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Limborg-Deprey, C

Publications and source records attributed to Limborg-Deprey, C.

10 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

An X-Band Gun Test Area at SLAC

The X-Band Test Area (XTA) is being assembled in the NLCTA tunnel at SLAC to serve as a test facility for new RF guns. The first gun to be tested will be an upgraded version of the 5.6 cell, 200 MV/m peak field X-band gun designed at SLAC in 2003 for the Compton Scattering experiment run in ASTA. This new version includes some features implemented in 2006 on the LCLS gun such as racetrack couplers, increased mode separation and elliptical irises. These upgrades were developed in collaboration with LLNL since the same gun will be used in an injector for a LLNL Gamma-ray Source. Our beamline includes an X-band acceleration section which takes the electron beam up to 100 MeV and an electron beam measurement station. Other X-Band guns such as the UCLA Hybrid gun will be characterized at our facility.

43 PARTICLE ACCELERATORS↗
DOE OSTI2011

Maximizing Brightness in Photoinjectors

If the laser pulse driving photoinjectors could be arbitrarily shaped, the emittance growth induced by space charge effects could be totally compensated for. In particular, for RF guns the photo-electron distribution leaving the cathode should have a 3D-ellipsoidal shape. The emittance at the end of the injector could be as small as the cathode emittance. We explore how the emittance and the brightness can be optimized for photoinjector based on RF gun depending on the peak current requirements. Techniques available to produce those ideal laser pulse shapes are also discussed. If the laser pulse driving photoinjectors could be arbitrarily shaped, the emittance growth induced by space charge effects could be totally compensated for. In particular, for RF guns, the photo-electron distribution leaving the cathode should be close to a uniform distribution contained in a 3D-ellipsoid contour. For photo-cathodes which have very fast emission times, and assuming a perfectly uniform emitting surface, this could be achieved by shaping the laser in a pulse of constant fluence and limited in space by a 3D-ellipsoid contour. Simulations show that in such conditions, with the standard linear emittance compensation, the emittance at the end of the photo-injector beamline approaches the minimum value imposed by the cathode emittance. Brightness, which is expressed as the ratio of peak current over the product of the two transverse emittance, seems to be maximized for small charges. Numerical simulations also show that for very high charge per bunch (10nC), emittances as small as 2 mm-mrad could be reached by using 3D-ellipsoidal laser pulses in an S-Band gun. The production of 3D-ellipsoidal pulses is very challenging, but seems worthwhile the effort. We briefly discuss some of the present ideas and difficulties of achieving such pulses.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

RF Design of the LCLS Gun

Final dimensions for the LCLS RF gun are described. This gun, referred to as the LCLS gun, is a modified version of the UCLA/BNL/SLAC 1.6 cell S-Band RF gun [1], referred to as the prototype gun. The changes include a larger mode separation (15 MHz for the LCLS gun vs. 3.5 MHz for the prototype gun), a larger radius at the iris between the 2 cells, a reduced surface field on the curvature of the iris between the two cells, Z power coupling, increased cooling channels for operation at 120 Hz, dual rf feed, deformation tuning of the full cell, and field probes in both cells. Temporal shaping of the klystron pulse, to reduce the average power dissipated in the gun, has also been adopted. By increasing the mode separation, the amplitude of the 0-mode electric field on the cathode decreases from 10% of the peak on axis field for the prototype gun to less than 3% for the LCLS gun for the steady state fields. Beam performance is improved as shown by the PARMELA simulations. The gun should be designed to accept a future load lock system. Modifications follow the recommendations of our RF review committee [2]. Files and reference documents are compiled in Section IV.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Wakefield Calculations for Radiation Stopper 1 (RST1)

The main result of this note is that no wakefield mitigation is required for the Radiation Stopper (RST1) in the LCLS injector. The RST1 geometry is not symmetric in the vertical direction, and we derive a slight modification to the diffraction model wake for a cylindrically symmetric (2D) cavity that can be used for this problem. Performing a full 3D MAFIA calculation for the nominal 1 mm (rms) long bunch, we show that the modified diffraction model well describes the wakefields generated in RST1. The results imply an on-axis emittance growth of 0.0075%, well below the 0.5% tolerance threshold. To reach the 0.5% threshold the beam would need to be mis-steered by a large amount - 7 mm - from the axis. One reason that the effect is small is that the beta functions at the RST1 are small.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

Wakefield Computations for the Injector (Part I)

In this document, we report on basic wakefield computations used to establish the impedance budget for the LCLS injector. Systematic comparisons between analytic formulae and results from ABCI are done. Finally, a comparison between 2D and 3D wakefield calculations are given for a cross. The three parts of the document are presented as follows: (1) ABCI computations for a few structures (Flange, Bellows...); (2) Comparison analytic with ABCI runs; and (3) Comparison Cross and Cavity using MAFIA.

43 PARTICLE ACCELERATORS↗
DOE OSTI2010

LCLS Injector Straight-Ahead Spectrometer

The spectrometer design was modified to allow the measurement of uncorrelated energy spread for the nominal lattice. One bunch from every 120 each second would be sent to the straight ahead spectrometer while the transverse cavity is on. The implementation of this 'stealing mode' will not be available for the LCLS commissioning and the early stage of operation. However, the spectrometer was redesigned to retain that option. The energy feedback relies independently on the beam position of the beam in the dispersive section of dogleg 1 (DL1). The main modification of the spectrometer design is the Pole face rotation of 7.5 degrees on both entrance and exit faces. The location and range of operation of the 3 quadrupoles remains unchanged relative to those of the earlier design.

43 PARTICLE ACCELERATORS↗