The Advanced Photoinjector Experiment (APEX) at the Lawrence Berkeley National Laboratory is dedicated to the development of a high-brightness high-repetition rate (MHz-class) electron injector for x-ray free-electron laser (FEL) and other applications where high repetition rates and high brightness are simultaneously required. The injector is based on a new concept rf gun utilizing a normal-conducting (NC) cavity resonating in the VHF band at 186 MHz, and operating in continuous wave (cw) mode in conjunction with high quantum efficiency photocathodes capable of delivering the required charge at MHz repetition rates with available laser technology. The APEX activities are staged in three phases. In phase 0, the NC cw gun is built and tested to demonstrate the major milestones to validate the gun design and performance. Also, starting in phase 0 and continuing in phase I, different photocathodes are tested at the gun energy and at full repetition rate for validating candidate materials to operate in a high-repetition rate FEL. In phase II, a room-temperature pulsed linac is added for accelerating the beam at several tens of MeV to reduce space charge effects and allow the measurement of the brightness of the beam from the gun when integrated in an injector scheme. The installation of the phase 0 beam line and the commissioning of the VHF gun are completed, phase I components are under fabrication, and initial design and specification of components and layout for phase II are under way. This paper presents the phase 0 commissioning results with emphasis on the experimental milestones that have successfully demonstrated the APEX gun capability of operating at the required performance.

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Abstract. The status is presented of the laser wakefield acceleration research at the 1'OASIS laboratory of the Center for Beam Physics at LBNL. Experiments have been performed on laser driven production of relativistic electron beams from plasmas using a high repetition rate (10 Hz), high power (10 TW) Tksapphire (0.8 jim) laser system. Large amplitude plasma waves have been excited in the self-modulated laser wakefield regime by tightly focusing (spot diameter 8 urn) a single high power (< 10 TW), ultrashort (> 50 fs) laser pulse onto a high density (> 10 19 cm" 3 ) pulsed gasjet (length 1.2 mm). Nuclear activation measurements in lead and copper targets indicate the production of electrons with energy in excess of 25 MeV. This result was confirmed by electron distribution measurements using a bending magnet spectrometer. Progress on implementing the colliding pulse laser injection method is also presented. This method is expected to produce low emittance (< ITT mm-mrad), low energy spread (< 1%), ultrashort (fs), 40 MeV electron bunches containing 10 7 electrons/bunch.

A one meter long plasma source has been developed for studies at the Stanford Linear Accelerator Center (SLAC) of plasma wakefield excitation by a 30 GeV electron beam in an extended plasma column. The plasma is formed by ionization of a Li-vapor with an ArF EXCIMER laser (193 nm). The Li-vapor is produced in a heat pipe oven which will be installed in the electron beam transport line. Through control of the oven temperature, neutral vapor densities reaching 2 £ 10 15 cm ¡ 3 are produced. We report the details of the oven construction and temperature profile measurements with and without Lithium vapor. In the experiment, the EXCIMER laser will be located about 15 m away from the plasma source. Beams produced by EXCIMER lasers operating with a stable resonator cavity are unsuitable due to the large number of modes present in such beams. A significant reduction of the modal content has been obtained through the use of an unstable resonator design. Results of the implementation of this cavity configuration on the propagation characteristics of the EXCIMER beam will be presented, including the design of the final telescope for spot size reduction.

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