C. Peters

Plasma lens focusing and plasma channel transport for heavy ion fusion

Abstract The capabilities of adiabatic, current-carrying plasma lenses for the final focus problem in heavy-ion-beam-driven inertial confinement fusion are explored and compared with the performance of non-adiabatic plasma lenses, and with that of conventional quadrupole lenses. A final focus system for a fusion reactor is proposed, consisting of a conventional quadrupole lens to prefocus the driver beams to the entrance aperture of the adiabatic lens, the plasma lens itself, and a high current discharge channel inside the chamber to transport the focused beam to the fusion pellet. Two experiments are described that address the issues of adiabatic focusing, and of transport channel generation and stability for ion beam transport. The test of the adiabatic focusing principle shows a 26-fold current density increase of a 1.5 MeV potassium ion beam during operation of the lens. The lens consist of a discharge of length 300 mm, filled with helium gas at a pressure of 1 Torr and is pulsed with a current between 5 and 15 kA. The investigations of discharge channels for ion beam transport show that preionization of the discharge channels with a UV laser can be an efficient way to direct and stabilize the discharge.

A Nb 3 Sn dipole magnet reacted after winding

A 5 cm bore dia., 1-m-long dipole model magnet was constructed by winding un-reacted cable, followed by reaction and epoxy-impregnation. Experience and test results are described on the 1.7 mm dia. internal-tin wire, the eleven-strand flattened cable, fiberglass insulation, and construction of the magnet. Each half of the magnet has two double-pancake-type windings that were reacted in a single operation. The two double-pancakes were then separately vacuum impregnated after soldering the flexible Nb-Ti leads to the Nb 3 Sn conductors. No iron flux return yoke was used. In initial tests a central field of 8.0 T was reached at 4.4 K. However, evidence from training behavior, and 1.8 K tests indicate that premature quenching, rather than critical current of the cable, limited the field intensity. The magnet was reassembled and more rigidly clamped; additional test results are reported.

2 MV injector as the Elise front-end and as an experimental facility

Abstract We report on progress in the preparation of the 2 MV injector at LBNL as the front end of Elise and as a multipurpose experimental facility for heavy ion fusion beam dynamics studies. Recent advances in the performance and understanding of the injector are described, and some of the ongoing experimental activities are summarized.

Engineering conceptual design of the relativistic klystron two-beam accelerator based power source for 1 TeV Next Linear Collider

Ultra-high gradient radio frequency linacs require network current. Efficient and reliable power sources. The induction linac has proven to be a reliable source of low energy, high current and high brightness electron beams. The low energy beam is bunched, transported through resonant transfer cavities in which it radiates microwave energy that is coupled to an adjacent high energy accelerator. The low energy beam is maintained at a constant energy by periodic induction accelerator cells. This paper describes the engineering aspects of the induction accelerator based relativistic klystron. The physics issues are covered in another paper at this conference.

Heavy ion fusion 2 MV injector

A heavy-ion-fusion driver-scale injector has been constructed and operated at Lawrence Berkeley Laboratory. The injector has produced 2.3 MV and 950 mA of K/sup +/, 15% above original design goals in energy and current. Normalized edge emittance of less than 1 /spl pi/ mm-mr was measured over a broad range of parameters. The head-to-tail energy flatness is less than /spl plusmn/0.2% over the 1 /spl mu/s pulse.

Designs of a DC ESQ accelerator for BNCT application

ESQ accelerators are capable of producing high current, DC megavolt beams, thus they are ideal for BNCT application. In our preliminary design, a 3.6 m long ESQ column with a 6 cm bore diameter will accelerate a proton beam up to 2.5 MeV. The accelerator column is surrounded by an air-core transformer stack which provides DC power to the ESQ electrodes. The assembly is enclosed inside a 6.1 m long 2.4 m diameter high pressure vessel. Computer simulation shows that the beam envelope remains small compare to the bore diameter thus allowing a wide range of operation for beam currents ranging from 25 mA to 125 mA.

Transverse combining of four beams in MBE-4

Abstract Transverse beam combining is a cost-saving option employed in many designs for induction linac heavy ion fusion drivers. The resultant transverse emittance increase, due predominantly to anharmonic space charge forces, must be kept minimal so that the beam remains focusable at the target. A prototype combining experiment has been built using the MBE-4 experimental apparatus. Four new sources produce up to 6.7 mA Cs+ beams at 200 keV. The ion sources are angled toward each other so that the beams converge. Focusing upstream of the merge consists of four quadrupoles and a final combined-function element (quadrupole and dipole). All lattice elements are electrostatic. Owing to the small distance between beams at the last element (about 3–4 mm), the electrodes here are a cage of small rods, each at different voltage. The beams emerge into the 30-period transport lattice of MBE-4 where emittance growth due to merging, as well as the subsequent evolution of the distribution function, can be diagnosed. The combiner design, simulation predictions and preliminary results from the experiment are presented.

Elise plans and progress

Abstract Elise is a heavy-ion induction linear accelerator that will demonstrate beam manipulations required in a driver for inertial fusion energy. With a line charge density similar to that of heavy-ions drivers, Elise will accelerate a beam pulse (duration of 1 μs or more) of K + ions from an initial energy of 2 MeV to a final energy 5 MeV or more. In the present design, the Elise electrostatic quadrupoles (ESQs) will have an aperture of radius 2.33 cm operating at ± 59 kV. The half-lattice periods range from 21 to 31 cm. The entire machine will be approximately 30 m long, half of which is the induction accelerator with the remaining half being the injector (including the Marx generator) and the matching section. Elise will be built in a way that allows future expansion into the full Induction Linear Accelerator Systems Experiments (ILSE) configuration, so it will have an array of four ESQ focusing channels capable of transporting up to a total of 3.2 A of beam current. Elise will also have an active alignment system with an alignment tolerance of less than 0.1 mm. Initially, only one beam channel will be used during nominal Elise operation. At the currently expected funding rate, the construction time will be 4.75 years, with FY95 being an extra year for research and development before construction. Total project cost is estimated to be US

Engineering research and development for the Elise Heavy Ion Induction Accelerator

25.9m, including contingency costs.

Design and testing of the 2 MV heavy ion injector for the Fusion Energy Research Program

The Fusion Energy Research engineering team has been conducting Research and Development Associated with the Construction (RDAC) of the Elise accelerator since the approval of Key Decision one (KD1 is start of construction). The engineering design effort has worked in close cooperation with the physics design staff to achieve all parameters of the Elise accelerator. The design included the 2 MV injector, matching section, combiner, induction cells, electric/magnetic quadrupoles, alignment system and controls. All major designs and some hardware testing will be discussed.