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On Asymmetric Collisions with Large Disruption Parameters

Description: Collisions between a weak electron bunch and a strong positron bunch are studied within a flat beam model. Electrons are tracked through the transverse space charge field of the positron bunch, and it is shown that positrons in a storage ring may remain stable after asymmetric collisions with a weak electron bunch in spite of large values of the electron disruption parameter. The plasma oscillations that effect collisions with large disruption parameters may be suppressed by properly matching the electrons.
Date: June 1, 1990
Creator: Krafft, Geoffrey; Fripp, Michael & Heifets, Sam
Partner: UNT Libraries Government Documents Department

Emittance Growth in TESLA

Description: The results of collective simulation of a typical TeV Energy Superconducting Linear Accelerator (TESLA) are reported. Because of accelerating gradient is low and the accelerator is long compared to other TeV colliders, betatron phase mixing must be suppressed along with the usual sources of emittance growth. Including single bunch effects, alignment tolerances consistent with reasonable emittance growth are given. When such tolerances are achieved, multibunch effects do not cause excessive effective emittance growth. In addition, longitudinal multibunch effects are discussed.
Date: May 1, 1991
Creator: Krafft, Geoffrey & Bisognano, Joseph
Partner: UNT Libraries Government Documents Department

Two Dimensional Simulations of Multipass Beam Breakup

Description: A vectorized two dimensional beam breakup code, TDBBU, is used to simulate bunch dynamics in recirculating accelerators. First, the code is briefly described, including effects needed to accurately model the CEBAF accelerator. Next, various code test are sketched. Finally, the multipass beam breakup threshold current is determined to be from 10-20 mA for the CEBAF accelerator, a result in agreement with other calculations of the threshold current.
Date: March 1, 1987
Creator: Krafft, Geoffrey & Bisognano, Joseph
Partner: UNT Libraries Government Documents Department

Simulations of High Disruption Colliding Beams

Description: Recent B-factory proposals taht use a linac beam colliding with the beam from a storage ring to achieve high luminosities (L > 10^34 cm^-2 sec^-1) result in very high disruption of the linac beam.The effects of such high disruption have been studied using the relativistic, 3-D code SWARM.We discuss the assumptions, parameters, and results of a series of runs that model such collisions.Regimes of high beam loss and methods to avoid them are also discussed.
Date: September 1, 1990
Creator: Krafft, Geoffrey & Boyce, James
Partner: UNT Libraries Government Documents Department

Multipass Beam Breakup in the CEBAF Superconducting Linac.

Description: Beam breakup (BBU) instabilities in superconducting linacs are a significant issue due to the potentially high Q values of the cavity higher order modes (HOMs). The CEBAF accelerator, which employs high CW current and 5- pass recirculation through two superconducting linacs, poses unique instability problems. An experimental investigation of multipass BBU along with energy recovery has been completed using a single recirculation through the CEBAF injector linac. Experimental results are compared with computer simulation of multipass BBU.
Date: June 1, 1986
Creator: Krafft, Geoffrey & Bisognano, Joseph
Partner: UNT Libraries Government Documents Department

Linac Optics for Energy Recovery Linac

Description: Several possible scenarios of Energy Recovery Linac (ERL) beam optics design are investigated to support the low emittance high current CW electron beam needed to drive a new ERL based X-ray Source. It is shown by numerical simulations that sufficiently high multipass beam break-up (BBU) threshold current can be achieved in a straightforward one-pass one-linac ERL scenario. A simple guideline for choosing optimal linac and recirculating transport line optics is suggested to realize best possible BBU threshold current.
Date: June 1, 2001
Creator: Bazarov, Ivan; Krafft, Geoffrey & Merminga, Lia
Partner: UNT Libraries Government Documents Department

Longitudinal Phase Space Manipulation in Energy Recovering Linac-Driven Free-Electron Lasers

Description: Energy recovering [1] an electron beam after it has participated in a free-electron laser (FEL) interaction can be quite challenging because of the substantial FEL-induced energy spread and the energy anti-damping that occurs during deceleration. In the Jefferson Lab infrared FEL driver-accelerator, such an energy recovery scheme was implemented by properly matching the longitudinal phase space throughout the recirculation transport by employing the so-called energy compression scheme [2]- In the present paper, after presenting a single-particle dynamics approach of the method used to energy-recover the electron beam, we report on experimental validation of the method obtained by measurements of the so-called--compression efficiency--and--momentum compaction--lattice transfer maps at different locations in the recirculation transport line. We also compare these measurements with numerical tracking simulations.
Date: February 1, 2003
Creator: Piot, Philippe; Douglas, David & Krafft, Geoffrey
Partner: UNT Libraries Government Documents Department

Diagnostics for Recirculating and Energy Recovery Linacs

Description: In this paper, the electron beam diagnostics developed for recirculating electron accelerators will be reviewed. The main novelties in dealing with such accelerators are: to have sufficient information and control possibilities for the longitudinal phase space, to have means to accurately set the recirculation path length, and to have a means to distinguish the beam passes on measurements of position in the linac proper. The solutions to these problems obtained at Jefferson Laboratory and elsewhere will be discussed. In addition, more standard instrumentation (profiling and emittance measurements) will be reviewed in the context of recirculating linacs. Finally, and looking forward, electron beam diagnostics for applications to high current energy recovered linacs will be discussed.
Date: May 1, 2002
Creator: Krafft, Geoffrey & Denard, Jean-Claude
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

Operation of the RF Controls in the CEBAF Injector

Description: The CEBAF injector has produced its first relativistic beam with two superconducting cavities.Six RF control modules are used to control amplitude and phase in the chopper cavities, the buncher, the capture section, and the two superconducting cavities.In this paper the required stability and actual performance of the modules are discussed.For the superconducting cavity control, performance is consistent with energy stability of ~ 10^-4.
Date: June 1, 1990
Creator: Sinclair, Charles; Krafft, Geoffrey; Hovater, J.; Fugitt, Jock & Simrock, Stefan
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

The CEBAF Injector RF Distribution and Bunch-Length Measurement System

Description: The CEBAF injector includes 22 RF control modules which require an intermediate frequency (IF) of 70 MHz and a local oscillator (LO) frequency of 1427 MHz. A STAR network distributes the signals over coaxial cables that are of equal length so that all systems see the same phase drifts due to ambient temperature changes. To obtain the signal levels required by the individual RF control modules, amplifiers are used in both the LO and IF distribution. Temperature-dependent phase drifts associated with the amplifiers are minimized by a phase-lock loop around each amplifier. In addition to the frequency distributio, an automated beam bunch-length measurement is incorporated in the chopper cavities' intermediate frequency. This allows the phase of the chopper cavities to be modulated and bunch-length measurements to be performed on the electron beam downstream.
Date: August 1, 1992
Creator: Bowling, Bruce; Krafft, Geoffrey; Hovater, J.; Crofford, Mark & Abbott, Richard
Partner: UNT Libraries Government Documents Department

JEMMRLA - Electron Model of a Muon RLA with Multi-pass Arcs

Description: We propose a demonstration experiment for a new concept of a 'dogbone' RLA with multi-pass return arcs -- JEMMRLA (Jlab Electron Model of Muon RLA). Such an RLA with linear-field multi-pass arcs was introduced for rapid acceleration of muons for the next generation of Muon Facilities. It allows for efficient use of expensive RF while the multi-pass arc design based on linear combined-function magnets exhibits a number of advantages over separate-arc or pulsed-arc designs. Here we describe a test of this concept by scaling a GeV scale muon design for electrons. Scaling muon momenta by the muon-to-electron mass ratio leads to a scheme, in which a 4.5 MeV electron beam is injected in the middle of a 3 MeV/pass linac with two double-pass return arcs and is accelerated to 18 MeV in 4.5 passes. All spatial dimensions including the orbit distortion are scaled by a factor of 7.5, which arises from scaling the 200 MHz muon RF to a readily available 1.5 GHz. The hardware requirements are not very demanding making it straightforward to implement. Such an RLA may have applications going beyond muon acceleration: in medical isotope production, radiation cancer therapy and homeland security.
Date: June 1, 2013
Creator: Bogacz, Slawomir Alex; Krafft, Geoffrey A.; Morozov, Vasiliy S. & Roblin, Yves R.
Partner: UNT Libraries Government Documents Department

Electron Model Of A Dogbone RLA With Multi-Pass Arcs

Description: The design of a dogbone Recirculated Linear Accelerator, RLA, with linear-field multi-pass arcs was earlier developed [1] for accelerating muons in a Neutrino Factory and a Muon Collider. It allows for efficient use of expensive RF while the multi-pass arc design based on linear combined-function magnets exhibits a number of advantages over separate-arc or pulsed-arc designs. Such an RLA may have applications going beyond muon acceleration. This paper describes a possible straightforward test of this concept by scaling a GeV scale muon design for electrons. Scaling muon momenta by the muon-to-electron mass ratio leads to a scheme, in which a 4.5 MeV electron beam is injected at the middle of a 3 MeV/pass linac with two double-pass return arcs and is accelerated to 18 MeV in 4.5 passes. All spatial dimensions including the orbit distortion are scaled by a factor of 7.5, which arises from scaling the 200 MHz muon RF to the frequency readily available at CEBAF: 1.5 GHz. The footprint of a complete RLA fits in an area of 25 by 7 m. The scheme utilizes only fixed magnetic fields including injection and extraction. The hardware requirements are not very demanding, making it straightforward to implement
Date: September 1, 2012
Creator: Beard, Kevin B.; Roblin, Yves R.; Morozov, Vasiliy; Bogacz, Slawomir Alex & Krafft, Geoffrey A.
Partner: UNT Libraries Government Documents Department

A Bunch Length Monitor for JLab 12 GeV Upgrade

Description: A continuous non-invasive bunch length monitor for the 12 GeV upgrade of Jefferson Lab will be used to determine the bunch length of the beam. The measurement will be done at the fourth dipole of the injector chicane at 123 MeV using the coherent synchrotron light emitted from the dipole. The estimated bunch length is 333 fs. A vacuum chamber will be fabricated and a Radiabeam real time interferometer will be used. In this paper, background, the estimated calculations and the construction of the chamber will be discussed.
Date: December 1, 2013
Creator: Ahmad, Mahmoud Mohamad Ali; Freyberger, Arne P.; Gubeli, Joseph F. & Krafft, Geoffrey A.
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

A Test Facility for MEIC ERL Circulator Ring Based Electron Cooler Design

Description: An electron cooling facility which is capable to deliver a beam with energy up to 55 MeV and average current up to 1.5 A at a high bunch repetition rate up to 750 MHz is required for MEIC. The present cooler design concept is based on a magnetized photo-cathode SRF gun, an SRF ERL and a compact circulator ring. In this paper, we present a proposal of a test facility utilizing the JLab FEL ERL for a technology demonstration of this cooler design concept. Beam studies will be performed and supporting technologies will also be developed in this test facility.
Date: May 1, 2013
Creator: Zhang, Yuhong; Derbenev, Yaroslav S.; Douglas, David R.; Hutton, Andrew M.; Krafft, Geoffrey A. & Nissen, Edward W.
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