L. Reginato

Recirculating induction accelerators as drivers for heavy ion fusion

A two‐year study of recirculating induction heavy ion accelerators as low‐cost driver for inertial‐fusion energy applications was recently completed. The projected cost of a 4 MJ accelerator was estimated to be about

Plasma lens focusing and plasma channel transport for heavy ion fusion

500 M (million) and the efficiency was estimated to be 35%. The principal technology issues include energy recovery of the ramped dipole magnets, which is achieved through use of ringing inductive/capacitive circuits, and high repetition rates of the induction cell pulsers, which is accomplished through arrays of field effect transistor (FET) switches. Principal physics issues identified include minimization of particle loss from interactions with the background gas, and more demanding emittance growth and centroid control requirements associated with the propagation of space‐charge‐dominated beams around bends and over large path lengths. In addition, instabilities such as the longitudinal resistive instability, beam‐breakup instability and betatron‐orbit instability were found to be controllable with careful design.

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

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.

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

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.

Heavy ion fusion 2 MV injector

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.

High Voltage Operation of Helical Pulseline Structures for Ion Acceleration

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

To accelerate ions using a helical pulseline requires the launching of a high voltage traveling wave with a waveform determined by the beam transport physics in order to maintain stability and acceleration. This waveform is applied to the front of the helix, creating a steep voltage ramp that moves down the helix, accelerating ions over distances much longer than the ramp length. An oil dielectric helix to demonstrate ion acceleration has been designed and fabricated. Helix design parameters, high voltage issues, input coupling methods, termination methods, and pulsers are described. Waveforms from the initial characterization of the oil dielectric helix are also described.

Elise plans and progress

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.

Recirculating induction accelerators for heavy-ion fusion

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.