The Novosibirsk FEL facility has three FELs installed on the first, second, and fourth orbits of the multiturn energy recovery linac (ERL). The first FEL covers the 90–240 μm range of wavelengths at an average radiation power of 0.5 kW with a pulse repetition rate of 5.6 or 11.2 MHz and a peak power of 1 MW. The second FEL operates in the 40–80 μm range of wavelengths at an average radiation power of 0.5 kW with a pulse-repetition rate of 7.5 MHz and a peak power of around 1 MW. These two FELs are the world’s most powerful (in terms of average power) sources of coherent narrow-band (less than 1%) radiation in their wavelength ranges. The third FEL was commissioned in 2015 to cover the 5–20 μm range of wavelengths. The Novosibirsk ERL is the world’s first and only multiturn ERL. Its distinctive features include a normally-conductive 180 MHz accelerating system, a direct current (DC) electrostatic electron gun with a control grid and thermionic cathode, three operating modes of the magnetic system, and a compact (6 × 40 m) design. The Novosibirsk FEL facility has been in operation for users of terahertz radiation since 2004.

The problem of producing high-current electron beams with relatively small lateral sizes and small velocity spread is more than a hundred years old. The continuous improvement of near-ultraviolet electromagnetic radiation sources (lasers with harmonics generators) allows significantly improving the parameters of existing electron guns. This paper discusses some problems in the development of electron guns with photocathodes and considers possible ways of using laser photocathodes in the electron guns designed at the Budker INP SB RAS.

Free electron lasers (FELs) are unique sources of electromagnetic radiation with tunable wavelength. A high-power FEL has been created at the G. I.Budker Institute for Nuclear Physics. Its radiation frequency can be tuned over a wide range in the terahertz and infrared spectral ranges. As the source of electron bunches, this FEL uses a multi-turn energy-recovery linac, which has five straight sections. Three sections are used for three FELs which operate in different wavelength ranges (90–240 μm for the first, 37–80 μm for the second, and 5–20 μm for the third ones). The first and the second FELs were commissioned in 2003 and 2009, respectively. They are used for various applied and research problems now. The third FEL is installed on the last, forth accelerator loop, in which the electron energy is the maximum. It comprises three undulator sections and a 40 m optical cavity. The first lasing of this FEL was obtained in the summer of 2015. The radiation wavelength was 9 μm and the average power was about 100 W. The design power is 1 kW at a pulse repetition rate of 3.75 MHz. Radiation of the third FEL will be delivered to user stations from the protected hall in the near future. The third FEL commissioning results are presented and the current status of the first and second FELs as well as their future development prospects are described.

A radio-frequency (RF) gun for a race-track microtron-recuperator injector driving the free-electron laser (FEL) (Budker Institute of Nuclear Physics) is being tested at a special stand. Electron bunches of the RF gun have an energy of up to 300 keV and a repetition rate of up to 90 MHz. The average electro-beam current can reach 100 mA in the continuous operation regime. The advantages of the new injector are as follows: long lifetime of the cathode for high average beam current; simple scheme of longitudinal beam bunching, which does not require an additional bunching resonator in the injector; absence of dark-current contamination of the injector beam; and comfortable RF gun operation due to the absence of a high potential of 300 kV at the cathode control circuits. In this study we describe the RF gun design, present the main characteristics of the injector with the RF gun, and give the results of testing.

Novosibirsk FEL facility is based on the first in the world multi-turn energy recovery linac (ERL). It comprises three FELs (stages). FELs on the first and the second tracks were commissioned in 2004 and 2009 respectively and operate for users now. The third stage FEL is installed on the fourth track of the ERL. It includes three undulator sections and 40-meters-long optical cavity. The design tuning range of this FEL is from 5 to 20 microns and the design average power at bunch repetition rate 3.74 MHz is about 1 kW. Recent results of the third stage FEL commissioning are reported.

Novosibirsk free electron laser (FEL) facility contains three FELs operating in the wavelength range 8-240 micron at average power up to 0.5 kW and peak power about 1 MW. Radiation users works at 6 user stations performing biological, chemical, physical and medical research.

The high-power free electron laser (FEL) facility NovoFEL has been created at Budker INP. Its wavelength can be tuned over a wide range in terahertz and infrared spectrum regions. This FEL uses a multi-turn energy recovery linac with five straight sections as a source of electron beam. Three sections are used for three FELs which operate in different wavelength ranges (the first at 90-240 mu m; the second at 37-80 mu m; the third at 5-20 mu m).The first and second FELs were commissioned in 2003 and 2009, respectively. They operate for users now. The third FEL is installed on the fourth accelerator track, which is the last one; the electron energy is maximal here. This FEL comprises three undulator sections and a 40-m optical cavity. The first lasing of this FEL was obtained in the summer of 2015. The radiation wavelength was 9 mu m and the average power was about 100 W. Radiation of the third FEL was delivered to the user stations, and the first user shifts were performed recently. The results of the commissioning of the third FEL, the current status of the first and second FELs and future development prospects are presented. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

CW 100 keV electron RF gun for 40 mA average beam current was developed, built, and commissioned at BINP SB RAS. The RF gun consists of normal conducting 100 MHz RF cavity with a gridded thermo cathode unit, CW 16 kW generator with GU-92A tetrode in the output stage, and a set of LLRF electronics. The gun was tested up to the design specifications at a test bench that includes a diagnostics beam line. The design features of different components of the gun are presented. Preparation and commissioning experience is discussed. The beam test results are summarized. INTRODUCKTION A 100 MHz RF electron injector was designed and manufactured at BINP for continuous wave (CW) powerful accelerator in RFNC-VNIIEF [1]. This compact accelerator, similar to the type of «RHODOTRON» [2], is designed for continuous production of short electron bunches with energy of 1.5 ÷ 7.5 MeV with power of 300 kW and higher. Each bunch passes through a single accelerating cavity of the accelerator several times. After each pass, the beam is turned in the bending magnets. In order to preserve the transverse dimensions of the electron bunches within the aperture after passing through the bends, the bunches should have small enough energy spread (<1%) and be quite short (<0.2 ns). An advantage of RF guns compared with static guns is the absence of cathode back bombardment with accelerated ions of residual gas ionized by an electron beam. This allows having a long lifetime of the cathodes and operating the gun continuously in the vacuum of 10 -6 ÷ 10 -7 Torr. Also, this enables raising the gun voltage and thus increasing the energy of the electron beam from 3040 keV to 100 keV proportionally to the beam current to the power of 2/3, in-accordance with the Poisson law. Furthermore, calculations showed that the increased voltage in the RF injector in combination with the effect of the longitudinal beam bunching therein provides a reduction in the energy spread of up to 0.3% (rms) in the first passage of the accelerator and the bunch shortening by up to 18 times.

The Novosibirsk ERL is used as a source of electron beams for the powerful Free Electron Laser. It is based on the normal conducting RF structure which operates in CW mode. The third stage of this facility which is the first in the world four-turn ERL has been commissioned recently. More than 90% of electrons were transported to the beam dump, which allowed to increase the average beam current up to 5 mA. The obtained parameters are sufficient to get lasing at the third stage FEL which will be installed at fourth track in the nearest future. In this paper we report the commissioning status and talk about further development of the Novosibirsk ERL and FEL facility.

The Novosibirsk terahertz FEL facility is based on the normal conducting CW energy recovery linac (ERL) with rather complicated lattice. This is the only multiorbit ERL in the world. It can operate in three different modes providing electron beam for three different FELs. The first FEL works for users since 2003. This FEL radiation is used by several groups of scientists which include biologists, chemists and physicists. Its maximum average and peak powers are 500 W and 1MW and wavelength can be tuned from 110 up to 240 microns. The high peak and average powers are used in experiments on material ablation and biological objects modification. The second FEL is installed on the second orbit. The first lasing of this FEL was achieved in 2009. Its radiation has almost the same average and peak powers and is delivered to the same user stations as the first FEL one, but its tunability range lies between 35 and 80 microns. The third FEL will be installed on the fourth orbit. In this paper we report the latest results obtained from the operating FELs as well as our progress with the commissioning of the two remaining ERL orbits. We also discuss possible options for the future upgrade.

A new electron source for the Race-Track Microtron Recuperator is being developed by BINP SB RAS. It will increase average beam current and brightness of synchrotron radiation. Instead of the static 300kV electron gun operated now we are developing RF gun with the same energy of electrons. This RF gun consists of RF cavity with a gridded thermo cathode mounted on the back wall. RF cavity is driven by a 60 kW generator with last stage equipped by GU101A tetrode tube. Operational frequency of the cavity is 90.2 MHz. It is equal to the second subharmonic of the Microtron RF system frequency. A set of low power electronics controls amplitude of the cavity voltage and its tuner. This system, including a diagnostics beam line, has been installed to serve as a test bench to test the RF cavity and for beam dynamics studies. In continuous regime the designed 300 kV voltages at the acceleration gap is obtained. This paper summarizes the first test results of the cavity in this configuration.

The Novosibirsk FEL (NovoFEL) generates tunable monochromatic coherent radiation as a continuous stream of 100-ps pulses with a repetition rate of up to 11.2 MHz and average power of up to 500 W. After commissioning of the second laser resonator in 2010, the spectral ranges of 120-240 μm and 40-80 μm are available to users. A review of experimental results for the past year is given.

Multiturn energy recovery linacs (ERL) looks very promising for making ERLs less expensive and more flexible, but have serious intrinsic problems. At this time only one multiturn ERL exists. This Novosibirsk ERL operates with two orbits and two free electron lasers now. The Novosibirsk terahertz radiation user facility provides 0.5 kW average power at 50 - 240 micron wavelength range. Different users work at six stations. Two another orbits and third free electron laser are under construction. The operation experience revealed specific problems of ERLs(especially, of multiturn ones). Some solutions were proposed recently.

High power THz applications on the Novosibirsk terahertz free electron laser are described.

Different mode regimes versus the extent modulation instability stabilization were investigated with a complex diagnostics system. Slippage due to frequency detuning of electron and light pulses turned out to be the main stabilization factor. Spectral and time parameters of the laser, especially the radiation of high harmonics, have been shown to strongly depend on the stabilization.

The first stage of Novosibirsk high power free electron laser (FEL) is in operation since 2003. One orbit for 11MeV energy with terahertz FEL lies in vertical plane. Other four orbits lie in the horizontal plane. The beam is directed to these orbits by switching on of two round magnets. In this case electrons pass four times through accelerating RF cavities, obtaining 40-MeV energy. Then, (at fourth orbit) the beam is used in FEL, and then is decelerated four times. At the second orbit (20 MeV) we have bypass with third FEL. When magnets of bypass are switched on, the beam passes through this FEL. The length of bypass is chosen to provide the delay, which necessary to have deceleration instead of acceleration at the third passage through accelerating cavities. Now two of four horizontal orbits are assembled and commissioned. The electron beam was accelerated twice and then decelerated down to low injection energy. Project average current 9 mA was achieved. First multiorbit ERL operation was demonstrated successfully. INTRODUCTION A source of terahertz radiation was commissioned in Novosibirskin 2003 [1]. It is CW FEL based on an accelerator–recuperator, or an energy recovery linac (ERL). It differs from other ERL-based FELs [2, 3] in the low frequency non-superconducting RF cavities and longer wavelength operation range. Full-scale Novosibirsk free electron laser facility is to be based on the four-orbit 40 MeV electron accelerator-recuperator (see Fig. 1). It is to generate radiation in the range from 5 micrometer to 0.24 mm [4, 5]. Figure 1: Scheme of the accelerator-recuperator based FEL. 1 injector, 2 accelerating RF structure, 3 180degree bends, 4 – undulator, 5 – beam dump, 6 – mirrors of the optical resonator. THE FIRST STAGE OF NOVOSIBIRSK ERL The first stage of the Novosibirsk free electron laser (Fig. 2.), based on the energy-recovery linac, generates coherent radiation tunable in the range 120-240 micron as a continuous train of 40-100 ps pulses at the repetition rate of 2.8-22.5 MHz. Maximum average output power is 500 W, the peak power is more than 1 MW [6,7]. The minimum measured linewidth is 0.3%, which is close to the Fourier-transform limit. Four user stations are in operation now. Two other are in progress.