Compton X-ray generation in a small S-band accelerator ~ LUCX Project at KEK-ATF ~ Collaborators KEK-ATF: S. Araki, M. Fukuda, Y. Higashi, Y. Honda, T. Taniguchi, N. Terunuma, J. Urakawa, S. Liu WASEDA University: K. Sakaue, M. Washio KYOTO University: N. Sasao, H. Yokoyama TOKYO University: H. Sakai POSIPOL 2007 Workshop, 23-25 May 2007, LAL, Orsay, France 25 May 2007 POSIPOL 2007 Workshop @LAL

Contents Introductionｓ Laser Undulator Compact X-ray Source (LUCX) in KEK-ATF Control System of the LUCX Multi-bunch Beam Operation LUCX X-ray Source Conclusions 25 May 2007 POSIPOL 2007 Workshop @LAL

Introduction Our aim is development of compact high brightness X-ray generator. It is required from various field. (medical diagnosis, biological sciences, etc.) For example, K-edge digital subtraction angiography. Angiography is a procedure that enables blood vessels to be visualized using the absorption by Iodine at 33keV XCOM: Photon Cross Section Database http://physics.nist.gov/PhysRefData/Xcom/Text/XCOM.html 25 May 2007 POSIPOL 2007 Workshop @LAL

X-ray generation We have developed an X-ray source based on Inverse Compton Scattering with a pulsed laser-wire Cavity. => LUCX (Laser Undulator Compact X-ray source) project. Pulsed Laser Cavity 43 MeV 43 MeV Parameter : Cavity Length: 420 mm Mirror Curvature radius: 250mm Finesse 1500 Enhancement factor ~ 780 l = 1064 nm (1.17eV) 6W (17nJ/pulse) 25 May 2007 POSIPOL 2007 Workshop @LAL

Merit Compact and Inexpensive Laser system is compact. Merit of the X-ray source using Inverse Compton Scattering X-ray source using an undulator at a GeV order storage ring. High intensity, High stability but, in general, large amount of money and huge facilities. X-ray source based on Inverse Compton Scattering X-rays can be produced by lower energy e- beam. The ring can be downsized. Compact and Inexpensive But, we need to demonstrate the method. Merit of the pulsed laser-wire cavity No amplifier system. Laser system is compact. But, difficult to raise finesse of Laser cavity. 25 May 2007 POSIPOL 2007 Workshop @LAL

Place of the accelerator for LUCX project The accelerator for LUCX project is constructed in ATF building // Here 25 May 2007 POSIPOL 2007 Workshop @LAL

LUCX Layout Energy 43 MeV Intensity 200nC/train Number of Bunch 100 bunches/train Bunch spacing 2.8ns Rep. Rate 12.5 Hz // 25 May 2007 POSIPOL 2007 Workshop @LAL

Current Beam line We plan to demonstrate the X-ray generation with the pulsed LW Cavity. Adding an accelerating tube to upgrade the beam energy. Current beam line e- beam Collision point UV: 3mJ/bunch X-ray solenoid Compton S-band accelerating tube (3m) X-ray detector Bending magnet Q-magnet Q-magnet Q-magnet RF Gun Chicane Cathode: Cs-Te An electron beam is accelerated Second phase Number of Bunch 100 bunches/train - Energy 43 MeV (Design) - Intensity 200nC/train (Design) : 50nC/train (MAX) Bunch spacing 2.8ns - Rep. Rate 12.5 Hz - 100-bunch electron beam is accelerated to 43 MeV. with 50nC /train charge generates.// 25 May 2007 POSIPOL 2007 Workshop @LAL

Photo cathode RF gun Q.E. : ~0.3% RF gun cavity (1.6cells) Solenoid RF gun Cu UV laser 266nm e- beam Cs2Te S-band 2856MHz (BNL Gun IV) UV laser / Q.E. : ~0.3% RF Gun Mo Cathode plug RF processing is continued from April 2006. (about 400 hours) 25 May 2007 POSIPOL 2007 Workshop @LAL

RF system Dummy Load S-band 2856MHz 25 May 2007 // 25 May 2007 POSIPOL 2007 Workshop @LAL

Beam monitor Collision point Emittance measurement Faraday Cup Top view BPM BPM ICT BPM BPM solenoid PRM PRM S-band accelerating tube (3m) RF Gun PRM PRM Bending magnet Q-magnet Q-magnet Cathode: Cs-Te Q-magnet Chicane e- beam However, these monitors ware transposed to LW chamber. Emittance measurement Side view ICT & Faraday Cup: Beam current monitor PRM BPM: Beam position monitor BPM ICT PRM: Beam Profile Monitor OTR target or Al2O3 (Cr3+ doped) Beam energy and energy spread measurement 25 May 2007 POSIPOL 2007 Workshop @LAL

Schematic Diagram of the Control System EPICS device support for network device !! # use Ethernet as a field-bus CAMAC (Toyo / CCNET [PC/104+] ) PLC (Yokogawa / FA-M3, Keyence / KV-1000) Data Logger (Yokogawa / DARWIN) Main PC is running a sequencer program for automatic RF-conditioning. A usual desktop PC is here. It’s running Linux-EPICS. An IOC program, MEDM displays and a Channel Archiver are running on the PC. This IOC program talks to a PLC. It’s a modulator controller. And there is PLC one more. ( It’s a KV-1000 made by KEYENCE. Co. ) We use this for a flow-meter monitor and interlock and screen monitor control. We have another PC, It’s single board computer, which is embedded in this CC/NET, a special intelligent CAMAC controller. Another IOC program is running on this CC/NET to measure the pressure and to control the magnets. Then, This is another CCNET, and for the beam monitor. Some monitors in the shield were done by using Looger. Temperature and the voltage measured it by using the Data LOGGER. The laser mirror and shutter was connected at RS232c. We have much 232c and GPIB. They are connectable with a network using an Ethernet converter. (LW)These will be completed in the near future. <? And a few controllers // -Main PC is running a sequencer program for automatic RF-conditioning.- It’s the main purpose of this control system. 25 May 2007 POSIPOL 2007 Workshop @LAL

Beam operation Energy: 40MeV (operation) Intensity: 50nC/train (MAX) We have started beam operation from July 2006. The multi-bunch beam could be transported to the beam dump. Energy: 40MeV (operation) Intensity: 50nC/train (MAX) Number of bunch: 100 bunches ~1MeV 25 May 2007 POSIPOL 2007 Workshop @LAL

Emittance measurement Collision point εx: 3.0 [mm・mrad] QF1 QD1 Beam current : 2.5nC/train, 5bunches Beam profile at Collision point εy: 4.7 [mm・mrad] σx: 86um σy: 36um CP1G (OTR) 25 May 2007 POSIPOL 2007 Workshop @LAL

Beam loading (simulation) Black line: without beam loading Blue line: with beam loading Input RF pulse Laser injection timing Beam Energy [MeV] 100bunches (280ns) Energy difference is within 1% at the laser injection timing of 3.7ms. The energy difference that two lines show is large. Mathematica simulation x‐axis is Laser injection timing, u-sec. y-axis is Beam energy, // Time [ msec ] 25 May 2007 POSIPOL 2007 Workshop @LAL

Beam loading measurement e- beam BPM7 (PPM5) ICT2 MS4G: Beam profile monitor MS4G (OTR) E大 0.9MeV/c E小 25 May 2007 POSIPOL 2007 Workshop @LAL

Compensation for Beam loading 50nC/100bunches Momentum vs Laser injection timing(5bunches) (3) (3) (1) (2) 280ns (100 bunches) Energy diff of bunches = 0.4MeV/c (2) set here (1) This shows is plot of Momentum vs Laser injection timing. A horizontal axis 0 corresponds to 3.5 u-seconds. The timing which puts a beam is changed with (1), (2), (3), and is measured 25 May 2007 POSIPOL 2007 Workshop @LAL

Operation Energy 43MeV 40MeV Intensity 200nC/train (Design) 30 ~ 50nC/train Number of Bunch 100 bunches/train - Bunch spacing 2.8ns - Rep. Rate 12.5 Hz - Collision point Faraday cup Top view BPM BPM ICT BPM BPM solenoid PRM S-band accelerating tube (3m) RF Gun PRM PRM Bending magnet Q-magnet Q-magnet Cathode: Cs-Te Q-magnet Chicane e- beam We have a 2 ICT , And 5 BPM, And 5PRM, And we installed LW chain bar. P: 40 MeV (1.5nC, 5bunches) sP/P : 0.15% 0.4MeV/c Side view PRM Momentum spread BPM ICT Momentum difference 25 May 2007 POSIPOL 2007 Workshop @LAL

X-ray generation (LUCX) We started to demonstrate the X-ray generation with Pulsed Laser. Collision angle is 20o in order to get as much intensity as possible. Head-on collision is best, but the e- beam will collide with the mirror. We started to demonstrate the X-ray generation with Pulsed Laser Cavity. Collision angle is 20o in order to get as much intensity as possible.@ Head-on collision is best, but the e- beam will collide with the mirror. Maximum X-ray energy is 33 keV. 25 May 2007 POSIPOL 2007 Workshop @LAL

LUCX-Required Spec. of Optical Resonator [ pulsed laser-wire ] Initial Laser : >6W@357MHz Cavity Length : 420mm Beam Waist : <170um in 2s Mirror Curvature : <250mm Finesse : >1550 Mirror Reflectivity : 99.7%, 99.9% Cavity Transmission We have a 6W pulse laser, We have finished the test of an optical resonator. It’s long keep on ~10 hour. FB ON (Loop Close) T. Jitter = 3ps Error signal 25 May 2007 POSIPOL 2007 Workshop @LAL

Optical Circuit P-LW-CAV installed in APR2007. e- beam e- beam We installed P-LW-CAV of the LUCX by the end of last month. 25 May 2007 POSIPOL 2007 Workshop @LAL

Optical Resonator R/D ~Preparation of install resonator~ Shutter speed = 10sec Optical Resonator R/D ~Preparation of install resonator~ After several studies to characterize and reduce the jitters, we decide to install the resonator to LUCX accelerator. The parameter of pulsed laser-wire is as follows. Frequency Finesse Waist Size (2) Inject laser power Laser power in resonator with FB 357 MHz 1889 ±31.5 178.4 ±7.5 mm 4.05 W @357 MHz 2.40 ±0.05 kW x 630 Inside of e-beam chamber was photocopied by Dig-CAM. (Purge with Nitrogen) 25 May 2007 POSIPOL 2007 Workshop @LAL

Expected number of X-rays Laser (in LWC)  = 1064 nm (1.17eV) 2.8 mJ /bunch 1.5x1013 photons/bunch s = 89 mm 10ps e- beam 43 MeV 0.5nC/bunch 3.1x109/bunch sx, sy = 80mm, 40mm 10ps 100 bunches/train 12.5 Hz Energy Intensity Beam size Pulse width Number of bunch Rep. Rate < 5mrad, >= 27 keV In view of the acceptance (< 5mrad), Expected number of X-rays 2 x 104 photons/sec (1.6 x 103 photons/train) 25 May 2007 POSIPOL 2007 Workshop @LAL

Collision Study of BG and the collision experiment were begun. [18MAY2007 ~] Just experiment now under going. Since BG signal is large. Sorry! No data shown to you… View of the transmitted laser 25 May 2007 POSIPOL 2007 Workshop @LAL

Conclusion We plan to demonstrate X-ray generation with Pulsed LW Cavity. To upgrade the beam energy, an accelerator tube was installed. ◯ ◯ We have built a fully-PC/Linux-based control system with EPICS for LUCX operation. After 400 hours processing, we start the beam operation. The multi-bunch beam (50nC/train, 100bunches) can be transported to the beam dump. ◯ We need to continue the rf processing to increase the beam energy and the beam charge and also to optimize the parameter (emittance, energy spread, solenoid current, etc) . ◯ ◯ The pulsed laser-wire cavity was installed. First step is to observe a signal of an X-ray. 25 May 2007 POSIPOL 2007 Workshop @LAL

Thanks for your attention! 25 May 2007 POSIPOL 2007 Workshop @LAL

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!Previous beam line Until Nov 2005, RF gun study was done for generating a high intensity multi-bunch beam. Previous beam line e- beam UV: 3mJ/bunch solenoid RF Gun Q-magnet Chicane Cathode: Cs-Te Faraday cup First phase 100 bunches Energy 5 MeV Intensity 300nC/train Number of Bunch 100 bunches/train Rep. Rate 12.5 Hz K. Hirano, et al. “High-intensity multi-bunch beam generation by a photo-cathode RF gun”, Nucl. Instr. and Meth. A560, pp233-239 (2006). 25 May 2007 POSIPOL 2007 Workshop @LAL

!Beam Optics Collision point e- beam Beam size at the collision point: sx 64 mm sy 32 mm Beam size is less than 3mm to avoid the BG signal caused by beam loss. 25 May 2007 POSIPOL 2007 Workshop @LAL

!Laser system (Gun) To gun Pockels cell(KD*P): Pulse width ≦ 280ns (100bunches) Fourth Harmonic Generation: Two BBOs, Conversion efficiency ~ 25% (IR -> UV) 266nm PC1 PC2 Seed laser To gun TBP, 357MHz mode-locked pulse laser Nd:YVO4 (λ:1064 nm, FWHM:9 ps) Two amplifier heads (Continuum, rod: Nd:YAG) Double pass configuration Gain ~ 2000 25 May 2007 POSIPOL 2007 Workshop @LAL

!Laser system (Gun) UV: 3uJ/pulse Spatial filter Pin hole: d=20um Telescope (f=+50mm, +50mm) Telescope (f=+300mm,-150mm) Intensity controller (half wave & PBS) UV: 3uJ/pulse 25 May 2007 POSIPOL 2007 Workshop @LAL

!RF phase (Gun) Momentum spread vs laser injection phase Phase plot σP/P [%] Beam current [a.u.] LaserをGunに入射する Gun RF phase をスキャン。エネルギー広がりが最小の場所にセット σP/P :Minimum Laser injection phase [deg] Laser injection phase [deg] 25 May 2007 POSIPOL 2007 Workshop @LAL

! Momentum spread vs RF phase (Accelerator) Momentum vs RF phase (Acc.) e- beam Momentum P [MeV/c] MS4G 1.5nC, 5bunches Momentum spread vs RF phase (Acc.) Min: 0.15% P: 34 MeV σP/P : 0.15% σP/P [%] 25 May 2007 POSIPOL 2007 Workshop @LAL

!Optical Resonator R/D ~Problems of Optical Resonator~ Width of resonance peak We should control the resonator length <0.1nm Gain=1000 Peak width (FWHM)<0.2nm No jitter is permitted!! Where are the jitters come from? >Mode-locked laser FB Timing stabilizer FB causes a jitter >Acoustic noises 1~2kHz acoustic jitter appears 25 May 2007 POSIPOL 2007 Workshop @LAL

Optical Resonator [PLL] ~ Analog circuit Transmission Measurement結果 　Mirror1 : T=0.221±0.004% 　Mirror2 : T=0.071±0.001% Lossを”0”として1-Tの値からReffを算出すると、 Reff=99.85%　(Finesse測定による結果 Reff=99.83%) [PLL] ~ Analog circuit Timing Error ⇒(FB) Laser Piezo Timing Error ⇒(FB) Cavity Piezo (FF) Laser Piezo Tilt Locking kept a long time. ~10h 25 May 2007 POSIPOL 2007 Workshop @LAL

!Tilt Locking Test FBが落ちる瞬間を モニターする。 Timing Errorが 大きく変化して Piezoが大きく動き、 FBが外れる。 ⇒FBが外れるときのほとんどが、Timing Errorが原因。 25 May 2007 POSIPOL 2007 Workshop @LAL