ATF Intrabeam Scattering Results Junji Urakawa and ATF collaboration Contents 1) Simple Review of the Measurement Method 2) Comparison with Simulation and Theory 3) Summary 11/19/2018 DR2003, Jan. 27 at Daresbury

Measurement Method to get the Results We measured the horizontal emittance in the extraction line using 5 wire scanners. Energy spread was measured by thin screen monitor in the extraction line with large dispersion. Vertical emittance was measured by 5 wire scanners in the extraction line, laser wire and SR interferometer in the damping ring. X-SR monitor indicates consistent results on transverse emittance. Bunch length has been measured by streak camera with large statistical error. Beam lifetime measurement has evaluated the emittance ratio with some assumptions. DR2003, Jan. 27 at Daresbury

Comparison Measurements Numerical Comparison with SAD Comparison with Simulation and Theory 11/19/2018 DR2003, Jan. 27 at Daresbury

Measurements Laser Wire in the ring SR Interferometer DR2003, Jan. 27 at Daresbury

Measurements Bunch Length by Streak Energy Spread by Screen Monitor Camera in the Ring Energy Spread by Screen Monitor at the Extraction Line

Numerical Comparison with SAD DR2003, Jan. 27 at Daresbury

Numerical Comparison with SAD DR2003, Jan. 27 at Daresbury

Comparison with Simulation and Theory DR2003, Jan. 27 at Daresbury

Comparison with Simulation and Theory

Summary Vertical dispersion only, with (h)rms=5.6mm and ey0=4.0pm (Solid). Coupling dominated with k=0.33% (dashes). Coupling dominated with k=1.2%, with the Coulomb log artificially increased by a factor 1.75 (dotdash). Same as Ex. 2 but assuming ey measurement error, i.e. adding 0.9% of the measured (and splined) ex to the calculated ey (the dots). Following is my suggestion (intention). Reject the artificial increase. Beam orbit tuning, dispersion and coupling correction have to do precisely. Beam Size Measurement has to do quickly and precisely. Improved tools will be prepared within 3 months. DR2003, Jan. 27 at Daresbury

Novel Electron-Beam Diagnostic (Laser Wire ) at St Catherine’s College, Oxford, England Junji Urakawa, KEK, Japan, July 10th 2003 1. Development of laserwire beam profile monitor based on stable Compton scattering in a Fabry-Perot optical cavity. (0.1mm(rms) position stability, 5mm(rms) beam collision.) 2. Future development 3. Conclusion Ultra-low emittance electron beam is good for you.

Introduction to laserwire motivation Linear Colliders require nm-size beams Damping rings produce ultra low emittance beams ATF experiment at KEK to demonstrate low emittance beam production develop handling / monitoring techniques study beam dynamics ( low emittance, multi-bunch ) ATF damping ring beam energy :1.28 GeV intensity : 1.2×1010 [e/ bunch] number of bunches : single / multi (2~20bunches) (2.8ns spacing) 1.1 ×10-9 [m rad] ( horizontal emit.) ~ 100 [mm] 0.5 ×10-11 [m rad] ( vertical emit.) ~ 7 [mm] need reliable beam size monitors

Introduction CW laserwire with optical cavity principle of laserwire monitor thin photon target (laserwire) transversely placed on the beam orbit scan across the electron beam “count” Compton scattered photons Important issues high intensity small waist size CW laserwire with optical cavity enhance laser power (high mirror reflectance ⇔ high power gain ) control laser waist size laser on/off for background subtraction

Introduction feature other monitors reliable beam size monitor in Damping ring non-invasive method direct measurement of the beam size dispersion negligible (straight section) multi-bunch beam (timing detection of gamma rays) work at almost zero current other monitors SR interferometer (arc) X-ray SR monitor (arc) wire scanner (ext) OTR/ODR (ext)

Experimental setup 1. laserwire 2. detector and collimator 3. data taking system

Chamber system replaced in 2002 summer shutdown cavity module

Optics whole system mounted on movable table movable both vertical/horizontal table position is monitored by laser position sensor

Laserwire setup vertical wire horizontal wire

Cavity resonance power inside cavity Fabry-Perot high power gain ⇔narrow resonance

Cavity control servo system feedback control control cavity length piezo actuator monolithic elastic hinge feedback control transmission intensity = reference voltage <0.1 nm resolution

Optical cavity and laser laser specification wavelength 532 nm CW power 300 mW linewidth <10 kHz (1msec) LightWave Series 142 diode-pumped solid state laser CW freq. doubled YAG laser cavity specification horizontal wire (vertical measurement) vertical wire (horizontal measurement) mirror front 99.1 % 99.8 % reflectance end 99.9 % mirror curvature 20 mm finesse 620 1700 power gain 660 1300 size (rms) 5.67　± 0.1 μm 14.7 ± 0.2 μm Rayleigh range 760 μm 5100 μm

Laser power modulation background subtraction background ~ 10kHz Laser-ON / Laser-OFF measurement modulate intra-cavity power (cavity length modulation) Laser-ON: Laser-OFF: 113 Hz sinusoidal modulation 30% (time) 85% of power (average) 30% (time) 7.5% of power (average)

Detector Compton scattering gamma ray detector time resolution 28.6 MeV (max gamma energy) 23.0 MeV ( 0.2 mrad scattering angle ) gamma ray detector [70 mm ×70 mm ×300 mm ] CsI(pure) crystal 2” photo-multiplier time resolution PMT signal leading edge 0.56 nsec resolution (signal energy region) enough to separate 2.8ns spacing bunches

Compton scattering signal Energy spectrum signal/background = 4 / 1 (vertical beamsize measurement) energy window (15MeV – 25MeV) “counting” method no event pile-up (10kHz rate / 2MHz ring revolution ) energy gate and leading edge detection bunch identification by gamma ray signal timing

Signal processing single bunch emittance (Mar 2003) 20 beam profiles (multi-bunch) at the same time bunch ID by hit timing (bunch marker) laser ON/OFF count rate single bunch emittance (Mar 2003)

Data taking scanning align collimators beam based alignment for collimators local orbit bump at laserwire position if needed scanning 1 round trip for 1 profile automatic scan vertical 10sec. for 1 position move 10 micron (6sec.) 6 min. for 1 scan error dominated by orbit drift horizontal 30sec for 1 position move 50 micron (10sec.) 15 min. for 1scan error dominated by statistics vertical “bad data”

Laser waist measurement longitudinal laser profile laser has parabolic shape small waist size ⇔　small Rayleigh length change x-position and confirm laser profile laserwire size = 5.67 ±0.1 μm (laser divergence method) laserwire size = 5.46 ±0.2 μm (fitting from focus scan)

Additional data beta function at two collision points dispersion measurement by laserwire itself change Ring RF scan beam by laserwire measure the beam position shift vertical dispersion = 2.0 mm (almost negligible) horizontal dispersion = 2.0 mm (negligible) beta function at two collision points for vertical measurement βx= 9.81 m, βy= 4.32 m for horizontal measurement βx= 7.83 m, βy= 4.90 m

Beam damping measurement beamsize measurement as a function of storage time study detector response after beam injection

Recent Results with calculated values on intra-beam scattering and pure inductive impedance Bunch Length Energy Spread Horizontal Emittance Vertical Emittance

Future plan possibilities How to improve resolution ? beam size : 5.5 [mm] 　⇔ 　　laser waist size: 5.6 [mm] close to the resolution limit possibilities stronger focusing fine tuning of cavity length sensitive to mirror geometries shorter Rayleigh length shorter wave length high quality mirror high power / stable laser use higher transverse mode

Twin peaks laserwire use TEM01 resonance mode in the optical cavity as a laserwire good resolution for small beam size factor 2~3 resolution improvement insensitive for beam orbit drift scan free

Higher mode resonances misaligned laser injection higher order mode resonate in the cavity mirror distortion 　　　　↓ transmitted light profiles of each mode mode degeneration TEM01/10 mirror distortion to split these modes

Higher mode test experiment stable realization of higher order modes TEM00 TEM01 TEM02

Conclusion Ultra-low emittance electron beam is good for you. Ultra-short bunched beams are good for my future R&D. Now we are going to do nano-beam orbit handling with international collaboration. Sub-nano meter and sub-100f second beam will be realized in the future. Beam diagnostics for above beam are necessary. Idea of such diagnostics exists. However, present technologies are not mature. So, we continue R&D with challenging spirit for future linear collider project.

Installation of 5 wire-scanners into ATF Linac Improvement of temperature control of cooling water Stabilization of Magnet Power Supply Increase QE of photo-cathode Vacuum backing (beam scrubbing) is necessary. Adding trim coils to both end poles of wigglers which will be finished in next summer shutdown. Other issues Stabilization of extraction kicker system More precise beam orbit control 100 bunches/pulse electron beam generation and acceleration Test on beam loading

Survey IBS in detail and Longitudinal instability until 3x1010 electrons/bunch. Multi-bunch instability until 3 trains with 20 bunches. Especially Fast Ion Instability with vacuum pump turn-off. Observation of different beam behavior with wiggler Schedule First ATF program (from 1997) will be finished until the end of JFY 2004. Second ATF program which includes nano-meter orbit handling and 1st bunch compression until 1psec(rms) has been already unofficially discussed.