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Dramatic success was recently achieved in a laboratory experiment by compressing an intense an ion beam fifty-fold. The resulting 4 nanosecond pulse puts heavy ion beams, for the first time, within range of the pulse lengths necessary for meaningful HEDP experiments and for fusion power application. The result adds great flexibility for the design of the high energy end of heavy ion fusion drivers for inertial fusion, lowering the cost, and potentially shortening the development timetable. The result is even more impressive when one considers it involves a new approach that was first conceived only 12 months ago.

In the NDCX-1a facility, which began operation December 9, 2004, an induction "tilt" core was used to place a velocity ramp on a 25 mA, 255 keV beam, inducing compression. Space charge repulsion during compression was essentially eliminated by neutralizing the beam with a pre-formed plasma downstream of the core. Modeling showed good agreement between the data and particle-in-cell simulations.

Grant Logan, director of the Heavy Ion Fusion Virtual National Laboratory, said that these new results "may revolutionize high peak power accelerators in a manner analogous to the role frequency chirp played in ultra-high power lasers."

The next step is to accelerate the beam before compression. For this, a new accelerator concept is being developed called the "Pulse-Line Ion Accelerator" (PLIA). First proposed by LBNL consultant Dick Briggs (Patent Disclosure August 2004), the PLIA is a traveling-wave accelerator, with a helical winding around the beam pipe acting as a transmission line to produce the wave which accelerates the beam. The novel idea here is to use dielectric around the helix to slow the wave to nearly match the ion speed. First operation of experiments using a 1 meter PLIA test accelerator section began May 5, 2005. The experimental PLIA test section delivers 0.2 volt-seconds of acceleration capability at 10x. lower overall total cost per MeV compared to induction acceleration. This technique would greatly lower the cost of heavy ion accelerators for both high energy density physics experiments and for fusion power plants. In addition, it is likely that the low-energy ends of many other accelerators can benefit from this concept.

For further information, contact Grant Logan (bglogan@lbl.gov).