1、1會計學ATFIntrabeamScatteringResultsATF束內散射的結果束內散射的結果12/14/2021DR2003, Jan. 27 at DaresburyDR2003, Jan. 27 at DaresburySR InterferometerLaser Wire in the ringEnergy Spread by Screen Monitorat the Extraction LineBunch Length by Streak Camera in the RingDR2003, Jan. 27 at DaresburyDR2003, Jan. 27 at Dare

2、sburyDR2003, Jan. 27 at DaresburyComparison with Simulation and TheoryDR2003, Jan. 27 at Daresburymotivation Linear Colliders require nm-size beams Damping rings produce ultra low emittance beams ATF experiment at KEKto demonstrate low emittance beam productiondevelop handling / monitoring technique

3、sstudy beam dynamics ( low emittance, multi-bunch )ATF damping ring1.1 10-9 m rad ( horizontal emit.) 100 mm0.5 10-11 m rad ( vertical emit.) 7 mmbeam energy :1.28 GeV intensity : 1.21010 e/ bunchnumber of bunches : single / multi (220bunches) (2.8ns spacing)need reliable beam size monitorsprinciple

4、 of laserwire monitorthin photon target (laserwire) transversely placed on the beam orbitscan across the electron beam“count” Compton scattered photons CW laserwire with optical cavityenhance laser power (high mirror reflectance high power gain )control laser waist size laser on/off for background s

5、ubtractionImportant issues high intensity small waist sizereliable beam size monitor in Damping ringnon-invasive methoddirect measurement of the beam sizedispersion negligible (straight section) multi-bunch beam (timing detection of gamma rays)work at almost zero current feature other monitors SR in

6、terferometer (arc)X-ray SR monitor (arc)wire scanner (ext)OTR/ODR (ext)1. laserwire2. detector and collimator3. data taking systemreplaced in 2002 summer shutdowncavity modulewhole system mounted on movable tablemovable both vertical/horizontaltable position is monitored by laser position sensorhori

7、zontal wirevertical wireFabry-Perot high power gainnarrow resonance power inside cavity feedback controltransmission intensity = reference voltage 0.1 nm resolution servo systemcontrol cavity lengthpiezo actuatormonolithic elastic hingelaser specification cavity specificationhorizontal wire(vertical

8、 measurement)vertical wire(horizontal measurement)mirror front99.1 %99.8 %reflectanceend99.9 %99.9 %mirror curvature20 mm20 mmfinesse6201700power gain6601300size (rms)5.67 0.1 m14.7 0.2 mRayleigh range760 m5100 mwavelength532 nmCW power300 mWlinewidth10 kHz (1msec)LightWave Series 142 diode-pumped s

9、olid state laser CW freq. doubled YAG laserLaser-ON: Laser-OFF: 113 Hz sinusoidal modulation background subtractionbackground 10kHzLaser-ON / Laser-OFF measurementmodulate intra-cavity power (cavity length modulation)30% (time)85% of power (average)30% (time) 7.5% of power (average) Compton scatteri

10、ng28.6 MeV (max gamma energy)23.0 MeV ( 0.2 mrad scattering angle ) gamma ray detector70 mm 70 mm 300 mm CsI(pure) crystal2” photo-multiplier time resolutionPMT signal leading edge0.56 nsec resolution (signal energy region)enough to separate 2.8ns spacing bunches Energy spectrumsignal/background = 4

11、 / 1 (vertical beamsize measurement)energy window (15MeV 25MeV) “counting” method no event pile-up (10kHz rate / 2MHz ring revolution )energy gate and leading edge detectionbunch identification by gamma ray signal timing20 beam profiles (multi-bunch) at the same time single bunch emittance (Mar 2003

12、) bunch ID by hit timing (bunch marker) laser ON/OFF count ratealign collimatorsbeam based alignment for collimatorslocal orbit bump at laserwire position if needed scanning1 round trip for 1 profileautomatic scan vertical 10sec. for 1 position move 10 micron (6sec.) 6 min. for 1 scan error dominate

13、d by orbit drift horizontal 30sec for 1 position move 50 micron (10sec.) 15 min. for 1scan error dominated by statisticsvertical“bad data”longitudinal laser profilelaserwire size = 5.67 0.1 m(laser divergence method)laserwire size = 5.46 0.2 m(fitting from focus scan)small waist size small Rayleigh

14、length change x-position and confirm laser profile laser has parabolic shapedispersion measurement by laserwire itselfchange Ring RFscan beam by laserwiremeasure the beam position shiftvertical dispersion = 2.0 mm (almost negligible)horizontal dispersion = 2.0 mm (negligible) beta function at two co

15、llision pointsfor vertical measurement x= 9.81 m, y= 4.32 mfor horizontal measurement x= 7.83 m, y= 4.90 mbeamsize measurement as a function of storage timestudy detector response after beam injectionHorizontalEmittanceVerticalEmittanceRecent Results with calculated values on intra-beam scattering a

16、nd pure inductive impedanceBunchLengthEnergySpreadHow 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 m

17、irror high power / stable laser use higher transverse modeuse TEM01 resonance mode in the optical cavity as a laserwirefactor 23 resolution improvementinsensitive for beam orbit driftscan freegood resolution for small beam sizemisaligned laser injectionmode degeneration TEM01/10mirror distortion to

18、split these modesmirror distortionhigher order mode resonate in the cavitytransmitted light profiles of each modestable realization of higher order modesTEM00TEM01TEM02ConclusionUltra-low emittance electron beam is good for you.Ultra-short bunched beams are good for my future R&D.Now we are goin

19、g 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 challe

20、nging spirit for future linear collider project. 1. Installation of 5 wire-scanners into ATF Linac2. Improvement of temperature control of cooling water 3. Stabilization of Magnet Power Supply4. Increase QE of photo-cathode5. Vacuum backing (beam scrubbing) is necessary.6. Adding trim coils to both

21、end poles of wigglers which will be finished in next summer shutdown. Other issues1. Stabilization of extraction kicker system2. More precise beam orbit control3. 100 bunches/pulse electron beam generation and acceleration4. Test on beam loading1. Survey IBS in detail and 2. Longitudinal instability

22、 until 3x1010 electrons/bunch.3. Multi-bunch instability until 3 trains with 20 bunches.4. Especially Fast Ion Instability with vacuum pump turn-off.5. Observation of different beam behavior with wigglerScheduleFirst ATF program (from 1997) will be finished until the end of JFY 2004.Second ATF progr

23、am which includes nano-meter orbit handlingand 1st bunch compression until 1psec(rms) has been already unofficially discussed.12/14/2021DR2003, Jan. 27 at Daresburyhorizontal wirevertical wirelaser specification cavity specificationhorizontal wire(vertical measurement)vertical wire(horizontal measurement)mirror front99.1 %99.8 %reflectanceend99.9 %99.9 %mirror