Rasmus Ischebeck

• Dr.
• Paul Scherrer Institute

MeV ultrafast electron diffraction has become a new frontier for the study of molecular dynamics. With the temporal resolution of MeV-UED being limited, in part, by the electron bunch length at the target, electron sources used for this technique are becoming ever more intricate in the push for shorter bunches length. However, moving to these compl...

An international collaboration between PSI and INFNLNF has been undertaken with the aim of developing the next generation of high brightness electron sources. Through this collaboration, two unique high gradient RF photoguns that operate in the C-band frequency regime have been designed and realized. Concurrent to this, a new high power test stand...

The bunch length in a linac driven Free Electron Laser (FEL) is a major parameter to be characterized to optimize the final accelerator performance. In linear machines, this observable is typically determined from the beam imaged on a screen located downstream of a Transverse Deflecting Structure (TDS) used to impinge a time dependent kick along th...

Wall current monitors (WCMs) are devices used to measure the bunch charge or current profile of a charged particle beam. They are commonly perceived as absolute charge measurement devices, which is not really true, since the pickup response at DC is zero. A charge value has to be determined from the variation of the output signal. For very short bu...

The international FCC study group published in 2019 a Conceptual Design Report for an electron-positron collider with a centre-of-mass energy from 90 to 365 GeV with a beam currents of up to 1.4 A per beam. The high beam current of this collider create challenging requirements on the injection chain and all aspects of the linac need to be carefully...

The 2020 update of the European Strategy for Particle Physics emphasised the importance of an intensified and well-coordinated programme of accelerator R&D, supporting the design and delivery of future particle accelerators in a timely, affordable and sustainable way. This report sets out a roadmap for European accelerator R&D for the next five to...

The 2020 update of the European Strategy for Particle Physics emphasised the importance of an intensified and well-coordinated programme of accelerator R&D, supporting the design and delivery of future particle accelerators in a timely, affordable and sustainable way. This report sets out a roadmap for European accelerator R&D for the next five to...

Novel high-gradient accelerators have demonstrated acceleration of electrons and positrons with electric field strengths of 1 to > 100 GeV/m. This is about 10 to 1000 times higher than achieved in RF-based accelerators, and as such they have the potential to overcome the limitations associated with RF cavities. Plasma-based accelerators have produc...

At the x-ray free-electron laser SwissFEL, at the Paul Scherrer Institute, Switzerland, beam loss monitors are used to determine loss positions along the linear accelerator and protect critical elements such as the undulator magnets from excess radiation. These monitors are integrated into the machine protection system (MPS) allowing beam losses to...

Results on fabrication and experimental characterization of wire scanners (WS) with submicrometer spatial resolution are presented. Independently fabricated at PSI and FERMI by means of nanolithography, the proposed WS solutions consist of 900 and 800 nm wide free-standing stripes ensuring a geometric resolution of about 250 nm. The nanofabricated...

The transverse emittance of the electron beam is a fundamental parameter in linac-based x-ray free-electron lasers (FELs). We present results of emittance measurements carried out at SwissFEL, a compact x-ray FEL facility at the Paul Scherrer Institute in Switzerland, including a description of the novel high-resolution measurement techniques and t...

Dielectric Laser Acceleration (DLA) achieves the highest gradients among structure-based electron accelerators. The use of dielectrics increases the breakdown field limit, and thus the achievable gradient, by a factor of at least 10 in comparison to metals. Experimental demonstrations of DLA in 2013 led to the Accelerator on a Chip International Pr...

Diagnostics of the beam transverse profile with ever more demanding spatial resolution is required by the progress on novel particle accelerators - such as laser and plasma driven accelerators - and by the stringent beam specifications of the new generation of X-ray facilities. In a linac driven Free-Electron-Laser (FEL), the spatial resolution con...

THz pulses have many unique properties in terms of radiation matter interaction. In particular, their non-ionizing exci-tation of phonons in matter makes them a preferred pump for pump-probe studies at free-electron laser facilities. Among many THz generation techniques, the one based on dielectric lined waveguide and electron beam is emerging as a...

A tomographic gas-density diagnostic using a Single-Beam Wollaston Interferometer able to characterize non-symmetric density distributions in gas jets is presented. A real-time tomographic algorithm is able to reconstruct three-dimensional density distributions. A Maximum Likelihood-Expectation Maximization algorithm, an iterative method with good...

A tomographic gas-density diagnostic using a single-beam Wollaston interferometer able to characterise non-symmetric density distributions in gas jets is presented. A real-time tomographic algorithm is able to reconstruct three dimensional density distributions. A Maximum Likelihood -- Expectation Maximisation algorithm, an iterative method with go...

The Accelerator on a Chip International Program (ACHIP), funded by the Gordon and Betty Moore Foundation for a 5 year period, pursues basic research and development for a super-compact accelerator on a chip, where the accelerating structure is a dielectric microstructure excited by femtosecond laser pulses. The Paul Scherrer Institute (PSI) will co...

The SwissFEL light-facility will provide coherent X-rays in the wavelength region 7-0.7 nm and 0.7-0.1 nm. In SwissFEL, view-screens and wire-scanners will be used to monitor the transverse profile of a 200/10pC electron beam with a normalized emittance of 0.4/0.2 mm.mrad and a final energy of 5.8 GeV. Compared to view screens, wire-scanners offer...

The SwissFEL Injector Test Facility operated at the Paul Scherrer Institute between 2010 and 2014, serving as a pilot plant and test bed for the development and realization of SwissFEL, the x-ray Free- Electron Laser facility under construction at the same institute. The test facility consisted of a laser-driven rf electron gun followed by an S-ban...

SwissFEL is a X-rays Free Electron Laser (FEL) driven by a 5.8 $\mathrm{GeV}$ linac under construction at Paul Scherrer Institut. In SwissFEL, wire-scanners (WSCs) will be complementary to view-screens for emittance measurements and routinely used to monitor the transverse profile of the electron beam during FEL operations. The SwissFEL WSC compose...

Having accurate and comprehensive photon diagnostics for the X-ray pulses delivered by free-electron laser (FEL) facilities is of utmost importance. Along with various parameters of the photon beam (such as photon energy, beam intensity, etc.), the pulse length measurements are particularly useful both for the machine operators to measure the beam...

Longitudinal diagnostics of the electron bunch shapes play a crucial role in the operation of linac-based light sources. Electro-optical techniques allow us to measure the longitudinal electron bunch profiles non-destructively on a shot-by-shot basis. Here we present results from measurements of electron bunches with a length of 200-900 fs rms at t...

The resolution of streak camera systems strongly depends on the slew rate of the deflecting element, being proportional to the amplitude and the frequency of the deflector. An attractive approach to reach femto and even sub-femto second resolution are THz driven electron streak cameras, which have been only recently proposed. Here, the ultra fast s...

SwissFEL is the Free Electron Laser (FEL) facility under construction at the Paul Scherrer institute (PSI), aiming to provide users with X-ray pulses of lengths down to 2 femtoseconds at standard operation. The measurement of the length of the FEL pulses and their arrival time relative to the experimental laser is crucial for the pump-probe experim...

The accurate measurement of the arrival time of a hard X-ray free electron laser (FEL) pulse with respect to a laser is of utmost importance for pump-probe experiments proposed or carried out at FEL facilities around the world. This manuscript presents the latest device to meet this challenge, a THz streak camera using Xe gas clusters, capable of p...

The recent entry of X-ray free electron lasers (FELs) to all fields of physics has created an enormous need, both from scientists and operators, for better characterization of the beam created by these facilities. Of particular interest is the measurement of the arrival time of the FEL pulse relative to a laser pump, for pump-probe experiments, and...

As Free Electron Lasers create ultra-short bunch lengths, the longitudinal diagnostic for such femto-second bunches becomes more difficult. We suggest a bunch length method using the spectral analysis of Optical Transition Radiation (OTR) in the visible frequency domain. The frequency content of OTR is measured by inserting an aluminium coated sili...

The quality of the beam transverse emittance at the cath-ode and the uniformity of the longitudinal compression of the electron bunch are essential for the lasing efficiency of a Free Electron Laser. In SwissFEL the longitudinal compression of the electron beam is performed by means of two magnetic chicanes and an off-crest acceleration scheme. The...

Initiating the gain process in a free-electron laser (FEL) from an external highly coherent source of radiation is a promising way to improve the pulse properties such as temporal coherence and synchronization performance in time-resolved pump-probe experiments at FEL facilities, but this so-called "seeding" suffers from the lack of adequate source...

The SwissFEL project, under development at the Paul Scherrer Institut, will produce FEL radiation in a wavelength range from 0.1 nm to 7 nm. The facility consists of an S-band rf-gun and booster, and a C-band main linac which accelerates the beam up to 5.8 GeV. Two magnetic chicanes will compress the beam between 2.5 fs rms and 25 fs rms depending...

The SwissFEL is an X-Ray (0.1nm-7nm) Free Electron Laser user facility which is being planned for the Paul Scherrer Institute in Switzerland. At the SwissFEL, view screens will be used to monitor the transverse profile of the electron beam. Wire scanners are also to be employed as the high beam densities of the electron beam will hamper the standar...

SwissFEL [1] is a hard X-ray FEL facility currently being designed at PSI. It uses a photocathode gun, S-band injector and C-band main linac to drive a hard X-ray undulator line with 100 Hz repetition rate. Beam commissioning of the hard X-ray undulator line called Aramis is scheduled to start in 2016. The Aramis line extends over a length of 177 m...

The sFLASH project at DESY is an experiment to study direct seeding using a source based on the high-harmonic generation (HHG) process. In contrast to SASE, a seeded FEL exhibits greatly improved longitudinal coherence and higher shot-to-shot stability (both spectral and energetic). In addition, the output of the seeded FEL is intrinsically synchro...

The SwissFEL injector test facility at the Paul Scherrer Institute is the principal test bed and demonstration plant for the SwissFEL project, which aims at realizing a hard-X-ray Free Electron Laser by 2017. The RF photoinjector facility has been in operation since 2010 and has recently reached its design energy of 250 MeV. A newly installed movab...

In this article we demonstrate the net acceleration of relativistic electrons using a direct, in-vacuum interaction with a laser. In the experiment, an electron beam from a conventional accelerator is first energy modulated at optical frequencies in an inverse-free-electron-laser and bunched in a chicane. This is followed by a second stage optical...

The sFLASH-experiment has been built at the Free-Electron Laser in Hamburg (FLASH) to study the high-gain-FEL amplification of a laser seed from a high har-monic generation (HHG) source. Ideally, the HHG-seed can be amplified up to a GW-power level, improving both the shot-to-shot stability and the longitudinal coherence of the FEL-pulse. In 2010/2...

Contribution to a conf. proceeding (book/online)

In August 2010 the Paul Scherrer Institute inaugurated the SwissFEL Injector Test Facility as a first step towards the Swiss hard X-ray FEL planned at PSI. The main purpose of the facility is to demonstrate and consolidate the generation of high-brightness beam as required to drive the 6 GeV SwissFEL accelerator. Additionally the injector serves as...

The scaling of the two important figures of merit, the transformer ratio T and the longitudinal electric field Ez, with the peak drive-bunch current Ip, in a nonlinear plasma wakefield accelerator is presented for the first time. The longitudinal field scales as Ip^0.623, in good agreement with nonlinear wakefield theory (~ Ip^0.5), while the unloa...

Experimental and simulation results of an electron gun test facility, based on pulsed diode acceleration followed by a two-cell rf cavity at 1.5 GHz, are presented here. The main features of this diode-rf combination are: a high peak gradient in the diode (up to 100MV/m) obtained without breakdown conditioning, a cathode shape providing an electros...

We present plasma wakefield acceleration experimental results showing that the energy gain by 28.5 GeV electrons scales with plasma length and reaches 14 GeV over a plasma with a density of 2.6×1017 cm−3 and a length of 31 cm. At this plasma density the average accelerating gradient is 36 GeV m−1. These results are in good agreement with the number...

In the framework of the SwissFEL project, an alternative electron source to an RF photo-gun was investigated. It consists of a high voltage (up to 500 kV), high gradient pulsed diode system followed by single stage RF acceleration at 1.5 GHz. The electrons are produced from photocathodes or from field emitter arrays. The final goal of this accelera...

We developed a powerful UV laser at a central wavelength varying from 260-283 nm. The laser system based on a frequency-trippled Ti:sapphire amplifier delivers mJ pulse energy within a duration of 1-10 ps (fwhm) with 1.5 nm spectral width (fwhm). The system is used to explore thermal emittance and quantum efficiency dependence on photon energy from...

The SwissFEL Injector Test Facility consists of an RF gun, an accelerating section for a final energy of 250 MeV, and two diagnostics sections. Transverse profiles of the electron beam can be recorded at 27 locations by imaging fluorescent crystals that can be inserted into the beam. At 21 of these, the fluorescent screens are complemented by optic...

The spectral and angular distribution of the radiation in-tensity by a single and individually radiating electron is in principle different from what expected from a high den-sity electron beam. The beam particle density modifies via a charge form factor the angular and spectral distri-butions characterizing the radiation emission by a single elect...

The free-electron laser facility FLASH at DESY (Hamburg) was upgraded during a five month shutdown in winter 2009 [1]. Part of this upgrade was the installation of a direct seeding experiment in the XUV spectral range. Beside all components for transport and diagnostics of the photon beam in and out of the accelerator environment, a new 10 m long v...

sFLASH is a seeded experiment in Free Electron Laser in Hamburg (FLASH) [1], which uses a 38nm high harmonic gain (HHG) based EUV-beam laser in tandem with FLASH electron bunches at the entrance of a 10m variablegap undulator. The temporal overlap between the electron and HHG beams is critical to the seeding process. Use of a 3rd harmonic accelerat...

Tests of an electron gun based on diode acceleration followed by a two-cell RF cavity at 1.5 GHz are being performed at PSI. The diode consists of a photocathode / anode assembly and is driven by a voltage pulse of 500 kV maximum in 200 ns FWHM. The diode configuration allows various types of cathode geometries including hollow cathode with field e...

A screen monitor containing OTR foils and scintillator crystals has been designed to measure the transverse profile of electron bunches in the PSI-XFEL. In conjunction with quadrupole magnets in FODO cells and a transverse de- flecting structure, the screen monitors will be used to mea- sure transverse and longitudinal phase space projections of th...

The costs and the time scales of colliders intended to reach the energy frontier are such that it is important to explore new methods of accelerating particles to high energies. Plasma-based accelerators are particularly attractive because they are capable of producing accelerating fields that are orders of magnitude larger than those used in conve...

The goals of this paper is: (1) to produce optically spaced electron microbunches; (2) to obtain independent verification and measure of microbunching; and (3) perform net acceleration of electrons with a laser.

Multi-GeV trapped electron bunches in a plasma wakefield accelerator (PWFA) are observed with normalized transverse emittance divided by peak current, $\epsilon_{N,x}/I_t$, below the level of 0.2 $\mu$m/kA. A theoretical model of the trapped electron emittance, developed here, indicates that emittance scales inversely with the square root of the pl...

When a highly relativistic electron is injected off-axis into an ion channel, the restoring force of the radial field of the ions will cause the electron to accelerate towards the axis, overshoot, and begin to undergo oscillations about the ion-column axis at a characteristic frequency; the betatron frequency. This so-called betatron motion will ca...

RF deflectors are crucial diagnostic tools for bunch length and slice emittance measurements with subpicoseconds resolution. Their use is essential in commissioning and operation of VUV and X-ray FELs. The 250MeV FEL injector [1], under construction at PSI, will use two RF deflectors. The first one will be installed after the gun at low energy (~7M...

Positron trapping and acceleration in a plasma wake using a four-bunch scheme [X. Wang , Phys. Rev. Lett. 101, 124801 (2008)PRLTAO0031-900710.1103/PhysRevLett.101.124801] is numerically investigated through 2D particle-in-cell simulations. This scheme that integrates positron generation, trapping, and acceleration into a single stage is a promising...

Contribution to a conf. proceeding (book/online)

In recent experiments plasma electrons became trapped in a plasma wakefield accelerator (PWFA). The transverse size of these trapped electrons on a downstream diagnostic yields an upper limit measurement of transverse normalized emittance divided by peak current, {var_epsilon}{sub N,x}/I. The lowest upper limit for {var_epsilon}{sub N,x}/I measured...

Recent experiments at SLAC have shown that high gradient acceleration of electrons is achievable in meter scale plasmas. Results from these experiments show that the wakefield is sensitive to parameters in the electron beam which drives it. In the experiment the bunch lengths were varied systematically at constant charge. The effort to extract a me...

We have recently proposed a new concept for generating, injecting and accelerating positrons in a plasma using a double-pulse electron bunch. Monte Carlo simulations show that the number of the positrons produced in a foil target has an exponentially decay energy spectrum. The energy threshold for the trapping of these positrons in a ultra-relativi...

An experimental effort is currently underway at the E-163 test beamline at Stanford Linear Accelerator Center to use a hollow-core photonic bandgap (PBG) fiber as a high-gradient laser-based accelerating structure for electron bunches. For the initial stage of this experiment, a 50pC, 60 MeV electron beam will be coupled into the fiber core and the...

Diagnostics with a transverse spatial resolution in the or-der or even higher than the intrinsic limit of the traditional OTR light spot imaging techniques is required for high energy and low emittance electron beams by FEL driver linac. High resolution measurements of the beam trans-verse size can be performed by moving the radiation de-tection fr...

A seeded free-electron laser (FEL) operating in the soft X-ray (XUV) spectral range will be added to the SASE FEL facility FLASH. The seed beam will be generated by higher harmonics of a near infrared laser system. A dedicated transport system will guide the radiation into the electron accelerator environment. Within the seed undula-tor section com...

The Free electron laser at Hamburg FLASH operates in the Self Amplified Spontaneous Emission SASE mode, delivering to users photons in the XUV wavelength range. The FEL seeding schemes promise to improve the properties of the generated radiation in terms of stability in intensity and time. Such an experiment using higher harmonics of an optical las...

Plasma density is one factor that contributes to the onset of ionization induced electron trapping in a plasma wakefield accelerator. Here, experimental measurements and theory exhibit the dependence of trapping on plasma density.

High gradient acceleration of electrons has recently been achieved in meter scale plasmas at SLAC. Results from these experiments show that the wakefield is sensitive to parameters in the electron beam which drives it. In the experiment the bunch lengths were varied systematically at constant charge. Here we investigate the correlation of peak beam...

A novel approach for generating and accelerating positron bunches in a plasma wake is proposed and modeled. The system consists of a plasma with an embedded thin foil into which two electron beams are shot. The first beam creates a region for accelerating and focusing positrons and the second beam provides positrons to be accelerated. Monte Carlo a...

To supply coherent, ultra-bright, and ultra-short XFEL photon beams covering a wide wavelength range from 0.1 nm to 7 nm, three FEL beamlines will be constructed in the planned PSI-XFEL facility. The FEL1 beamline will use a 6 GeV normal conducting S-band linac to generate hard X-rays from 0.1 nm to 0.7 nm, while the FEL2 beam-line will use a 3.4 G...

We report the production of optically spaced attosecond electron microbunches produced by the inverse free-electron-laser (IFEL) process. The IFEL is driven by a Ti:sapphire laser synchronized with the electron beam. The IFEL is followed by a magnetic chicane that converts the energy modulation into the longitudinal microbunch structure. The microb...

Summary form only given. Plasma-based accelerators have made remarkable progress in the last few years. In particular, the energy doubling of 42GeV incoming electrons has been demonstrated over a plasma length of only 85cm in a particle beam-driven plasma-based accelerator or plasma wakefield accelerator (PWFA). This distance is about 2000 times sh...

First measurements of the breakdown threshold in a dielectric subjected to GV/m wakefields produced by short (30-330 fs), 28.5 GeV electron bunches have been made. Fused silica tubes of 100 microm inner diameter were exposed to a range of bunch lengths, allowing surface dielectric fields up to 27 GV/m to be generated. The onset of breakdown, detect...

We present a series of laser-driven particle acceleration experiments that are aimed at studying laser-particle acceleration as an inverse-radiation process. To this end we employ a semi-open vacuum setup with a thin planar boundary that interacts with the laser and the electromagnetic field of the electron beam. Particle acceleration from differen...

Paul Scherrer Institute (PSI) is presently developing a low-emittance electron source for the PSI-XFEL project. The electron gun consists of an adjustable diode config- uration subject to pulses of 250 ns (FWHM) with am- plitude up to 500 kV from an air-core transformer-based high-voltage pulser. The facility allows high gradient tests with differe...

The Paul Scherrer Insitut (PSI) is presently developing a low emittance electron source for the PSI-XFEL project. The target beam parameters at the source are I=5.5 A, Q=0.2 nC and a slice emittance below 0.2 mm.mrad. The gun concept consists of a high gradient "diode" stage followed by a two-frequency two-cell cavity to allow fine tuning of the lo...

To check the performance of a planned low emittance gun for the PSI-XFEL project, a 500 kV pulsed diode based gun test facility was constructed at PSI in 2007. The gun was specially designed to have an adjustable gap between the cathode and the anode, and to allow extensive high gra-dient tests. Since the electron temperature at the cathode determi...

The electron hosing instability in the blow-out regime of plasma-wakefield acceleration is investigated using a linear perturbation theory about the electron blow-out trajectory in Lu et al. [in Phys. Rev. Lett. 96, 165002 (2006)10.1103/PhysRevLett.96.165002]. The growth of the instability is found to be affected by the beam parameters unlike in th...

The first phase of an experiment to study the performance of dielectric Cerenkov wakefield accelerating structures at extremely high gradients in the GV/m range has been completed. This experiment takes advantage of the unique SLAC FFTB electron beam and its demonstrated ultra-short pulse lengths and high currents (e.g., σz = 20 μm at Q = 3 nC). Th...

Contribution to a conf. proceeding (book/online)

Starting from next year the technical feasibility of a direct seeding scheme at 30 and 13 nm will be studied at the Free electron LASer in Hamburg FLASH . During a major shutdown the SASE FEL facility will be upgraded and it is planned to install in addition a high harmonic generation HHG seed laser, a new chain of 10m variable gap undulators and a...

Conference presentation

A typical diagnostic used to determine the bunch length of ultra-short electron bunches is the auto-correlation of coherent transition radiation. This technique can produce artificially short bunch length results due to the attenuation of low frequency radiation if corrections for the material properties of the Michelson interferometer and detector...

In the E-167 plasma wakefield acceleration experiment, electrons with an initial energy of 42 GeV are accelerated in a meter-scale lithium plasma. Particles are leaving plasma with a large energy spread. To determine the spectrum of the accelerated particles, a two-plane spectrometer has been set up.

The laser acceleration experiments conducted for the El63 project at the NLC Test Accelerator facility at SLAC have stringent requirements on the temporal properties of the electron and laser beams. A system has been implemented to measure the relative phase stability between the RF sent to the gun, the RF sent to the accelerator, and the laser use...