Electron Cloud Simulation Work at Cornell Jim Crittenden

Electron Cloud Simulation Work at Cornell Jim Crittenden Cornell Laboratory for Accelerator-Based Sciences and Education

Overview • ECLOUD program V 3. 2 (2 D, developed at CERN 1997 -2003) – Adapted to Cesr. TA machine studies experiments – CESR-c tune shift measurements 2007 – Cesr. TA North Area Triple-RFA arrangement – Continued development (output info, graphics, field calculations) • Standalone RFA modelling (Previously Mat. Lab, now F 90) – Compute expected RFA currents incl. tracking & secondary generation • Vector Fields OPERA model for RFA detectors – Includes electrostatics calculation with B field superposed – Calculates electron trajectories (no energy loss, no secondaries) – Electric field map provided to local standalone development • POSINST (3 D) ramping up – Visit to SLAC this week 13 May 2008 Cesr. TA Collaboration Web. Ex / J. A. Crittenden 2

CESR-c Tune Measurements Train of 10 1. 9 Ge. V 0. 75 m. A bunches generates the electron cloud Measure tune shift and beamsize for witness bunches at various spacings ECLOUD points to parameters critical for determining tune shifts: • Beam-pipe shape • 4. 5 x 2. 5 cm elliptical • B-field • Field-free rather than 800 G • % reflected s. r. photons • Less than 20 -30% Successfully predicts magnitude of vertical tune shift, but predicted horizontal tune shift somewhat high. Further investigation of E field calculation underway. 13 May 2008 Cesr. TA Collaboration Web. Ex / J. A. Crittenden 3

North Area RFA's • Two APS-type RFA's • One CESR-design thin RFA Now using electron beam owing to occluded e+ sr photons 13 May 2008 Presently investigating energy spectrum and azimuthal dependence Cesr. TA Collaboration Web. Ex / J. A. Crittenden 4

OPERA RFA Model Cesr. TA will measure electron cloud charge buildup in both dipole and wiggler magnets RFA Wiggler VC Delivered 13 May 2008 Cesr. TA Collaboration Web. Ex / J. A. Crittenden 5

EC Growth Studies • Install chambers with EC growth diagnostics and mitigation – Goal is to have implemented diagnostics in each representative chamber type by mid-2009 • Heavy reliance on segmented Retarding Field Analyzers – Wiggler chambers in L 0 straight w/mitigation – Dipole chambers in arcs w/mitigation – Quadrupole chambers w/mitigation • L 0 and L 3 straights – Drifts • Diagnostics adjacent to test chambers • Solenoids – Some components to be provided by collaborators March 5, 2008 TILC 08 - Sendai, Japan 6

EC Growth Studies • Install chambers with EC growth diagnostics and mitigation – Goal is to have implemented diagnostics in each representative chamber type by mid-2009 • Heavy reliance on segmented Retarding Field Analyzers – Wiggler chambers in L 0 straight w/mitigation – Dipole chambers in arcs w/mitigation – Quadrupole chambers w/mitigation • L 0 and L 3 straights – Drifts • Diagnostics adjacent to test chambers • Solenoids – Some components to be provided by collaborators March 5, 2008 TILC 08 - Sendai, Japan 7

Components of the EC Growth Plan • L 3 Straight – Instrument large bore quadrupoles and adjacent drifts – Proposed location for diagnostic chicane March 5, 2008 TILC 08 - Sendai, Japan 8

Beam Dynamics Studies • Prerequisites – Instrumentation to characterize bunch trains at ultra low emittance • Multibunch detectors and readouts • High resolution beam profile monitor – Ring operation at ultra low emittance • Instability Studies – Focus on witness bunch studies where EC density controlled by intensity of leading train and delay to witness bunches – Detailed study of instability thresholds and emittance growth versus the witness bunch-train parameters – Detailed electron-positron comparisons to help distinguish the dynamics and to evaluate EC impact on the electron beam – Have de-scoped plans to study fast ion effects for the electron beam as part of this program • Measurements of instabilities and emittance growth along electron bunch trains • Explore the dependence on emittance, bunch charge and spacing, train gaps and vacuum pressure March 5, 2008 TILC 08 - Sendai, Japan 9

Witness Bunch Studies – e+ Vertical Tune Shift • Initial train of 10 bunches generate EC • Measure tune shift and beamsize for witness bunches at various spacings • Bunch-by-bunch, turn-by-turn beam position monitor March 5, 2008 TILC 08 - Sendai, Japan 10

Data and Simulation • Initial comparisons for CESR – Growth modeling for dipole chambers – Initial level of agreement is promising • Ongoing Effort – Model full ring and explore parameter space – Limited MS opportunities during final CLEO-c run March 5, 2008 TILC 08 - Sendai, Japan 11

Witness Bunch Studies – e- Vertical Tune Shift • Same setup as for positrons • Negative vertical tune shift and long decay consistent with EC – Implications for the electron DR? March 5, 2008 TILC 08 - Sendai, Japan 12

EC Induced Instability • Vertical beam size along 45 bunch e+ trains (2 Ge. V, 14 ns bunch spacing) – Range of bunch currents – 200 50 -turn averages collected for each point • Observe onset of instability moving forward in train with increasing bunch current – consistent with EC March 5, 2008 TILC 08 - Sendai, Japan 13

Present Focus – Engineering Prep • During final CLEO-c production run – Limited machine studies time – Main focus on engineering preparations for Cesr. TA downs in May and July • Key pieces for EC program – L 0 wiggler experimental area – EC diagnostics • Retarding Field Analysers • Suitable readout electronics – Vacuum chamber designs – Instrumentation preparation March 5, 2008 TILC 08 - Sendai, Japan 14

L 0 Wiggler Region • L 0 wiggler experimental region design work well underway – Installation during July down – Heavily instrumented throughout with vacuum diagnostics – Targeting full design review this month followed by full scale production March 5, 2008 • Note: Part of CLEO will remain in place – At present unable to remove full detector – Time savings TILC 08 - Sendai, Japan 15

Retarding Field Analysers • Beam tests have continued through CLEO-c conclusion • Upgraded readout electronics for large channel count RFAs are now ready for production • Thin RFA structure performing well March 5, 2008 TILC 08 - Sendai, Japan 16

Chambers with Thin RFAs RFA Wiggler VC Delivered • Loss of US collaborators impacted development heavily – Cornell has picked up detailed design – Now ready for final design review – Working with KEK to see whether construction support might be available March 5, 2008 TILC 08 - Sendai, Japan 17

Cesr. TA Vacuum Chambers March 5, 2008 TILC 08 - Sendai, Japan 18

CESR Dipole Chamber RFA on Dipole VC March 5, 2008 TILC 08 - Sendai, Japan 19

X-Ray Beam Size Monitor for CESRTA Bunch-by-bunch measurements of beam profile for fast emittance determination • Image individual bunches spaced by 4 ns. • Transverse resolution << 10~15 m beam size • Non-destructive measurement. • Flexible operation. • Start simple, allow various upgrade paths. 13 May 2008 Cesr. TA Collaboration Web. Ex 20

Features that affect performance Optical path: Zone Plate: Magnification Backgrounds Diffraction - finite D Chromatic aberration Transparency 13 May 2008 Cesr. TA Collaboration Web. Ex 21

Interrelationships and Optimization 13 May 2008 Cesr. TA Collaboration Web. Ex 22

Parameters for CESRTA xray Beam Size Monitor 13 May 2008 Cesr. TA Collaboration Web. Ex 23

Sidebar: Resolution, Precision, and Photon Statistics • Optical transfer function is characterized by a resolution (point spread function). This is a fixed property of the optical system. For CESRTA design, it is 2 -3 m. (Figure at right assumes 3. 5 m) • Photon statistics (and electronic noise, if applicable) fluctuate from snapshot to snapshot. • The measurement precision of this system is determined by the stochastic element, not the fixed correction*. * Residual uncertainty in the optical resolution will appear as a systematic error 13 May 2008 Cesr. TA Collaboration Web. Ex 24

Sensors • Ga. As/In. Ga. As 1 -dim photodiode array – 512 diodes, 25 m x 500 m – Hamamatsu G 9494 -512 D – Off-the-shelf • Why Ga. As? – High carrier mobility (8400 cm 2/Vs) & drift velocity (200 m/ns) – High Z, high density • short abs length • ~ 1 m at 2. 5 ke. V – Room temperature ops. – Good radiation hardness – Commodity parts available; • IR receivers for 10 Gbps optical ethernet 13 May 2008 Cesr. TA Collaboration Web. Ex 25

Prototype study, in CHESS (Slide 1) Hard bend magnet, = 31 m Beam energy 5. 3 Ge. V 45 bunches, 150~200 m. A Bunch charge 6~8 x 1010 Horizontal slit (1 mm) Single Ga. As photodiode (46 m dia) Optics: pinhole. (40 m vertical slit) White beam (no monochromator) Data acquisition: 72 MHz (14 ns interval); 12 bit ADC. Mechanically scanned vertically and horizontally through the beam -“synthetic aperture camera” Single bunch, single pass data - no averaging over turns. 13 May 2008 Cesr. TA Collaboration Web. Ex 26

Prototype study, in CHESS (Slide 2) Result of vertical beam scan (single pixel) Measured: • S/Ne = 27 • photons per bunch is ~400 • Signal risetime << 300 ps • Observed beam size 142 9 m (expect ~150) Calculated: • Energy abs’d/bunch 6. 0 Me. V • Ionization per bunch 230 f. C • Averge photon energy: 13 ke. V electronic noise Radiation damage post-study: 700 GRad over 4 days, diode current dropped x 2. (Comment: electronic noise was not optimized!) 13 May 2008 Cesr. TA Collaboration Web. Ex 27

Prototype study, in CHESS (Slide 3) Beam size ( y) measurement. Finite optical resolution: Fixed offset in y measurement fixed correction. 59 m here. Finite photon statistics: Stochastic error from one measurement to the next. 6. 5% here* 13 May 2008 Cesr. TA Collaboration Web. Ex 28

x. BSM Positron Optics Line March 5, 2008 TILC 08 - Sendai, Japan 29

Slit Mounting Structure March 5, 2008 TILC 08 - Sendai, Japan 30

Collaborator Issues • As stated previously, a key part of the Cesr. TA proposal was collaborator involvement • The following slide is taken verbatim from the Joint NSF/DOE Review of the Cesr. TA proposal last July… March 5, 2008 TILC 08 - Sendai, Japan 31

Dealing with Challenges and Risks • Experimental program is designed to deal with discoveries and changes in direction through the course of the R&D – Schedule allows for re-evaluation of key physics issues and technologies as the program proceeds • Course corrections are expected along the way • This makes the program robust against short term technical and/or physics surprises – Technology down-selects can be employed as data is obtained to optimize the program along the way – Program relies heavily on support from collaborators • Key technical drivers for the program are: – Electron Cloud Growth Studies • Chamber construction • Implementation of diagnostics – Beam Dynamics Studies • Issues affecting our ability to achieve ultra low emittance (see later talks) • Issues affecting our implementation of high resolution emittance diagnostics (see later talks) • Key assets – A well-understood machine – An experienced accelerator staff – A highly expert group of collaborators July 16 -17, 2007 Joint NSF/DOE Review of Cesr. TA Proposal 32

Collaboration Issues • Present funding situation has several major impacts – Plans for providing experimental hardware must be revamped • Wiggler chamber design and fabrication • Support for coating tests – Loss of experimentalists to participate in Cesr. TA running • Revamping run plan to accommodate a smaller number of experimenters • Preserving ~240 running days during program – Loss of simulation and analysis support • In US, base program support may cover portions of this • Exploring Project X collaboration • Hope to work closely with colleagues from KEK, CERN and elsewhere • Presently working to fill remaining gaps March 5, 2008 TILC 08 - Sendai, Japan 33

Conclusion • CESR offers – Damping wigglers meeting the ILC specification – Flexible energy and emittance range for experimental studies – Experimental studies with electrons and positrons in the identical environment – Experienced staff and well-developed tools • The Cesr. TA program will provide – Detailed studies of electron cloud growth and validation of mitigation techniques in time for the ILC TDP-I – Beam dynamics results on electron cloud in time for the ILC TDP -I – Assurance that the ILC DR design is feasible by benchmarking our simulations with data in the relevant parameter regime March 5, 2008 TILC 08 - Sendai, Japan 34