Showing papers on "Perveance published in 1993"

An advanced high-current low-emittance dc microwave proton source

Abstract: The high-current low-emittance microwave proton source introduced two years ago act the Chalk River Laboratories has been extensively redesigned. The 2.45 GHz microwave line was modified to incorporate a 50 kV dc break and a rectangular-to-ridged waveguide transition. The layered microwave window has been replaced by a single plate of aluminum nitride. The solenoids were electrically isolated from the plasma chamber. Only the plasma chamber remains at the extraction potential. The total beam current and the proton beam current have been measured as a function of the microwave power, the hydrogen mass flow and the solenoid positions and currents. More than 95 mA dc of hydrogen ions with a proton fraction in excess of 85% were extracted from a single 2.5 mm radius aperture with only 500 W of microwave power and 2.0 sccm (3 μg/s) of hydrogen mass flow. The perveance at minimum divergence and the minimum emittance have been determined for various extraction geometries. The variation of the perveance with the aspect ratio of the extraction system was found to be virtually identical for microwave and arc discharge ion sources. The normalized rms emittance was less than 0.13 p mm mrad whatever the extraction geometry.

Sheet-beam klystron RF cavities

Abstract: A high-frequency sheet-beam klystron operating at a low perveance per square can produce high peak power at high efficiency. In order to provide beam stability and to maximize power extraction efficiency for a flat beam with a finite width, we have designed RF cavities in which the electric field is nearly constant across the width of the beam (on the order of several wavelengths). However, in such cavities, the electric field in the fundamental mode can couple to the TE propagating mode in the drift section if any cavity or beam asymmetry is present. The dipole field can couple between adjacent cavities even in the absence of these asymmetries as long as the frequency is above cutoff of the drift tube. The effects of coupling between RF cavities are calculated using an equivalent circuit model. Threshold parameters for onset of RF oscillation in the fundamental mode as a result of cavity coupling are obtained. We have designed choke cavities which effectively prevent such possible oscillations. >

Magnetic deflection system for ion beam implanters

Abstract: Deflection apparatus is shown for high perveance ion beams, operating at 20 Hz fundamental and substantially higher order harmonics, having a magnetic structure formed of laminations with thickness in range between 0.2 and 1 millimeter. Additionally, a compensator is shown with similar laminated structures with resonant excitation circuit, operating at 20 Hz or higher, in phase locked relationship with the frequency of the previously deflected beam. Furthermore, features are shown which have broader applicability to producing strong magnetic field in magnetic gap. Among the numerous important features shown are special laminated magnetic structures, including different sets of crosswise laminations in which the field in one lamination of one set is distributed into multiplicity of laminations of the other set of coil-form structures, field detection means and feedback control system, cooling plate attached in thermal contact with number of lamination layers. Surfaces on the entry and exit sides of the compensator magnetic structure have cooperatively selected shapes to increase the length of path exposed to the force field dependently with deflection angle to compensate for contribution to deflection angle caused by higher order components. The entry and exit surfaces of the magnetic scanner and compensator structures cooperating to produce desired eam profile and desired limit on angular deviation of ions within the beam. Also shown is an accelerator comprising a set of accelerator electrodes having slotted apertures, a suppressor electrode at the exit of the electrostatic accelerator, a post-accelerator analyzer magnet having means for adjusting the angle of incidence by laterally moving the post-accelerator analyzer magnet, and a magnet to eliminate aberration created by the post-accelerator analyzer magnet. In the case of use of a spinning substrate carrier for scanning in one dimension, the excitation wave form of the scanner relates changes in scan velocity in inverse dependence with changes in the radial distance of an implant point from the rotation axis. Also an oxygen implantation method is shown with 50 mA ion beam current, the ion beam energy above 100 KeV, and the angular velocity of a rotating carrier above 50 rpm.

Longitudinal instability of space-charge dominated beams in transport channels with complex wall impedances

Abstract: The longitudinal instability of space‐charge dominated beams in transport channels with complex wall impedances is studied. The dispersion equation, derived from the one‐dimensional Vlasov equation, characterizes the instability with all the relevant parameters including the space charge, the beam energy spread, the real and imaginary parts of the complex wall impedances. For a beam without energy spread, the growth rates of the instability in the different parameter ranges are discussed. The application of the theory to a resistive‐wall channel and to a channel with induction gaps is presented. For a beam with energy spread, Lorentzian and Gaussian distributions are treated and the results presented illustrate the dependence of the stable regions on the beam perveance, the energy spread and the wall properties.

First test of the X-band pulsed magnicon

Abstract: The magnicon belongs to the class of high power RF sources where a modulation is provided by the beam circular deflection and it is an advanced version of a gyrocon. The first magnicon was built and tested in Novosibirsk in the mid 80s. The power of 2.6 MW has been obtained for the frequency 915 MHz and pulse duration 30 mcsec, the electron efficiency has been 85%. Good results obtained during investigations show that the magnicon can be an adequate RF source for the next generation of accelerators, especially for future linear colliders and accelerators for transmutation of nuclear waste. The magnicon conception described allow one to increase significantly the beam perveance, compared with the first magnicon, and to achieve the pulse power of tens and hundreds megawatts at the beam voltage not greater than 400-600 kV. The device is an amplifier working in frequency doubling mode and is a prototype of RF source for linear colliders with high acceleration gradient. The magnicon is designed for an output power of 50 MW, an operating frequency of 7 GHz and a pulse duration of 2 mcsec. >

Producing magnetic fields in working gaps useful for irradiating a surface with atomic and molecular ions.

Abstract: A deflection apparatus for high perveance ion beams, operating at 20 Hz fundamental and substantially higher order harmonics, has a magnetic structure formed of laminations (72) with thickness in range between 0.2 and 1 millimeter. A compensator with similar laminated structures (71, 75) with resonant excitation circuit, operating at 20 Hz or higher, is in phase locked relationship with the frequency of the previously deflected beam. Other features with broader applicability to produce strong magnetic field in magnetic gap are shown.

Determination of electron temperature in partial space-charge-compensated high-perveance ion beams

Abstract: For heavy-ion inertial-fusion drivers, high-perveance ion beams are required. Space-charge compensation is enhancing the current limit of low-energy beam transport lines (LEBT). The knowledge of the temperature of the compensating electrons and the charge density of the electrons on axis is needed for the calculation of beam transport under the influence of space-charge compensation. A low-energy beam transport line (typically 9 keV, 3 mA DC, He+) has been set up and the radial density distribution of the beam ions was measured. Using this data in a one-dimensional numerical simulation, a multiplicity of possible states of the compensated beam can be calculated. Comparing the results of the simulation with measured beam potentials, it is possible to determine the electron temperature as well as the electron density on axis. First experimental results are presented together with the fundamental theory.

Space charge effects in neutralized ion-compensated beams

Abstract: Space charge effects in transport channels may be suppressed by using neutralized beams with equal currents of negative and positive ions. Variations of beam envelopes in strong focusing channels result in an increase of the incoherent oscillation frequency with the current. The frequency of the quardrupole coherent oscillations increases as well and it moves to the resonance appearing due to strong focusing. Moreover, the beam perveance is limited by non-linear coherent resonances of the same kind as in uniform beams. Space charge limitations with account of all these effects have been calculated.

Efficiency of an electrostatic barrier in an electron beam energy recuperator

Abstract: The efficiency of an intense electron beam energy recuperator with a potential minimum is analyzed. The value of “an electrostatic barrier perveance” is shown to be characteristic of the potential minimum efficiency. The optimum condition for an three-electrode recuperator are formulated. Two recuperators with different geometries of the electrodes, which form an electrostatic barrier, are compared experimentally. The first geometry is optimal, the second one coincides with that used on the LEAR electron cooling device. For high magnitudes of the collector perveance, a four-electrode recuperator is suggested.

Performance characteristics of a multiple-sample, cesium-sputter, negative ion source

Abstract: A multiple-sample, cesium-sputter, negative-ion source which permits sample changes without disruption of on-line tandem electrostatic accelerator operations is described. The source is equipped with provisions for remotely selecting and moving into the beam position any one of 60 samples by means of stepping motors equipped with absolute shaft encoders. A spherical-sector cesium ionizer is used to produce the cesium beam for sputtering the sample material. The source is equipped with a three-element electrode system which has been designed to increase the perveance for cesium ion beam generation and to improve negative ion beam extraction from the source. Details of the mechanical design features and optics of the three-element electrode system are presented. Data pertinent to source operation and the dependence of negative ion yields on certain source operational parameters are also given.

ILSE-ESQ injector scaled experiment

Abstract: A 2 MeV, 800 mA, K/sup +/ injector for the Heavy Ion Fusion Induction Linac Systems Experiments is under development at LBL. It consists of a 500 keV-1 MeV diode pre-injector followed by an electrostatic quadrupole accelerator (ESQ). One of the key issues for the ESQ centers around the control of beam aberrations due to the "energy effect": in a strong electrostatic quadrupole field, ions at beam edge will have energies very different from those on the axis. The resulting kinematic distortions lead to S-shaped phase spaces, which, if uncorrected, will lead eventually to emittance growth. These beam aberrations can be minimized by increasing the injection energy and/or strengthening the beam focusing. It may also be possible to compensate for the "energy effect" by proper shaping of the quadrupoles electrodes. In order to check the physics of the "energy effect" of the ESQ design a scaled experiment has been designed that will accommodate the parameters of the source, as well as the voltage limitations, of the Single Beam Transport Experiment (SBTE). Since the 500 KeV pre-injector delivers a 4 cm converging beam, a quarter-scale experiment will fit the 1 cm converging beam of the SBTE source. Also, a 10 mA beam in SBTE, and the requirement of equal perveance in both systems, forces all the voltages to scale down by a factor 0.054. Results from this experiment and corresponding 3D PIC simulations are presented. >

Novel electron beam cathode

Abstract: : Experiments have been conducted during the past year to develop an electron beam cathode which is capable of producing a moderate perveance beam for several microsecond pulse lengths and is not susceptible to diode closure. The requirements, successfully met by this salt-based cold emission cathode, include operating in modest vacuums of 10-5 Torr, voltages less than or equal 160 kV, and the ability to generate solid or annular cross section space-charge- limited electron beams. Data on the operating performance of this salt cathode and streak photographs showing the uniformity of the emission of the electron beam are presented. Comparisons of this salt cathode will be made with other electron beam cathode materials.... Cathode, Electron beam, Diode, Perveance, Diode collapse, Cesium iodide

Low-current traveling wave tube for use in the microwave power module

Abstract: The results of a traveling-wave-tube/multistage depressed-collector (TWT-MDC) design study in support of the Advanced Research Projects Agency/Department of Defense (ARPA/DOD) Microwave Power Module (MPM) Program are described. The study stressed the possible application of dynamic and other tapers to the RF output circuit of the MPM traveling wave tube as a means of increasing the RF and overall efficiencies and reducing the required beam current (perveance). The results indicate that a highly efficient, modified dynamic velocity taper (DVT) circuit can be designed for the broadband MPM application. The combination of reduced cathode current (lower perveance) and increased RF efficiency leads to (1) a substantially higher overall efficiency and reduction in the prime power to the MPM, and (2) substantially reduced levels of MDC and MPM heat dissipation, which simplify the cooling problems. However, the selected TWT circuit parameters need to be validated by cold test measurements on actual circuits.

Use of an Energy Analyzer Probe in the Characterization of a High Perveance Ion Beam

Abstract: We have developed an energy analyzer probe which measures the energy of slow ions produced in ion implanters by beam collisions with the residual gas molecules. Since the beam potential is directly related to the wafer potential, we show that such a device can be used as a real-time, non-invasive monitor of wafer charging.

/sup 3/He high power neutral beams for TEXTOR comparison of 55 KeV particle beam and vacuum system data with /sup 4/He, deuterium and hydrogen

Abstract: Neutral particle beams of the /sup 3/He isotope in the megawatt range were successfully produced by the neutral beam injectors of TEXTOR. Measurements of beam and ion source characterizing data, i.e. perveance, divergence, neutralization efficiency, beamline transmission and gas flow rates for 50 kV, 49 A, 2.5 MW, 3 sec /sup 3/He beams are compared with relevant data of hydrogen, deuterium and /sup 4/He. The LHe cryo condensation pumps are capable of pumping the resulting /sup 3/He gas flow rates of 50 mbl/s without technical modification at 4.2 K, if covered prior to each beam pulse by an amount of argon frost with proper ratio of Ar/He. Beamline pressure, reionization losses and preliminary results of /sup 3/He-injection into TEXTOR are given.