A relativistic electron beam propagating through an unmagnetized, underdense plasma exhibits a transverse instability due to the coupling of the beam centroid to plasma electrons at the "ion-channel" edge. The transverse wake field corresponding to this "electron-hose" effect is calculated in the "frozen-field" approximation for a low-current, cylindrical beam in a radially infinite plasma. The asymptotic growth of beam-centroid oscillations is computed, and the growth length is found to be very rapid, indeed much less than the betatron period of the beam. Results for a radially finite plasma and for a slab beam are noted. Damping and saturation mechanisms are discussed.PACS numbers: 52.40. Mj, 29.15.Dt, 52.50.Gj In recent years, the demands of the TeV-energy electron-positron collider [l] have spurred considerable interest in the transport of intense relativistic electron beams in the "ion-focused regime" (IFR). Proposed applications include the plasma lens [2], the continuous plasma focus [3,4], the plasma emittance damper [5], and plasma wake-field acceleration [6,7]. At the same time, coherent radiation from intense beams in the IFR has also been the subject of much theoretical [8][9][10][11] and experimental [12] work. These novel applications draw on a large body of work in beam-plasma physics [13][14][15] and extensive application of the IFR in accelerator and radiation research [16,17].Typically the IFR refers to propagation along a narrow plasma channel which is "underdense" (i.e., with charge density much less than that of the beam) and in addition has total plasma charge per unit length less than that of the beam. In this limit, all plasma electrons are ejected radially to large distances. However, for many novel applications, the plasma may initially extend to large radii, or a broad plasma may be created by beam and secondary ionization. In this Letter, we show that propagation in such a regime suffers from a previously unrecognized hose instability, similar in character to the "transverse two-stream" instabilities [18,19] (e.g., the "ion-hose" instability [15]). This instability results from the electrostatic coupling of transverse beam displacements to plasma electrons at the boundary between the ion channel and the surrounding quasineutral plasma, beyond the beam volume. We show that the growth length for the "electron-hose" instability is so short that IFR transport in this regime is problematic at best.To compute this growth length, we consider first equilibrium propagation of a relativistic electron beam in a uniform, unmagnetized, preionized plasma of density rie, and infinite radial extent. We assume unperturbed beam charge density of the form pboir,s)'= -enij(s)H(a -r), where H is the step function, -^ is the electron charge, rib is the beam density on axis, a is the beam radius ( Fig. 1), s-t -zic is the retarded time, t is time, z is axial displacement, and c is the speed of light. As the beam head propagates through the plasma, it expels plasma electrons from the beam volume on the sho...

It is shown that the proton-proton elastic scattering data at large angles can be described by a trajectory with the same shape as the + (J) trajectory.Many detailed theoretical models of the I) ( J ) particles' have been proposed since their f i r s t discovery. The experimental status at the p r e sent does not allow us to tell which one (or perhaps none) of these models is correct. The underlying philosophy of the present work is to commit ourselves to no specific model, but to assume that $(3.7) i s a Regge recurrence (or a daughter r ecurrence) of J (3.1), and to study the consequences of this one assumption. Besides the high m a s s e s of the resonances, one obvious feature of the Regge trajectory associated with the 7) ( J ) p a rticles is that it is unusually flat. Assuming that the I)(3.7) is associated with the next Regge r ecurrence of J(3.1), the slope i s about $.It is quite interesting that a comparably flat trajectory h a s already been observed in a most well-known process, namely, proton-proton elastic scattering a t large angles.' Consistent with this observation, a recent p r e c i s e fit? to all the nondiffractive pp data indicates that two traject o r i e s a r e needed, one with a conventional slope, which dominates a t small momentum transfers, and another with a much smaller slope, which dominates a t l a r g e momentum transfers.It is tempting to identify the $ ( J ) particles a s bound states on the flat trajectory which dominates a t l a r g e momentum transfer in pp scattering.One additional feature of pp scattering could b e consistent with this identification: The differential c r o s s section at l a r g e angles i s several o r d e r s of magnitude below that a t smaller angles. Thus, the flat trajectory may b e much m o r e weakly coupled to pp than the conventional ( p , w) trajectory. This, in turn, would be consistent with the narrow widths of the 7) (J) particles. We will s e e that the shape of the $ ( J ) trajectory matches very well with the shape of the t r ajectory which dominates in large-angle pp elastic scattering. However, the present study indic a t e s that it is possible that the latter trajectory is a broad-width degenerate partner of the $ ( J ) .The intriguing aspect of this possibility i s that there exists exchange degeneracy involving the $ ( J ) and a trajectory which couples more strongly t o pp.T o explore these ideas quantitatively, one must extrapolate the pp data f r o m the scattering region into the resonance region. T h e r e i s no modelindependent way of doing this. However, since dual models have crossing and analyticity built in, they offer a very natural tool for such purposes. Unfortunately, the Veneziano model falls off too f a s t a t large angles to b e phenomenologically useful. A generalization of the Veneziano model, on the other hand, h a s been shown3 to provide an excellent framework for f i t s to pp data. In addition, it is superior to a single-effective-trajectory analysis. We will, therefore, again use t h i s amplitude for the p...

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

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We describe the status of our effort to realize a first neutrino factory and the progress made in understanding the problems associated with the collection and cooling of muons towards that end. We summarize the physics that can be done with neutrino factories as well as with intense cold beams of muons. The physics potential of muon colliders is reviewed, both as Higgs factories and compact highenergy lepton colliders. The status and time scale of our research and development effort is reviewed as well as the latest designs in cooling channels including the promise of ring coolers in achieving longitudinal and transverse cooling simultaneously. We detail the efforts being made to mount an international cooling experiment to demonstrate the ionization cooling of muons.