Experience with Novosibirsk FEL Getmanov Yaroslav Budker INP, Russia Dec. 2012, Berlin, Germany Unwanted Beam Workshop

N.A.Vinokurov, V.S.Arbuzov, P.D.Vobly, V.N.Volkov, M.G.Vlasenko, Ya.V.Getmanov, E.I.Gorniker, E.N.Dementyev, B.A.Dovzhenko, B.A.Knyazev, E.I.Kolobanov, A.A.Kondakov, V.R.Kozak, E.V.Kozyrev, V.V.Kubarev, G.N.Kulipanov, E.A.Kuper, I.V.Kuptsov, G.Ya.Kurkin, L.E.Medvedev, L.A.Mironenko, V.K.Ovchar, B.Z.Persov, A.M.Pilan, V.M.Popik, V.V.Repkov, T.V.Salikova, I.K.Sedlyarov, G.V.Serdobintsev, S.S.Serednyakov, A.N.Skrinskiy, D.A.Skorokhod, S.V.Tararyshkin, V.G.Cheskidov, K.N.Chernov, M.A.Scheglov, O.A.Shevchenko NovoFEL Team 2

OUTLINE Scheme of NovoFEL facility First Stage (one-pass ERL) Second Stage (two-pass ERL) Four-pass ERL Main factors of beam losses low energy FEL lasing multi-pass operation Diagnostic system Status of four-pass ERL Conclusion 3

Novosibirsk FEL

1 – injector, 2 – linac, 3 – bending magnets, 4 – undulator, 5 – dump Energy Recovery Linac 5

Lasing (1) Lasing (4) Lasing (2) groups of undulators and IR FELs (under construction and fabrication) One track in vertical plane (terahertz FEL) Common for all FELs accelerator system 6 Two tracks in a horizontal plane (IR FEL) Four tracks in a horizontal plane Full scale Novosibirsk FEL 6

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First stage of NovoFEL (one-pass ERL) Electron beam from the gun passes through the buncher (a bunching RF cavity), drift section, 2 MeV accelerating cavities and the main accelerating structure and the undulator, where a fraction of its energy is converted to radiation. After that, the beam returns to the main accelerating structure in a decelerating RF phase, decreases its energy to its injection value (2 MeV) and is absorbed in the beam dump. 8

First stage of NovoFEL  Wavelength, mkm  Repetition rate, MHz11.2  Pulse duration, FWHM, ps ~70  Average power, kW0.4  Pulse energy, mJ0.04  Minimum relative linewidth, FWHM

2 nd stage FEL undulator Main linac 1 st stage FEL undulator Horizontal tracks 10

Second Stage  Wavelength, mkm  Electron energy, MeV22  Average current, mA30 11

Third stage  Wavelength, mkm5-30  Electron energy, MeV42  Average current, mA100 12

Third track 13

Third trackFourth track 14

Magnetic elements with Long Edge Fields Edge fields of different elements can intersect Residual induced magnetic fields Noticeable effect of Earth magnetic field High space charge of the bunch. High energy spread in mode with FEL lasing Magnetic elements are used to control two different types of the bunches – ac. and dec. Unknown initial parameters in injector Time variation of the parameters (phases of RF) due to transition period Main problems with operation 15

I = 250 A I = 10 A Representation of real quadrupole with ideal one 16

Intersection of the magnets with long edge fields 17

Representation of real RF cavity field in Trace-3D Solid red line – real field distribution, dotted red line – Trace-3D cavity field distribution with L eff = 70 cm, black boxes – cavity boundary position. 18

External magnetic field correction Using the wire field correction allowed to exclude vertical correctors At the energy 10 MeV, the deviation after 30 m will be about 0.7 m 19

Interaction of electrons with radiation in FEL leads to large energy spread. Moreover the relative energy spread increases at deceleration. Therefore the longitudinal acceptance is very important parameter of ERLs which work for FELs Before FELAfter FEL Energy spread 20

Beam position monitors Vacuum pump and controls Thermo control sensors Beam current sensors Radiation sensors FEL light analysis system (monochromator and Fourier spectrometer) System of the radiation control and localization with optical fiber Diagnostic system 21

Beam position monitors  BPMs system of the NovoFEL is designed to detect and separate two bunches following each other.  This system can be used to calculate the lengths of turns for multipass ERL.  There are two different modes of operation – “laboratory” and “reference”.  BPM works as warning system 22

1-st stage: 37 BPMs 23

3-d stage: 152 BPMs 24

BPM signal of single electron bunch. The sinusoidal RF signal (green) makes possible direct measurement of the orbit lengths. Orbit length measurement 25

Radiation control  Large area of the losses localization  Calibration of sensors depends on the place 26

Thermocontrol Example of the program for temperature control  Small area of the losses localization  Calibration of sensors depends on the place 27

1 2 3 Spectrum is measured in real time Measurement spectrum of radiation 28

Accidents 29

30 Third Stage NovoFEL: four pass ERL 95% of the beam current goes to the dump 1,5% 3,5% 30

Conclusion Unwanted beam losses can exist due to low energy effects, generation and insufficiently flexibility of system in multipass mode. Protection system, well working in regular mode, should be changed for tuning and adjusting mode. At this time, in Novosibirsk FEL based on one-turn ERL operates with the highest power in terahertz region; FEL based on the first in the world two-passes ERL operates in infrared region; at the four-pass ERL is achieved the 95% recuperation and 1 mA current. The commissioning of the NovoFEL ERL proves the opportunity of the operation multipass ERLs. 31

Thank you for your attention! 32