NuMI BEAM POSITION MONITOR via MAIN INJECTOR, and RECYCLER

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NuMI BEAM POSITION MONITOR via MAIN INJECTOR, and
RECYCLER
Brajesh Choudhary, 06.Mar.2003 MINOS
Collaboration Meeting University of South
Carolina, Columbia.
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FERMILAB ACCELERATOR COMPLEX
Booster Circumference 474.2m. Booster Harmonic
No. 84
NuMI
MI/Boster Circumference 3319.42m (474.2m7) MI
harmonic No. 847588
TeV Circumference 2000? m TeV Harmonic No.
8413.25
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MAIN INJECTOR BASICS

• The Fermilab MI is a synchrocyclotron which
  accelerates
• Protons from 8.9GeV to 120GeV, for
• anti-proton production
• low intensity slow resonant extraction (slow
  spill) for test beam
• high intensity slow spill for dedicated kaon
  experiments
• high intensity fast single turn extraction for
  NuMI/MINOS
• Protons from 8.9Gev to 150GeV for collider
  operation, and
• Anti-protons from the Accumulator and the
  Recycler (when integrated) from 8.9GeV to 150GeV
  for collider operation.
• Only 6 Booster cycles are utilized to fill the
  MI, allowing rest of the space for the abort gap.

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RECYCLER RING BASICS

• Recycler Ring is an 8 GeV storage ring
  constructed using permanent magnets. It is
  expected to increase the Tevatron collider
  luminosity in two ways
• Maintain high anti-proton production rate in the
  Accumulator by periodically sending the
  anti-proton stack to the Recycler, and
• By recycling the left over anti-protons from the
  Tevatron to the Recycler and further cooling it,
  before injecting again in the Tevatron. May Not
  Happen - AAC has advised against it 4-6, Feb
  2003.

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WHAT IS A BPM?

• A beam position monitor is a non-intercepting
  device, used in particle accelerators and beam
  lines to measure the beam position by processing
  the beam induced signal on the pickup electrodes.
• In the limit of very high beam energy, the fields
  are pure transverse electric and magnetic(TEM).
  So, if a beam is displaced from the center of a
  hollow conducting enclosure, the magnetic and
  electric fields are modified accordingly.
  Detailed knowledge of how the magnetic and
  electric fields depend on the beam position
  allows accurate determination of the beam
  position.
• A conventional beam position monitor has a pair
  of electrodes (or 2 pairs, if 2 beam position
  coordinates are to be measured) on which signals
  are induced. The ratio of the amplitudes of the
  induced signals at the carrier frequency, either
  the beam-bunching frequency or a harmonic, is
  uniquely related to the beam position.

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WHY DO WE NEED A PRECISION BPM SYSTEM?

• A precision BPM system is needed to
• Reproducibly center the orbit in the physical
  aperture of the machine, thereby maximizing
  acceptance (1mm position error leads to 10 loss
  in aperture)
• Verify stable orbit position from day to day,
  ensuring stable tuning condition
• Have an accurate turn by turn measurement (ex to
  measure lattice function of the machine,
  non-linear properties of the lattice, injection
  oscillation etc. etc.)
• Understand geometrical and optical defects in the
  ring in terms of a calibrated geometrical survey
• Understand and interpret the results of a beam
  experiments which are expected to produce static
  or transient beam orbit changes (pinging, orbit
  bumps, synchrotron oscillation, understanding the
  kicker behavior for NuMI)
• Monitor and adjust the beam position in the
  injection and extraction lines, and the single
  turn orbit between the lambertson and the kicker
  in the ring
• Independently measure orbit closure and injection
  oscillations.

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RECYCLER BPMs
End View
4.4cm
Top View
9.6cm
30cm
Split tube BPM Design
Pictures - Courtesy Jim Crisp
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MI BPMs
Large Aperture BPM
Long face outer/inner size 4.75/4.625 Short
face outer/inner size 2.1/1.9
MI Ring BPM
Plate diameter outer/inner 4.75/4.625
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NuMI SPLIT PIPE BPMs
Target BPM
Transport BPM
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BPMs TO BE UPGRADED

• In the RR we need to upgrade 104 horizontal and
  107 vertical beam position monitors. We also need
  to upgrade 26 BPMs in the associated transfer
  lines. The total estimated cost is about 920K.
  (Phyics requirements defined Technology
  approved Purchase Order placed)
• In the MI, we need to upgrade 203 ring BPM and 5
  large aperture BPM. We also need to upgrade 64
  BPM in MI8 line, 16 BPM in A1line, 15 BPM in P1
  line and 11 BPM in P2 line. The total estimated
  cost will be 1.2M. (Physics requirements
  defined.)
• NuMI needs only 26 BPM. The estimated cost will
  be around 100K. (Physics requirements defined.)

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WHY UPGRADE MI BPM?

• Present MI BPM electronics is blind to 2.5MHz
  time structure, and unreliable for position
  measurement of a single coalesced 53MHz bunch, as
  well as for ?20-30 bunches of 53MHz beam.
• The system is quite limited. It is essentially a
  single user, single buffer system. The data in
  the buffer gets overwritten every time any valid
  MI reset occurs.
• The system is self (beam intensity threshold)
  triggered. It does not have a general purpose
  beam synch clock based trigger.
• The system has limited resolution (beyond ?10 mm)
  because of the non-linearity of AM to PM
  detection, the BPM geometry, and the 8-bit ADC
  used in the present electronics.
• The firmware is written in Z80 machine code,
  which is now obsolete. Only one person (Alan
  Baumbaugh) at the laboratory is familiar with the
  code. Sharon Lackey used it 15yrs ago for
  switchyard, and if it is really needed she can be
  called to help.
• The system is 20 years old and is approaching
  its end-of-life.

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WHAT IS NEEDED ?

• The MI BPM electronics should be functional at
  2.5MHz, 53MHz time structure. It should be
  reliable for position measurement either with a
  single Booster bunch, or a single coalesced bunch
  (53 MHz), as well as with multiple bunches, and
  multiple batches in the MI.
• The system should be event driven to support
  multi-user with multi-buffer, so that different
  type of data can be taken during the same MI
  cycle, and the data taken with a particular MI
  reset does not overwrite the data taken with
  other MI reset.
• Attenuation due to varying cable lengths, limits
  the dynamic range of the system and thus
  detection of small bunch intensities. Gain should
  be adjusted to account for this variation.
• The system should at user option be self (beam
  intensity threshold) triggered as well as beam
  synch. clock triggered.
• The present(old) multi-bus based system with
  8-bit ADC computer interface should be replaced
  by a modern and better supported architecture
  (for ex with a VME contained system) using
  12/14-bit ADCs (for a bit resolution of 50mm) .
  Engineers to determine how this condition will
  be met.

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WHAT DO WE NEED TO MEASURE?

• We need to measure
• Beam Position at every BPM
• Beam Intensity at every BPM, and
• Calibrate every BPM properly.

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DESIGN RESOLUTION MI BPM
Beam Position Horizontal(mm) Vertical(mm)
? 5mm 100mm 150mm
5mm ? x ? 10mm 150mm 150-200mm
10mm ? x ? 15mm 200-300mm 200-300mm
15mm ? x ? 20mm 300-600mm 300-600mm
? 20mm 1-4 mm -----------
Measured Resolution for beam position ? 5mm
varies between 50-150 mm. Lets preserve the
level of resolution.
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MEASURED RESOLUTION
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MEASURED RESOLUTION
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DYNAMIC RANGE FOR MI
1. Protons or anti-protons to/from the RR, and anti-protons from the Accumulator (2.5 MHz) 0.5E10/bunch (2.0E10 total) to 7.5E10/bunch (30E10 total). s(t) 25ns to 50ns.
2. Protons from the Booster (53MHz) (19ns spacing) From 1 to 84 bunches. Min. Intensity 0.5E10/bunch. Max. Intensity 12E10/bunch
3. Protons to the Tevatron (5-9 bunches, typically 7) (53 MHz) (19 ns spacing) Up to 30 Booster bunch for tune up. Each bunch intensity between 1-12E10. For Collider running up to 4.5E10/bunch or 30E10 after coalescing. (27E10 TeV Run IIB doc.)
4. Anti-Protons to(from) the Tevatron. (53 MHz bunch in 2.5 MHz spacing). 36 single bunches, 4 bunches each in 9 separate batch (4X9), each bunch with intensity of ?11E10(5E10). (9.4E10 TeV Run IIB doc.)
5. For the Fixed Target Running. (including NuMI/MINOS) (53MHz) 0.5E10 to 12E10 per bunch for 50-504 bunches.
The BPM system should be capable of measuring
beam position with 6 batches in the MI.
DYNAMIC RANGE OF 24
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MEASUREMENT PRECISION OVER THE FULL DYNAMIC RANGE
- MI
This is a 3? requirement, or 99.73 of the measurements should be within these limits.
Position Accuracy 0.40mm ? 5 of the actual position. Difference between two measurements on pulses with stable beam. It covers long term stability and resolution.
Calibration precision of 0.20mm 1.25 of the the actual position
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BPMs in NuMI BEAM LINE

• The NuMI beam line will have a total of 26 BPMs
• A large aperture BPM with 6 long plates and a
  4.625 aperture, at Q608 near Lambertson,
• 21 split pipe BPM called the transport BPM. The
  outer/inner diameter of the split pipe is
  4(10.1cm)/3.875(9.8cm, aperture) , and
• 4 split pipe BPM called the target BPM. The
  outer/inner diameter of the split pipe is
  2.125(5.4cm)/2(5.1cm, aperture)
• The position accuracy, and the stability(calibrati
  on) requirement for the transport and target BPM
  differ (as shown in table later).
• Every BPM needs to measure the beam position
  individually for each batch of the proton beam.
• For at least one house (for the 4 target BPM),
  the BPM system should be capable of making
  multiple measurements within at-least one batch
  of the proton beam.

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NuMI MEASUREMENT PRECISION/BATCH (3? REQUIREMENT)
Transport BPM (particle/bunch) Target BPM (particle/bunch)
Position Accuracy 0.50mm_at_?1E10 1.00mm_at_?0.5E10 (over 20mm) 0.25mm_at_?1E10 0.50mm_at_?0.5E10 (over 6mm)
Calibration Accuracy 0.20mm_at_?1E10 0.25mm_at_?0.5E10 (over 20mm) 0.10mm_at_?1E10 0.15mm_at_?0.5E10 (over 6mm)
Intensity Precision ?5 for Position ?2 for Calibration ?5 for Position ?2 for Calibration
If the transport BPM meets the MI BPM precision
requirement, NuMI will be satisfied.
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NuMI PRECISION

• The precision for Transport BPM comes from the
  knowledge of beam control requirements based on
  previous usage of Autotune beam control, as to
  be used in NuMI. For example, the corresponding
  numbers for some experiments were
• Switchyard system - activate tuning for 0.4 mm
  deviation from nominal (0.2 mm for septa
  lineup) then, correct to lt 0.2mm (0.1 mm)
  accuracy. (NuMI has no septa).
• KTeV (with a very large targeting optics
  magnification) - activate for 1.0 mm deviation
  along the transport (0.05 mm deviation at target)
• The precisions were determined initially from
  detailed calculations of error functions using
  transport matrices, and verified in beam
  operation.
• The precision for Target BPM comes from MINOS
  target width of 6.4mm, and the upstream baffle
  beam hole diameter of 11mm.

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DIGITAL DOWN CONVERSION

• Sample the waveform at a fixed sampling rate.
• Multiply the sample by sine and cosine function
  of the bunch frequency (I and Q) and integrate
  over a fixed gate.
• The signal strength measurement I2Q2 is
  independent of the phase of the signal.
• Tested with EchoTek 814, 8 channel 60MHz 14bit
  A/Ds
• AD6620 Digital Receiver Digital mixer followed
  by 3 digital filters (for integration and
  smoothing of the edges).
• VME format
• Like digital radio Can be tuned to receive
  essentially any frequency 89KHz, 2.5MHz, and 53
  MHz.

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IN-PHASE QUADRATURE SAMPLING
A - B gives bunch-by-bunch in-phase signal
D - (CE)/2 gives bunch-by-bunch
out-of-phase or quadrature signal
Vector Sum sqrt(I2 Q2) is insensitive to
clock jitter
Argument for sampling at 4 X Frequency to be
sampled
Courtesy BILL FOSTER
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DDC TEST RESULTS WITH 53MHz BEAM
Sampling of 84 consecutive 53MHz(19ns) waveform
at every 17ns (60MHz clock). One would like to
sample at twice or more of the frequency rate.
Ideally at 106MHz. Best at 212MHz. Under
Sampled. But due to long train of pulses (84
bunches) one can get away with under sampling.
Raw ADC
Sample Number 17ns sampling
Courtesy WARREN SCHAPPERT
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DDC TEST RESULTS WITH 53MHz BEAM

• The measurement was done in MI54 line, in front
  of MiniBoone hall.
• Beam moving around.
• Measured resolution is 0.18 of the aperture.
• Intrinsic resolution of the BPM will be better
  than the number presented here.

Batch Position (Average of 84 Bunches)
Courtesy WARREN SCHAPPERT
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DDC TEST RESULTS WITH 53MHz BEAM

• Resolution is limited due to beam motion.
• Intrinsic resolution of the BPM better than
  measurement presented here.
• Being worked upon.

Moving Beam
Courtesy WARREN SCHAPPERT
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BEAM POSITION MEASUREMENT PRECISION (2.5MHz
STRUCTURE)
HP426
VP427
RMS19mm
RMS9mm
IBEAM 1.24E11 RMS 10 20 mm
HP428
VP429
RMS18mm
RMS13mm
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BEAM POSITION STABILITY FOR REPEAT INJECTION
Repeated injection with different IBEAM of
1.25E11, 5E10, 2E10, 9E9, 4E9 and 2.5E9 and then
went back to IBEAM of 5E10, 1.25E11 and 2.47E11
HP428
VP427
VP429
HP426
1850
1920
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BEAM POSITION STABILITY FOR REPEAT INJECTION
Beam position for all the four BPMs are very
stable for different injections with different
beam intensity.
HP428
VP427
VP429
HP426
1935
2000
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BEAM POSITION STABILITY FOR REPEAT INJECTION
HP428
Beam position does not change as we make fresh
injections with varying beam intensity.
VP427
VP429
HP426
2030
2100
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SCHEDULE and SUMMARY

• SCHEDULE
• NuMI time frame is independent of MI needs. The
  technology decision for the NuMI BPM must be
  taken before the DOE review in 6/2003, and the
  system should be ready by the spring of 2004.
• SUMMARY
• NuMI BPM physics requirements have been defined.
  It is needed to commission the beam line, and
  will be ready in time.