P. Davis

Initial measurements of the UCLA rf photoinjector

The 1.5 cell standing wave rf photoinjector has been operated for the past several months using a copper cathode. The photoinjector drive laser produces sub 2 ps pulses of UV (A = 266 nm) light with up to 200 p~J/pulse which generates up to 3 nC of charge. The emittance of the photoinjector was measured as a function of charge, rf launching phase, and peak accelerating field. Also, the quantum efficiency and pulse lengths of the laser beam and the electron beam were measured.

Initial operation of the UCLA plane wave transformer (PWT) linac

We report on the initial operation of a novel compact rf linac-the plane wave transformer (PWT). The PWT is a 42 cm long, 8 cell standing-wave structure, operated at S-band, in a /spl pi/-mode. We present the properties of this linac at rf power levels from 4 MW to 8 MW and beam energy from 7 MeV to 10 MeV, measured initially using both dark current and photo-electrons. Some technical issues associated with the operation are discussed. Future improvements of the PWT, using a modified design, are also studied.

Quantum efficiency measurements of a copper photocathode in an RF electron gun

A 4.5 MeV photocathode RF gun has been commissioned at UCLA. A photo-injector drive laser produces sub 2 ps pulses of UV (/spl lambda/=266 nm) light with up to 200 /spl mu/J/pulse, and illuminates a copper cathode. The photoelectrons are accelerated to an energy of 3.5 MeV within the gun. The electron beam charge is measured as a function of laser energy using an integrating current transformer (ICT). We present measurements of quantum efficiency as a function of laser polarization for injection angles of 2/spl deg/ and 70/spl deg/ with respect to the cathode normal. At 70/spl deg/ incidence a 50% enhancement in quantum efficiency (>10/sup -4/) is observed for p-polarized light over s-polarized light.<<ETX>>

Transverse dynamics of a short, relativistic electron bunch in a plasma lens

Dynamic focusing of a 3.8 MeV, 25 ps long, full width at half‐maximum (FWHM), electron bunch by an overdense (np≫nb, where np and nb are the plasma and bunch densities, respectively) plasma lens has been studied experimentally. The plasma focused the bunch from an initial transverse size of approximately 2.4 mm (FWHM) to about 0.5 mm, 21 cm downstream of the plasma. The sharp rise time (7 ps 10%–90%) of the electron bunch, excites a large‐amplitude (<1 MeV/m) plasma wave (plasma wake field). The peak focusing force of the lens is partly (60%) due to the beam‐generated, azimuthal magnetic field and partly (40%) due to the radial component of the electrostatic wake field.

Emittance measurements of the 4.5 MeV UCLA RF photoinjector

The 1.5 cell RF photoinjector has been operated for the past several months using a copper cathode illuminated by 4 ps long pulses of UV (246 nm light, with a variable energy of between 0 to 300 /spl mu/J. This typically produces up to 3 nC of charge per bunch. Because space charge forces dominate the electron beam transport a pepper pot measurement system is used to measure the emittance. The emittance is measured as a function of charge, peak accelerating field, laser spot size and initial phase with respect to the RF field. This is accomplished with an automated control and data acquisition system which can measure single shot emittances at a rate of 5 Hz developed at UCLA. The experimental results obtained are then compared with theory and simulations.<<ETX>>

Initial operation and beam characteristics of the UCLA S-band RF photo-injector

The UCLA RF photo-injector system has been commissioned. All of the sub-components such as the high power RF, pico-second laser, RF photo-injector cavity, diagnostics, and supporting hardware have been tested and are operational. We briefly discuss the performance of the various components since the details of each subsystem are very lengthy. The laser delivers a sub 4 ps pulse containing 0-300 /spl mu/J of energy per pulse. The photo-injector produces 0-3 nC per bunch with an RF induced emittance of 1.5 /spl pi/(mm-mrad).<<ETX>>

Streak camera measurements of electron bunch length from a copper photocathode in an RF gun

Short laser pulses (sub 2 ps) of UV (/spl lambda/=266 nm) light with 200 /spl mu/J/pulse are used to produce electrons from a copper cathode in an RF gun. The electron bunch length is measured by streaking the Cerenkov radiation (/spl lambda/=530 nm) from a thin (250 /spl mu/m) fused silica etalon. Streaks for both 0/spl deg/ and 70/spl deg/ laser incidence angles with respect to the cathode normal are presented with a temporal resolution of 3.6 ps. The shortest electron bunch length measured was 9 ps.<<ETX>>

The UCLA IR FEL project

Abstract A 10.6 μm free electron laser (FEL) operating in the high gain regime is under construction of UCLA. FEL physics significant to future short wavelength operation will be emphasized including optical guiding, superradiance, saturation and self-amplified spontaneous emission (SASE). A 5 MeV rf photocathode gun illuminated by a UV laser will supply a high brightness electron beam which will be injected into a plane wave transformer (PWT) linac for acceleration to 20 MeV. Recent measurements of the gun emittance as well as quantum efficiency are presented. The undulator is of modified hybrid design producing ∼7.5 kG peak field on axis with 5 mm gap spacing and 1.5 cm pole period. Simulation results which include three-dimensional effects are furnished. The present status and future plans of the project are summarized.

Experimental demonstration of plasma lens focusing

The magnetic self-focusing of a relativistic electron beam propagating through a plasma is demonstrated. The plasma which is produced by an RF discharge in a glass tube with no externally applied magnetic field focuses a 3.5 MeV, 25 ps (FWHM) long electron beam from an initial size of 2.5 mm (FWHM) to about 0.5 mm (FWHM) at a focal length of 18 cm.<<ETX>>

The UCLA compact infrared free-electron laser

Abstract We present the status of a compact infrared free-electron laser, driven by a 20 MeV, S-band linac with a photoinjector. The 60 cm long hybrid undulator has a 1.5 period and a field on axis of 7.3 kG. The FEL will operate at 10.6 μm as a high-gain amplifier, to study the high-gain FEL regime including the effects of self amplified spontaneous emission, optical guiding and saturation. The linac is the prototype of the plane-wave transformer. TDA simulation of the FEL shows a gain length of 10 cm, and a saturation power of 50 MW.