a high-intensity antiproton beam (LESBII) at the AGS. The beam momentum entering the target will be known to approximately +- /sup 1///sub 2/%. The target is surrounded by a stereoscopic cylindrical drift chamber, and thus the total charge of the event will be measured. Since the vertex will be reconstructed with an accuracy of approximately +- 2 mm, studies of annihilations with high resolution down to approximately 150 MeV/c will be possible. On one side of the target a large-aperture (2.3 x .62 m/sup 2/) magnet covered on both sides with drift chambers and triggering--TOF scintillation counters, will measure particle and ..gamma..-ray energies with high resolution, as well as identify particles. The primary objective is to look for peaks in the ..gamma.. spectra coming from annihilations at rest by converting them in a thin (.05 x/sub 0/) radiator before the magnet. Narrow peaks (< 1 MeV) which are produced with frequencies of approximately 10/sup -3/ or better are expected to be seen as 5 sigma effects. The principle and details of the spectrometer are presented.
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.
59889859
Computer facilities for Isabelle data handling
The analysis of data produced by Isabelle experiments will need a large system of computers. Included in the array should be a substantial computer system at each Isabelle intersection in use. These systems must include enough computer power to keep experimenters aware of the status of the experiment. This will require at least one very fast sophisticated processor in the system, the size depending on the experiment. Other features of the intersection systems must be a good, high speed graphic display, ability to record data on magnetic tape at 500 to 1000 KB, and a high-speed link to a central computer. The operating system software must support multiple interactive users. A substantially larger capacity computer system, shared by the six intersection region experiments, must be available with good turnaround for experimenters while Isabelle is running. The computer mainframes should ideally be compatible members of the same family of computers. A very large computation load will be generated by the post experiment data reduction. Much of this may have to be run at lower priority. A computer support group will be required to maintain the computer system and to provide and maintain software common to all experiments. Such software support maymore » include providing a compatible compiler. Special superfast computing hardware or special function processors constructed with microprocessor circuitry may be necessary both in the data gathering and data processing work. Thus, both the local and central processors should be chosen with the possibility of interfacing such devices in mind.« less
122880341
Search for a double-pomeron-exchange contribution in the reaction K-p --> K-(pi-pi+)p at 14.3 GeV/c
123458840
Channel cross-sections of K−p reactions from 1.26 to 1.84 GeV/c
SummaryWe present the results on total channel cross-sections obtained in the Saclay 180 l HBC exposed to a separated K− beam at Nimrod. The cross-sections for each channel are given at 13 incident K− momenta between 1.26 and 1.84 GeV/c.RiassuntoPresentiamo i risultati sulle sezioni d’urto totali dei canali ottenute a Nimrod nella camera a bolle a idrogeno di 1801 di Saclay esposta a fasci separati di K−. Le sezioni d’urto per ciascun canale sono date per 13 momenti incidenti di K− fra 1.26 e 1.84 GeV/c.РеэюмеМы предлагаем реэультаты по полным канальным поперечным сечениям, полученным в Сакле на 180 литровой водородной пуэырьковой камере, зкспонированной в выделенном К−-пучке. Поперечные сечения для каждого канала приводятся для 13 эначений начальных импульсов K−-меэонов в области от 1.26 до 1.84ГзВ/с.