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Why an Antiproton source?

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Title: Why an Antiproton source?


1
Why an Antiproton source?
  • p pbar physics with one ring
  • Dense, intense beams for high luminosity
  • Run II Goals
  • 36 bunches of 3 x 1010 pbars
  • Small energy spread
  • Small transverse dimensions
  • Collect 1 x 10-5 pbars/proton on target
  • MANY CYCLES
  • Store and Accumulate
  • Discuss today
  • Accelerator Physics
  • Pbar Production
  • Pbar Collection
  • Pbar Storage Rings
  • Stochastic Cooling

2
Some Necessary Accelerator Physics
  • All Classical (Relativistic) EM
  • Hamiltonian of a charged particle in EM field
  • Small angle approximation around CENTRAL ORBIT
  • Set of Conjugate variables
  • x, x horizontal displacement and angle
  • y, y vertical displacement and angle
  • E, s energy and longitudinal position
  • s bct sometimes use t instead
  • Equation of Motion
  • C is circumference of accelerator -- Periodicity!

3
Solutions to Equations of Motion
  • Restoring force k(s) is dependent on location
  • Dipoles
  • Quadrupoles
  • Drifts
  • General Solution
  • b(s) is solution to a messy 2nd order Diff Eqn
  • Beam size depends on Amplitude of oscillation and
    value of b(s)
  • Can change Position by changing angle 90?
    upstreamused for extraction/injection/cooling/IP
    position

4
Beam Size
  • Relate the INVARIANT EMITTANCE (phase space area)
    to physical size
  • Gaussian Beams
  • 95 (Fermi Standard)
  • s2 eb / 6p
  • Include relativistic contraction (beams gets
    smaller as they are accelerated!)
  • At B0 b(s) b(1s2/b2)
  • For 20p mm mr beams at IP
  • s (20p x10-6 m r 0.35 m / 6pg)1/2 3.5 x
    10-5 m 35 mm

5
Longitudinal Effects
  • Longitudinal Acceleration
  • Time Varying Fields to get net acceleration
  • Synchronous PHASE and Particle
  • Path Length can depend on ENERGY
  • Revolution Frequency can depend on ENERGY
  • Expressed via Phase Slip Factor h
  • gt transition energy
  • Accelerating phase needs to change by 180 as
    cross transition

6
Final Points
  • Frequency Spectrum
  • Time Domain ???(tnT0) at pickup
  • Frequency Domainharmonics of revolution
    frequency f0 1/T0
  • AccumulatorT01.6 ?sec (1e10 pbar 1 mA)f0
    (core) 628955 Hz
  • 127th Harmonic 79 MHz

7
General Characteristics of Pbar Source
  • 120 GeV Protons on Ni target
  • Focus Negative Particles Lithium Lens
  • Select 8 GeV with AP2 line
  • Bend magnets along the line
  • Inject into Debuncher
  • p, K, m, etc. decay
  • Decay products at different momenta and fall out
  • Electrons radiate and fall out
  • Left with stable negative particles at 8 GeV
  • PBARs!
  • RF Debunch
  • Stochastically cool in H, V, p
  • Inject into Accumulator
  • Stochastically cool in H, V, p
  • Accumulate a dense core
  • Extract for use in collider
  • Decelerate for use in fixed target (E835)

8
Momentum Choices120 GeV
  • Why 120 GeV protons?
  • Phenomenological formula to describe pbar
    production
  • From fits to available data in 1983
  • Above 150 GeV, yield/time changes slowly
  • Yield increases but have to include Main Ring
    Cycle time!
  • 120 GeV Emax for extraction in medium straight
    section such as F17
  • Operating cost increases as Energy increases

9
Momentum Choices8 GeV
  • Why 8 GeV pbars?
  • Optimum production at 10 GeV
  • gt90 of optimum in range 7.5-13 GeV
  • Main Ring injection (Booster Energy)
  • 8 GeV
  • Inject directly from Accumulator to Main Ring
  • Booster p -gt Main Ring -gt Accumulator
  • Momentum choices stay the same for Main Injector

10
Target Station
  • 120 GeV protons on target
  • Smaller spot size, larger acceptance
  • Larger energy depositions
  • Energy Deposition -gt melting
  • 500 J/g -gt T 1700 K
  • Shock Waves -gt mechanical deformations
  • Pressures 5 GPa
  • Sweeping system (in small circle) to go to
    smaller spot size and not destroy targets
  • Lithium Lens for focussing

120 GeV
Proton Beam
Nickel
Lots of Particle
Target
Pions Kaons Protons
Collection Lens
Anti-Protons, etc
11
Pbar Collection
  • Lithium Lens
  • Longitudinal Current (pulsed 650 kA)
  • Develops Azimuthal Field
  • Radial Focussing Force (H V in same device!)
  • 750 T/m field strength
  • 1 cm aperture (60 mradian acceptance)
  • AP2 4 momentum spread

12
Pbar Storage Rings
  • Two Storage Rings in Same Tunnel
  • Debuncher
  • Larger Radius
  • few x 107 stored for cycle length
  • 2.4 sec for MR, 1.5 sec for MI
  • few x 10-7 torr
  • RF Debunch beam
  • Cool in H, V, p
  • Accumulator
  • 1012 stored for hours to days
  • few x 10-10 torr
  • Stochastic stacking
  • Cool in H, V, p
  • Both Rings are triangular with six fold symmetry

13
Debuncher Ring
  • Main Purpose
  • Debunch RF Time Structure (84 buckets)RF
    locked to Main Injector
  • Rotation in Phase Space
  • DE, Dt conjugate variables
  • Initial large DE (off target), small Dt (RF)
  • 5 MV RF in 1/4 turn down to 100 kV
  • Small DE, large Dt
  • Adiabatically turn off RF (10 msec)
  • Lots of time left (1.5 sec cycle)
  • Cool in H, V, p

14
Accumulator Ring
  • Not possible to continually inject beam
  • Violates Phase Space Conservation
  • Need another method to accumulate beam
  • Inject beam, move to different orbit (different
    place in phase space), stochastically stack
  • RF Stack Injected beam
  • Bunch with RF (2 buckets)
  • Change RF frequency (but not B field)
  • ENERGY CHANGE
  • Decelerates 30 MeV
  • Stochastically cool beam to core
  • Decelerates 60 MeV

15
Idea Behind Stochastic Cooling
  • Phase Space compression Dynamic Aperture
    Area where particles can orbit Liouvilles
    Theorem Local Phase Space Density for
    conservative system is conserved Continuous
    Media Discrete Particles Swap Particles
    and Empty Area -- lessen physical area
    occupied by beam

16
Idea Behind Stochastic Cooling
  • Principle of Stochastic cooling
  • Applied to horizontal btron oscillation
  • A little more difficult in practice.
  • Used in Debuncher and Accumulator to cool
    horizontal, vertical, and momentum distributions
  • COOLING? Temperature ltKinetic Energygtminimize
    transverse KE minimize DE longitudinally

17
Stochastic Coolingin the Pbar Source
  • Standard Debuncher operation
  • 108 pbars, uniformly distributed
  • 600 kHz revolution frequency
  • To individually sample particles
  • Resolve 10-14 seconds100 GHz bandwidth
  • Dont have good pickups, kickers, amplifiers in
    the 100 GHz range
  • Sample Ns particles -gt Stochastic process
  • Ns N/2TW where T is revolution time and W
    bandwidth
  • Measure ltxgt deviations for Ns particles
  • Higher bandwidth the better the cooling

18
Betatron Cooling
  • With correction gltxgt, where g is gain of system
  • New position x - gltxgt
  • Emittance Reduction RMS of kth particle
  • Add noise (characterized by U Noise/Signal)
  • Add MIXING
  • Randomization effects M number of turns to
    completely randomize sample

19
Stochastic Stacking
  • Momentum Stacking explained in context of Fokker
    Planck Equation
  • Case 1 Flux 0 Restoring Force
    a(E-E0) Diffusion D0
  • Small group with Ei-E0 gtgt D0
  • Forced into main distribution
  • MOMENTUM STACKING

20
Stochastic Stacking
  • Gaussian Distribution
  • CORE
  • Injected Beam (tail)
  • Stacked

21
Stochastic Stacking
  • Simon van Der Meer solution
  • Constant Flux
  • Solution
  • Exponential Density Distribution generated by
    Exponential Gain Distribution

Using log scales on vertical axis
22
Implementation in Accumulator
  • Stacktail and Core systems
  • How do we build an exponential gain distribution?
  • Beam Pickups
  • Charged Particles E B fields generate image
    currents in beam pipe
  • Pickup disrupts image currents, inducing a
    voltage signal
  • Octave Bandwidth (1-2, 2-4 GHz)
  • Output is combined using binary combiner boards
    to make a phased antenna array

23
Beam Pickups
  • Pickup disrupts image currents, inducing a
    voltage signal

24
Beam Pickups
  • At ACurrent induced by voltage across
    junction splits in two, 1/2 goes out, 1/2 travels
    with image current

25
Beam Pickups
  • At BCurrent splits in two paths, now
    with OPPOSITE sign
  • Into load resistor 0 current
  • Two current pulses out signal line

I
B
DT L/bc
26
Beam Pickups
  • Current intercepted by pickup
  • Use method of images
  • Placement of pickups to give proper gain
    distribution

w/2
-w/2
y
d
x
Dx
Current Distribution
27
Beam Pickups
  • Prototype Measurements
  • Use Network Analyzer

NA
Pickup
Kicker
Beam
28
Accumulator Pickups
  • Placement, number of pickups, amplification are
    used to build gain shape

Core A - B
Stacktail
Energy
Gain
Core
Stacktail
Energy
29
Accumulator
  • Not quite as simple
  • -Real part of gain cools beam
  • frequency depends on momentumDf/f -hDp/p
    (higher f at lower p)
  • Position depends on momentumDx DDp/p
  • Particles at different positions have different
    flight times
  • Cooling system delay constant
  • OUT OF PHASE WITH COOLING SYSTEM AS MOMENTUM
    CHANGES

30
(No Transcript)
31
Stochastic Cooling
  • Tevatron 1 Run I
  • Debuncher 2-4 GHz
  • Accumulator
  • Stacktail 1-2 GHz
  • Core 2-4 GHz and 4-8 GHz
  • Fermi III Run II
  • Debuncher 4-8 GHz
  • Accumulator
  • Stacktail 2-4 GHz
  • Core 2-4 GHz and 4-8 GHz

32
Upgrades for Run II
  • Target Station
  • Beam Sweeping System
  • Magnets and pulsed power supplies
  • Transfer Lines
  • Aperture improvements and beam line model
  • Debuncher
  • All stochastic cooling systems
  • Larger bandwidth (4-8 GHz vs. 2-4 GHz)
  • All new electronics and signal transmission
  • Lower Noise (Liquid Helium vs. Liquid Nitrogen)
  • Different Technology
  • Slot coupled waveguides vs. Octave bandwidth
    pickups
  • Remove H V trim magnets to make room for
    cooling tanks
  • Move quadrupoles for use in steering
  • Adjust quad positions in D-to-A line to make room
    for cooling tanks

33
Debuncher Upgrade
  • Slot Coupled Waveguide
  • Narrow Band (0.5 GHz), High Sensitivity
  • Cover 4 bands (2 GHz bandwidth)

34
Debuncher Upgrade
  • Slow Wave Structure size, spacing, and number
    of slots determines sensitivity and bandwidth

35
Upgrades for Run II
  • Accumulator
  • Stacktail Stochastic Cooling Systems
  • Larger Bandwidth (2-4 GHz vs. 1-2 GHz)
  • New technologies for signal combination
  • Recycled (from Debuncher) and new Electronics to
    cover larger bandwidth
  • Lattice changes
  • Halve phase slip factor (h)
  • Driven by Stacktail upgrade
  • Keep dispersion, phase advance (pickup to kicker)
    injection and extraction regions, tunes,
    aperture, chromaticity the same
  • Requires construction 4 new quadrupoles (strength
    vs. current characteristics)
  • Reworking of power supplies

36
Why change h?
  • ?f/f ???p/p h/DDx/x
  • Momentum Spread100 MeV
  • Frequency Spread 160 Hz
  • fcentral 628900 Hz
  • ?f /f 2.5e-4
  • Stacktail assumes position(energy) frequency
    relation in design
  • 1 GHz 1590 Harmonic
  • ?f 254000 Hz
  • 2 GHz 3180 Harmonic
  • ?f 508000 Hz
  • 3 GHz 4770 Harmonic
  • ?f 763000 Hz
  • Frequency Spread gt harmonic frequency!
  • Frequency ? Energy Map no longer 1 ? 1

37
AntiProton Source
  • Shorter Cycle Time in Main Injector
  • Target Station Upgrades
  • Debuncher Cooling Upgrades
  • Accumulator Cooling Upgrades
  • GOAL gt20 mA/hour
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