NLC - The Next Linear Collider Project Cavity BPM studies Marc Ross Explore uses (and limitations)...

NLC - The Next Linear Collider Project

Cavity BPM studies

Marc Ross

Explore uses (and limitations) of uwave cavity BPM’sDevelop nanometer resolution

10x better than FFTB/ShintakeDigital mixing / angle control

Develop beam phase space monitorsTilt-meter

ATF is the ideal location for these tests – very stable beam and low emittance

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Slide #2ISG 9 at KEK Marc Ross/SLAC11.12.02

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 resolution2. Study beam stability

• study the stability of the ATF extraction line beam3. Stabilize with active movers/sensors

• Stabilize the magnets that focus the beam (they probably need it)• Stabilize the BPM itself

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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 )

2sincos

2)( t

t tqatV

)sin()( taqtVy

TVV tt

y

t

24

Papers:CLIC – 244:“Measurements for Adjusting BNS Damping in CLIC” 17.08.94 W. WuenschEPAC 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 tolerance d = 200 nm• Cavity Frequency F = 11.424 GHz• Ratio of tilt to position sensitivity ½ft = 0.012• A bunch tilt of 200 nm / 200 m (1 mrad) yields as much signal as a

beam offset of 0.012 * 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

Cavity BPMFFTB (Shintake) ATF ext line (Vogel) X-band (Naito)

f 5.712 6.426 11.424 (GHz)position resolution 20 200 200 (nm)Vt/Vy (200um sig_z) 0.6% 0.7% 1.2% (.5 pi sig_t f)achieved 'projected dipole resolution' (200um sig_z) 3.3 29.7 16.7 umachieved 'tilt' angle resolution 17 149 84 mradachieved 'trajectory angle resolution' 3 26 30 uradcavity 'length' 15 15 8 mm

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 precisionBeam position/beam traj angle

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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

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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

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Tiltmeter Tests 12.02

• 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

controlsTop 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

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C-band RF at ATF!• CW TWT amplifier (use pulse only)• 600 W nom – 1kW measured• On loan from C-band group

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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

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Typical cavity signal

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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

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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

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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

Ellip

ticity

(da-

en)

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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

Data file Condition ellipticity bunch length (mm) ATF-01-01datac8 nominal I= 3.5mA 0.81 8.5 9.0datac9 0.39 mA 0.64 6.9 6.3datac10 1.7 mA 0.74 7.7 7.5datac11 .465 mA 0.61 6.6 6.8datac12 0.3mA Vc 150 KV 0.79 8.3 8.8

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

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C-band BPM limiting resolution (Vogel/BINP)

Cavity properties:• For 1010 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 4x10-21 • Thermal noise position (ideal) = 0.4nm

• Note that deposited energy goes as offset^2 and as beam charge ^2.

Signal:• A 1nm offset deposits 2.4x10-20 J in the

cavity.

• Output power for 1 nm offset is 2.4x10-13 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)

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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-47000 0.7dB 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: JS2-02000800-08-0A (for future upgrade).

• Mixer: Use Hittite GaAs parts - likely to be radiation resistant.• IF amplifier. 30dB gain, 0.1-50 MHz. Various options from Mini Circuits or

Analog modules. Need Noise Figure << 10dB. > 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 68040 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.

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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.

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Plan2) 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?

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NLC - The Next Linear Collider Project Cavity BPM studies Marc Ross Explore uses (and limitations)...

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