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.

A two-year study of recirculating induction heavy ion accelerators as low-cost driver for inertial-fusion energy applications was recently completed. The projected cost of a 4 MJ accelerator was estimated to be about $500 M (million) and the efficiency was estimated to be 35%. The principal technology issues include energy recovery of the ramped dipole magnets, which is achieved through use of ringing inductive/capacitive circuits, and high repetition rates of the induction cell pulsers, which is accomplished through arrays of field effect transistor (FET) switches. Principal physics issues identified include minimization of particle loss from interactions with the background gas, and more demanding emittance growth and centroid control requirements associated with the propagation of space-charge-dominated beams around bends and over large path lengths. In addition, instabilities such as the longitudinal resistive instability, beam-breakup instability and betatron-orbit instability were found to be controllable with careful design.

A new technique was developed to measure the transverse interaction impedance of the DARHT-2 induction cells, designed to accelerate a 2-4 kA, 2 µ sec electron beam pulse. An extensive campaign to minimize the transverse resistive impedance of these massive metglas-filled structures lead to a design with thin ferrite tiles in the form of a ring placed along one wall of the radial line connecting the pulseline feeds to the accelerator gap. This ferrite ring heavily damped all transverse modes. To measure the broadband m=1 impedance, one cell is excited by a matched twinlead on the axis of the beamtube. The ratio of the radial RF magnetic field in the accelerator gap to the azimuthal RF magnetic field at the beamtube wall (far away from the gap) determines the complex impedance, as explained in the paper. This technique is much simpler than the TSD approach for these very large bore systems. It also covers the full frequency band including the reactive impedance at low frequency related to the "image displacement instability". Results with the 10 inch diameter bore "standard cell" indicate a peak resistive impedance of 280 ohms per meter around 575 MHz (Q = 6).

We report on progress in the preparation of the 2 MV Injector at LBNL as the front-end of Elise, and as a multi-purpose experimental facility for Heavy Ion Fusion beam dynamics studies.Recent advances on the performance and understanding of the injector are described, and some of the on-going experimental activities are summarized. 1.

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