ERL2017 - Table of Session: MOPSPP (Poster Session)

Paper	Title	Page
MOPSPP001	Study of Microbunching Instability in MESA
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	A. Khan, O. Boine-Frankenheim Institut Theorie Elektromagnetischer Felder, TU Darmstadt, Darmstadt, Germany K. Aulenbacher IKP, Mainz, Germany
	Funding: Supported by the DFG through GRK 2128 The Institute for Nuclear Physics (KPH) at Mainz is building a multi-turn energy recovery linear accelerator, the Mainz Energy-recovering Superconducting Accelerator (MESA), to deliver a CW beam at 10⁵ MeV with short pulses, high current and small emittance for physics experiments with an internal target. Space charge effects potentially cause beam quality degradation for medium energy beams in smaller machines like MESA. As beam quality preservation is a major concern in an ERL during recirculation. We present a study on Microbunching Instability (MBI) caused by Longitudinal Space Charge (LSC) in MESA. Our results demonstrate the impact of the MESA arc lattice design on the development of Microbunching Instability.
	Slides MOPSPP001 [3.369 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2017-THICCC002
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MOPSPP002	Development of an ERL RF Control System
THIBCC005	use link to access more material from this paper's primary paper code
	S. Orth, D. Domont-Yankulova, H. Klingbeil TEMF, TU Darmstadt, Darmstadt, Germany
	Funding: Work supported by Deutsche Forschungsgemeinschaft (DFG): GRK 2128 "AccelencE" The Mainz Energy-recovering Superconducting Accelerator (MESA), currently under construction at Johannes Gutenberg-Universität Mainz, requires a newly designed digital low-level radio frequency (LLRF) system. Challenging requirements have to be fulfilled to ensure high beam quality and beam parameter stability. First, the layout with two recirculations and the requirements will be shown from an LLRF point of view. Afterwards, different options for the control system are presented. This includes the generator-driven system, the self-excited loop and classical PID controller as well as more sophisticated solutions.
	Slides MOPSPP002 [4.066 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2017-THIBCC005
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MOPSPP003	RF Performance and Beam Parameter Measurement of the 2nd 3.5 Cell SRF Gun for ELBE
	A. Arnold, M. Freitag, P.N. Lu, P. Murcek, H. Vennekate, R. Xiang HZDR, Dresden, Germany G. Ciovati, P. Kneisel, L. Turlington JLab, Newport News, Virginia, USA
	In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time in order to serve user experiments at the superconducting CW accelerator ELBE. In our contribution we will report on the commissioning of the SRF gun by presenting a full set of RF performance results as well as detailed beam parameter measurements up to a bunch charge of 300 pC. Additionally, we will present the results of the first two user experiments (neutron and THz generation) that demonstrated the reliability of this gun concept.
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MOPSPP004	Investigation of K₂CsSb Photocathodes	4
	V. Bechthold, K. Aulenbacher, M.A. Dehn, S. Friederich IKP, Mainz, Germany K. Aulenbacher HIM, Mainz, Germany
	Funding: BMBF-HOPE II The interest in multi alkali antimonide photocathodes, e.g. K₂CsSb, for future ERL projects like BERLinPro (Berlin Energy Recovery Linac Prototype) and MESA (Mainz Energy-Recovering Superconducting Accelerator) has grown in recent years. In particular for the case of RF-sources the investigation of the time response is of great importance. In Mainz we are able to synthesize these kinds of photocathodes and investigate their pulse response at 1 picosecond level using a radio frequency streak method. We present on the one hand the cathode plant which is used for synthesizing the multi alkali antimonide photocathodes and on the other hand first measurements showing pulse responses of K₂CsSb at 400 nm laser wavelength. Furthermore, an analyzing chamber has been installed, which allows investigation of lifetime under laser heating and in-situ measurements of the work function using a UHV Kelvin Probe.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2017-MOPSPP004
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MOPSPP005	The Small Thermalized Electron Source at Mainz (STEAM)	9
	S. Friederich, K. Aulenbacher IKP, Mainz, Germany
	Funding: Work supported by BMBF-HOPE II and DFG through RTG 2128. The Small Thermalized Electron Source at Mainz (STEAM) is a photoelectron source which will be operated using NEA GaAs excited near its band gap with an infrared laser wavelength to reach smallest emittances. CST simulations indicate that emittance growth due to vacuum space charge effects can be controlled up to bunch charges of several tens of pC. The goal of the project is to demonstrate that the intrinsical high brightness can still be achieved at such charges. The current status will be presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2017-MOPSPP005
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MOPSPP006	SPOCK - a Triode DC Electron Gun With Variable Extraction Gradient	13
	L.M. Hein, K. Aulenbacher, V. Bechthold, M.A. Dehn, S. Friederich, C. Matejcek IKP, Mainz, Germany
	Funding: German Federal Ministry of Education and Research (BMBF project HOPE-II FKZ 05K16UMA) and the Cluster of Excellence "PRISMA The electron source concept SPOCK (Short Pulse Source at KPH) is a 100kV DC source design with variable extraction gradient. Due to its triode inspired design the extraction gradient can be reduced for e.g. investigations of cathode physics, but also enhanced to mitigate space charge effects. In the framework of the MESA-Project (Mainz Energy-Recovering Superconducting Accelerator) its design has been further optimized to cope with space charge dominated electron beams. Although it injects its electron beams directly into the LEBT matching section, which excludes any adjustments of the electron spin, the source SPOCK will allow higher bunch charges than the MESA standard source.
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MOPSPP007	Beam Dynamics and Collimation Following MAGIX at MESA	17
	B. Ledroit, K. Aulenbacher IKP, Mainz, Germany
	Funding: Supported by the DFG through GRK 2128 The Mainz Energy-recovering Superconducting Accelerator (MESA) will be an electron accelerator allowing operation in energy-recovery linac (ERL) mode. After the beam hits the target at the MESA Internal Gas Target Experiment (MAGIX), the beam is phase shifted and recirculated back into the linac sections. These will transfer the kinetic beam energy back to the RF-field by deceleration of the beam and allow for high beam power with low RF-power input. Since most of the beam does not interact with the target, the beam will mostly just pass the target untouched. However, a fraction of the scattered electrons may be in the range outside the accelerator and detector acceptances and therefore cause malicious beam dynamical behavior in the linac sections or even damage to the machine. The goal of this work is to determine the beam behavior upon target passage by simulation and experiment and to protect the machine with a suitable collimation system. The present status of the investigations is presented.
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MOPSPP008	Low Energy Beam Transport System for MESA	20
	C. Matejcek, K. Aulenbacher, S. Friederich, L.M. Hein IKP, Mainz, Germany
	An important part of the new accelerator MESA (Mainz Energy recovering Superconducting Accelerator) is the low energy beam transport system connecting the 100 keV electron source with the injector accelerator. Here the spin manipulation and the bunch preparation for the injector accelerator take place. Due to the low energy, space charge will be an challenging issue in this part. Therefore, start-to-end simulations were done with a combination of the two particle dynamics codes PARMELA* and CST*. At the moment, a test setup is being built up to check the functionality of devices and compare the beam parameters with the simulation. Here the focus lies on the bunch preparation system because at this part we expect high impact of the space charge by reason of the necessary bunch compression. The advance of the test setup, the simulations and measurements done so far will be shown. Phase and Radial Motion in Ion Linear Accelerators ** Computer Simulation Technology
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MOPSPP009	Beam Break Up Simulations for the MESA Accelerator	26
	C.P. Stoll, F. Hug, D. Simon IKP, Mainz, Germany
	Funding: Supported by DFG through GRK 2128 MESA is a recirculating superconducting accelerator under construction at Johannes Gutenberg-Universität Mainz. It will be operated in two different modes: the first is the external beam (EB) mode, where the beam is dumped after being used at the experiment. The required beam current in EB mode is 150 µA with polarized electrons at 155 MeV. In the second operation mode MESA will be run as an energy recovery linac (ERL) with an unpolarized beam of 1 mA at 10⁵ MeV. In a later construction stage of MESA the achievable beam current in ERL-mode shall be upgraded to 10 mA. To understand the behavior of the superconducting cavities under recirculating operation with high beam currents simulations of beam breakup have to be performed. Current results for transverse beam break up calculations and simulations with Beam Instability (bi) code are presented.
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MOPSPP011	Resonant Coherent Diffraction Radiation System at KEK-cERL
	Y. Honda, A. Aryshev, T. Miyajima, T. Obina, R. Ryukou, M. Shimada, R. Takai, N. Yamamoto KEK, Ibaraki, Japan
	Coherent radiation from a short bunched electron beam has been expected to be a high power source in THz regime. Especially the feature of the modern energy recovery linac is suitable for a high averaged power source. We propose to test an advanced scheme of resonantly exciting coherent diffraction radiation in an optical cavity. By stimulating the radiation in a multi-bunch beam, highly enhanced radiation power can be extracted. This system can excite all the cavity longitudinal modes at the same time, it can be a broadband source. We are preparing an experimental setup to test the resonant radiation in the cERL at KEK.
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MOPSPP012	Identification of Ion Bombardment Area on the Photocathode After 900 µA CW Beam Operation at cERL
	M. Yamamoto, Y. Honda, X.J. Jin, T. Miyajimapresenter, T. Obina KEK, Ibaraki, Japan Y. Kameta e-JAPAN IT Co. Ltd, Hitachi, Japan T. Kawasaki Toshiba, Yokohama, Japan N. Nishimori QST, Tokai, Japan N. Nishimori Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
	Compact-ERL (cERL) which is under development as an ERL demonstration machine at KEK succeeded in stable supply of CW beam exceeding 900 uA from a GaAs photocathode mounted on a DC-gun in March 2016. In the case of high current beam operation, the ions generated by collision of the beam and the residual molecules on the beam axis is increase and its flow back to the electron gun. As a result, the quantum efficiency (QE) of the photocathode decreases due to ion bombardment is the main factor of determining the cathode lifetime. After the CW operation of the accumulated extracted charge of ~10 Coulomb, steady decrease in QE due to ion bombardment has not yet been clearly confirmed. In order to analyze the area damaged by ion bombard, 2D QE distribution (QE map) measurement system was newly installed in the cathode preparation system. From QE map analysis before and after the CW operation, we confirmed two types of QE decrease. The area about 2 mm diameter near the center of the photocathode that the QE recovery is insufficient by the reactivation process is presumed the damage by ion bombardment.
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MOPSPP013	Proposal of Sharing 6-GeV Class CW Superconducting Linac With ILC and High Brilliance X-ray Light Source
	M. Shimada, M. Yamamoto, K. Yokoya KEK, Ibaraki, Japan R. Hajima QST, Tokai, Japan
	We propose sharing of the 6-GeV class CW superconducting linac with ILC and X-ray light source. ILC utilizes it for the positron source and the two boosters for the 5-GeV damping ring. The conventional positron source, which is based on a collision of the multi-GeV electron with the target, was chosen to lengthen the macro-pulse duration for avoiding the heat loading. In this proposal, the CW linac realizes the long macro-pulse duration beam operation of the positron beam as well as the electron for collision with the target. Simultaneously, the CW linac can used as the 5-GeV booster of the polarized electron beam at the same bunch pattern. Because of the low average current of beams of ILC, the CW linac have enough ability to accelerate/decelerate the high quality electron beam for the high brilliant X-ray light source such as 6-GeV class ERL light source and XFELO. Each electron beam has different injection energy, injects at the different merger and accelerates at the different RF phase. Therefore, the electron energies are different at the end of the CW linac and it makes the simultaneous operation possible.
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MOPSPP015	Development of a Multialkali Photocathode DC Gun for High Current Operation	29
THICCC003	use link to see paper's listing under its alternate paper code
	N. Nishimori Tohoku University, Research Center for Electron Photon Science, Sendai, Japan R. Hajima, R. Nagai, M. Sawamura QST, Tokai, Japan
	Funding: This work is partially supported by a JSPS Grant-in-Aid for Scientific Research in Japan (15K13412). We have developed a DC gun test stand at National Institutes for Quantum Radiological Science and Technology (QST) for high current electron beam generation. The gun test stand consists of an alkali antimonide photocathode preparation chamber, a DC gun with a 250kV-50mA Cockcroft Walton high voltage power supply, and beam line with a water cooled beam dump to accommodate 1.5 kW beam power. We successfully fabricated a Cs₃Sb photocathode with quantum efficiency of 5.8 % at 532 nm wavelength and generated 150 keV beam with current up to 4.3 mA with 500 mW laser at 532 nm wavelength. Unfortunately, we encountered a vacuum incident during beam transport of high current beam and the development has been halted. We will fix the vacuum problem and restart the gun development as soon as possible.
	Slides MOPSPP015 [22.138 MB]
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MOPSPP016	Discharge Mechanism of Ultra-High Vacuum Gap Derived From the HV Conditioning Result of the cERL DC-Gun
	M. Yamamoto KEK, Ibaraki, Japan N. Nishimoripresenter QST, Tokai, Japan N. Nishimoripresenter Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
	Funding: JSPS Grant-in-Aid for Scientific Research in Japan (15H0359, 16K05385) Development of a high brightness electron beam source is indispensable for realizing high repetition X-FEL and CW EUV-FEL as a next generation light source. The high voltage (HV) DC-gun that realized acceleration voltage of > 500 kV and electric field of > 5 MV/m is one of the candidates. In order to stably DC-gun operation, the HV conditioning process is an essential step as preparation of DC-gun operation. The HV conditioning was carried out on compact-ERL (cERL) electron gun and clarified the following four points. i) The voltage at which discharge stops (discharge stop voltage) exists, ii) The discharge stop voltage increases almost continuously with the number of discharges, iii) The gas released at the occurrence of discharge is almost proportional to the difference between the discharge start voltage and the discharge stop voltage, iv) The hold-off time of the voltage is very long under the discharge stop voltage. We focused on the electron stimulated desorption (ESD) phenomenon occurring at the anode can explain these phenomena in a consistent and considered the mechanism of discharge generation in DC field and HV conditioning progression in ultrahigh vacuum (UHV).
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MOPSPP017	Energy Distribution and Work Function Measurements for Metal Photocathodes With Measured Levels of Surface Roughness
	T.S. Beaver, L.B. Jones, B.L. Militsyn, T.C.Q. Noakes, R. Valizadeh STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom S. Mistry STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom
	Funding: The work is part of EuCARD2, partly funded by the European Commission, GA 312453. Funded by the Science and Technology Facilities Council. The minimum achievable emittance in an electron accelerator depends strongly on the intrinsic emittance of the photocathode electron source which is measureable as the mean longitudinal and transverse energy spreads in the photoemitted electrons. Reducing emittance in an accelerator driving a Free Electron Laser (FEL) delivers significant reduction in the saturation length for an X-ray FEL, reducing machine cost and increasing X-ray beam brightness. There are many parameters which affect the intrinsic emittance of a photocathode. Surface roughness is a significant factor, and consequently the development of techniques to manufacture low roughness photocathodes with optimum emission properties is a priority for the electron source community. In this work, we present transverse energy distribution and work function measurements made using our TESS facility* for electrons emitted from copper and molybdenum photocathodes with differing levels of measured surface roughness. * Proc. FEL '06, THPPH013, 583586 ** Proc. FEL '13, TUPPS033, 290293
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Paper

Title

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MOPSPP001

Study of Microbunching Instability in MESA

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A. Khan, O. Boine-Frankenheim
Institut Theorie Elektromagnetischer Felder, TU Darmstadt, Darmstadt, Germany
K. Aulenbacher
IKP, Mainz, Germany

Funding: Supported by the DFG through GRK 2128
The Institute for Nuclear Physics (KPH) at Mainz is building a multi-turn energy recovery linear accelerator, the Mainz Energy-recovering Superconducting Accelerator (MESA), to deliver a CW beam at 10⁵ MeV with short pulses, high current and small emittance for physics experiments with an internal target. Space charge effects potentially cause beam quality degradation for medium energy beams in smaller machines like MESA. As beam quality preservation is a major concern in an ERL during recirculation. We present a study on Microbunching Instability (MBI) caused by Longitudinal Space Charge (LSC) in MESA. Our results demonstrate the impact of the MESA arc lattice design on the development of Microbunching Instability.

Slides MOPSPP001 [3.369 MB]

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MOPSPP002

Development of an ERL RF Control System

THIBCC005

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S. Orth, D. Domont-Yankulova, H. Klingbeil
TEMF, TU Darmstadt, Darmstadt, Germany

Funding: Work supported by Deutsche Forschungsgemeinschaft (DFG): GRK 2128 "AccelencE"
The Mainz Energy-recovering Superconducting Accelerator (MESA), currently under construction at Johannes Gutenberg-Universität Mainz, requires a newly designed digital low-level radio frequency (LLRF) system. Challenging requirements have to be fulfilled to ensure high beam quality and beam parameter stability. First, the layout with two recirculations and the requirements will be shown from an LLRF point of view. Afterwards, different options for the control system are presented. This includes the generator-driven system, the self-excited loop and classical PID controller as well as more sophisticated solutions.

Slides MOPSPP002 [4.066 MB]

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MOPSPP003

RF Performance and Beam Parameter Measurement of the 2nd 3.5 Cell SRF Gun for ELBE

A. Arnold, M. Freitag, P.N. Lu, P. Murcek, H. Vennekate, R. Xiang
HZDR, Dresden, Germany
G. Ciovati, P. Kneisel, L. Turlington
JLab, Newport News, Virginia, USA

In May 2014 the 1st superconducting photo injector (SRF gun) at HZDR was replaced by a new gun, featuring a new resonator and cryostat. The intention for this upgrade was to reach higher beam energy, higher bunch charge and lower emittance at the same time in order to serve user experiments at the superconducting CW accelerator ELBE. In our contribution we will report on the commissioning of the SRF gun by presenting a full set of RF performance results as well as detailed beam parameter measurements up to a bunch charge of 300 pC. Additionally, we will present the results of the first two user experiments (neutron and THz generation) that demonstrated the reliability of this gun concept.

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MOPSPP004

Investigation of K₂CsSb Photocathodes

4

V. Bechthold, K. Aulenbacher, M.A. Dehn, S. Friederich
IKP, Mainz, Germany
K. Aulenbacher
HIM, Mainz, Germany

Funding: BMBF-HOPE II
The interest in multi alkali antimonide photocathodes, e.g. K₂CsSb, for future ERL projects like BERLinPro (Berlin Energy Recovery Linac Prototype) and MESA (Mainz Energy-Recovering Superconducting Accelerator) has grown in recent years. In particular for the case of RF-sources the investigation of the time response is of great importance. In Mainz we are able to synthesize these kinds of photocathodes and investigate their pulse response at 1 picosecond level using a radio frequency streak method. We present on the one hand the cathode plant which is used for synthesizing the multi alkali antimonide photocathodes and on the other hand first measurements showing pulse responses of K₂CsSb at 400 nm laser wavelength. Furthermore, an analyzing chamber has been installed, which allows investigation of lifetime under laser heating and in-situ measurements of the work function using a UHV Kelvin Probe.

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MOPSPP005

The Small Thermalized Electron Source at Mainz (STEAM)

9

S. Friederich, K. Aulenbacher
IKP, Mainz, Germany

Funding: Work supported by BMBF-HOPE II and DFG through RTG 2128.
The Small Thermalized Electron Source at Mainz (STEAM) is a photoelectron source which will be operated using NEA GaAs excited near its band gap with an infrared laser wavelength to reach smallest emittances. CST simulations indicate that emittance growth due to vacuum space charge effects can be controlled up to bunch charges of several tens of pC. The goal of the project is to demonstrate that the intrinsical high brightness can still be achieved at such charges. The current status will be presented.

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MOPSPP006

SPOCK - a Triode DC Electron Gun With Variable Extraction Gradient

13

L.M. Hein, K. Aulenbacher, V. Bechthold, M.A. Dehn, S. Friederich, C. Matejcek
IKP, Mainz, Germany

Funding: German Federal Ministry of Education and Research (BMBF project HOPE-II FKZ 05K16UMA) and the Cluster of Excellence "PRISMA
The electron source concept SPOCK (Short Pulse Source at KPH) is a 100kV DC source design with variable extraction gradient. Due to its triode inspired design the extraction gradient can be reduced for e.g. investigations of cathode physics, but also enhanced to mitigate space charge effects. In the framework of the MESA-Project (Mainz Energy-Recovering Superconducting Accelerator) its design has been further optimized to cope with space charge dominated electron beams. Although it injects its electron beams directly into the LEBT matching section, which excludes any adjustments of the electron spin, the source SPOCK will allow higher bunch charges than the MESA standard source.

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MOPSPP007

Beam Dynamics and Collimation Following MAGIX at MESA

17

B. Ledroit, K. Aulenbacher
IKP, Mainz, Germany

Funding: Supported by the DFG through GRK 2128
The Mainz Energy-recovering Superconducting Accelerator (MESA) will be an electron accelerator allowing operation in energy-recovery linac (ERL) mode. After the beam hits the target at the MESA Internal Gas Target Experiment (MAGIX), the beam is phase shifted and recirculated back into the linac sections. These will transfer the kinetic beam energy back to the RF-field by deceleration of the beam and allow for high beam power with low RF-power input. Since most of the beam does not interact with the target, the beam will mostly just pass the target untouched. However, a fraction of the scattered electrons may be in the range outside the accelerator and detector acceptances and therefore cause malicious beam dynamical behavior in the linac sections or even damage to the machine. The goal of this work is to determine the beam behavior upon target passage by simulation and experiment and to protect the machine with a suitable collimation system. The present status of the investigations is presented.

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MOPSPP008

Low Energy Beam Transport System for MESA

20

C. Matejcek, K. Aulenbacher, S. Friederich, L.M. Hein
IKP, Mainz, Germany

An important part of the new accelerator MESA (Mainz Energy recovering Superconducting Accelerator) is the low energy beam transport system connecting the 100 keV electron source with the injector accelerator. Here the spin manipulation and the bunch preparation for the injector accelerator take place. Due to the low energy, space charge will be an challenging issue in this part. Therefore, start-to-end simulations were done with a combination of the two particle dynamics codes PARMELA* and CST**. At the moment, a test setup is being built up to check the functionality of devices and compare the beam parameters with the simulation. Here the focus lies on the bunch preparation system because at this part we expect high impact of the space charge by reason of the necessary bunch compression. The advance of the test setup, the simulations and measurements done so far will be shown.
* Phase and Radial Motion in Ion Linear Accelerators
** Computer Simulation Technology

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MOPSPP009

Beam Break Up Simulations for the MESA Accelerator

26

C.P. Stoll, F. Hug, D. Simon
IKP, Mainz, Germany

Funding: Supported by DFG through GRK 2128
MESA is a recirculating superconducting accelerator under construction at Johannes Gutenberg-Universität Mainz. It will be operated in two different modes: the first is the external beam (EB) mode, where the beam is dumped after being used at the experiment. The required beam current in EB mode is 150 µA with polarized electrons at 155 MeV. In the second operation mode MESA will be run as an energy recovery linac (ERL) with an unpolarized beam of 1 mA at 10⁵ MeV. In a later construction stage of MESA the achievable beam current in ERL-mode shall be upgraded to 10 mA. To understand the behavior of the superconducting cavities under recirculating operation with high beam currents simulations of beam breakup have to be performed. Current results for transverse beam break up calculations and simulations with Beam Instability (bi) code are presented.

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MOPSPP011

Resonant Coherent Diffraction Radiation System at KEK-cERL

Y. Honda, A. Aryshev, T. Miyajima, T. Obina, R. Ryukou, M. Shimada, R. Takai, N. Yamamoto
KEK, Ibaraki, Japan

Coherent radiation from a short bunched electron beam has been expected to be a high power source in THz regime. Especially the feature of the modern energy recovery linac is suitable for a high averaged power source. We propose to test an advanced scheme of resonantly exciting coherent diffraction radiation in an optical cavity. By stimulating the radiation in a multi-bunch beam, highly enhanced radiation power can be extracted. This system can excite all the cavity longitudinal modes at the same time, it can be a broadband source. We are preparing an experimental setup to test the resonant radiation in the cERL at KEK.

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MOPSPP012

Identification of Ion Bombardment Area on the Photocathode After 900 µA CW Beam Operation at cERL

M. Yamamoto, Y. Honda, X.J. Jin, T. Miyajimapresenter, T. Obina
KEK, Ibaraki, Japan
Y. Kameta
e-JAPAN IT Co. Ltd, Hitachi, Japan
T. Kawasaki
Toshiba, Yokohama, Japan
N. Nishimori
QST, Tokai, Japan
N. Nishimori
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan

Compact-ERL (cERL) which is under development as an ERL demonstration machine at KEK succeeded in stable supply of CW beam exceeding 900 uA from a GaAs photocathode mounted on a DC-gun in March 2016. In the case of high current beam operation, the ions generated by collision of the beam and the residual molecules on the beam axis is increase and its flow back to the electron gun. As a result, the quantum efficiency (QE) of the photocathode decreases due to ion bombardment is the main factor of determining the cathode lifetime. After the CW operation of the accumulated extracted charge of ~10 Coulomb, steady decrease in QE due to ion bombardment has not yet been clearly confirmed. In order to analyze the area damaged by ion bombard, 2D QE distribution (QE map) measurement system was newly installed in the cathode preparation system. From QE map analysis before and after the CW operation, we confirmed two types of QE decrease. The area about 2 mm diameter near the center of the photocathode that the QE recovery is insufficient by the reactivation process is presumed the damage by ion bombardment.

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MOPSPP013

Proposal of Sharing 6-GeV Class CW Superconducting Linac With ILC and High Brilliance X-ray Light Source

M. Shimada, M. Yamamoto, K. Yokoya
KEK, Ibaraki, Japan
R. Hajima
QST, Tokai, Japan

We propose sharing of the 6-GeV class CW superconducting linac with ILC and X-ray light source. ILC utilizes it for the positron source and the two boosters for the 5-GeV damping ring. The conventional positron source, which is based on a collision of the multi-GeV electron with the target, was chosen to lengthen the macro-pulse duration for avoiding the heat loading. In this proposal, the CW linac realizes the long macro-pulse duration beam operation of the positron beam as well as the electron for collision with the target. Simultaneously, the CW linac can used as the 5-GeV booster of the polarized electron beam at the same bunch pattern. Because of the low average current of beams of ILC, the CW linac have enough ability to accelerate/decelerate the high quality electron beam for the high brilliant X-ray light source such as 6-GeV class ERL light source and XFELO. Each electron beam has different injection energy, injects at the different merger and accelerates at the different RF phase. Therefore, the electron energies are different at the end of the CW linac and it makes the simultaneous operation possible.

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MOPSPP015

Development of a Multialkali Photocathode DC Gun for High Current Operation

29

THICCC003

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N. Nishimori
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan
R. Hajima, R. Nagai, M. Sawamura
QST, Tokai, Japan

Funding: This work is partially supported by a JSPS Grant-in-Aid for Scientific Research in Japan (15K13412).
We have developed a DC gun test stand at National Institutes for Quantum Radiological Science and Technology (QST) for high current electron beam generation. The gun test stand consists of an alkali antimonide photocathode preparation chamber, a DC gun with a 250kV-50mA Cockcroft Walton high voltage power supply, and beam line with a water cooled beam dump to accommodate 1.5 kW beam power. We successfully fabricated a Cs₃Sb photocathode with quantum efficiency of 5.8 % at 532 nm wavelength and generated 150 keV beam with current up to 4.3 mA with 500 mW laser at 532 nm wavelength. Unfortunately, we encountered a vacuum incident during beam transport of high current beam and the development has been halted. We will fix the vacuum problem and restart the gun development as soon as possible.

Slides MOPSPP015 [22.138 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-ERL2017-MOPSPP015

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MOPSPP016

Discharge Mechanism of Ultra-High Vacuum Gap Derived From the HV Conditioning Result of the cERL DC-Gun

M. Yamamoto
KEK, Ibaraki, Japan
N. Nishimoripresenter
QST, Tokai, Japan
N. Nishimoripresenter
Tohoku University, Research Center for Electron Photon Science, Sendai, Japan

Funding: JSPS Grant-in-Aid for Scientific Research in Japan (15H0359, 16K05385)
Development of a high brightness electron beam source is indispensable for realizing high repetition X-FEL and CW EUV-FEL as a next generation light source. The high voltage (HV) DC-gun that realized acceleration voltage of > 500 kV and electric field of > 5 MV/m is one of the candidates. In order to stably DC-gun operation, the HV conditioning process is an essential step as preparation of DC-gun operation. The HV conditioning was carried out on compact-ERL (cERL) electron gun and clarified the following four points. i) The voltage at which discharge stops (discharge stop voltage) exists, ii) The discharge stop voltage increases almost continuously with the number of discharges, iii) The gas released at the occurrence of discharge is almost proportional to the difference between the discharge start voltage and the discharge stop voltage, iv) The hold-off time of the voltage is very long under the discharge stop voltage. We focused on the electron stimulated desorption (ESD) phenomenon occurring at the anode can explain these phenomena in a consistent and considered the mechanism of discharge generation in DC field and HV conditioning progression in ultrahigh vacuum (UHV).

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MOPSPP017

Energy Distribution and Work Function Measurements for Metal Photocathodes With Measured Levels of Surface Roughness

T.S. Beaver, L.B. Jones, B.L. Militsyn, T.C.Q. Noakes, R. Valizadeh
STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
S. Mistry
STFC/DL, Daresbury, Warrington, Cheshire, United Kingdom

Funding: The work is part of EuCARD2, partly funded by the European Commission, GA 312453. Funded by the Science and Technology Facilities Council.
The minimum achievable emittance in an electron accelerator depends strongly on the intrinsic emittance of the photocathode electron source which is measureable as the mean longitudinal and transverse energy spreads in the photoemitted electrons. Reducing emittance in an accelerator driving a Free Electron Laser (FEL) delivers significant reduction in the saturation length for an X-ray FEL, reducing machine cost and increasing X-ray beam brightness. There are many parameters which affect the intrinsic emittance of a photocathode. Surface roughness is a significant factor*, and consequently the development of techniques to manufacture low roughness photocathodes with optimum emission properties is a priority for the electron source community. In this work, we present transverse energy distribution and work function measurements made using our TESS facility** for electrons emitted from copper and molybdenum photocathodes with differing levels of measured surface roughness.
* Proc. FEL '06, THPPH013, 583586
** Proc. FEL '13, TUPPS033, 290293

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