Scientific Highlights from the Department "Large Research Facilities" (GFA)

GFA Scientific Highlights

X-band prototype structure

08.11.2016 Radio-frequency structures at X-band frequencies (~ 12 GHZ) are being considered for applications in compact Free Electron Lasers, medical linacs, a future linear collider (CLIC project) and as a diagnostic for measuring ultra-short (femtosecond) electron pulses in FELs. A first prototype of such a structure has been built at PSI employing the realization procedures that have been developed for the C-Band (6 GHz) structures of the SwissFEL linac. The structure was designed in the framework of a collaboration between CERN and the Large Research Facilities Division (GFA) of PSI with the financial support of the SNF (grant 20FL20_147463). The individual cells were precision machined by the company “VDL Enabling Technologies Group Switzerland AG” and the structure brazed by the mechanical engineering department (AMI) at PSI. In the near future, it will be tested at high power on a test bench at CERN.

First acceleration with the SwissFEL C-band module

13.09.2016 On Thursday 08/09/2016, the first C-band module boosted an electron beam from 150MeV to 390 MeV. This is the first beam acceleration test of a C-band module in PSI and is an important milestone for the project, since the main accelerator consists of 26 C-band modules of the same kind. In the module, the RF pulse is first generated by a pulsed modulator- klystron amplifier, placed in the technical gallery, and is guided to the pulse compressor (BOC), where it is compressed by a factor four and split to the four accelerating cavities in the beam tunnel. The 104 accelerating cavities are two meters long and have been developed at PSI, produced together with the VDL Enabling Technologies Group Switzerland AG. The 26 BOCs have been developed and fully produced at PSI. An outstanding feature of the SwissFEL C-band module is that for the first time, accelerating structures and pulse compressors have been produced on frequency, i.e. without any tuning of the frequency. During the acceleration test, the module was operating at the nominal RF power setting of 36 MW and 3 microseconds pulse at 5.712GHz and a repetition rate of 10Hz. The measured beam energy gain was 240 MeV, with excellent agreement with the expected value of 233 MeV. The installation of the C-band modules has been completed with the mounting of the last unit on Tuesday 13/09/2016.

First Electron Beam in the SwissFEL Facility

24.08.2016 On August, 24th 2016, the electron gun accelerated the first photo-electrons in SwissFEL up to the energy of 7 MeV, initiating the beam commissioning phase of the new SwissFEL facility. After several days of RF conditioning, the gun reached the nominal acceleration gradient of 100MV/m at an input power of 17MW with a pulse-width of 1 micro second at an operating frequency of at 2998.8 MHz. This gun has previously already been commissioned in the SwissFEL Test Facility from June until October 2014 and then relocated to the new SwissFEL facility in the forest of Würenlingen. During this period, several upgrades to the system have been carried out; The klystron and pulsed high power modulator systems have been relocated and equipped with new, improved high voltage connectors, a rectifier unit, suitable to allow 100 Hz stable operation, and a new isolation oil purification system. The RF-system has also been equipped with a new interlock system to ensure safe operation. Additionally, a new optical based reference signal system provides ultra-low phase jitter rf signals in the few femto seconds range which guarantees, together with a new sophisticated low level RF system, stable operation and synchronization with all other subsystems. The low level RF system is well integrated into the EPICS control system and delivers detailed beam synchronous data for every RF pulse.

21st International Conference on Cyclotrons and their Applications

11.09.2016 The 21st conference in this series takes place from September 12 to 16, 2016 at the Federal Institute of Technology in Zürich. The cyclotron is a simple and efficient particle accelerator and its invention for the purpose of performing fundamental research dates back to 1929. Ernest Lawrence received the Nobel Prize for his idea in 1939. Today cyclotrons are used in a broad range of applications from large and complex facilities for basic research to highly optimized and cost effective solutions for industrial and medical applications. The series of cyclotron conferences provides a forum for the world leading experts to meet and to discuss technological and physics advancements in the field. The Paul Scherrer Institute operates two outstanding accelerator facilities that are driven by cyclotrons – the High Intensity Proton Accelerator HIPA, generating a very intense beam of 1.4 MW power, and the proton therapy facility Proscan with 3 Gantries. These facilities support research activities ranging from particle physics with intense muon beams and ultra-cold neutrons through solid state physics using thermal neutrons and surface muons to isotope production and cancer treatment with precise proton beam irradiation. A large international user community, including many researchers at PSI and ETH make ample use of these opportunities, and numerous important results have been achieved. In the 57 years history of cyclotron conferences this is the second time that the event is being held at the ETH in Zürich. We expect that on this occasion, as then in 1975, a good exchange of ideas will lead towards further development of these accelerators, providing even greater opportunities for research and applications with cyclotron based facilities.

Proton Accelerator Operation Statistics 2015

05.02.2016 For the first time in the history of the High Intensity Proton Accelerator the availability of the facility reached an outstanding value of 95% in 2015 with a record value of 99.3% in week 44. In comparison to the two previous years this corresponds to a reduction of the downtime by 50%. The user operation in 2015 was started as scheduled and already in the first week the machine was available 97% of the scheduled beam time. In addition to the smooth operation of the facility, high intensity beam experiments could regularly be performed with currents of up to 2.4 mA. The extraordinary performance of the facility could mainly be achieved by the commitment of the technical groups who managed to overcome the problems with the aluminium cavity in the Ring cyclotron. By coating parts of the cavity’s surface with a carbon layer, multipactoring and resulting x-ray emission could be reduced by two orders of magnitude leading to fewer short interruptions and a smooth operation of the whole facility.

GFA delivers the SwissFEL magnets on schedule

29.01.2016 The Paul Scherrer Institut is building an X-ray free electron laser (SwissFEL) providing a source of intense, ultra-short pulses of coherent radiation in the wavelength range of 0.1 nm to 0.7nm. For the hard X-ray beam line, the magnet section in GFA/ATK has the responsibility for the design, the procurement and the magnetic qualification of 267 electro-magnets of 22 different types. Several design studies were performed in an attempt to meet the required magnet specifications while optimizing construction and operation cost. Various types of dipole magnets (26 units in total) are used to bend the electron beam either horizontaly or vertically, whereas quadrupoles of 45 mm, 22 mm and 12 mm aperture (173 units), solenoids (10 units) and sextupoles (14 units) provide linear and non-linear focusing. Separate dipole correctors (44 units) complete the production. The majority of the magnets were manufactured in industry according to detailed magnet section specifications. A strict Quality Assurance strategy based on (1) the qualification of the manufacturing tools, (2) the monitoring of the critical steps in the assembly phase and (3) the application of the qualified procedures and full traceability was applied. A dedicated magnet measurement plan for the magnetic qualification, in house, of all the magnets at their operating conditions and within the required tolerances was implemented. It includes an accurate assessment of the field quality and the determination of the magnetic axis position. Dedicated measurements systems were used for this purpose: the field quality of the quadrupoles was measured with an accuracy of 0.1 % using two small aperture rotating coils, designed and produced by CERN following magnet section specifications, and a vibrating wire system was built in GFA/ATK to determine the magnetic axis position with an accuracy of 50 micro meters. Several developments on the magnet section Hall probes were also carried out for magnetic field mapping in small aperture magnets. All the magnets for the hard X-ray beam line were delivered on time and progressively installed. The developed equipment and the experience gained during the design, the fabrication and the series tests are a significant asset for the production of the magnetic elements for the Athos beam line and future PSI light sources.

ETH-Medal 2015 for outstanding MSc thesis

17.04.2015 The detailed understanding of particle motion in the outer region (halo) of a bunched beam is of utmost importance for all existing and future high intensity hadron accelerators in view of minimizing particle losses and machine activation. Particle-core models separate the motion of halo particles from the core and treat them as test-particles. Therefore these reduced-order models are computationally inexpensive compared to full particle-in-cell simulations and can, to some extent, be derived analytically, thus giving insights into the non-linear mechanism of halo formation. These models have been successfully applied to linear accelerators, first by Gluckstern in 1994, for coasting round beams. The key point of Pirmin Berger's thesis is the extension of the model to ellipsoidal 3D bunched beams including dispersion, acceleration, and a self-consistent prediction of the core motion. A fully analytic model and a numerical model, the so-called extended particle-core model, have been derived. The new models were then applied to a simplified cyclotron but with parameters (e.g. tunes, energies) similar to the PSI Injector 2.

A division of the phase space into four characteristic regions (A: unstable fix-point, B: inner separatrix, C: stable fix-point and D: outer separatrix) has been observed, as depicted in Figure 1. The purely analytic model (left of Fig. 1) compares, within limits, very well to the numerical model. We speculate that such reduced-order models may be the nucleus of future on-line models, accurately describing halo phenomena in high intensity hadron accelerators such as the Injector 2 and the PSI Ring cyclotron.

First beam from the SwissFEL electron gun

6.06.2014 The new 3 GHz photocathode gun will provide the electron bunches for SwissFEL and has recently been installed in the SwissFEL injector test facility. There, it replaced the CTF2-gun 5, borrowed from CERN. The new gun is capable now of operation with 100Hz repetition frequency and a higher field on cathode and improved field symmetry. After RF conditioning of about 4 days, the gun reached the nominal acceleration gradient of 100 MV/m at an input power of about 17 MW and pulse-width of 1 microsecond. The gun incorporates the same type of copper cathode plugs, as the CTF2-gun and accelerates the electrons in 3 cells up to a kinetic energy of 6.6 MeV. Each cell has a pick-up for amplitude and phase monitoring. The first measurements of the electron beam on the spectrometer arm confirm the expected kinetic energy. Next weeks of test injector operation will be dedicated to gun commissioning and more detailed beam quality measurements.

RF Pulse compressor for the SwissFEL

11.06.2013 The SwissFEL C-band (5.712 GHz) linac consists of 26 RF modules. Each module is composed of a single 50 MW klystron feeding a pulse compressor and four two meter long accelerating structures. The pulse compressor is a passive device that compresses in time the 3 μs pulse from klystron into a 330 ns pulse. The compressed power is then guided to the four accelerating structures. The pulse compressor is based on a single Barrel Open Cavity (BOC). The BOC makes use of a “whispering gallery” mode which has an intrinsically high quality factor and operates in resonant rotating wave regime (Figure 1); moreover, and contrary to the conventional SLED scheme, a single cavity is sufficient to define the pulse compressor, without the need for two cavities. A prototype has been manufactured by the Dutch company VDL (Figure 2) and successfully power tested in PSI reaching a peak power of 300 MW.

MEGAPIE samples delivered to partners for post irradiation investigation

24.05.2013 The MEGAWatt Pilot Experiment was operated for neutron generation with the PSI high intensity proton beam in 2006. The experiment utilized liquid target material, a lead bismuth eutectic. This marked a major milestone towards Accelerator Driven Systems (ADS), which are intended to be used for the incineration of nuclear waste. Now, after a 5 year long campaign at PSI and in ZWILAG, unique material samples from the irradiated target have been produced and distributed amongst the partners of this international initiative. The sample material – mostly structural material used for the construction of the target vessel – will, for the first time ever, allow scientists to investigate damage of these materials due to irradiation and liquid metal corrosion/erosion at the same time. On May 15th 2013 the last shipment of samples has left PSI towards Japan. With more than 800 material samples the post irradiation examination of MEGAPIE is the biggest effort of its kind. PSI scientists from NUM, GFA and NES were involved in the project.