Results from the experimental testing of the prototype TESLA Test Facility (TTF) RF photoinjector are summarized. Preliminary measurements of the performance of the injector indicate that, with refinement, the design values for the transverse emittances (20 x 20 pi mm-mr) are not unrealistic, with uncompressed transverse emittances of 40 pi mm mr having been obtained under somewhat less ideal circumstances than those simulated. Preliminary pulse length measurements with and without the pulse compressor suggest pulse compression, but further study is required.
The NEPTUNE Laboratory, under construction at UCLA, will be a user facility for exploring concepts useful for advanced accelerators.  The programmatic goal for the laboratory is to inject extremely high quality electron bunches into a laser-driven plasma beat wave accelerator (PBWA)  and explore ideas for extracting a high quality DE/E < 0.1, epsilon_n < 10 pi mm-mrad), high energy (100 MeV) beam from a plasma structure operating at about 1 THz and about 3 GeV/m. The lab will combine an upgraded MARS CO2 laser and the state-of-the-art SATURNUS RF gun and linac.  The new MARS laser will be about 1 TW (100 J, 100 ps), up from 0.2 TW (70 J, 350 ps). This allows for doubling the spot size at the IP and quadrupling the interaction length while still driving gradients of 3 GeV/m. The SATURNUS gun will be upgraded to the Brookhaven 1.6 cell design.  A novel, multi-cell Plane-Wave Transformer (PWT) RF gun is also under development.  A sync-pumped, sub-ps dye laser is available to directly produce ultrashort electron pulses (1/5 of an accelerating bucket). Part of the research program will be devoted to studying pulse compression  and phaselocking techniques at these ultrahigh frequencies and diagnosing microbunches generated by such structures.  Finally, shaped electron pulses will be studied for the electron driven Plasma Wakefield Accelerator (PWFA) concept.
High current CW proton linac accelerators have been recently proposed for a number of applications based on the use of a large flux of spallation neutrons. In this context, an R&D program on an accelerator driven system for nuclear waste transmutation has been recently approved in Italy. Our specific task is to develop, together with the national industry, a design of the high energy part of the proton accelerator, along with prototype development for the most critical components. In this paper we present a revised version of the design proposed at Linac'96, using five cell cavities, rather than the original four cells. This modification, together with a new criterion for using the transit time factor curve for non resonant proton velocities, results in a more modular and efficient design. A 1.6 GeV linac, operated at 25 mA, allows to reach 40 MW beam power. The beam power upgrade is achievable using additional couplers per cavity. (5 References).
The symmetrized 1.6 cell S-band photocathode gun developed by the BNL/SLAC/UCLA collaboration is in operation at the Brookhaven Accelerator Test Facility (ATF). A novel emittance compensation solenoid magnet has also been designed, built and is in operation at the ATF. These two subsystems form an emittance compensated photoinjector used for beam dynamics, advanced acceleration and free electron laser experiments at the ATF. The highest acceleration field achieved on the copper cathode is 150 MV/m, and the guns normal operating field is 130 MV/m. The maximum rf pulse length is 3 mu s. The transverse emittance of the photoelectron beam were measured for various injection parameters. The 1 nC emittance results are presented along with electron bunch length measurements that indicated that at above the 400 pC, space charge bunch lengthening is occurring. The thermal emittance, epsilon_0, of the copper cathode has been measured. (7 References).
The beam dynamics of an integrated S-band RF photoinjector based on the plane wave transformer (PWT) concept, proposed as part of an SBIR collaboration between UCLA and DULY Research, are studied. The design, which calls for an 11.5 cell structure run at a peak accelerating field of 60 MV/m and uses a compact solenoid around the initial 2.5 cells, is based on a recently developed theory of emittance compensation. It calls for matching the beam onto a generalized equilibrium envelope, which produces a beam which diminishes in transverse size monotonically with acceleration. This condition minimizes the emittance, which is 1 mm-rad at Q=1 nC. This design is also scaled to produce nearly identical performance at X-band, giving an injector appropriate to running an FEL at the SLAC NLCTA. These designs are insensitive to RF emittance increase, allowing a wide choice of injection phase, and the option to compress the emitted pulse. (8 References).
This paper presents an experimental study of the transverse beam dynamics of an electron beam in a high-gradient, standing wave linear accelerator. A 3.6 MeV beam from the UCLA RF Photoinjector (SATURNUS) is injected at various phases and rf field amplitudes into the plane wave transformer (PWT) linac (peak acceleration 40 MeV/m), and its transverse dynamics measured by a corrector magnet sweeping method. This method allows us to reconstruct the transverse matrix elements, which are compared to analytical predictions (J.B. Rosenzweig and L. Serafini, Physical Review E 49, 1599 (1994)). The determinant of the experimentally derived matrix is found to be the ratio of the initial to final momentum, verifying the theory, and providing direct evidence of adiabatic damping of transverse trace space. (9 References).
We describe how to achieve minimum transverse emittance in RF photoinjectors by applying theoretical predictions from a fully analytical model of beam dynamics in a split injector. This device consists of a short two cell (full+partial) RF gun followed by a drift and a booster RF linac. Matching the beam in the booster to the invariant envelope, an equilibrium mode of laminar beam flow, is shown to be the basis of emittance correction. Analytical predictions are compared to numerical simulations, finding excellent agreement. We also show how a further improvement of the beam quality can be obtained by matching the beam out of the booster into a Brillouin flow with proper control of the envelope oscillations. If these are actually coherent plasma oscillations in the laminar regime, then the normalized RMS transverse emittance can be even further reduced. (7 References).
While it has been proposed for several years that strongly asymmetric (sigma_x >> sigma_y) beams can be employed in RF photoinjectors to obtain asymmetric emittances for linear collider applications, it is known that the emittances obtained directly from RF photocathode guns are not suitably small for this purpose. Because of this, simulation work has been performed in an attempt to apply the principle of emittance compensation to recover the small and asymmetric emittances after suitable focusing and acceleration of photoinjector beams. In order to guide this difficult three-dimensional analysis, we present an extension of a previous theoretical model of the emittance compensation process in axisymmetric photoinjectors. In the extended model, we first analyze the general quadrupolar oscillations in a symmetric accelerating system, and then proceed to examine a propagation mode under asymmetric focusing. This mode is a generalization of the previously analyzed axisymmetric invariant envelope, allowing an optimization of the compensation process. Design philosophies, including rf cavity considerations, are included in the discussion.
For long term stability analysis, time variation of tunes is important. We have proposed and tested a technique for measuring the magnitude of this variation. This was made possible by using tune extraction algorithms that require small number of turns thus giving an instantaneous tune of the machine. In this paper we demonstrate the measured effect of the tune modulation with 60 Hz power supplies ripple, power line interference from the SLAC linac operating at 30 Hz repetition rate, and non-periodic variation. (8 References).
The frequency map analysis of a Hamiltonian system recently introduced to accelerators physics in combination with turn-by-turn phase space measurements opens new experimental opportunities for studying nonlinear dynamic in storage rings. In this paper we report on the experimental program at SPEAR having the goal of measuring the frequency map of the machine. In this paper we discuss the accuracy of the instantaneous tune extraction from experimental data and demonstrate the possibility of frequency map measurement. (7 References).
We develop a novel photoelectron linear accelerator using a plane wave transformer (PWT) design. In this design, the input RF power is coupled to the accelerating cavities via a large concentric manifold cavity. The scheme makes possible very strong coupling between the accelerating cells, and relaxes manufacturing tolerances. The compact photoelectron linac integrates a photocathode directly into a PWT linac structure, and eliminates the drift space between a photoinjector and the linac which would otherwise lengthen the electron bunches. Using an emittance compensation scheme, the PWT photoelectron linac produces a high-brightness beam. We have demonstrated by simulations the feasibility of a 20 MeV PWT photoelectron linac design with a set of eleven iris-loaded disks suspended and cooled by four water tubes inside a large cylindrical tank. (5 References).
When a tightly focused electron beam propagates
in an underdense plasma (beam density greater than the
plasma electron density,
), the plasma electrons
are expelled radially by the space-charge of the beam,
forming an ion channel which in turn provides a
uniform, linear focusing force on the beam. When the
beam is short (
), making it suitable as a driver
for plasma wake-field acceleration (PWFA),
requirements on the beam properties (current, eminence
and energy) to achieve ion channel self-focusing become
more difficult to satisfy. If the beam is initially
matched to the focusing gradient, that is, the
is initially equal to
are the rms transverse beam radius and emittance, the
transverse distribution in the body of the beam is nearly
stationary, while that near the head expands radially. The
loss in beam density near the head associated with this
expansion further retards the plasma electron response
and causes the pinch point (where sufficient focusing
gradient develops) to move backwards in the beam
frame. The fast relaxation distance for these beam head
dynamics is roughly
, or 5 cm for our experimental
conditions, which is less than half of the plasma length,
The present experiments were motivated by the
proposed use of the underdense regime as the basis for a
PWFA (the blowout regime) which is very attractive
in terms of drive and accelerating beam guiding, in that
when a plasma-electron free ion column is formed, the
focusing force in this region is linear and the
acceleration gradient is independent of radius.