NLC - The Next Linear Collider Project Cavity BPM studies Marc Ross Explore uses (and limitations) of uwave cavity BPM’s Develop nanometer resolution 10x better than FFTB/Shintake Digital mixing / angle control Develop beam phase space monitors Tilt-meter ATF is the ideal location for these tests – very stable beam and low emittance

Author Name Date Slide # 2 ISG 9 at KEK Marc Ross/SLAC Goal – ATF Nano-BPM project Prove that nanometer sized beams can be kept in collision –short time scales – vibration –long time scales – thermal drift Steps: 1.Measure with nanometer resolution –design and test a BPM that has ~ 1 nanometer resolution 2.Study beam stability study the stability of the ATF extraction line beam 3.Stabilize with active movers/sensors Stabilize the magnets that focus the beam (they probably need it) Stabilize the BPM itself

Author Name Date Slide # 3 ISG 9 at KEK Marc Ross/SLAC Multi-bunch feedback – final step There will still be some instability from the ring / extraction kicker It may be possible to stabilize the trajectory within a long pulse train need good – multibunch – BPM’s ‘FONT’ experiment at NLCTA 4. Use a long extracted pulse and stabilize the back section of the train FONT = Feedback On Nanosecond Timescales

Tilted bunch Point charge offset by  Centered, extended bunch tilted at slope  t Tilt signal is in quadrature to displacement The amplitude due to a tilt of  is down by a factor of: with respect to that of a displacement of  (~bunch length / Cavity Period ) Papers: CLIC – 244: “Measurements for Adjusting BNS Damping in CLIC” W. Wuensch EPAC 2002: “Beam Tilt Signals as Emittance Diagnostic in the Next Linear Collider Main Linac” P. Tenenbaum…

Example Bunch length  t = 200  m/c = 0.67 ps Tilt toleranced = 200 nm Cavity FrequencyF = GHz Ratio of tilt to position sensitivity½  f  t = A bunch tilt of 200 nm / 200  m (1 mrad) yields as much signal as a beam offset of * 200 nm = 2.4nm Need BPM resolution of ~ 2 nm to measure this tilt Challenging ! –Getting resolution –Separating tilt from position Use higher cavity frequency? Need 1 mrad tilt sensitivity for linac tuning

Angled trajectories A trajectory that is not parallel to the cavity axis also introduces a quadrature signal (in phase with ‘tilt’ signal) Projected ‘dipole’ sensitivity is increased by  z /cavity length –~ 50  ATF  z ~ 8mm gives expected tilt resolution ~ 0.1mrad  y res /  y ~ 5%  y’ res /  y’ ~ 10x Relative normalized precision Beam position/beam traj angle

Author Name Date Slide # 7 ISG 9 at KEK Marc Ross/SLAC Tiltmeter plans (Dec 02) All offsets / angles must be zero in order to have maximum sensitivity control to correct ‘yaw’ –beam must be parallel to axis to minimize quadrature phase signal installation of ‘beam tilter’ –cavity + drive power + synchronization (not totally necessary) roll - yokoyure / ou ten pitch - tateyure yaw – katayure (?) Dec 2 – 6, 2002

Author Name Date Slide # 8 ISG 9 at KEK Marc Ross/SLAC Parasitic bunch In May 02 we saw a parasitic ‘satellite’ bunch one RF bucket (1/714 MHz) later than primary bunch Because of the large spacing, the tiltmeter will measure the angle between the two bunches We are making a parasitic bunch detector that uses synchrotron radiation –‘Single photon’ counter –(parasitic bunch may be very small with new gun

Author Name Date Slide # 9 ISG 9 at KEK Marc Ross/SLAC Tiltmeter Tests Generate tilt using deflecting cavity –Cavity is unlocked so deflection will be random pulse to pulse –Some bunches will be tilted, some simply kicked Use downstream cavity BPM (MM4X) with I/Q detection circuit –Almost digital downconversion Calibrate position response using movers Measure beam jitter/cavity resolution combination –Tilt jitter? –Angle response

MM4X Cavity BPM position/angle controls Top to bottom (6 movers for 4 degrees of freedom): x stage y stage z stage for orthogonalizing pitch x stage for orthogonalizing yaw Rotary table (yaw) Pitch ‘tilter’

C-band deflection cavity

Author Name Date Slide # 12 ISG 9 at KEK Marc Ross/SLAC C-band RF at ATF! CW TWT amplifier (use pulse only) 600 W nom – 1kW measured On loan from C-band group

Author Name Date Slide # 13 ISG 9 at KEK Marc Ross/SLAC Pill box cavity design Rectangular pillbox standing wave cavity with off-axis beam pipe Estimated kick about 5 kV Measured kick about 10KV peak/peak with 600W input power Installed 700 mm downstream of QD7X

Author Name Date Slide # 15 ISG 9 at KEK Marc Ross/SLAC Typical cavity signal

Author Name Date Slide # 16 ISG 9 at KEK Marc Ross/SLAC Calibration using mover Typical response: 30 mV/micron Measured circuit noise: 300 uV Estimated resolution: 10 nm To be tested using 3 BPM’s in 03.03

Author Name Date Slide # 17 ISG 9 at KEK Marc Ross/SLAC Deflection cavity on I/Q cavity response with deflection cavity at full voltage Axes show directions of pure displacement (black) and pure angle (bluish) (green is 90 from pure displacement) –Tilter motion is not quite orthogonal Ellipticity is the ellipse aspect ratio (jiyouou) This plot shows equivalent ‘angle trajectory’

Comparison – 3.5 and.4 mA Effective beam tilt scale ‘full width dipole projection’ is 0.9 of displacement for 8 mm bunch (scales with bunch length) See 29 um peak to peak kick at full I and 20 um projected dipole at monitor –Good vertical streak of 7 um beam! –Tilt angle 20um/8mm = 2.5 mrad 29um 21um dipole 3.5mA 0.4mA 25um 14um dipole ellipticity Preliminary result

Author Name Date Slide # 19 ISG 9 at KEK Marc Ross/SLAC Estimate of bunch length from ellipticity Ellipse min/max vs bunch length (mm) for C-band Only length scale used is RF wavelength ATF bunch length range mm Ellipticity (da-en)

Author Name Date Slide # 20 ISG 9 at KEK Marc Ross/SLAC Summary of bunch length measurements First bunch length measurement made entirely using RF cavities Beam/monitor jitter ~ 1 um (very stable over hours!) Beam/monitor tilt jitter ~ 1 um  surprisingly large Preliminary result

1) Nano-BPM test – ATF extraction line Mechanically connect several BPM’s (4 – 5?) Must control cavity position and angle Electronics similar to tiltmeter – optimized for best possible resolution ATF ext line (BINP) – 250 nm FFTB (Shintake) – 25 nm Joe Frisch, Steve Smith, T. Shintake

Author Name Date Slide # 22 ISG 9 at KEK Marc Ross/SLAC C-band BPM limiting resolution (Vogel/BINP) Cavity properties: For Electrons, single bunch (assumed short compared to C-band). Assume cavity time constant of 100 nanoseconds (1.6MHz bandwidth) (guess) Assume beta >> 1 for cavity. (All power is coupled out). Thermal noise energy is kT or 4x Thermal noise position (ideal) = 0.4nm Note that deposited energy goes as offset^2 and as beam charge ^2. Signal: A 1nm offset deposits 2.4x J in the cavity. Output power for 1 nm offset is 2.4x Watt. Output power for 1 cm offset (cavity aperture?) is ~25 Watts (maximum single bunch) Output power for 10 bunch train can be 2500 Watts! (Need to terminate for multi-bunch operation)

Author Name Date Slide # 23 ISG 9 at KEK Marc Ross/SLAC Electronics, Noise and Dynamic range Thermal noise = -168dBm/Hz. Assume signal loss before amplifier = 3dB. 1.2x10-13 Watt = -99dBm Signal power after amplifier for 1nm offset = -79 dBm Dynamic range at amplifier output = 91 dB, or ~35,000:1 position, or 25 microns. –Assume maximum signal into mixer (13dBm LO) = ~8dBm. (Joe thinks this should be ~0 dBm) –Full range (1 dB compression): 8 dBm into mixer –(Note: for good linearity, probably want –20 dBm into mixer, or ~1 micron range) Mixer conversion loss ~8dB. Maximum output = 0 dBm Front end broad band amplifier – 20 dB –Assume noise figure = 3dB (better available) = -165dBm/Hz input noise. –Front end amplifier bandwidth = 10GHz -> -65dBm noise input. –Front end gain = 20dB -> -45 dBm noise power output (OK). IF amplifier – 30 dB –Final bandwidth = 1.6 MHz. Noise in band power after amplifier = -83 dBm

Cavities - assume existing C band BPMs Filters: Approximately Q=10 to help limiter. May not need if fast limiter is available. Limiters: Available from Advanced Control. 100W peak input, Limit to about 15dBm output. Try ACLM-4700F feedback limiter 0.8dB loss, 100W max pulse input, 13.5dBm max output. Unknown speed. Also see ACLM dB loss, 100W input, 20dBm max output. Amplifier: Available from Hittite with ~3dB noise figure. Stage to get ~30dB Gain. NOTE: need to find an amplifier which can survive the 15dBm output from the limiter. Hittite parts seem to only handle 5dBm. (Maybe OK pulsed?) Amplifiers available from Miteq ($$$?) with 0.8dB noise figure and 20dBm allowable input power: JS A (for future upgrade). Mixer: Use Hittite GaAs parts - likely to be radiation resistant. IF amplifier. 30dB gain, MHz. Various options from Mini Circuits or Analog modules. Need Noise Figure 2V p-p swing. Equipment

Support electronic equipment / software Digitizer: Use spare SIS (VME) units from 8-pack LLRF system. Each is 100Ms/s, 12 bit, +/-1 V (?) input signal. C-band source: Use existing ATF synthesizer. Does not need to be locked. C-band distribution amplifier. Need to drive 8 x 13dBm references. Approximately 25dBm output (including losses). Use existing ZVE-8G amplifier (purchased for tiltmeter work). C-band distribution splitter: 1:8 splitter. Probably exists, otherwise mini- circuits. Control System: Use existing controller and existing crate. Linda thinks it is easy to interface this to Matlab on a PC for data analysis. Matlab software: Use modified version of tiltmeter software. Digitizes decaying signal from cavity BPMs and reference signal, with stripline BPM as time reference. Does not require phase locked reference, or good frequency match between cavities.

Author Name Date Slide # 26 ISG 9 at KEK Marc Ross/SLAC Mechanical X/Y Tilt Stage: Check Newport U400 mirror mounts (~$300 each). May be strong enough to move cavity. X/Y Tilt stage drive: Use picomotors (~$450/channel motor + ~300/channel for driver), or steppers (??/channel). Steppers would provide position read back. X/Y translation stage: Use existing stages.

Mechanics Mechanical Issues The ATF beam has a position jitter of ~1 micron. In order to demonstrate 1nm bpm resolution, we need to do line fits between 3 (or more) bpms. This requires a position stability for these bpms of <1nm for several pulses (10-30 seconds). For bpms spaced by meters, the ground motion and vibration will be substantially larger than this, probably hundreds of nanometers. For the final measurement the bpms must be mounted from a common reference block. That reference block must be on supports which are sufficiently soft to not transmit vibrations which can excite internal modes in the block, probably a 10Hz mechanical support frequency is reasonable. Thermal expansion of metals is ~2x10-5/C. For a 30cm scale length, this requires temperature stability of 2x10-4C in a measurement time (~1 minute). With insulation and in the controlled ATF environment this may be possible. Use if Invar or a similar low expansion mounting frame may provide a factor of 10 relaxation in this requirement. (Not more, since it is impractical to make to cavities or cavity mounts out of Invar. If the temperature requirements cannot be met, an interferometer (or "queensgate" style capacitive system) will need to be used relative to an Invar or Zerodur reference block.

Author Name Date Slide # 28 ISG 9 at KEK Marc Ross/SLAC Plan 2) Study beam stability – pulse to pulse and long term – using nanoBPM Assume that the ATF beam is not stable at the nanometer level and cannot be made stable 3) Use the FONT feedback on a long multi-bunch train (coll with UK group) requires: 1.increasing the bandwidth of the nano BPM to ~20 MHz (from 1.5 MHz) 2.Extra long trains – lengthen the train by extracting 3 trains that were injected in a sequence 3.Installation of the FONT feedback kicker and sampler Can we stabilize the back section to the nanometer level?