FEL2013 - List of Authors (Todd, A.M.M.)

Paper	Title	Page
TUPSO57	Generation of Ultrafast, High-brightness Electron Beams	355
	J.H. Park, H. Bluem, J. Rathke, T. Schultheiss, A.M.M. Todd AES, Medford, NY, USA
	Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-SC0009556. The production and preservation of ultrafast, high-brightness electron beams is a major R&D challenge for free electron laser (FEL) and ultrafast electron diffraction (UED) because transverse and longitudinal space charge forces drive emittance dilution and bunch lengthening in such beams. Several approaches, such as velocity bunching and magnetic compression, have been considered to solve this problem but each has drawbacks. We present a concept that uses radial bunch compression in an X-band photocathode radio frequency electron gun. By compensating for the path length differential with a curved cathode in an extremely high acceleration gradient cavity, we have demonstrated numerically the possibility of achieving more than an order of magnitude increase in beam brightness over existing electron guns. The initial thermo-structural analysis and mechanical conceptual design of this electron source are presented.

TUPSO58	Developments of a High-average-current Thermionic RF Gun for ERLs and FELs	359
	J.H. Park, H. Bluem, J. Rathke, T. Schultheiss, A.M.M. Todd AES, Medford, NY, USA
	Funding: Supported by ONR under Contract No. N00014-10-C-0191. The development of a high-average-current thermionic RF gun with the required beam performance for lasing would provide significant cost of ownership and reliability gains for high-average-power energy recovery linac (ERL) and free electron laser (FEL) devices. The beam for these applications requires high quality and high performance, specifically: low transverse emittance, short pulse duration and high average current. We are developing a gridded thermionic cathode embedded in a copper one-and-half cell UHF cavity to generate the electron beam. The fundamental RF and higher harmonics are combined on the grid and a gated DC voltage controls the beam emission from the cathode. Simulations indicate that short pulse ~ 10 psec, < 1 MeV electron beams with low-emittance ~ 15 mm-mrad at currents ≥ 100 mA can be generated. The elimination of sensitive photocathodes and their drive laser systems would provide significant capital cost saving, improved reliability and uptime due to increased robustness and hence operating and lifecycle cost savings as well. We will present the gun design and performance simulations and the progress achieved to date in optimizing the device.

TUPSO74	A Coaxially Coupled Deflecting-accelerating Mode Cavity System for Phase-space Exchange (PSEX)	395
	Y.-M. Shin, P. Piot Northern Illinois University, DeKalb, Illinois, USA M.D. Church Fermilab, Batavia, USA J.H. Park, A.M.M. Todd AES, Medford, NY, USA
	A feasible method to readily remove energy spread (R56 term) due to thick lens effect of a deflecting mode RF-cavity has been widely investigated for emittance exchange in 6D phase-space,. By means of theoretical calculation and numerical analysis, it was found that an accelerating cavity effectively cancel the longitudinal phase space chirp. We have extensively investigated the combined deflecting-accelerating mode phase-space exchanger with the simple RF distribution system of the beam-pipe coaxial coupler. EM simulations proved the coupling scheme with eigenmode and S-parameter analyses. Currently we are looking into 3D beam dynamics in the system with tracking/particle-in-cell (PIC) simulations and wakefield analysis. Proof-of-concept (POC) experiment is planned with a high-Q normal conducting cavity built in a cryogenic cooling system (liquid nitrogen) in Fermilab. P. Emma, et. al., Phys. Rev. ST Accel. Beams 9, 100702 (2006) ** Zholents and M. Zolotorev, LBNL CBP Seminar (2010) and No. ANL/APS/LS-327(2011)

WEPSO30	Integrating the FHI-FEL Into the FHI Research Environment - Design and Implementation Aspects	562
	H. Junkes, W. Erlebach, S. Gewinner, U. Hoppe, A. Liedke, G. Meijer, W. Schöllkopf, M. Wesemann, G. von Helden FHI, Berlin, Germany H. Bluem, D. Dowell, R. Lange, A.M.M. Todd, L.M. Young AES, Medford, NY, USA S.B. Webb ORNL, Oak Ridge, Tennessee, USA
	The new mid-infrared FEL at the Fritz-Haber-Institut (FHI) was presented at the FEL12 conference. It will be used for spectroscopic investigations of molecules, clusters, nanoparticles and surfaces. This facility must be easy to use by the scientists at FHI, and should be seamlessly integrated into the existing research environment. The Experimental Physics and Industrial Control System (EPICS) software framework was chosen to build the FHI-FEL control system, and will also be used to interface the user systems. The graphical operator interface is based on the Control System Studio (CSS) package. It covers radiation safety monitoring as well as controlling the complete set of building automation and utility devices, regardless of their particular function. A user interface (subset of the operator interface) allows user-provided experiment-control software (KouDa, LabVIEW, Matlab) to connect with an EPICS Gateway providing secured access. The EPICS Channel Archiver continuously records selected process variable data and provides a web server offering archive and near real-time data. A sample experiment installation demonstrates how this user interface can be used efficiently. W. Schöllkopf et al., FIRST LASING OF THE IR FEL AT THE FRITZ-HABER-INSTITUT, BERLIN, Conference FEL12

WEPSO62	The IR and THz Free Electron Laser at the Fritz-Haber-Institut	657
	W. Schöllkopf, W. Erlebach, S. Gewinner, G. Heyne, H. Junkes, A. Liedke, G. Meijer, V. Platschkowski, G. von Helden FHI, Berlin, Germany H. Bluem, D. Dowell, K. Jordan, R. Lange, J. Rathke, A.M.M. Todd, L.M. Young AES, Medford, NY, USA M.A. Davidsaver BNL, Upton, New York, USA S.C. Gottschalk STI, Washington, USA U. Lehnert, P. Michel, W. Seidel, R. Wünsch HZDR, Dresden, Germany H. Loos SLAC, Menlo Park, California, USA
	A mid-infrared oscillator FEL with a design wavelength range from 4 to 50 μm has been commissioned at the Fritz-Haber-Institut in Berlin, Germany, for applications in molecular and cluster spectroscopy as well as surface science. The accelerator consists of a thermionic gridded electron gun, a subharmonic buncher and two S-band standing-wave copper structures. The device was designed to meet challenging specifications, including a final energy adjustable in the range of 15 to 50 MeV, low longitudinal emittance (< 50 keV-psec) and transverse emittance (< 20 π mm-mrad), at more than 200 pC bunch charge with aμpulse repetition rate of 1 GHz and a macro pulse length of up to 15 μs. Two isochronous achromatic 180 degree bends deliver the beam to the undulators, only one of which is presently installed, and to the beam dumps. Calculations of the FEL gain and IR-cavity losses predict that lasing will be possible in the wavelength range from less than 4 to more than 50 μm. First lasing was achieved at a wavelength of 16 μm in 2012. We will describe the FEL system design and performance, provide examples of lasing, and touch on the first anticipated user experiments. W. Schöllkopf et al., MOOB01, Proc. FEL 2012.

Paper

Title

Page

Generation of Ultrafast, High-brightness Electron Beams

355

J.H. Park, H. Bluem, J. Rathke, T. Schultheiss, A.M.M. Todd
AES, Medford, NY, USA

Funding: This work was supported by the U.S. Department of Energy, under Contract No. DE-SC0009556.
The production and preservation of ultrafast, high-brightness electron beams is a major R&D challenge for free electron laser (FEL) and ultrafast electron diffraction (UED) because transverse and longitudinal space charge forces drive emittance dilution and bunch lengthening in such beams. Several approaches, such as velocity bunching and magnetic compression, have been considered to solve this problem but each has drawbacks. We present a concept that uses radial bunch compression in an X-band photocathode radio frequency electron gun. By compensating for the path length differential with a curved cathode in an extremely high acceleration gradient cavity, we have demonstrated numerically the possibility of achieving more than an order of magnitude increase in beam brightness over existing electron guns. The initial thermo-structural analysis and mechanical conceptual design of this electron source are presented.

TUPSO58

Developments of a High-average-current Thermionic RF Gun for ERLs and FELs

359

J.H. Park, H. Bluem, J. Rathke, T. Schultheiss, A.M.M. Todd
AES, Medford, NY, USA

Funding: Supported by ONR under Contract No. N00014-10-C-0191.
The development of a high-average-current thermionic RF gun with the required beam performance for lasing would provide significant cost of ownership and reliability gains for high-average-power energy recovery linac (ERL) and free electron laser (FEL) devices. The beam for these applications requires high quality and high performance, specifically: low transverse emittance, short pulse duration and high average current. We are developing a gridded thermionic cathode embedded in a copper one-and-half cell UHF cavity to generate the electron beam. The fundamental RF and higher harmonics are combined on the grid and a gated DC voltage controls the beam emission from the cathode. Simulations indicate that short pulse ~ 10 psec, < 1 MeV electron beams with low-emittance ~ 15 mm-mrad at currents ≥ 100 mA can be generated. The elimination of sensitive photocathodes and their drive laser systems would provide significant capital cost saving, improved reliability and uptime due to increased robustness and hence operating and lifecycle cost savings as well. We will present the gun design and performance simulations and the progress achieved to date in optimizing the device.

TUPSO74

A Coaxially Coupled Deflecting-accelerating Mode Cavity System for Phase-space Exchange (PSEX)

395

Y.-M. Shin, P. Piot
Northern Illinois University, DeKalb, Illinois, USA
M.D. Church
Fermilab, Batavia, USA
J.H. Park, A.M.M. Todd
AES, Medford, NY, USA

A feasible method to readily remove energy spread (R56 term) due to thick lens effect of a deflecting mode RF-cavity has been widely investigated for emittance exchange in 6D phase-space*,**. By means of theoretical calculation and numerical analysis, it was found that an accelerating cavity effectively cancel the longitudinal phase space chirp. We have extensively investigated the combined deflecting-accelerating mode phase-space exchanger with the simple RF distribution system of the beam-pipe coaxial coupler. EM simulations proved the coupling scheme with eigenmode and S-parameter analyses. Currently we are looking into 3D beam dynamics in the system with tracking/particle-in-cell (PIC) simulations and wakefield analysis. Proof-of-concept (POC) experiment is planned with a high-Q normal conducting cavity built in a cryogenic cooling system (liquid nitrogen) in Fermilab.
* P. Emma, et. al., Phys. Rev. ST Accel. Beams 9, 100702 (2006)
** Zholents and M. Zolotorev, LBNL CBP Seminar (2010) and No. ANL/APS/LS-327(2011)

WEPSO30

Integrating the FHI-FEL Into the FHI Research Environment - Design and Implementation Aspects

562

H. Junkes, W. Erlebach, S. Gewinner, U. Hoppe, A. Liedke, G. Meijer, W. Schöllkopf, M. Wesemann, G. von Helden
FHI, Berlin, Germany
H. Bluem, D. Dowell, R. Lange, A.M.M. Todd, L.M. Young
AES, Medford, NY, USA
S.B. Webb
ORNL, Oak Ridge, Tennessee, USA

The new mid-infrared FEL at the Fritz-Haber-Institut (FHI) was presented at the FEL12 conference*. It will be used for spectroscopic investigations of molecules, clusters, nanoparticles and surfaces. This facility must be easy to use by the scientists at FHI, and should be seamlessly integrated into the existing research environment. The Experimental Physics and Industrial Control System (EPICS) software framework was chosen to build the FHI-FEL control system, and will also be used to interface the user systems. The graphical operator interface is based on the Control System Studio (CSS) package. It covers radiation safety monitoring as well as controlling the complete set of building automation and utility devices, regardless of their particular function. A user interface (subset of the operator interface) allows user-provided experiment-control software (KouDa, LabVIEW, Matlab) to connect with an EPICS Gateway providing secured access. The EPICS Channel Archiver continuously records selected process variable data and provides a web server offering archive and near real-time data. A sample experiment installation demonstrates how this user interface can be used efficiently.
* W. Schöllkopf et al., FIRST LASING OF THE IR FEL AT THE FRITZ-HABER-INSTITUT, BERLIN, Conference FEL12

WEPSO62

The IR and THz Free Electron Laser at the Fritz-Haber-Institut

657

W. Schöllkopf, W. Erlebach, S. Gewinner, G. Heyne, H. Junkes, A. Liedke, G. Meijer, V. Platschkowski, G. von Helden
FHI, Berlin, Germany
H. Bluem, D. Dowell, K. Jordan, R. Lange, J. Rathke, A.M.M. Todd, L.M. Young
AES, Medford, NY, USA
M.A. Davidsaver
BNL, Upton, New York, USA
S.C. Gottschalk
STI, Washington, USA
U. Lehnert, P. Michel, W. Seidel, R. Wünsch
HZDR, Dresden, Germany
H. Loos
SLAC, Menlo Park, California, USA

A mid-infrared oscillator FEL with a design wavelength range from 4 to 50 μm has been commissioned at the Fritz-Haber-Institut in Berlin, Germany, for applications in molecular and cluster spectroscopy as well as surface science. The accelerator consists of a thermionic gridded electron gun, a subharmonic buncher and two S-band standing-wave copper structures. The device was designed to meet challenging specifications, including a final energy adjustable in the range of 15 to 50 MeV, low longitudinal emittance (< 50 keV-psec) and transverse emittance (< 20 π mm-mrad), at more than 200 pC bunch charge with aμpulse repetition rate of 1 GHz and a macro pulse length of up to 15 μs. Two isochronous achromatic 180 degree bends deliver the beam to the undulators, only one of which is presently installed, and to the beam dumps. Calculations of the FEL gain and IR-cavity losses predict that lasing will be possible in the wavelength range from less than 4 to more than 50 μm. First lasing was achieved at a wavelength of 16 μm in 2012*. We will describe the FEL system design and performance, provide examples of lasing, and touch on the first anticipated user experiments.
* W. Schöllkopf et al., MOOB01, Proc. FEL 2012.