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Expressions for the threshold current of multipass beam breakup in recirculating linacs from single cavity models

Description: We investigate multipass beam breakup (BBU) in a recirculating linear accelerator in the framework of a single cavity model. We present expressions for the beam breakup threshold current for various situations derived from a perturbative solution of BBU equations. These formulae should serve as a guide to understand the BBU phenomenon for a particular system and also as a tool to estimate the BBU threshold current quickly. Many of the results presented are more general than previous considerations because they include the effects of coupling between the two transverse polarizations in each dipole higher order mode.
Date: October 1, 2005
Creator: Yunn, Byung C.
Partner: UNT Libraries Government Documents Department

Beam Breakup in Recirculating Linacs

Description: In general, a recirculation path length in a recirculating accelerator has to be an integer multiple of RF wavelength if recirculations are all in the same direction. However, it is not necessary to require such a relation to be satisfied with respect to the bunching frequency, when the bunch repetition rate is different from the RF frequency. An analytic model of multipass beam breakup (BBU) in recirculating linacs studied by Bisognano and Gluckstern has been generalized to include the case of a subharmonic bunching scheme in the operation of such linacs.
Date: May 1, 1991
Creator: Yunn, Byung
Partner: UNT Libraries Government Documents Department

The Loss Parameters for Very Short Bunches

Description: Semi-empirical formulas for the transverse and longitudinal loss factors generated by cavity and step discontinuities are given in the limit of short bunch length.The parametric transition between the cavity and step approximations is considered.The differences between the impedances offered by periodic structures and isolated single cavities are also discussed.
Date: June 1, 1988
Creator: Yunn, Byung; Bisognano, Joseph & Heifets, Sam
Partner: UNT Libraries Government Documents Department

A High Peak Current Source for the CEBAF Injector

Description: The CEBAF accelerator can drive high power IR and UV FELs, if a high peak current source is added to the existing front end. We present a design for a high peak current injector which is compatible with simultaneous operation of the accelerator for cw nulear physics (NP) beam. The high peak current injector provides 60 A peak current in 2 psec long bunches carrying 120 pC charge at 7.485 MHz. At 10 MeV that beam is combined with 5 MeV NP beam (0.13pC, 2 psec long bunches at 1497 MHz) in an energy combination chicane for simultaneous acceleration in the injector linac. The modifications to the low-energy NP transport are described. Results of optical and beam dynamics calculations for both high peak current and NP beams in combined operation are presented.
Date: July 1, 1992
Creator: Yunn, Byung; Sinclair, Charles; Krafft, Geoffrey & Liger, Philippe
Partner: UNT Libraries Government Documents Department

Design Considerations for Simultaneous FEL and Nuclear Physics Operation at CEBAF

Description: As conceived in a recent design study, electron beams of quite distinct character would be provided for nuclear physics experiments and FEL wigglers at CEBAF. When full nuclear physics operation begins, coordination between these two programs becomes critical. FEL operation requires electron bunches carrying charge of 120 pC at repetition rates of 2.5 and 7.5 MHz, whereas the nuclear physics users need a relatively small charge per bunch, ~ 0.13 pC, but at a repetition rate of 1.5 GHz. To allow maximal operation of the FEL facility without interfering with CEBAF's primary mission of conducting nuclear physics research, the principal mode of operation should accelerate and deliver the two disparate beams simultaneously with negligible degradation of beam quality. Various RF power, RF control, wakefield, and beam transport questions that are encountered in designing for concurrent operation are discussed.
Date: August 1, 1991
Creator: Yunn, Byung; Douglas, David; Neuffer, David; Krafft, Geoffrey; Bisognano, Joseph & Simrock, Stefan
Partner: UNT Libraries Government Documents Department

Automated measurement of cavity frequency and cavity tuning at CEBAF

Description: We propose a method here which allows the measurement of the cavity resonance frequency in a frequency range up to {plus_minus}5 kHz from the operating frequency. This is achieved by phase modulation of the incident signal with noise to drive the cavity with a broad band spectrum. The cavity resonance frequency can then be determined from the response signal of the field probe, which has a narrow frequency spectrum due to the high loaded Q of the cavity of 6.6{times}10{sup 6}, corresponding to a cavity bandwidth of 125 Hz.
Date: June 1, 1993
Creator: Li, Rui; Simrock, S. N. & Yunn, Byung C.
Partner: UNT Libraries Government Documents Department

Scaling of Wakefield Effects in Recirculating Linacs

Description: Expressions for the induced energy spread and emittance degradation of a single bunch due to the longitudinal and transverse impedance of rf cavities at the end of a linac structure are presented. Scaling of the formulae with rf frequency is derived. Scaling of the threshold current for the multibunch, multipass beam breakup (BBU) instability in recirculating linacs with accelerator and beam parameters is also derived.
Date: June 1, 2001
Creator: Merminga, Lia; Neil, George R.; Yunn, Byung C. & Bisognano, Joseph J.
Partner: UNT Libraries Government Documents Department

Transverse Beam Break-Up Study of the SNS SC Linac

Description: Numerical simulation indicates that cumulative beam breakup (BBU) instability is not a concern to SNS SC linac. First, simulation is carried out for CW operation mode where the driving harmonics are those with frequency multiples of bunch frequency 402.5 MHz. Even when the median HOM frequency is exactly on resonance with multiples of bunch frequency of 402.5 MHz, the cavity-to-cavity HOM frequency spread can ensure operation of linac. Second, in the case of pulsed operation mode, additional driving harmonics of 1 MHz and 60 Hz are added on top of those of CW mode. The shunt impedance of these additional modes is relatively small. BBU is not a concern also for pulsed mode operation, as is verified for a few most dangerous modes. More systematic analysis of BBU of pulsed mode operation is done by Sundelin et al [1] and presented at this conference.
Date: June 1, 2001
Creator: Jeon, D.; Wei, J.; Merminga, Lia; Krafft, Geoffrey; Yunn, Byung; Sundelin, Ron et al.
Partner: UNT Libraries Government Documents Department

Status Report on the CEBAF IR and UV FELs

Description: The CEBAF five pass recirculating, superconducting linac, being developed as a high power electron source for nuclear physics, is also an ideal FEL driver.The 45 MeV front end linac is presently operational with a CW (low peak current) nuclear physics gun and has met all CEBAF performance specifications including low emittance and energy spread (< 1 * 10^-4). Progress will be reported in commissioning.This experience leads to predictions of excellent FEL performance.Initial designs reported last year have been advanced.Using the output of a high charge DC photoemission gun under development with a 6 cm period wiggler produces kilowatt output powers in the 3.6 to 17 micrometer range in the fundamental.Third harmonic operation extends IR performance down to 1.2 micrometer.Beam at energies up to 400 MeV from the first full CEBAF linac will interact in a similar but longer wiggler to yield kilowatt UV light production at wavelengths as short as 0.15 micrometers.Full power FEL
Date: July 1, 1993
Creator: Leemann, Christoph; Bisognano, Joseph; Douglas, David; Harwood, Leigh; Krafft, Geoffrey; Liger, Philippe et al.
Partner: UNT Libraries Government Documents Department

Use of the CEBAF Accelerator for IR and UV Free Electron Lasers

Description: The CEBAF superconducting linac is capable of accelerating electron beams suitable for driving high-power free-electron lasers. The 45 MeV injector linac with a 6 cm period wiggler can produce kilowatt output powers of infrared light (3.6-17 micrometer), while the 400 MeV north linac can produce ultraviolet light (~200 nm) at similar powers. The FELs require the addition of a high-peak intensity electron source (~ 60 A peak current) and extraction beam lines to wigglers with appropriate electron and photon optics. FEL operation is compatible with simultaneous baseline CEBAF nuclear physics operation. A design for a CEBAF-based FEL facility has been developed. The current status of the FEL project is reported.
Date: August 1, 1992
Creator: Yunn, Byung; Sinclair, Charles; Leemann, Christoph; Rode, Claus; Douglas, David; Neuffer, David et al.
Partner: UNT Libraries Government Documents Department

LEIC - A Polarized Low Energy Electron-ion Collider at Jefferson Lab

Description: A polarized electron-ion collider is envisioned as the future nuclear science program at JLab beyond the 12 GeV CEBAF. Presently, a medium energy collider (MEIC) is set as an immediate goal with options for a future energy upgrade. A comprehensive design report for MEIC has been released recently. The MEIC facility could also accommodate electron and proton/ion collisions in a low CM energy range, covering proton energies from 10 to 25 GeV and ion energies with a similar magnetic rigidity, for additional science reach. In this paper, we present a conceptual design of this low energy collider, LEIC, showing its luminosity can reach above 10{sup 33} cm{sup -2}s{sup -1}. The design specifies that the large booster of the MEIC is converted to a low energy ion collider ring with an interaction region and an electron cooler integrated into it. The design provides options for either sharing the detector with the MEIC or a dedicated low energy detector in a third collision point, with advantages of either a minimum cost or extra detection parallel to the MEIC operation, respectively. The LEIC could be positioned as the first and low cost phase of a multi-stage approach to realize the full MEIC.
Date: June 1, 2013
Creator: Derbenev, Yaroslav S.; Hutton, Andrew M.; Krafft, Geoffrey A.; Li, Rui; Lin, Fanglei; Morozov, Vasiliy et al.
Partner: UNT Libraries Government Documents Department

The Jefferson Lab Free Electron Laser Program

Description: A Free Electron Laser (FEL) called the IR Demo is operational as a user facility at Thomas Jefferson National Accelerator Facility in Newport News, Virginia, USA. It utilizes a 48 MeV superconducting accelerator that not only accelerates the beam but also recovers about 80% of the electron-beam power that remains after the FEL interaction. Utilizing this recirculation loop the machine has recovered cw average currents up to 5 mA, and has lased cw above 2 kW output at 3.1 microns. It is capable of output in the 1 to 6 micron range and can produce {approx}0.7 ps pulses in a continuous train at {approx}75 MHz. This pulse length has been shown to be nearly optimal for deposition of energy in materials at the surface. Upgrades under construction will extend operation beyond 10 kW average power in the near IR and produce multi-kilowatt levels of power from 0.3 to 25 microns. This talk will cover the performance measurements of this groundbreaking laser, scaling in near-term planned upgrades, and highlight some of the user activities at the facility.
Date: January 1, 2001
Creator: Neil, George R.; Benson, Steve; Biallas, George; Boyce, James; Dillon-Townes, L.A.; Douglas, David et al.
Partner: UNT Libraries Government Documents Department

First Lasing of the Jefferson Lab IR Demo FEL

Description: As reported previously [1], Jefferson Lab is building a free-electron laser capable of generating a continuous wave kilowatt laser beam. The driver-accelerator consists of a superconducting, energy-recovery accelerator. The initial stage of the program was to produce over 100 W of average power with no recirculation. In order to provide maximum gain the initial wavelength was chosen to be 5 mu-m and the initial beam energy was chosen to be 38.5 MeV. On June 17, 1998, the laser produced 155 Watts cw power at the laser output with a 98% reflective output coupler. On July 28th, 311 Watts cw power was obtained using a 90% reflective output coupler. A summary of the commissioning activities to date as well as some novel lasing results will be summarized in this paper. Present work is concentrated on optimizing lasing at 5 mu-m, obtaining lasing at 3 mu-m, and commissioning the recirculation transport in preparation for kilowatt lasing this fall.
Date: May 1, 1999
Creator: Benson, Stephen; Biallas, George; Bohn, Court; Douglas, David; Dylla, H.F.; Evans, R. et al.
Partner: UNT Libraries Government Documents Department