Optical diagnostics for beam halo (I) Coronagraph (II) OTR halo monitor for J-PARC T. Mitsuhashi, KEK

(I) Coronagraph

Everything was start with astronomer’s dream…… Eclipse is rare phenomena, and only few second is available for observation of sun corona, prominence etc. Artificial eclipse was dream of astronomers, but……..

Why we can see sun corona by eclipse without diffraction fringe? Because no aperture between sun and moon. It means no diffraction source in eclipse. Question is can we make same system with artificial way?

Diffraction source aperture is in here. Compare two setup, eclipse and artificial eclipse. Answer is to eliminate diffraction fringe from aperture. …but how????

Objective lens Magnifier lens Opaque disk to block glare of central image Observation with normal telescope Diffraction fringes vs. halo

Diffraction fringes Gaussian profile Convolution between diffraction fringes and object profile

Diffraction makes fringes surrounding from the central beam image. Intensity of diffraction fringes are in the range of of the peak intensity. (electron beam) The diffraction fringes disturb observation of week object corona surrounding which has intensity range of of bright sun sphere.

Diffraction fringes Gaussian profile Convolution between diffraction fringes and beam profile Blocked by opaque disk

The coronagraph to observe sun corona Developed by B.F.Lyot in 1934 for a observation of sun corona by artificial eclipse. Special telescope having a “re-diffraction system” to eliminate a diffraction fringe.

Optical system of Lyot’s corona graph Objective lens Field lens Baffle plate (Lyot stop) Relay lens Opaque disk Anti-reflection disk Baffle plates to reduce reflection

Re-diffraction optics system to eliminate the diffraction fringe

Opaque disk Lyot stop Re-diffraction optics system Opaque disk Field lens Objective lens Re-diffraction optical system

Objective lens with anti-reflection disk to block reflected light from opaque disk

R r The integration performs r and R r : radius of Anti-reflection disk R : radius of objective lens aperture Objective lens diffraction

Disturbance of light F  on opaque disk is given by; In here f(  is disturbance of light on objective lens.

Opaque disk Lyot stop Re-diffraction optics system Opaque disk Field lens Objective lens Re-diffraction optical system Function of the field lens : make a image of objective lens aperture onto Lyot stop

  The integration performs  1 and     : radius of field lens   : radius of opaque disk Field lens diffraction

Disturbance of light on Lyot’s stop by re-diffraction system is given by;

Geometrical image of the aperture of objective lens Intensity distribution of diffraction fringes on focus plane of field lens

Block the re- diffraction fringes

Opaque disk Lyot stop Re-diffraction optics system Opaque disk Field lens Objective lens Re-diffraction optical system Function of the field lens : make a image of objective lens aperture onto Lyot stop Blocking diffraction fringe by Relay lens to relay corona image onto final focus point

Lyot stop Blocking diffraction fringe by Relay of corona image to final focus point

 The integration performs  1   : radius of Lyot stop Relay lens diffraction

Disturbance of light on final focus point V(x) is given by; U(x) is still not 0 inside of relay lens pupil!

Background in classical coronagraph Re-diffraction intensity on the Lyot stop Diffraction fringe exists here This leakage of the diffraction fringe can make background level (depends on Lyot stop condition).

Observation of the sun corona by coronagraph

Front view of the coronagraph Photographs of coronagraph

Objective lens with anti-reflection disk to block reflected light from opaque disk

Field lens Lyot’s stop View from the back side

Fast gated camera set on the final focusing point

Zoom up of opaque disk. Shape is cone and top-angle is 90º

Opaque disk assembly

Background source in coronagraph 1.Scattering by defects on the lens surface (inside) such as scratches and digs. 2. Scattering from the optical components (mirrors) near by coronagraph. 3. Reflections in inside wall of the coronagraph. 4. Scattering from dust in air.

1.Scattering by defects on the lens surface (inside) such as scratches and digs. 2. Scattering from the optical components (mirrors) near by coronagraph. 3. Reflections in inside wall of the coronagraph. Cover the inside wall with a flock paper (light trapping material). 4. Scattering from dust in air. Use the coronagraph in clean room.

Scattering from defects on the lens surface such as scratches and digs. With normal optical polishing, for example S&D 60/40 scattered light intensity : about times of input light intensity.

S&D 60/40 surface of the glass 5mm

Result of careful optical polishing for the objective lens 5mm

Scattering from the optical components (mirrors) between source point and coronagraph.

SR beam electron beam orbit Set up of SR monitor at the Photon factory mirror 2900 source point Scattering from Be-mirror is about 5x10 -7 Scattering from the mirror which set at 2m in front of coronagraph is about 6x10 -5 coronagraph

Scattering background from mirrors near by coronagraph will not acceptable! Use same quality of optical polishing for mirrors!

Observation of beam halo at the Photon Factory, KEK

Beam profile

Beam halo

Intentionally spread some dust on the mirror in 2m front of the coronagraph

Diffraction tail observed without Lyot’s stop Entrance pupil is intentionally rotated by 30º to recognize diffraction tail easily. 30 °

in  Diffraction fringe Beam halo Comparison between beam tail and diffraction tail

Move the opaque disk slightly to show the edge of central beam image (diamond ring!)

65.8mA61.4mA 54.3mA 45.5mA35.5mA 396.8mA Multi-bunch bunch current 1.42mA Beam tail images in the single bunch operation at the KEK PF measured at different current

Single bunch 65.8mA Exposure time of CCD : 3msec Exposure time of CCD : 100msec Intensity in here : 2.05x10 -4 of peak intensity 2.55x10 -6 Background leavel : about 6x10 -7 Halo in deep outside Observation for the more out side

Strong tail Weak tail in outside x 33

Conclusions The coronagraph was designed and constructed for the observation of weak object (such as tail and halo) surrounding from central glare of the beam. Optical polish of the objective lens is key point to realize good S/N ratio, and we reached ratio of background to peak intensity 6x Spatial resolution is about 50  m (depends opening of optics) By using the coronagraph, we observe beam tail at the photon factory storage ring. As results; 1. a strong beam tail was observed in inside of RF bucket 2. a weak, and wide-spread tail is observed in outside of RF bucket.

Recent investigation in coronagraph Astronomers have a dream to observe planet system in outside of solar system. They need contrast level of !

Background in classical coronagraph Re-diffraction intensity on the Lyot stop Diffraction fringe exists here This leakage of the light can make background level (depends on Lyot stop condition).

Background level of 6x10 -7 will good enough ? no Yes Use classical coronagraph Spatial coherence is good enough? Source like a point no No solution now Null- interferometeric coronagraph

Null interferometeric coronagraph Background level : about (?) Objective lens Field lens Baffle plate (Lyot stop) Relay lens Phase mask Opaque disk Classical coronagraph Null interferometric coronagraph

Arrangement of null-interferometric coronagraph. Astronomers say we can reach to the background level ! Phase plate instead of opaque disk

(II) OTR halo monitor for J-PARC

Optical design for OTR profile monitor in beam tranportline between 3.5GeV Rapid Cycle Synchrotron and 50GeV main ring The beam size of proton beam is 5cm! 2d observation of beam halo is also Very important! Light source is OTR. 5cm

Beam halo Beam core screen with hole OTR from beam halo Beam halo observation by screen with hole

Beam halo in far outside observed by fluorescent screens Fluorescent screens

Fundamental design of OTR monitor

RCS 3GeV PS 12GeV OTR intensity conpair with 12GeV proton synchrotron at KEK

Angular distribution of OTR from 3.5GeV Al foil target and proton beam PS 12GeV RCS 3GeV Peak is in 350mrad!

Imaging device few mrad lens OTR screen 45º Large field depth by large object Typical OTR profile monitor at electron machine

Imaging device 50 mrad OTR screen 45º Large field depth by large object Toyoda, Mitsuhashi 2009 for slow extraction line at J-PARC 6000mm 300mm

Large field depth by large object 500mrad 500mm 45degree set up of target will impossible! Too long field depth!

500mrad 500mm beam Foil target must be normal to the beam!

Proton beam Offner relay system Spherical 1 st mirror D=600mm R=500mm Spherical 2ed mirror D=200mm R=250mm 500 mrad D=300mm ２枚

Design of Offner relay system Object size: 50mm General aperture 300mm

Thank very much for your attention!