M.A. Tiunov

A 100 MW electron source with extremely high beam area compression

Abstract The development at INP electron optical system for a 7 GHz magnicon incorporating the high voltage diode gun based on a 120 mm oxide cathode with microperveance of 0.83 and high electrostatic compression of a beam as well as the guiding magnetic system are described here. The main problems and the concepts used for the formation of the super dense relativistic beam in the diode gun and its matching with magnetic system are described in detail. The geometry of the whole electron optical system is given and the results of numerical calculations for the beam dynamics are described. The experimental results of the formation of electron beam and its transportation through the guiding magnetic system are described. As a result of these experiments a beam of 100 MW ( U = 436 kV, I = 236 A) in a pulse of 2 μs is obtained. The measured diameter of a beam in magnetic system is about 2.5 mm and it is close to that of the Brillouins. Thus, the total measured compression of a beam over area exceeds 2000, power density in a beam achieves 2000 MW/cm 2 and an energy density in a beam exceeds 4 kJ/cm 2 .

Characterization of 1 MW, 40 keV, 1 s neutral beam for plasma heating

Neutral beam with geometrical focusing for plasma heating in moderate-size plasma devices has been developed in Budker Institute of Nuclear Physics, Novosibirsk. When operated with hydrogen, the neutral beam power is 1 MW, pulse duration is 1 s, beam energy is 40 keV, and angular divergence is 1.2 degrees. Initial ion beam is extracted and accelerated by triode multiapertures ion-optical system. To produce 1 MW neutral beam, about 40 A proton current is extracted with nominal current density of 320 mA/cm(2). Ion-optical system has 200 mm diameter grids with 44% transparency. The grids have inertia cooling and heat is removed between the pulses by water flowing in channels placed on periphery of the grids. A plasma emitter for ion extraction is produced by rf-plasma box. Ion species mix of rf plasma source amounts to 70%, 20%, and 10% of H(+), H(2)(+), and H(3)(+) ions, respectively, by current. Heavy impurities contribute less than 0.3%.

Multiaperture negative ion source

The long-pulse multiaperture surface-plasma source with negative ion production on a cesiated grid is under construction at Budker Institute. The ion source includes RF plasma driver, an expansion chamber with multicusp magnetic filed, an external magnetic filter and a four-electrode ion-optical system for beam extraction and acceleration. The projected parameters of the ion source are: beam current 1.5 A, beam energy 120 keV, pulse duration 100 s, RF power in plasma 40 kW, hydrogen filling pressure < 0.5 Pa, e/H− ratio 1:1, H− ions emission current density 30 mA/cm2.

Development of a negative ion-based neutral beam injector in Novosibirska)

A 1000 keV, 5 MW, 1000 s neutral beam injector based on negative ions is being developed in the Budker Institute of Nuclear Physics, Novosibirsk in collaboration with Tri Alpha Energy, Inc. The innovative design of the injector features the spatially separated ion source and an electrostatic accelerator. Plasma or photon neutralizer and energy recuperation of the remaining ion species is employed in the injector to provide an overall energy efficiency of the system as high as 80%. A test stand for the beam acceleration is now under construction. A prototype of the negative ion beam source has been fabricated and installed at the test stand. The prototype ion source is designed to produce 120 keV, 1.5 A beam.

Simulation of high current electron and ion beam dynamics for EBIS

The results of the modeling of formation and transportation of ion and electron beams for EBTS BNL are presented. Simulations have been done with SAM, BEAM, and ExtraSAM codes. Some features of the codes are given as well. The codes provide high accuracy for simulating a wide range of tasks at EBTS, including electron gun, trap, collector, extraction, and transportation of the ion beam. Several examples of those computing can be found in the report. An effect of radial modulation of current density of electron beam in the magnetic field due to the sag between an edge and a center of the beam was noted.

Formation and collection of electron beams for EBIS

Some peculiarities of the electron beam for EBIS are described. The best achievements of computer simulation are presented for high current density beams in electron tubes (transport systems) and current densities from cathodes for varies cathode types of the same lifetimes. Possibilities of formation of the electron beam by a gun with different degree of immersion of the cathode into the magnetic field have been examined. Behavior of the electron beam in a collector has been studied.

STATUS OF THE PESTOV SPARK COUNTER DEVELOPMENT FOR THE ALICE EXPERIMENT

Abstract The performance of a new ALICE prototype of the Pestov spark counter was measured both in a dedicated test beam as well as in a high multiplicity heavy-ion environment. Results in terms of time resolution and background behaviour are presented.

Pestov Spark Counter prototype development for the CERN-LHC ALICE experiment

Abstract A prototype Pestov Spark Counter with two-dimensional position resolution has been developed. The position resolution is 0.32 mm and

Negative ion production in the RF multiaperture surface-plasma source

The experiments on negative hydrogen ion beam production in a multi-aperture long-pulse surface-plasma source are described. H- ions are produced on the surface of a plasma grid covered by cesium and illuminated by fast plasma particles. The source uses a radio-frequency driver to generate plasma. A composite magnet system made of external permanent magnets confines and filters electrons in the plasma region, and deflects them in the extraction area. A multiaperture, multi-electrode ion optical system is used for beam formation. The electrode heating and cooling during long pulses is accomplished by circulating a heat transfer fluid through channels drilled in the electrodes bodies. H- ions extraction through a single aperture and 21 apertures was performed and studied. A stable H- beam with the current up to 0.7 A, energy up to 74 kV, and pulse duration up to 7 s was routinely obtained

Formation of an ion beam in an elementary cell with inhomogeneous emission current density.

A well-known Pierce solution that allows focusing a beam of charged particles using properly shaped electrodes outside the beam aperture is generalized to the case of an accelerating system with inhomogeneous emission current density. It is shown that the defocusing effect of the space charge can, in principle, be evenly compensated over the entire cross section of the beam. In contrast to the beam with a uniform emission current density, both the electric potential and the transverse electric field must be controlled along the beam boundary in order to eliminate the angular divergence. However, eliminating the angular spread evenly across the beam constitutes a mathematically ill-posed problem which needs to be solved with the use of one or another method of regularization. An alternative way of diminishing beam emittance is proposed for the beam where the emission current is uniform across the entire aperture except for a narrow beam edge layer and a simple formula for the Pierce electrodes is derived. Numerical simulation has proved the reasonable accuracy of our analytical theory.