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

Gas desorption and electron emission coefficients were measured for 1 MeV potassium ions incident on stainless steel at grazing angles (between 80 and 88 from normal incidence) using a new gaselectron source diagnostic (GESD). Issues addressed in design and commissioning of the GESD include effects from backscattering of ions at the surface, space-charge limited emission current, and reproducibility of desorption measurements. We find that electron emission coefficients e scale as 1= cos up to angles of 86 , where e 90. Nearer grazing incidence, e is reduced below the 1= cos scaling by nuclear scattering of ions through large angles, reaching e 135 at 88. Electrons were emitted with a measured temperature of 30 eV. Gas desorption coefficients 0 were much larger, of order 0 10 4. They also varied with angle, but much more slowly than 1= cos. From this we conclude that the desorption was not entirely from adsorbed layers of gas on the surface. Two mitigation techniques were investigated: rough surfaces reduced electron emission by a factor of 10 and gas desorption by a factor of 2; a mild bake to 220 had no effect on electron emission, but decreased gas desorption by 15% near grazing incidence. We propose that gas desorption is due to electronic sputtering.

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.

Contaminating clouds of electrons are a concern for most accelerators of postive-charged particles, but there are some unique aspects of heavy-ion accelerators for fusion and high-energy density physics which make modeling such clouds especially challenging. In particular, self-consistent electron and ion simulation is required, including a particle advance scheme which can follow electrons in regions where electrons are strongly-, wealdy-, and un-magnetized. We describe o w approach to such self-consistency, and in particular a scheme for interpolating between full-orbit (Boris) and dr&kinetic particle pushes that enables electron time steps long compared to the typical gyro period in the magnets. We present tests and applications: simulation of electron clouds produced by t h e e Werent lcinds of sowces indicates the sensitivity of the cloud shape to the nature of the source; first-of-a-kind self-consistent simulation of electron-cloud experiments on the High-Current Experiment (HCX)

The Heavy-Ion Fusion Sciences Virtual National Laboratory is pursuing an approach to target heating experiments in the Warm Dense Matter regime, using space-

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.

For the High Current Beam Transport Experiment~HCX! at Lawrence Berkeley National Laboratory, an injector is required to deliver up to 1.8 MV of 0.6 A K ϩ beam with an emittance of '1 p-mm-mrad. We have successfully operated a 10-cm-diameter surface ionization source together with an electrostatic quadrupole~ESQ! accelerator to meet these requirements. The pulse length is '4 ms, firing at once every 10-15 s. By optimizing the extraction diode and the ESQ voltages, we have obtained an output beam with good current density uniformity, except for a small increase near the beam edge. Characterization of the beam emerging from the injector included measurements of the intensity profile, beam imaging, and transverse phase space. These data along with comparison to computer simulations provide the knowledge base for designing and understanding future HCX experiments.

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