Merminga, L.
(Lia Merminga)

TUBOS02 Longitudinal Space Charge Effects in the JLAB IR FEL SRF Linac
Carlos Hernandez-Garcia, Kevin Beard, Chris Behre, Stephen Vincent Benson, George Herman Biallas, James Boyce, David Douglas, Fred Dylla, Richard Evans, Al Grippo, Joe Gubeli, David Hardy, Kevin Jordan, Lia Merminga, George Neil, Joe Preble, Michelle D. Shinn, Tim Siggins, Richard Walker, Gwyn Williams, Byung Yunn, Shukui Zhang (Jefferson Lab, Newport News, Virginia)

Observations of energy spread asymmetry when operating the Linac on either side of crest and longitudinal emittance growth have been confirmed by extending PARMELA simulations from the injector to the end of the first SRF Linac module. The asymmetry can be explained by the interaction of the accelerating electric field with that from longitudinal space charge effects within the electron bunch. This can be a major limitation to performance in FEL accelerators.

WEBOS03 Suppression of Multipass, Multibunch Beam Breakup in Two Pass Recirculating Accelerators
Chris Tennant, David Douglas, Kevin Jordan, Lia Merminga, Eduard Pozdeyev (Jefferson Lab, Newport News, Virginia), Todd I. Smith (Stanford University, Stanford, Califormia)

Beam Breakup (BBU) occurs in all accelerators at sufficiently high currents. In recirculating accelerators, such as the energy recovery linacs used for high power FELs, the maximum current has historically been limited by multipass, multibunch BBU, a form that occurs when the electron beam interacts with the high order modes (HOMs) of an accelerating cavity on one pass and then again on the second pass. This effect is of particular concern in the designs of modern high average current energy recovery accelerators utilizing superconducting technology. In such two pass machines rotation of the betatron planes by 90°, first proposed by Smith and Rand in 1980 [1], should significantly increase the threshold current of the multibunch BBU. Using a newly developed 4-dimensional tracking code, we study the effect of rotation on the threshold current of the JLAB FEL Upgrade. We examine several optical rotator schemes based on quadrupoles and solenoids and evaluate their performance in terms of the instability threshold current increase and their effect on the FEL optics.

TUCOS02 High Power Lasing in the IR Upgrade FEL at Jefferson Lab
Stephen Vincent Benson, Kevin Beard, Chris Behre, George Herman Biallas, James Boyce, David Douglas, Fred Dylla, Richard Evans, Al Grippo, Joe Gubeli, David Hardy, Carlos Hernandez-Garcia, Kevin Jordan, Lia Merminga, George Neil, Joe Preble, Michelle D. Shinn, Tim Siggins, Richard Walker, Gwyn Williams, Byung Yunn, Shukui Zhang (Jefferson Lab, Newport News, Virginia), Hiroyuki Toyokawa (KEK, Ibaraki)

We report on progress in commissioning the IR Upgrade facility at Jefferson Lab. Operation at high power has been demonstrated at 5.7 microns with over 4 kW of continuous power output and a recirculated electron beam power of up to 800 kW. We report on the features and limitations of the present design and on efforts to increase the power to over 10 kW.