CesrTA E-cloud Activities (Jan. 2009) J.W. Flanagan, KEK

Organization CesrTA meeting slides from WebEx, provided by Mark Palmer – Have tried to attribute original authors correctly. Supplemental slides on some contributions from KEK

February 11, 2009CesrTA-KEK Update3 CesrTA Run & Down Recap Completed experimental run 2/2/2009 – Low emittance correction in GeV baseline optics – X-ray Beam Size Monitor (xBSM) commissioning – EC Measurements RFA & TE wave measurements Dynamics – General instrumentation/feedback tests/commissioning 13 visitors – LET - J. Jones, A. Wolski – xBSM – J. Flanagan, H. Sakai – EC – S. De Santis, R. Holtzapple, K. Shibata, L. Wang – Feedback – D. Teytelman, M. Tobiyama – CLIC – H. Schmickler – Instrumentation – A. DellaPenna, I. Pinayev 2 nd upgrade down is underway… – Installation of PEP-II experimental hardware – Installation of photon stop chamber for 5GeV operation of the CesrTA L0 wiggler straight – Replacement of SRF cavity that failed during summer 2008 – Installation of xBSM beam line front end for electron beam – Continue with instrumentation upgrade for 4ns bunch train operation – Contingency item: Repair of 15BW dipole coils M. Palmer (CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update4 Optics and LET Low emittance GeV optics loaded and corrected – Correction methods tested – Beam-based alignment measurements – Coupling and dispersion bumps created for tuning Emittance measurements begun… – Touschek lifetime measurements initially used to characterize beam size – xBSM measurements as detector and optics were characterized Ongoing program of magnet alignment to improve emittance – Alignment work continued throughout the run – 2 anomalous locations in the ring have been identified which are being scrutinized. D. Rubin (CesrTA Mtg)

February 11, 2009CesrTA-KEK Update5 Measured energy acceptance = 0.7%   v ~ 32pm From xBSM  v ~ 15  5  m   v ~ 38pm Appear to be within a factor of 2 of the 20pm target First Detailed Optics Correction  Touschek Study  xBSM Measurement (Preliminary) Wolski A. Wolski (CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update6 xBSM Snapshots (Preliminary) Scan of coupling knob Coded aperture measurements Smallest recorded size: ~15  m (but further calibration work needed) Simulations Measurement Fresnel Zone Plate Coded Aperture <20  m beam size J. Alexander (CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update7 EC Data-Simulation Updates Simulations of tune shifts in POSINST at Cornell and LBNL, using a new option in POSINST for offseting the bunches, have shown that the tune shifts of a single bunch are different if the whole train is oscillating coherently, than if just the single bunch is oscillating. – Horizontal tune shifts in a dipole are much smaller when the whole train is oscillating coherently. This is particularly relevant for the tune shift measurements at CesrTA, since we kick the whole train coherently to do the measurement. – Tune shifts calculated for a coherently oscillating beam give better agreement with measurements: see following three slides. January run – Studies of systematic effects in the tune shift measurements were carried out. – Measurements of tune shift vs. current for long trains (10, 20, 45 and 116 and 145 bunches) were carried out (evidence of instability developing at the end of the 116 and 145 bunch trains) – RFA and TE wave measurements to characterize EC density in drifts, dipoles and wigglers – Work on comparisons between RFA and TE wave measurements as well as systematics checks for both G. Dougan(CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update8 10 Bunch Train with Trailing Witness Bunch(es) Data-POSINST Comparison (Preliminary) Positron Beam Blue  Vertical  Q Red  Horizontal  Q Squares  Simulation Circles  Data G. Dougan(CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update9 Electron Beam 10 Bunch Train with Trailing Witness Bunch(es) Data-POSINST Comparison (Preliminary) Blue  Vertical  Q Red  Horizontal  Q Squares  Simulation Circles  Data G. Dougan (CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update10 Drift vs Dipole Contributions Comparison of drift (red) and dipole (blue) contributions to tune shifts in each dimension Horizontal Vertical G. Dougan (CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update11 Positron Beam 45 Bunch Train: Data-POSINST Comparison (Preliminary) Blue  Vertical  Q Red  Horizontal  Q Squares  Simulation Circles  Data G. Dougan (CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update12 L0 RFA Data 2/3/08 Wiggler with RFAs and uncoated Cu VC Wiggler with RFAs and TiN-coated VC e+ e- 2E Segmented RFA 2W Segmented RFA G. Dougan (CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update13 Electron-Positron Comparisons (1x45 Current Scans) Segmented drift Cu wiggler (pole center)  Positrons   Electrons  2W detector downstream of wigglers for e+ beam 2E detector downstream of wigglers for e- beam Cu wiggler (pole center) Segmented drift G. Dougan (CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update14 Cu wiggler, pole center Drift (Cu VC) Dipole (Al VC) Long Train Data 1x145 e+ – 14 ns spacing  79% of ring filled – Multipacting stripe Strongly visible in dipole Weaker in L0 wiggler and drift regions G. Dougan (CesrTA Mtg.)

February 11, 2009CesrTA-KEK Update15 Plans 15E/W test chamber design for coating tests Segmented RFA Shielded Pickups CESR layout modifications to be completed by March 1 – 4 Experimental areas for EC build-up and mitigation studies L0 wiggler straight – Configured for RFA and TE Wave measurements of EC build-up – 4 wiggler comparisons planned (CU-KEK-LBNL-SLAC collab.) » Cu vacuum chamber (installed) » TiN coated vacuum chamber (installed) » Grooved vacuum chamber (  summer ’09 installation) » Clearing electrode vacuum chamber (  fall ’09 installation) L3 straight w/PEP-II chicane and SEY sample station – Sample station tests (CU-FNAL-SLAC collab.) – Grooved chamber tests (CU-SLAC collab.) 15E/W – Flexible location for testing chambers with dipole synchrotron radiation – Presently planned comparisons (summer/fall ’09) » Al vacuum chamber »  carbon coated VC (CERN-CU collab.) » Enamel chamber with electrode (Project X collab.) » TiN-coated Al vacuum chamber – Detailed beam dynamics studies at ultra low emittance Mid-2009  end of program Characterize instability thresholds High resolution bunch-by-bunch beam size measurements to characterize incoherent emittance growth Witness bunch studies for flexible control of EC interaction with beam M. Palmer (CesrTA Mtg.)

KEK Participation in CesrTA Several members of KEKB are participating in CesrTA: – K. Ohmi (electron cloud instability dynamics studies and simulation) – M. Tobiyama (instrumentation and feedback) – K. Kanazawa, Y. Suetsugu, K. Shibata (vacuum group: electron cloud mitigation measures) – J. Flanagan (e-cloud studies and diagnostics, x-ray beam size monitor) – +H. Fukuma, N. Ohuchi, … – Note: Funding provided by US-Japan Cooperation Program (Nichibei) ATF members also participating: – H. Sakai (U. Tokyo): X-ray beam size monitor – K. Kubo: Low emittance tuning – Reverse direction (from Cornell): – Jim Alexander -> KEK for x-ray monitor readout tests – Jim Shanks -> ATF for low emittance tuning – Others likely not listed

Bunch-by-bunch Feedback Longitudinal feedback at 4 ns successfully demonstrated in January 2009 by Dmitry Teytelman (Dimtel, formerly SLAC) using iGp – iGp: Next generation digital feedback system developed by collaboration of SLAC (J. Fox, D. Teytelman), KEK (M. Tobiyama), INFN (A. Drago), Dimtel – Transverse feedback also demonstrated.

Mitigation methods: PRELIMINARY results from KEKB Techniques also being tested at CesrTA – Clearing Electrode (Suetsugu, Fukuma et al. design) Design being worked on for CesrTA – Grooved Chamber (Pivi et al. design) Being installed at CesrTA for testing in summer run

Clearing Electrode 1 Study on clearing electrode also started for mitigation of electron cloud in magnets. Clearing electrode and electron detector were installed in wiggler magnet of LER. (placed at the center of pole) To demonstrate the effect of electrode, the electron density was measured by the electron detector with 7 strips. Sustainability for high beam current was also tested. 19 The 14 th KEKB Review on 9-11 February 2009 at KEK Very thin electrode (0.1 mm, Tungsten) and insulator (0.2 mm, Al 2 O 3 ) were developed. (Thermal Spray) 7 strips can measure the horizontal spatial distribution of the electron cloud. 440 mm Stainless steel Tungsten Al 2 O 3 40 mm Feed- through Y. Suetsugu et al., NIM- PR-A, 598 (2008) 372 K. Shibata (KEKB Review)

Clearing Electrode 2 20 The 14 th KEKB Review on 9-11 February 2009 at KEK Electrode [W] (~ +1 kV) Collector (7 strips, w 5 mm) Cooling channel Insulator [Al 2 O 3 ] ( t ~0.2 mm) Grid (~ 1 kV) Vacuum seal by metal O-ring Cooling Water paths Shield Monitor Block Electrode Block  2 mm holes R47 Limited by magnet aperture ( w 40, l 440, t ~0.1) Beam Cross-section Test chamber Wiggler magnet Magnetic filed : 0.77 T Effective length : 346 mm Aperture (height) : 110 mm Electron detector Clearing electrode Y. Suetsugu et al., NIM- PR-A, 598 (2008) 372 K. Shibata (KEKB Review)

Clearing Electrode 3 Drastic decrease in electron density was demonstrated by applying positive voltage. 21 [8ns] [6ns] [4ns] [16ns] I e [A] V elec [V] Number of electrons was reduced to 1/10  1/100 if applied voltage of clearing electrode was more than 300 V for any bunch spacing. The 14 th KEKB Review on 9-11 February 2009 at KEK V r =  1.0 kV B = 0.77 T I e [A] V elec [V] Collectors 1 x x x x x bunches (B s ~ 6 ns) ~1600 mA Collector : #4 V elec = 0 positive negative Y. Suetsugu et al., NIM- PR-A, 598 (2008) 372 K. Shibata (KEKB Review)

Clearing Electrode 5 Electrode was very effective, but modification of the feed-through connection part is required for high beam current. Insulation resistivity decreased from 2 M  to several 10 k  during the trial period due to discharge at feed-through connection part. Connection part Improved clearing electrode will be installed this winter. 22 electrode insulator The 14 th KEKB Review on 9-11 February 2009 at KEK Y. Suetsugu K. Shibata (KEKB Review)

Clearing electrode for CesrTA

Groove Surface 1 Effect of groove surface was also studied last autumn. (collaboration with SLAC) Electrode was replaced by groove surface. Same setup for clearing electrode was utilized. Groove structure was designed and manufactured in SLAC. TiN~200 nm Flat surface with TiN coating was also tested for reference. R47 Beam [Groove] [Monitor] Magnetic field Y. Suetsugu, ILCDR2008 Groove surface [SUS + TiN] Flat surface [SUS + TiN] TiN~200 nm 24 The 14 th KEKB Review on 9-11 February 2009 at KEK K. Shibata (KEKB Review)

Groove Surface 2 Electrons for groove surface was reduced to 1/5  1/10 the number for flat surface (3 buckets spacing). 1x10 -6 Flat surface Groove surface 25 Y. Suetsugu Preliminary result Further R&D will be carried out toward the practical use of groove surface. The 14 th KEKB Review on 9-11 February 2009 at KEK K. Shibata (KEKB Review)

Mitigation Performance Comparison ~1x10 12 e - /m 3 ~1x10 1 １ ~1x10 10 ~1x10 9 V r = -1 kV (1/1585/3.06) Ranking of estimated performance in magnet is ; Clearing electrode is much more effective than groove surface and TiN coating. Electrode >> TiN+Groove >> TiN(Flat) > Cu(Flat)  10  5  10  2  3 26 Preliminary result The 14 th KEKB Review on 9-11 February 2009 at KEK Electrode and groove surface are very promising, but more studies are required to achieve the practical use of them. K. Shibata (KEKB Review)

X-ray monitor: Coded Aperture Imaging Simulated detector response for various beam sizes Example of beam size measurement at CesrTA (  y =~ 45  m) Uniformly Redundant Array (URA) mask being tested at CesrTA Technique developed by x-ray astronomers using a mask to modulate incoming light. Resulting image must be de-convolved through mask response (including diffraction and spectral width effects) to reconstruct object. Open aperture of 50% gives high flux throughput for bunch-by-bunch measurements. A heat-sensitive monochromator not needed. red : data green : simulation preliminary A*G : system point-spread function ~  function P=O*A A : mask or aperture, G: post processing array : reconstructed object, P: picture, O: object, * : convolution

Coded Aperture. 1/28/2009 CESR condition same as for the 18um case on previous page

X-ray Beam Size Monitor X-ray beam size monitor results: – Beam size = um (using both Fresnel Zone Plate and Coded Aperture Mask) Corresponds to emittance of ~38 pm. Touschek lifetime measurements indicate an emittance of ~30 pm.