IPAC2021 - List of Authors (Oppelt, A.)

Paper	Title	Page
TUPAB034	Development of Multi-Alkali Antimonides Photocathodes for High-Brightness RF Photoinjectors	1416
	S.K. Mohanty, M. Krasilnikov, A. Oppelt, H.J. Qian, F. Stephan DESY Zeuthen, Zeuthen, Germany G. Guerini Rocco, C. Pagani Università degli Studi di Milano & INFN, Segrate, Italy W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany P. Michelato, L. Monaco, D. Sertore INFN/LASA, Segrate (MI), Italy
	Multi-alkali antimonide-based photocathodes are suitable candidate for the electron sources of next-generation high brightness RF photoinjectors due to their excellent photoemissive properties especially, like low thermal emittances and high sensitivity to visible light. The former stands out, paving the way towards CW operations. Based on the previous successful development of Cesium Telluride photocathodes, we are now channelling our efforts toward an R&D activity focused on KCsSb and NaKSb(Cs) photocathodes. Parallel to that R&D activity, we have installed a new dedicated photocathode production system at the INFN-LASA to start the preparation of these photocathodes for their test in the PITZ photoinjector at DESY in Zeuthen. In this paper, detailed experimental results obtained from the KCsSb, along with a preliminary result from the NaKSb(Cs) photocathode material as well as the status of the overall project are presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB034
About •	paper received ※ 19 May 2021 paper accepted ※ 21 June 2021 issue date ※ 31 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPAB071	Beam Line Design and Instrumentation for THz@PITZ - the Proof-of-Principle Experiment on a THz SASE FEL at the PITZ Facility	1528
	T. Weilbach, P. Boonpornprasert, G.Z. Georgiev, G. Koss, M. Krasilnikov, X. Li, A. Lueangaramwong, F. Mueller, A. Oppelt, S. Philipp, F. Stephan, L.V. Vu DESY Zeuthen, Zeuthen, Germany H. Shaker CLS, Saskatoon, Saskatchewan, Canada
	In order to allow THz pump-X-ray probe experiments at full bunch repetition rate for users at the European XFEL, the Photo Injector Test Facility at DESY in Zeuthen (PITZ) is building a prototype of an accelerator-based THz source. The goal is to generate THz SASE FEL radiation with a mJ energy level per bunch using an LCLS-I undulator driven by the electron beam from PITZ. Therefore, the existing PITZ beam line is extended into a tunnel annex downstream of the existing accelerator tunnel. The beam line extension in the PITZ tunnel consists of three quadrupole magnets, a bunch compressor, a collimation system and a beam dump. In the second tunnel a dipole magnet allows to serve two beam lines, one of them the THz@PITZ beam line. It consists of one LCLS-I undulator for the production of the THz radiation, a quadrupole triplet in front of it and a quadrupole doublet behind it. For the electron beam diagnostic six new screen stations are built, three of them also allow for the observation of the THz radiation for measurements. In addition six BPMs and a new BLM system for machine protection and FEL gain curve measurement will be installed. The progress of this work will be presented.
	Poster TUPAB071 [1.978 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB071
About •	paper received ※ 18 May 2021 paper accepted ※ 14 June 2021 issue date ※ 13 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB040	Characterization of Low Emittance Electron Beams Generated by Transverse Laser Beam Shaping	2690
	M. Groß, N. Aftab, P. Boonpornprasert, G.Z. Georgiev, J. Good, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, D. Melkumyan, S.K. Mohanty, R. Niemczyk, A. Oppelt, H.J. Qian, G. Shu, F. Stephan, G. Vashchenko DESY Zeuthen, Zeuthen, Germany Y. Chen, G. Loisch DESY, Hamburg, Germany I. Will MBI, Berlin, Germany
	Linac based X-ray free electron laser demand a high beam quality from the electron source, therefore RF photoinjectors are used to generate the electron bunches for state of the art beam brightness. One important figure of merit for these injectors is the transverse emittance of the generated electron beam, which can be minimized by shaping the photocathode laser pulses. Best performance can be achieved with ellipsoidal laser pulses, but 3D shaping is technically challenging. Typically, a quasi-uniform transverse laser profile is truncated from the Gaussian profile generated by the laser with an aperture to reduce the transverse nonlinear space charge forces. This is investigated in detail by optimizing the laser transverse profile at the Photoinjector Test facility at DESY in Zeuthen (PITZ), where photoinjector R&D is conducted for the E-XFEL and FLASH free electron lasers at DESY in Hamburg. In this contribution we present experimental results at high acceleration gradients (up to 60 MV/m) for both 250 pC and 500 pC. For a bunch charge of 500 pC an emittance reduction of about 30% compared to the commonly used transverse flat-top laser distribution was achieved.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB040
About •	paper received ※ 17 May 2021 paper accepted ※ 02 June 2021 issue date ※ 19 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB115	Beam Preparation with Temporally Modulated Photocathode Laser Pulses for a Seeded THz FEL	2866
	G.Z. Georgiev, N. Aftab, P. Boonpornprasert, J. Good, M. Groß, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, A. Lueangaramwong, D. Melkumyan, S.K. Mohanty, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko, T. Weilbach DESY Zeuthen, Zeuthen, Germany N. Chaisueb Chiang Mai University, Chiang Mai, Thailand W. Hillert University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
	The need for carrier-envelope-phase (CEP) stable THz pump pulses is recognized at many pump-probe experiments at the European XFEL. At the Photo Injector Test Facility at DESY in Zeuthen (PITZ), a proof-of-principle experiment of an accelerator-based THz FEL source is in preparation. Since the CEP stability of FEL pulses is not guaranteed in the SASE regime, a seeding scheme is needed. A common scheme for seeding is to drive the microbunching process with external laser pulses, which are power-limited in the THz range. Alternatively, a pre-bunched beam, generated for example by applying a temporally modulated photocathode laser pulse, can be used to drive the FEL. The beam dynamics with such a seeding method are studied with ASTRA tracking code simulations with space-charge forces as well as experimentally. The results of these studies are shown and discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB115
About •	paper received ※ 19 May 2021 paper accepted ※ 27 July 2021 issue date ※ 26 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB257	Matching of a Space-Charge Dominated Beam into the Undulator of the THz SASE FEL at PITZ	3244
	X. Li, Z. Aboulbanine, G.D. Adhikari, N. Aftab, Z.G. Amirkhanyan, P. Boonpornprasert, M.E. Castro Carballo, N. Chaisueb, G.Z. Georgiev, J. Good, M. Groß, C. Koschitzki, M. Krasilnikov, O. Lishilin, A. Lueangaramwong, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, G. Shu, F. Stephan, G. Vashchenko, T. Weilbach DESY Zeuthen, Zeuthen, Germany
	The Photo Injector Test facility at DESY in Zeuthen (PITZ) is developing a THz SASE FEL as a prototype high repetition rate accelerator-based source for the THz-pumped, X-ray-probed experiments at the European XFEL. For the generation of THz pulses of mJ-level energy from SASE, an electron beam with a high charge (up to 4 nC) and high peak current (~200 A) will be injected into an LCLS-I undulator, which is currently being installed at the end of the photo-injector. The narrow vacuum chamber (11x5 mm) between the magnetic poles and the strong vertical focusing from the undulator, as well as the lack of beam diagnostics, have made it a challenge to match the space-charge dominated beam into the undulator without beam loss during the following transport. In this paper, boundary conditions of a matched electron beam will be discussed and the simulation and experimental study on our matching strategy will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB257
About •	paper received ※ 08 May 2021 paper accepted ※ 02 July 2021 issue date ※ 13 August 2021
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

FRXB06	Direct response time measurements on semiconductor photocathodes
	G. Loisch, M. Groß, D.K. Kalantaryan, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, F. Stephan, G. Vashchenko, T. Weilbach DESY Zeuthen, Zeuthen, Germany Y. Chen, S. Lederer DESY, Hamburg, Germany L. Monaco, D. Sertore INFN/LASA, Segrate (MI), Italy R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
	Semiconductor photocathodes like Cs₂Te enable stable electron sources with high photon to electron conversion rate (quantum efficiency, QE) for high brightness photoinjectors. Besides QE, work function and vacuum stability, bunch lengthening is a key figure of merit for these sources, resulting from UV photon penetration into the semiconductor and scattering of excited electrons before emission. These processes and their statistical variation lead to a delay, as well as to lengthening of the extracted electron bunch w.r.t. the incident laser pulse, often referred to as "response time". Thus far, no direct measurement of the response time of Cs₂Te, one of the most widely used cathode materials, has been reported. As such a measurement is crucial for photocathode laser based bunch shaping, short bunch applications, emission modeling and for evaluating new cathode materials like CsKSb, a measurement procedure has been established at the photoinjector test facility at DESY in Zeuthen (PITZ) to measure longitudinal bunch shape variation due to cathode emission effects. Here, we introduce the method and show first results on direct cathode response measurements of Cs₂Te cathodes.
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Development of Multi-Alkali Antimonides Photocathodes for High-Brightness RF Photoinjectors

1416

S.K. Mohanty, M. Krasilnikov, A. Oppelt, H.J. Qian, F. Stephan
DESY Zeuthen, Zeuthen, Germany
G. Guerini Rocco, C. Pagani
Università degli Studi di Milano & INFN, Segrate, Italy
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany
P. Michelato, L. Monaco, D. Sertore
INFN/LASA, Segrate (MI), Italy

Multi-alkali antimonide-based photocathodes are suitable candidate for the electron sources of next-generation high brightness RF photoinjectors due to their excellent photoemissive properties especially, like low thermal emittances and high sensitivity to visible light. The former stands out, paving the way towards CW operations. Based on the previous successful development of Cesium Telluride photocathodes, we are now channelling our efforts toward an R&D activity focused on KCsSb and NaKSb(Cs) photocathodes. Parallel to that R&D activity, we have installed a new dedicated photocathode production system at the INFN-LASA to start the preparation of these photocathodes for their test in the PITZ photoinjector at DESY in Zeuthen. In this paper, detailed experimental results obtained from the KCsSb, along with a preliminary result from the NaKSb(Cs) photocathode material as well as the status of the overall project are presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB034

About •

paper received ※ 19 May 2021 paper accepted ※ 21 June 2021 issue date ※ 31 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPAB071

Beam Line Design and Instrumentation for THz@PITZ - the Proof-of-Principle Experiment on a THz SASE FEL at the PITZ Facility

1528

T. Weilbach, P. Boonpornprasert, G.Z. Georgiev, G. Koss, M. Krasilnikov, X. Li, A. Lueangaramwong, F. Mueller, A. Oppelt, S. Philipp, F. Stephan, L.V. Vu
DESY Zeuthen, Zeuthen, Germany
H. Shaker
CLS, Saskatoon, Saskatchewan, Canada

In order to allow THz pump-X-ray probe experiments at full bunch repetition rate for users at the European XFEL, the Photo Injector Test Facility at DESY in Zeuthen (PITZ) is building a prototype of an accelerator-based THz source. The goal is to generate THz SASE FEL radiation with a mJ energy level per bunch using an LCLS-I undulator driven by the electron beam from PITZ. Therefore, the existing PITZ beam line is extended into a tunnel annex downstream of the existing accelerator tunnel. The beam line extension in the PITZ tunnel consists of three quadrupole magnets, a bunch compressor, a collimation system and a beam dump. In the second tunnel a dipole magnet allows to serve two beam lines, one of them the THz@PITZ beam line. It consists of one LCLS-I undulator for the production of the THz radiation, a quadrupole triplet in front of it and a quadrupole doublet behind it. For the electron beam diagnostic six new screen stations are built, three of them also allow for the observation of the THz radiation for measurements. In addition six BPMs and a new BLM system for machine protection and FEL gain curve measurement will be installed. The progress of this work will be presented.

Poster TUPAB071 [1.978 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-TUPAB071

About •

paper received ※ 18 May 2021 paper accepted ※ 14 June 2021 issue date ※ 13 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB040

Characterization of Low Emittance Electron Beams Generated by Transverse Laser Beam Shaping

2690

M. Groß, N. Aftab, P. Boonpornprasert, G.Z. Georgiev, J. Good, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, D. Melkumyan, S.K. Mohanty, R. Niemczyk, A. Oppelt, H.J. Qian, G. Shu, F. Stephan, G. Vashchenko
DESY Zeuthen, Zeuthen, Germany
Y. Chen, G. Loisch
DESY, Hamburg, Germany
I. Will
MBI, Berlin, Germany

Linac based X-ray free electron laser demand a high beam quality from the electron source, therefore RF photoinjectors are used to generate the electron bunches for state of the art beam brightness. One important figure of merit for these injectors is the transverse emittance of the generated electron beam, which can be minimized by shaping the photocathode laser pulses. Best performance can be achieved with ellipsoidal laser pulses, but 3D shaping is technically challenging. Typically, a quasi-uniform transverse laser profile is truncated from the Gaussian profile generated by the laser with an aperture to reduce the transverse nonlinear space charge forces. This is investigated in detail by optimizing the laser transverse profile at the Photoinjector Test facility at DESY in Zeuthen (PITZ), where photoinjector R&D is conducted for the E-XFEL and FLASH free electron lasers at DESY in Hamburg. In this contribution we present experimental results at high acceleration gradients (up to 60 MV/m) for both 250 pC and 500 pC. For a bunch charge of 500 pC an emittance reduction of about 30% compared to the commonly used transverse flat-top laser distribution was achieved.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB040

About •

paper received ※ 17 May 2021 paper accepted ※ 02 June 2021 issue date ※ 19 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB115

Beam Preparation with Temporally Modulated Photocathode Laser Pulses for a Seeded THz FEL

2866

G.Z. Georgiev, N. Aftab, P. Boonpornprasert, J. Good, M. Groß, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, A. Lueangaramwong, D. Melkumyan, S.K. Mohanty, R. Niemczyk, A. Oppelt, H.J. Qian, H. Shaker, G. Shu, F. Stephan, G. Vashchenko, T. Weilbach
DESY Zeuthen, Zeuthen, Germany
N. Chaisueb
Chiang Mai University, Chiang Mai, Thailand
W. Hillert
University of Hamburg, Institut für Experimentalphysik, Hamburg, Germany

The need for carrier-envelope-phase (CEP) stable THz pump pulses is recognized at many pump-probe experiments at the European XFEL. At the Photo Injector Test Facility at DESY in Zeuthen (PITZ), a proof-of-principle experiment of an accelerator-based THz FEL source is in preparation. Since the CEP stability of FEL pulses is not guaranteed in the SASE regime, a seeding scheme is needed. A common scheme for seeding is to drive the microbunching process with external laser pulses, which are power-limited in the THz range. Alternatively, a pre-bunched beam, generated for example by applying a temporally modulated photocathode laser pulse, can be used to drive the FEL. The beam dynamics with such a seeding method are studied with ASTRA tracking code simulations with space-charge forces as well as experimentally. The results of these studies are shown and discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB115

About •

paper received ※ 19 May 2021 paper accepted ※ 27 July 2021 issue date ※ 26 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

WEPAB257

Matching of a Space-Charge Dominated Beam into the Undulator of the THz SASE FEL at PITZ

3244

X. Li, Z. Aboulbanine, G.D. Adhikari, N. Aftab, Z.G. Amirkhanyan, P. Boonpornprasert, M.E. Castro Carballo, N. Chaisueb, G.Z. Georgiev, J. Good, M. Groß, C. Koschitzki, M. Krasilnikov, O. Lishilin, A. Lueangaramwong, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, G. Shu, F. Stephan, G. Vashchenko, T. Weilbach
DESY Zeuthen, Zeuthen, Germany

The Photo Injector Test facility at DESY in Zeuthen (PITZ) is developing a THz SASE FEL as a prototype high repetition rate accelerator-based source for the THz-pumped, X-ray-probed experiments at the European XFEL. For the generation of THz pulses of mJ-level energy from SASE, an electron beam with a high charge (up to 4 nC) and high peak current (~200 A) will be injected into an LCLS-I undulator, which is currently being installed at the end of the photo-injector. The narrow vacuum chamber (11x5 mm) between the magnetic poles and the strong vertical focusing from the undulator, as well as the lack of beam diagnostics, have made it a challenge to match the space-charge dominated beam into the undulator without beam loss during the following transport. In this paper, boundary conditions of a matched electron beam will be discussed and the simulation and experimental study on our matching strategy will be presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2021-WEPAB257

About •

paper received ※ 08 May 2021 paper accepted ※ 02 July 2021 issue date ※ 13 August 2021

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

FRXB06

Direct response time measurements on semiconductor photocathodes

G. Loisch, M. Groß, D.K. Kalantaryan, C. Koschitzki, M. Krasilnikov, X. Li, O. Lishilin, D. Melkumyan, R. Niemczyk, A. Oppelt, H.J. Qian, F. Stephan, G. Vashchenko, T. Weilbach
DESY Zeuthen, Zeuthen, Germany
Y. Chen, S. Lederer
DESY, Hamburg, Germany
L. Monaco, D. Sertore
INFN/LASA, Segrate (MI), Italy
R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom

Semiconductor photocathodes like Cs₂Te enable stable electron sources with high photon to electron conversion rate (quantum efficiency, QE) for high brightness photoinjectors. Besides QE, work function and vacuum stability, bunch lengthening is a key figure of merit for these sources, resulting from UV photon penetration into the semiconductor and scattering of excited electrons before emission. These processes and their statistical variation lead to a delay, as well as to lengthening of the extracted electron bunch w.r.t. the incident laser pulse, often referred to as "response time". Thus far, no direct measurement of the response time of Cs₂Te, one of the most widely used cathode materials, has been reported. As such a measurement is crucial for photocathode laser based bunch shaping, short bunch applications, emission modeling and for evaluating new cathode materials like CsKSb, a measurement procedure has been established at the photoinjector test facility at DESY in Zeuthen (PITZ) to measure longitudinal bunch shape variation due to cathode emission effects. Here, we introduce the method and show first results on direct cathode response measurements of Cs₂Te cathodes.

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)