Drift Compression of an Intense Neutralized Ion Beam

Abstract

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

Longitudinal emittance growth due to nonlinear space charge effect

“…In this study, we consider only the channel design for the smaller angle. Each channel consists of bends, a matching section, a plasma-filled neutralized drift [8], and final focusing section. The pipe is perfectly conductive with a uniform radius 10 cm to allow space for beams going through bends without hitting the wall.…”

Controlling Charge and Current Neutralization of an Ion Beam Pulse in a Background Plasma by Application of a Small Solenoidal Magnetic Field

“…Beam propagation in a plasma is considered to be an effective way to compress intense beam pulses both longitudinally and transversely by applying a small velocity tilt [8,9]. A number of possible instabilities during propagation of beam pulses through a background plasma in a solenoidal magnetic field [21,22] can be effectively mitigated by a small velocity tilt and plasma density inhomogeneity [23,24].…”

“…The plasma electrons can effectively neutralize the beam charge, and the background plasma can provide an ideal medium for beam transport and focusing. Neutralization of the beam charge and current by a background plasma is an important issue for many applications involving the transport of fast particles in plasmas, including astrophysics [1][2][3][4], accelerators [4,5], and inertial fusion, in particular fast ignition [6] and heavy ion fusion [7,8].…”

Recent US advances in ion-beam-driven high energy density physics and heavy ion fusion

“…Longitudinal compression of an ion bunch using a velocity ramp head-to-tail while traveling through neutralizing background plasma provides a means of generating ion beam pulses short enough to be consistent with the hydro expansion time of few-micron-thick target foils for near-term warm dense matter physics experiments. In the Neutralized Drift Compression Experiment [4] (NDCX- Fig. 1), an induction core adds a velocity ramp from the head to the tail of a selected 200 to 400 ns portion of a 25 mA , 300 kV K + ion beam.…”