Synchrotron Radiation Center
http://digital.library.wisc.edu/1793/48677
2019-10-13T23:28:19ZMultipole specifications for insertion devices in LF15
http://digital.library.wisc.edu/1793/79196
Multipole specifications for insertion devices in LF15
Bosch, Robert A.
Imperfections in the magnetic field of an insertion device affect the electron storage ring, thereby impacting the users of all beamlines. To minimize adverse effects, the manufacturer is required to meet specifications on the multipoles of the longitudinally integrated magnetic field. For 800-MeV ring operation in the LF15 low-emittance lattice, specifications are obtained for insertion devices located in the long straight sections and the short straight sections.
This is a 9-page document.
2005-04-26T00:00:00ZLongitudinal wake of a suddenly accelerated electron bunch
http://digital.library.wisc.edu/1793/79195
Longitudinal wake of a suddenly accelerated electron bunch
Bosch, Robert A.
We consider the longitudinal wake of an electron bunch that is suddenly accelerated. This wake approximates the edge-radiation wake of an electron exiting a bending magnet, the wake of an electron accelerated in a high-field gradient, and the wake of forward transition radiation. The on-axis wake is large within the radiation formation zone, where it provides resistive impedance that decelerates the bunch electrons. A comparison with the computed wake downstream of a bending magnet yields good agreement. For schemes in which a bunch produced by laser-plasma acceleration drives a VUV or xray FEL, the wake causes large energy losses that may spoil the FEL process.
This is a 8-page document.
2007-02-23T00:00:00ZOff-energy injection of Aladdin
http://digital.library.wisc.edu/1793/79194
Off-energy injection of Aladdin
Bosch, Robert A.
Injection of the Aladdin 800-MeV electron storage ring is performed at a low ring energy of 108 MeV, where the stacking time period of 0.8 s is much smaller than the radiation damping time. Electrons are injected from inside the ring at a location where the horizontal dispersion is large, using an injected beam whose energy is 0.7 MeV lower than the equilibrium energy of the storage ring. We consider the initial horizontal offset of each injected electron to be the sum of an energy (“synchrotron”) oscillation and a betatron oscillation, and assume that the oscillations of different electrons decohere in the stacking time period. This model correctly predicts the successful stacking for off-energy injection at a location with large horizontal dispersion, and the poor stacking that occurs when injecting into a lattice whose horizontal dispersion is small at the injection location. The model also predicts that the maximum stacked current may be increased by nearly a factor of three if a 200-MeV linac is used for injection.
This is a 13-page document.
2007-07-19T00:00:00ZTwo-stage bunch compression with resistive impedance approximation of coherent synchrotron radiation
http://digital.library.wisc.edu/1793/79193
Two-stage bunch compression with resistive impedance approximation of coherent synchrotron radiation
Bosch, Robert A.
Two-stage bunch compression, where each stage compresses a chirped beam in a magnetic chicane, may be utilized in the design of a driver for a free-electron laser (FEL). For the high currents required of an FEL, compressor performance may be adversely affected by the wake of coherent synchrotron radiation (CSR). When the CSR wake is dominated by edge radiation downstream of the chicane magnets, it may be approximated as the wake from resistive impedance. For a typical bunch-compressor chicane magnet, this approximation applies for wavelengths exceeding 1 micron. For a preliminary two-stage bunch compressor design that compresses by a factor of twenty, longitudinal tracking with resistive impedance approximates the longitudinal phase space obtained from three-dimensional tracking with computed CSR. By approximating CSR as resistive impedance, longitudinal CSR effects may be studied analytically, and tracking with “CSR” may be performed without modeling the transverse dynamics. With this approximation, we develop formulas that describe when part of the bunch becomes upright in phase space, producing a large current spike and energy depression. The formulas correctly predict good performance when Gaussian bunches with peak current of 50 A and rms bunch length zσ of 1 mm are compressed, and that the bunch tail becomes upright in phase space when parabolic bunches with peak current of 50 A and zσ of 0.4 mm are compressed. The formulas also show how the compressor design may be modified to prevent the upright bunch behavior with the shorter bunch length. We obtain analytic formulas for the jitter in the bunch arrival time resulting from bunch-to-bunch variation in current, energy and chirp. The formulas determine the permitted variations that give arrival-time jitter less than 15 fs in the preliminary design. Bunch-to bunch peak current variation should be less than 6.5 A, which is 13% of the peak current. The bunch-to-bunch energy variation should be less than 5.6 keV, which is 5105.4−× times the bunch energy when entering the compressor. The bunch-to-bunch chirp variation should be less than 7103.3× eV/m, which is 3% of the design chirp. Analytic small-signal gain formulas for microbunching describe the output current and energy modulations that result from given input current and energy modulations, including the suppression at short wavelengths by the bunch’s energy spread. Large output modulations of the bunch current may be caused by relatively small input energy modulations. Heating the uncompressed bunches by a laser heater so that the energy spread is 5-10 keV is predicted to suppress microbunching for initial wavelengths less than 100 microns. In this case, initial energy modulations at wavelengths around 100 microns should be smaller than ~500 eV to prevent large current modulations in the compressed bunches.
This is a 66-page document.
2007-06-08T00:00:00Z