Longitudinal compression oC a tailored-vciocity, intcmc neutralized ion heam hns been demonstmtcd. The compression tnlm plnec in a 1-2 m driit seetion Blled with plam~n to provide spacedierge neutduntioo. An induction cell produces a head-to-tnil velocity ramp that longitudinally compresses theneutrdized beam, enhancingthe b-peak current hyafndor of 50 audprodudag a pulse duration OC about 3 us. T h i s m m e m e n t hns been confirmed indopmdsntly with two darercot diagnostic eystems. The simultaneous l m v e r a e nnd longihdinal compression oI an ion heam is reguired t o achieve the high intensities necrssnry to create high energy density matter and fusion conditions. A recent driver study for inertial fusion, for Longitudinal compression of space-chargedominated beams has been studied extensively intheory and simulations [ll-E]. The compression is initiated by imposing a linear head-to-tail velocity tilt to a driitiig beam. Longitudinal space-&urge forces limit the beam compression ratio, the ratio oI the initial to i i nmal current, to about ten in most applications. iments on NDCX. To provjde the head-ta-tail velocity tilt, aninduction module withvariablewltagewaveronn is placed immedintely downstream of the last quadrupole mnpet. This is IoUmved hy a neutralized drii section which consists of a one -meter-long plasma column produced hy an AI cathodic cm: [ZO]. A diagnostic hmc is located at the downstream end of the plwarna column Thebeampmducedfromthesourcehasa5 paflat-top. The inductiontit voltage 'c~rves' out a -300 115 segment ofthe flat-top which compresseslongitudinallyas it driits through the plasma column. The final compressed beam is m e w e d in the dormetrenm diagnostic box.The induction cell consists oi 14 independently-driven magnetic cores in a preastnizad gas @Fa) region that is separated Erom the vnouum by a conventional high voltage insulator. The rvnveforms applied t o the 14 coria inductively add at the acceleration gap. Each core is driveu by a thyratronawitched modulator. Because the modulntor for each core can be designed to produce different waveiorms and can be triggered independently, a variety or wavdorms CM bs produced nt the acceleration gap using the 14 discrete building bloclw.The plasma column is formed hy two pulsed a u m i n u m cathodic arc sources loceted at the d m s t r e a m ond. Each source is equipped with a 45O open-arcutechm

Multiple-mirror magnetic confinement is investigated experimentally with a pulsed hydrogen plasma produced by a theta-pinch source. The gun output at the end of the guide field between the theta-pinch coil and the multiple-mirror region was a sharp plasma pulse of strength ∼1014 cm−3 with a ratio of drift to thermal velocity close to unity (∼ 10 eV). The seven multiple-mirror cells were stabilized with a linked quadrupole field. Transient experiments were performed with hydrogen in the favourable multiple-mirror regime (n ∼ 1013 cm−3, T ∼ 10 eV) where the ion mean free path is comparable to a cell length. The quadrupole field achieved partial plasma stabilization and the plasma lifetime inside the device was increased from 10–30 μs in the unstabilized simple mirror geometry to 50–80 μs at high values of the stabilizing current. The plasma pulse was successfully injected into the multiple-mirror region but was mainly trapped in the first half of the device, because of a non-uniform introduction region of two cells and because of the low value of the pulse drift velocity. The main features of the plasma build-up and decay were studied analytically and numerically with a simple simulation of the experiment. The numerical results were in qualitative agreement with the density profiles observed experimentally inside the device. The strong density gradients, obtained at the large values of the quadrupole current for which the flux surfaces are strongly elliptical, greatly enhanced the classical radial losses, particularly from ion-ion collisions. When included in the numerical model, the theoretical radial loss rates indicated a significant (up to 30%) decrease of the plasma lifetime inside the multiple mirror for the large values of the quadrupole current necessary for stability, in reasonable agreement with the experimental results.

We have demonstrated experimental techniques to provide active neutralization for space-charge dominated beams as well as to prevent uncontrolled ion beam neutralization by stray electrons. Neutralization is provided by a localized plasma injected from a cathode arc source. Unwanted secondary electrons produced at the wall by halo particle impact are suppressed using a radial mesh liner that is positively biased inside a beam drift tube. We present measurements of current transmission, beam spot size as a function of axial position, beam energy and plasma source conditions. Detailed comparisons with theory are also presented.

has been designed to study the final focus and neutralization of high perveance ion beams ͓E.

Current amplification of heavy-ion beams is an integral feature of the induction linac approach to heavy-ion fusion ͑HIF͒. In this paper we report on amplification experiments conducted on a single beam of the Multiple Beam Experiment ͑MBE-4͒, a heavy-ion ͑Cs ϩ ͒ induction linac. Earlier MBE-4 experiments ͓H. Meuth et al., Nucl. Instrum. Methods Phys. Res. A 278, 153 ͑1989͔͒ had demonstrated up-to-9ϫ current amplification but had been accompanied by an up-to-2ϫ increase of normalized transverse emittance. Experiments to pinpoint the causes of this emittance growth indicated various factors were responsible, including focusing aberrations and mismatch difficulties between the injector diode and the accelerator transport lattice, a localized quadrupole misalignment problem, and the interaction of transversely large beams with the nonlinear elements of the focusing lattice. Following ameliorative measures, new current amplification experiments, both with and without acceleration, showed that current amplifications of up to 3ϫ and line charge density increases of up to Ϸ2ϫ could be achieved without increasing the beam's normalized transverse emittance. Finally, both the transverse beam dynamics, and beam current and energy measurements were accurately modeled by numerical particle-in-cell simulations and longitudinal dynamics codes, respectively.