Florian Hug

Bio: Florian Hug is an academic researcher from Technische Universität Darmstadt. The author has contributed to research in topics: Linear particle accelerator & Particle accelerator. The author has an hindex of 7, co-authored 51 publications receiving 183 citations.

MESA - an ERL Project for Particle Physics Experiments

Abstract: The Mainz Energy-recovering Superconducting Accelerator (MESA) will be constructed at the Institut für Kernphysik of the Johannes Gutenberg University of Mainz. The accelerator is a low energy continuous wave (CW) recirculating electron linac for particle physics experiments. MESA will be operated in two different modes serving mainly three experiments: the first is the external beam (EB) mode, where the beam is dumped after being used with the external fixed target experiment P2, whose goal is the measurement of the weak mixing angle with highest accuracy. The required beam current for P2 is 150 μA with polarized electrons at 155 MeV. Additionally a so called beam-dump experiment (BDX) is planned to run in parallel to P2. In the second operation mode MESA will be run as an energy recovery linac (ERL). The experiment served in this mode is a (pseudo) internal fixed target experiment named MAGIX. It demands 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. Within this contribution an overview of the MESA project will be given highlighting the latest accelerator layout and the challenges of operation with high density internal gas targets.

Results from a 850 c heat treatment and operational findings from the 3 ghz srf cavities at the s-dalinac*

Abstract: Reaching the design quality factors and lowering the residual losses of the cavities at the superconducting electron linac in Darmstadt (S-DALINAC) is still an ongoing activity. After installation of an UHV furnace in Darmstadt two years ago, six cavities have now been heat treated at 850 C to remove residual hydrogen from the niobium cavity surface. A gas analysis during the heat treatment procedure showed that the cavities were strongly contaminated which might explain the low Q. We will report about the furnace, the heat treatment procedure and the results of subsequent surface resistance measurements. Prior to the heat treatment the field flatness of the 20 cell elliptical cavities was measured leading to unexpected results: After almost 10 years of operation, the field flatness of some cavities was heavily distorted. This might be an indication that the frequency tuning of the cavity, which is done by compressing the cavity longitudinally, does not act uniformly on each cell even though the cavity is only supported at the end cells.

Construction and Status of the Thrice Recirculating S-DALINAC

Abstract: The S-DALINAC was extended from a twice to a thrice recirculating linear accelerator to increase the maximum achievable energy close to its design value of 130 MeV by adding a third recirculation and thus enabling a fourth main accelerator passage. The new beam line also allows to operate the S-DALINAC as an ERL. A 180° phase shift in comparison to the RF-phase is possible due to a special path length adjustment system. During its operation, designated dipole magnets are moved on rails to increase or decrease the distance travelled by the beam. Both existing recirculations hold similar systems but are only capable to change the phase of up to a fraction of the RF-phase. The new system allows a 360° phase shift in total. The major pillars of this project have been the design (magnets, beam dynamics, lattice, etc.) [1], the planning of the whole project and the construction work done at the accelerator. These steps will be concluded by a commissioning. This contribution presents some insights into the construction time as well as an overview on the alignment procedure with the resulting precisions.

3 GHz digital rf control at the superconducting Darmstadt electron linear accelerator: First results from the baseband approach and extensions for other frequencies

Abstract: The low level rf system for the superconducting Darmstadt electron linear accelerator (S-DALINAC) developed 20 years ago and operating since converts the 3 GHz signals from the cavities down to the baseband and not to an intermediate frequency. While designing the new, digital rf control system this concept was kept: the rf module does the I=Q and amplitude modulation/demodulation while the low frequency board, housing an field programmable gate array analyzes and processes the signals. Recently, the flexibility of this concept was realized: By replacing the modulator/demodulators on the rf module, cavities operating at frequencies other than the one of the S-DALINAC can be controlled with only minor modifications: A 6 GHz version, needed for a harmonic bunching system at the S-DALINAC and a 324 MHz solution to be used on a room temperature cavity at GSI, are currently under design. This paper reviews the concept of the digital low level rf control loops in detail and reports on the results gained during first operation with a superconducting cavity.

New injector cryostat module based on 3 GHz SRF cavities for the S-Dalinac

Abstract: Each cryostat module of the superconducting Darmstadt electron linear accelerator S-DALINAC houses two 20 cell elliptical niobium cavities cooled by a helium bath at 2 K. They are operated at a frequency of 3 GHz and used to accelerate electron beams with gradients up to 5 MV/m. The accelerator itself consists of an injector and four main linac cryostats. A new cryostat module has been built to replace the actual injector module. It features a new waveguide transition line and will be operated with new cavities in order to increase the beam current and energy for nuclear physics experiments behind the injector section of the S-DALINAC. In addition, the frequency tuner for the cavities will be equipped with piezoelectric actuators, which will replace the current magnetostrictive fine tuner. We review the latest changes in the design of the module and its RF transition line and present some findings from the production of new cavities. The results of a measurement in liquid helium at 2 K with the piezoelect...

Status Report of the Berlin Energy Recovery Linac Project BERLinPro

Abstract: The Helmholtz Zentrum Berlin is constructing the Energy Recovery Linac (ERL) bERLinPro on its site in Berlin Adlershof. The project is intended to expand the required accelerator physics and technology knowledge essential for the design, construction and operation of future ERL based large scale facilities. The project goal is the generation of a high current (100 mA), high brilliance (norm. emittance below 1 mm mrad) cw electron beam. We report on the project progress: The building will be ready for occupancy in January 2017. The planning phase for the first project stage is completed. Most of the components have been ordered and are in fabrication or have already been delivered. An update of the status of the various subprojects as well as a summary of upcoming activities will be given. Project milestones and details of the timeline finally will be reviewed.

Superconducting CH-Cavity Heavy Ion Beam Testing at GSI

Abstract: Recently the first section of a standalone superconducting (sc) continuous wave (cw) heavy ion Linac as a demonstration of the capability of 217MHz multi gap Crossbar H-mode structures (CH) has been commissioned and extensively tested with beam from the GSI High Charge State Injector (HLI). The demonstrator set up reached acceleration of heavy ions up to the design beam energy and beyond. The required acceleration gain of 0.5MeV/u was achieved with heavy ion beams even above the design mass to charge ratio at maximum available beam intensity and full beam transmission. This contribution presents systematic beam measurements with varying RF-amplitudes and -phases of the CH-cavity, as well as versatile phase space measurements for heavy ion beams with different mass to charge ratio. The worldwide first and successful beam test with a superconducting multi gap CH-cavity is a milestone of the R&D work of Helmholtz Institute Mainz (HIM) and GSI in collaboration with Goethe University Frankfurt (GUF) in preparation of the sc cw heavy ion Linac project and other cw-ion beam applications. INTRODUCTION R&D and prototyping (demonstrator project) [1,2] in preparation of the proposed HElmholtz LInear ACcelerator (HELIAC) is assigned to a collaboration of GSI, HIM and GUF. The demonstrator setup, embedded in a new radiation protection cave, is located in straightforward direction of the HLI (Fig.1). Figure 1: CH-cavity test environment at GSI. The liquid helium (LHe) supply is covered by a 3000l tank, while the consumed helium gas is collected in a 25m3 recovery balloon and bottled by a compressor. The demonstrator [3] comprises a 15 gap sc CH-cavity (CH0) embedded by two superconducting solenoids; all three components are mounted on a common support frame [46]. The support frame, as well as the accelerator components, are suspended each by eight tie rods in a cross-like configuration balancing the mechanical stress during the cool down and warm up. The beam focusing solenoids provide maximum fields of 9.3T, the free beam aperture is 30mm. A configuration of one main Nb3Sn-coil and two compensation coils made from NbTi shields the maximum magnetic field of 9.3 T within a longitudinal distance of 10cm down to 30mT. The solenoids are connected to LHe ports inside the cryostat by copper tapes allowing dry cooling. The sc CHstructure CH0 (Fig. 2) is the key component and offers a variety of research and development. [7] Figure2: Sectional drawing of the 15-gap demonstrator CH-cavity (CH0). EQUUS BEAM DYNAMICS AND ADVANCED LINAC LAYOUT The beam dynamics layout of the entire sc cw-Linac (see Fig. 3) is based on the EQUidistant mUltigap Structure (EQUUS) concept, as proposed in [8]. It features high acceleration efficiency with longitudinal and transversal stability, as well as a straightforward energy variation. Energy variation can easily be achieved by varying the applied RF-voltage or the RF-phase of the amplifier. Highly charged ions with a mass-to-charge ratio of maximum 6 will be accelerated from 1.4 MeV/u up to 3.57.3 MeV/u. Figure 3: Advanced layout with three sc CH-cavities per cryomodule (two of four cryomodules are shown). Captions: QT = Quadrupole Triplet, RB = Rebuncher, S=Solenoid, B = 2-Gap-Buncher, D = Diagnostics. Energy variation while maintaining a high beam quality is the core issue with respect to beam dynamics, simulatTh is is a pr ep ri nt — th e fin al ve rs io n is pu bl ish ed w ith IO P 9th International Particle Accelerator Conference IPAC2018, Vancouver, BC, Canada JACoW Publishing ISBN: 978-3-95450-184-7 doi:10.18429/JACoW-IPAC2018-TUPAK004

Fully Digital and White Rabbit-Synchronized Low-Level RF System for LIPAc

Abstract: The International Fusion Materials Irradiation Facility (IFMIF) is an international project to study and qualify candidate materials for the construction of a future fusion reactor. One of the objectives of the IFMIF-Engineering Validation and Engineering Design Activity Project is to build a linear prototype accelerator (LIPAc) to validate the final IFMIF accelerator concept. LIPAc, which is currently under construction in Rokkasho (Japan), will generate a 9-MeV deuteron beam of 125-mA current with 100% duty cycle. CIEMAT (Spain) is in charge of providing the RF power system, including the low-level radio frequency (LLRF) system. Most of the developed LLRF systems are not completely digital, as they use analog front ends for intermediate frequency conversion before or after digitalization. However, the LIPAc LLRF system is a fully digital system: no analog frequency conversion is performed, the radio frequency (RF) signals are directly digitally synthesized and sampled by means of high-speed digital-to-analog converters and analog-to-digital converters. This is a clear advantage in terms of flexibility, reliability, reconfigurability, cost, and response time, as all the signal processing is performed in the digital domain. The other main advantages and novelties are the use of White Rabbit (WR) for timing synchronization and master oscillator distribution (distributed RF over WR). The LIPAc LLRF system is the first LLRF based on WR, and it has been designed and fabricated using the most advanced technology. This paper presents the detailed description of the LIPAc LLRF system and its advantages, performance evaluation, and verification.

Development and commissioning of a digital rf control system for the S-DALINAC and migration of the accelerator control system to an EPICS-based system

Abstract: The high resolution scattering experiments conducted at the superconducting Darmstadt electron linear accelerator S-DALINAC call for a small energy spread of (ΔE/E) ≈ 1×10⁻⁴ of the beam. This requires stabilization of amplitude and phase of the electric field inside the accelerating cavities to (ΔA/A)ᵣₘₛ = 8×10⁻⁵ and (Δφ)ᵣₘₛ = 0.7°. The design and the commissioning of a new digital rf control system is the subject of this thesis. At the S-DALINAC two types of cavities are in use. The normal-conducting chopper and buncher cavities only need corrections for slow temperature drifts and can be controlled by a generator-driven resonator control algorithm. The superconducting accelerating cavities have a very high quality factor and thus are very susceptible to vibrations. Therefore they are operated in a self-excited loop. The rf control system is based on in-house developed hardware that converts the rf signal down to the baseband, digitizes it and feeds it into an FPGA. Inside this FPGA, a soft digital signal processor executes the control algorithm. The resulting correction is modulated onto the rf signal again and sent back to the cavity. All accelerator components are remote-controlled from a central room via an accelerator control system. Since complex and re-programmable devices are not supported well by the existing in-house developed control system, the design and implementation of a new accelerator control system is also subject of this thesis. Further important aspects are expandability, usability and maintainability of the system. Therefore the new accelerator control system uses the EPICS framework as a basis since it already provides much of the basic functionality like graphical user interfaces and flexible control servers that can be customized rapidly. This allowed the implementation of more advanced functionality like extensive read-out and diagnostics for the rf control system. The read out data can be visualized with a software oscilloscope and a spectrum analyzer software. Additionally the system provides on-line rms errors that can be used to optimize the control parameters very precisely and to monitor the performance of the controllers. Measurements show that the performance of the rf control system has been improved by one order of magnitude compared to the analog system, yielding a phase stability of (Δφ)ᵣₘₛ = 0.8° and an amplitude stability of (ΔA/A)ᵣₘₛ = 7×10⁻⁵ and thus meeting the specification. The described rf control system has been commissioned and successfully used for beam operation for two years. During this time the system has proven to be significantly more stable and reliable than the old analog system.

Design and construction of a test stand for photocathode research and experiments

Abstract: Within the scope of this thesis, a test stand Photo-CATCH for research on semiconductor photocathodes used at the spin-polarized electron injector of the superconducting Darmstadt electron linear accelerator S-DALINAC is constructed and brought into operation. Ultra-high vacuum conditions are achieved in all parts of the system. Atomic-hydrogen assisted low-temperature cleaning of cathodes in a chamber with base pressure better than 3 E-11 mbar is used for preparing clean cathode surfaces for negative electron affinity (NEA) activation. Using a standardised activation procedure, atomic-hydrogen cleaning of heavily contaminated bulk-GaAs samples is optimized to an upper limit of 10 kL hydrogen-dosage. Cleaning of samples has been performed with a dosage as low as 0.7 kL. Activation of photocathodes with Cs+O2 and Cs+Li+O2 have been studied in a dedicated vacuum chamber with base pressure better than 2 E-11 mbar. By using a 405 nm laser, quantum efficiencies above 25 % have been achieved from an NEA-GaAs photocathode. Oxygen-induced quantum-efficiency degradation of NEA cathodes has been investigated. A vacuum lifetime of (298+/-35) hours was observed in the activation chamber for a novel two-stage activation using Cs, O2 and Li. This system can provide photocathodes with high quantum efficiency and lifetime for polarized and unpolarized beam production at the 60 keV electron beamline of Photo-CATCH. Additionally, atomic-hydrogen cleaned cathode samples can be transported to the photoelectron source at S-DALINAC using a transport-vessel conceptualized in this work.