High current transport experiment for heavy ion inertial fusion

Abstract

National Laboratory is part of the U.S. program to explore heavy-ion beam transport at a scale representative of the low-energy end of an induction linac driver for fusion energy production. The primary mission of this experiment is to investigate aperture fill factors acceptable for the transport of space-charge-dominated heavy-ion beams at high intensity (line charge density 0:2 C=m) over long pulse durations (4 s) in alternating gradient focusing lattices of electrostatic or magnetic quadrupoles. This experiment is testing transport issues resulting from nonlinear space-charge effects and collective modes, beam centroid alignment and steering, envelope matching, image charges and focusing field nonlinearities, halo, and electron and gas cloud effects. We present the results for a coasting 1 MeV K ion beam transported through ten electrostatic quadrupoles. The measurements cover two different fill factor studies (60% and 80% of the clear aperture radius) for which the transverse phase space of the beam was characterized in detail, along with beam energy measurements and the first halo measurements. Electrostatic quadrupole transport at high beam fill factor (80%) is achieved with acceptable emittance growth and beam loss, even though the initial beam distribution is not ideal (but the emittance is low) nor in thermal equilibrium. We achieved good envelope control, and rematching may only be needed every ten lattice periods (at 80% fill factor) in a longer lattice of similar design. We also show that understanding and controlling the time dependence of the envelope parameters is critical to achieving high fill factors, notably because of the injector and matching section dynamics.

Intense Ion Beam Transport in Magnetic Quadrupoles: Experiments on Electron and Gas Effects

“…Electrons produced by beam-background gas interactions or from halo loss at limiting apertures are effectively cleared by the fields established by the quadrupole electrodes at ±17-25 kV. These electrostatic transport results [4] are an electron-free comparison to transport in magnetic quadrupoles. While electrostatic quadrupoles are suitable at low energy, magnetic quadrupoles are desireable for most of a HIF driver.…”

Development and testing of a lithium ion source and injector

“…The choice of aluminosilicate is based on successes with other alkalis such as K þ [6] which have shown good reproducibility, low emittance, and high current from large surface area sources capable of operating at >1 Hz. Also, there have been demonstrated reliable Li þ sources developed as tokamak plasma diagnostics [7,8].…”

Critical issues for high-brightness heavy-ion beams --prioritized

“…We can measure the effects of electrons with slit scans, either conventional double slit [7] or optical slit scans with either solenoids and quadrupoles [32]; and we have developed techniques to measure the absolute value of the electron density in quadrupoles [1]. In solenoids, we need to develop and validate tools to measure the electron accumulation.…”

“…6. Transported a 1 MeV, 0.18 A K+ beam through 10 electrostatic quadrupoles with little or no beam loss or degradation, even for the beam filling 60% and 80% of the electrode radius [7].…”