The New IR FEL Facility at the Fritz-Haber-Institut in Berlin

A mid-infrared oscillator FEL has been commissioned at the Fritz-Haber-Institut. The accelerator consists of a thermionic gridded gun, a subharmonic buncher and two S-band standing-wave copper structures [1,2]. It provides a final electron energy adjustable from 15 to 50 MeV, low longitudinal (<50 keV-ps) and transverse emittance (<20 π mm-mrad), at more than 200 pC bunch charge with a micro-pulse repetition rate of 1 GHz and a macro-pulse length of up to 15 μs. Regular user operation started in Nov. 2013 with 6 user stations. Pulsed radiation with up to 100 mJ macro-pulse energy at about 0.5% FWHM bandwidth is routinely produced in the wavelength range from 4 to 48 μm. We will describe the FEL design and its performance as determined by IR power, bandwidth, and micro-pulse length measurements. Further, an overview of the new FHI FEL facility and first user results will be given. The latter include, for instance, spectroscopy of bio-molecules (peptides and small proteins) conformer selected or embedded in superfluid helium nano-droplets at 0.4 K, as well as vibrational spectroscopy of mass-selected metal-oxide clusters and protonated water clusters in the gas phase

Commissioning Status of the Fritz Haber Institute THz FEL

The THz Free-Electron Laser (FEL) at the Fritz Haber Institute (FHI) of the Max Planck Society in Berlin is designed to deliver radiation from 3 to 300 microns using a single-plane-focusing mid-IR undulator and a two-plane-focusing far-IR undulator that acts as a waveguide for the optical mode. A key aspect of the accelerator performance is the low longitudinal emittance, < 50 keV-psec, that is specified to be delivered at 200 pC bunch charge and 50 MeV from a gridded thermionic electron source. We utilize twin accelerating structures separated by a chicane to deliver the required performance over the < 20 - 50 MeV energy range. The first structure operates at near fixed field while the second structure controls the output energy, which, under some conditions, requires running in a decelerating mode. "First Light" is targeted for the centennial of the sponsor in October 2011 and we will describe progress in the commissioning of this device to achieve this goal. Specifically, the measured performance of the accelerated electron beam will be compared to design simulations and the observed matching of the beam to the mid-IR wiggler will be described

First Lasing of the IR FEL at the Fritz-Haber-Institut Berlin

A new mid-infrared FEL has been commissioned at the Fritz-Haber-Institut in Berlin. The oscillator FEL operates with 15 – 50 MeV electrons from a normal-conducting Sband linac. Calculations of the FEL gain and IR-cavity losses predict that lasing will be possible in the wavelength range from less than 4 to more than 50 μm. First lasing was achieved at a wavelength of 16 μm with an electron energy of 28 MeV. At these conditions, lasing was observed over a cavity length scan range of 100 μm

The polarized SRF gun experiment.

RF electron guns are capable of producing electron bunches with high brightness, which outperform DC electron guns and may even be able to provide electron beams for the ILC without the need for a damping ring. However, all successful existing guns for polarized electrons are DC guns because the environment inside an RF gun is hostile to the GaAs cathode material necessary for polarization. While the typical vacuum pressure in a DC gun is better than 10{sup -11} torr the vacuum in an RF gun is in the order of 10{sup -9} torr. Experiments at BINP Novosibirsk show that this leads to strong ion back-bombardment and generation of dark currents, which destroy the GaAs cathode in a short time. The situation might be much more favorable in a (super-conducting) SRF gun. The cryogenic pumping of the gun cavity walls may make it possible to maintain a vacuum close to 10{sup -12} torr, solving the problem of ion bombardment and dark currents. Of concern would be contamination of the gun cavity by evaporating cathode material. This report describes an experiment that Brookhaven National Laboratory (BNL) in collaboration with Advanced Energy Systems (AES) is conducting to answer these questions

Status of the Fritz Haber Institute THz FEL

The THz FEL at the Fritz Haber Institute (FHI) in Berlin is designed to deliver radiation from 4 to 400 microns. A single-plane-focusing undulator combined with a 5.4 m long cavity is used is the mid-IR (< 50 micron), while a two-plane-focusing undulator in combination with a 7.2 m long cavity with a 1-d waveguide for the optical mode is used for the far-IR. A key aspect of the accelerator performance is low longitudinal emittance, < 50 keV-psec, at 200 pC bunch charge and 50 MeV from a gridded thermionic electron source. We utilize twin accelerating structures separated by a chicane to deliver the required performance over the < 20 - 50 MeV energy range. The first structure operates at near fixed field while the second structure controls the output energy, which, under some conditions, requires running in a decelerating mode. "First Light" is targeted for the centennial of the FHI in October 2011 and we will describe progress in the commissioning of this device. Specifically, the measured performance of the accelerated electron beam will be compared to design simulations and the observed matching of the beam to the mid-IR wiggler will be described

Design and Performance of the Wedged Pole Hybrid Undulator for the Fritz-Haber-Institut IR FEL

An IR and THz FEL with a design wavelength range from 4 to 500 μm has been commissioned at the Fritz- Haber-Institut (FHI) in Berlin, Germany. Lasing at 28 MeV and a wavelength of 16 μm was achieved in February 2012 [1]. We describe the performance of the undulator built and installed at FHI by STI Optronics for use in the mid-IR range (<50 μm) and 15- to 50-MeV beam energy. The undulator was a high-field-strength wedged-pole hybrid (WPH) with 40-mm period, 2.0-m long, and minimum gap 16.5 mm. A new improvement was including radiation resistance in the magnetic design. We will discuss the measured magnetic and mechanical performance, central and zero steering/offset end-field magnetic designs, key features of the mechanical design and gap adjustment system, genetic shimming algorithms, and control system

First Results from HaloSat – A CubeSat to Study the Hot Galactic Halo

HaloSat is the first CubeSat for astrophysics funded by NASA\u27s Science Mission Directorate and is designed to map soft X-ray oxygen line emission across the sky in order to constrain the mass and spatial distribution of hot gas in the Milky Way. HaloSat will help determine if hot halos with temperatures near a million degrees bound to galaxies make a significant contribution to the cosmological budget of the normal matter (baryons). HaloSat was deployed from the International Space Station in July 2018 and began routine science operations in October 2018. We describe the on-orbit performance including calibration of the X-ray detectors and initial scientific results including an observation of a halo field and an observation of solar wind charge exchange emission from the helium-focusing cone

High-power beam injectors for 100 KW free-electron lasers

A key technology issue on the path to high-power FEL operation is the demonstration of reliable, high-brightness, high-power injector operation. We describe two ongoing programs to produce 100 mA injectors as drivers for 100 kW free-electron lasers. In one approach, in collaboration with the Thomas Jefferson National Accelerator Facility, we are fabricating a 750 MHz superconducting RF cryomodule that will be integrated with a room-temperature DC photocathode gun and tested at the Laboratory. In the other approach, in collaboration with Los Alamos National Laboratory, a high-current 700 MHz, normal-conducting, RF photoinjector is being designed and will undergo thermal management testing at the Laboratory. We describe the design, the projected performance and the status of both injectors