Collimation with hollow electron lenses G. Stancari, A. Drozhdin, G. - - PowerPoint PPT Presentation

▶
collimation with hollow electron lenses
SMART_READER_LITE
LIVE PREVIEW

Collimation with hollow electron lenses G. Stancari, A. Drozhdin, G. - - PowerPoint PPT Presentation

Mar 06, 2024 129 likes •511 views

Collimation with hollow electron lenses G. Stancari, A. Drozhdin, G. Kuznetsov, V. Shiltsev, D. Still, A. Valishev, L. Vorobiev (FNAL), A. Romanov (BINP Novosibirsk), J. Smith (SLAC), R. Assmann, R. Bruce (CERN) Accelerator Advisory Committee

slide-1
SLIDE 1

Collimation with hollow electron lenses

  • G. Stancari, A. Drozhdin, G. Kuznetsov, V. Shiltsev, D. Still, A. Valishev,
  • L. Vorobiev (FNAL), A. Romanov (BINP Novosibirsk), J. Smith (SLAC),
  • R. Assmann, R. Bruce (CERN)

Accelerator Advisory Committee Meeting Fermilab, 29 Jul 2010

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 1 / 38

slide-2
SLIDE 2

Motivation

In high-energy colliders, stored beam energy can be large:

  • R. Assmann et al., EPAC02

Beam-beam collisions, intrabeam scattering, beam-gas scattering, rf noise, resonances, ground motion, etc. contribute to formation of beam halo Uncontrolled particle losses of even a small fraction of the circulating beam can damage components, quench superconducting magnets, produce intolerable experimental backgrounds

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 2 / 38

slide-3
SLIDE 3

Motivation

Goals of collimation:

1

reduce beam halo

2

concentrate losses in absorbers Conventional schemes: collimators (5-mm W at 5σ in Tevatron, 0.6-m carbon jaw at 6σ in LHC) absorbers (1.5-m steel jaws at 6σ in Tevatron, 1-m carbon/copper at 7σ in LHC)

  • R. Assmann
  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 3 / 38

slide-4
SLIDE 4

Concept of hollow electron beam collimator (HEBC)

Cylindrical, hollow, magnetically confined, pulsed electron beam overlapping with halo and leaving core unperturbed Halo experiences nonlinear transverse kicks

Shiltsev, BEAM06, Yellow Report CERN-2007-002 Shiltsev et al., EPAC08

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 4 / 38

slide-5
SLIDE 5

Hollow-beam collimation concept

Advantages

electron beam can be placed close to core (∼ 3–4σ) no material damage low impedance, no instabilities position controlled by magnetic field, no motors or bellows gradual removal, no loss spikes due to beam jitter no ion breakup transverse kicks are not random in space or time → resonant excitation tuned to betatron frequency is possible abundance of theoretical modeling, technical designs, and operational experience on interaction of keV–MeV electrons with MeV–TeV (anti)protons

electron cooling Tevatron electron lenses

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 5 / 38

slide-6
SLIDE 6

Existing Tevatron electron lenses

TEL1 used for abort-gap clearing during normal operations TEL2 used as TEL1 backup and for studies Typical parameters Peak energy 10 keV Peak current 3 A Max gun field Bg 0.3 T Max main field Bm 6.5 T Length L 2 m

  • Rep. period

21 µs Rise time <200 ns

Shiltsev et al., Phys. Rev. ST AB 11, 103501 (2008) Shiltsev et al., New J. Phys. 10, 043042 (2008)

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 6 / 38

slide-7
SLIDE 7

TEL2 timing example

cathode current collector current pickup signal revolution marker bunch train proton bunch antiproton bunch abort gap

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 7 / 38

slide-8
SLIDE 8

Losses during store #7407

Beam intensity Ring energy Total losses show large fluctuations Abort-gap losses are smooth (TEL1 clearing)

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 8 / 38

slide-9
SLIDE 9

Example of HEBC at TEL2 location in Tevatron

Lattice:

βx = 66 m, βy = 160 m Dx = 1.18 m, Dy = −1.0 m

Protons:

ǫ = 20 µm (95%, normalized) ∆p/p = 1.2 × 10−4 xco = +2.77 mm, yco = −2.69 mm σx = 0.46 mm, σy = 0.71 mm

Antiprotons:

ǫ = 10 µm (95%, normalized) ∆p/p = 1 × 10−4 xco = −2.77 mm, yco = +2.69 mm σx = 0.32 mm, σy = 0.50 mm

Electrons:

I = 2.5 A Bg = 0.3 T, Bm = 0.74 T r1 = 4.5 mm, r2 = 7.62 mm at gun rmin = 2.9 mm = 4σp

y , rmax = 4.9 mm in main solenoid

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 9 / 38

slide-10
SLIDE 10

Requirements and constraints

Placement: ∼ 4–5σ + field line ripple (∼0.1 mm) Transverse compression controlled by field ratio: rm/rg =

  • Bg/Bm

fields must provide efficient transport instability threshold < Bm 10 T (technology)

Large amplitude functions (βx, βy) to translate transverse kicks into large displacements If proton beam is not round (βx = βy), separate horizontal and vertical scraping is required Cylindrically symmetric current distribution ensures zero electric field on axis; if not, mitigate by:

segmented control electrodes near cathode crossed-field (E × B) drift of guiding centers tuning kicks to halo tune (= core tune)?

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 10 / 38

slide-11
SLIDE 11

Hollow-beam collimation concept

Disadvantages

kicks are small, large currents required alignment of electron beam is critical hollow beams can be unstable cost: ≈ 5 M$ (2 M$ material and supplies, 3 M$ salaries)

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 11 / 38

slide-12
SLIDE 12

Transverse kicks for protons

In cylindrically symmetrical case,

θmax = 2 I L (1 ± βeβp) rmax βe βp c2 (Bρ)p 1 4πǫ0

  • − :

vp · ve > 0 + : vp · ve < 0 Example (vp · ve > 0)

I = 2.5 A L = 2.0 m βe = 0.19 (10 kV) rmax = 3.5 mm (5σ in TEL2) p energy (TeV) 0.150 0.980 7 kicks (µrad): hollow-beam max 2.4 0.36 0.051 collimator rms (Tevatron) 110 17 collimator rms (LHC) 4.5

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 12 / 38

slide-13
SLIDE 13

Modeling

kick maps ⇒ in overlap region analytical form ideal case 2D from measured profiles Poisson solver 3D particle-in-cell Warp code, effects of

TEL2 bends profile evolution alignment

tracking software with lattice and apertures

STRUCT lifetrac SixTrack DMAD

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 13 / 38

slide-14
SLIDE 14

Simulation of HEBC in Tevatron

  • A. Drozhdin

STRUCT code, complete description of element apertures, helices, rf cavities,

sextupoles Halo defined as [5σ < x < 5.5σ, 0.2σ < y < 0.5σ] or [0.2σ < x < 0.5σ, 5.5σ < y < 6σ] Hollow beam 5σ < r < 6.4σ Effect of resonant excitation

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 14 / 38

slide-15
SLIDE 15

Simulation of HEBC in Tevatron

  • A. Valishev

Lifetrac code with fully-3D beam-beam, nonlinearities, chromaticity

Simplified aperture: single collimator at 5σ Halo particles defined as ring in phase space with 3.5σ < x, y < 5σ Hollow beam 3.5σ < r < 5σ No resonant pulsing Halo losses vs turn number for maximum kick of 0.5 µrad and 3.0 µrad

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 15 / 38

slide-16
SLIDE 16

Simulation of HEBC in LHC

Smith et al., PAC09, SLAC-PUB-13745

first impact (1D) and SixTrack codes

Collimator at 6σ Beam halo defined as ring 4σ < x < 6σ Hollow beam at 4σ < r < 6σ cleaning ≡ 95% hits collimator significant increase in impact parameter

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 16 / 38

slide-17
SLIDE 17

Collimation scenarios

HEBC probably too weak to replace collimators → ‘staged’ collimation scheme: HEBC + collimators + absorbers HEBC can act as ‘soft’ collimator to avoid loss spikes generated by beam jitter HEBC as scraper for intense beams increase in impact parameter is significant HEBC may allow collimators to be retracted (probably not relevant for LHC) resonant kicks are very effective tune shifts too small to drive lattice resonances effects should be detectable in Tevatron

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 17 / 38

slide-18
SLIDE 18

Design of 15-mm-diameter hollow gun

Convex tungsten dispenser cathode with BaO:CaO:Al2O3 impregnant 7.6-mm outer radius, 4.5-mm-radius bore Electrode design based upon existing 0.6-in SEFT (soft-edge, flat-top) gun previously used in TEL2 Calculations with SAM code

  • L. Vorobiev

Mechanical design

  • G. Kuznetsov

Cathode (w/o bore) Assembled gun

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 18 / 38

slide-19
SLIDE 19

Test bench at Fermilab

Built to develop TELs, now used to characterize electron guns and to study plasma columns for space-charge compensation High-perveance electron guns: ∼amps peak current at 10 kV, pulse width ∼µs, average current <2.5 mA Gun / main / collector solenoids (<0.4 T) with magnetic correctors and pickup electrodes Water-cooled collector with 0.2-mm pinhole for profile measurements

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 19 / 38

slide-20
SLIDE 20

Performance of hollow cathode vs voltage and temperature

700 800 900 1000 1100 0.001 0.005 0.050 0.500 ESTIMATED TEMPERATURE (C) COLLECTOR CURRENT (A) 29 32 38 45 50 55 60 66 70 HEATER POWER (W) 0.05 kV 0.1 kV 0.25 kV 0.5 kV 1 kV 2 kV 4 kV 8 kV

  • 50

100 200 500 1000 5000 20000 0.002 0.010 0.050 0.200 1.000 CATHODE VOLTAGE (V) COLLECTOR CURRENT (A)

5.58 A (696 C) 5.79 A (741 C) 5.99 A (771 C) 6.2 A (810 C) 6.43 A (832 C) 6.65 A (868 C) 6.93 A (918 C) 7.21 A (978 C) 7.45 A (1030 C) 7.75 A (1090 C) 7.92 A (1130 C) 8.17 A (1150 C) 7.75 A (1150 C)

  • Perveance is 4 µperv
  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 20 / 38

slide-21
SLIDE 21

Profile measurements

Horizontal and vertical magnetic steerers deflect electron beam Current through 0.2-mm-diam. pinhole is measured vs steerer strength

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 21 / 38

slide-22
SLIDE 22

Measured profile: 0.5 kV 44 mA 0.3 T

HOLLOW GUN October 21, 2009 Vacuum: 2x10-8 mbar Filament: 66 W (7.75 A) Cathode voltage: -0.5 kV HV PS current: 1.0 mA Pulse width: 6 us

  • Rep. period: 0.6 ms

Peak current: 44 mA Solenoids: 3-3-3 kG

0.0 0.5 1.0 1.5 −4 −2 2 4 −4 −2 2 4

  • HORIZ. STEERER CURRENT (A)
  • VERT. STEERER CURRENT (A)
  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 22 / 38

slide-23
SLIDE 23

Measured profile: 9.0 kV 2.5 A 0.3 T

HOLLOW GUN October 26, 2009 Vacuum: 2x10-8 mbar Filament: 66 W (7.75 A) Cathode voltage: -9.0 kV HV PS current: 1.43 mA Pulse width: 6 us

  • Rep. period: 80 ms

Peak current: 2.5 A Solenoids: 3-3-3 kG

0.0 0.1 0.2 0.3 0.4 0.5 −4 −2 2 4 −4 −2 2 4

  • HORIZ. STEERER CURRENT (A)
  • VERT. STEERER CURRENT (A)
  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 23 / 38

slide-24
SLIDE 24

Profile evolution with increasing current and voltage

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 24 / 38

slide-25
SLIDE 25

Hollow-beam instabilities

Profiles measured 2.8 m downstream of cathode In previous plots, magnetic field kept constant at 0.3 T If current density is not axially symmetric, neither are space-charge forces Guiding-center drift velocities v ∝ E × B depend on r and φ Electron beam behaves like incompressible, frictionless 2D fluid Typical nonneutral plasma slipping-stream (‘diocotron’) instabilities arise, vortices appear

Kyhl and Webster, IRE Trans. Electron Dev. 3, 172 (1956) Levy, Phys. Fluids 8, 1288 (1965) Kapatenakos et al., Phys. Rev. Lett. 30, 1303 (1973) Driscoll and Fine, Phys. Fluids B 2, 1359 (1990) Perrung and Fajans, Phys. Fluids A 5, 493 (1993)

Current-density distribution evolves as the beam propagates (evolution time) ∝ (current) (magnetic field) × (voltage)

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 25 / 38

slide-26
SLIDE 26

Properties of hollow profiles

Interesting nonneutral plasma physics; all well known? For predicting profiles and electric field distributions in TEL2:

Simulation and modeling: Warp / Synergia / Dubin’s code (UCSD) — work in progress Experimental investigation of scaling properties of profiles in test bench:

from dimensional analysis of fundamental equations one expects I ∼ V 3/2 (Child-Langmuir law) to preserve transverse profiles (∼ L), one finds B ∼ V 1/2 ∼ I 1/3

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 26 / 38

slide-27
SLIDE 27

CATHODE VOLTAGE (kV) MAGNETIC FIELD (T) 0.25 0.5 1 1.5 2 3 4 5 6 7.5 9 0.0 0.1 0.2 0.3 0.4 0.5 0.01 0.1 0.5 1 1.5 2 2.5 BEAM CURRENT (A) 0.0 0.1 0.2 0.3 0.4 0.5

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 27 / 38

slide-28
SLIDE 28

Profile reproducibility

0.5 kV 2 kV 7.5 kV Oct 2009 Jan 2010 (Filament heater was turned off and on between measurements)

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 28 / 38

slide-29
SLIDE 29

Profiles vs temperature

0.5 kV 7.5 kV 32 W (741 C) 66 W (1090 C)

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 29 / 38

slide-30
SLIDE 30

Warp calculation of 2D fields from measured profiles

(thanks to D. Grote, J.-L. Vay, M. Venturini (LBNL) for kind support)

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 30 / 38

slide-31
SLIDE 31

Electric field at 2 kV, 330 mA

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 31 / 38

slide-32
SLIDE 32

Electric fields at 0.5 kV, 44 mA

CALCULATED HOLLOW−BEAM FIELD from MEASURED PROFILE at 66W 0.5kV 3kG 44mA

TRANSVERSE POSITION / (σy = 0.71 mm) ELECTRIC FIELD STRENGTH (kV/m) −15 −10 −5 5 10 15 0.05 0.10 0.20 0.50 1.00 2.00 5.00 10.00 20.00 Bg = 0.3 T E(x,0) Bm=0.33 T E(0,y) Bm=0.33 T E(x,0) Bm=0.74 T E(0,y) Bm=0.74 T E(x,0) Bm=1.33 T E(0,y) Bm=1.33 T

2D WARP calculation

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 32 / 38

slide-33
SLIDE 33

Electric fields at 2 kV, 330 mA

CALCULATED HOLLOW−BEAM FIELD from MEASURED PROFILE at 66W 2kV 3kG 330mA

TRANSVERSE POSITION / (σy = 0.71 mm) ELECTRIC FIELD STRENGTH (kV/m) −15 −10 −5 5 10 15 0.2 0.5 1.0 2.0 5.0 10.0 20.0 50.0 Bg = 0.3 T E(x,0) Bm=0.33 T E(0,y) Bm=0.33 T E(x,0) Bm=0.74 T E(0,y) Bm=0.74 T E(x,0) Bm=1.33 T E(0,y) Bm=1.33 T

2D WARP calculation

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 33 / 38

slide-34
SLIDE 34

Electric fields at 7.5 kV, 2040 mA

CALCULATED HOLLOW−BEAM FIELD from MEASURED PROFILE at 66W 7.5kV 3kG 2040mA

TRANSVERSE POSITION / (σy = 0.71 mm) ELECTRIC FIELD STRENGTH (kV/m) −15 −10 −5 5 10 15 2 5 10 20 50 100 200 Bg = 0.3 T E(x,0) Bm=0.33 T E(0,y) Bm=0.33 T E(x,0) Bm=0.74 T E(0,y) Bm=0.74 T E(x,0) Bm=1.33 T E(0,y) Bm=1.33 T

2D WARP calculation

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 34 / 38

slide-35
SLIDE 35

Electric fields at 9 kV, 2490 mA

CALCULATED HOLLOW−BEAM FIELD from MEASURED PROFILE at 66W 9kV 3kG 2490mA

TRANSVERSE POSITION / (σy = 0.71 mm) ELECTRIC FIELD STRENGTH (kV/m) −15 −10 −5 5 10 15 1 2 5 10 20 50 100 200 Bg = 0.3 T E(x,0) Bm=0.33 T E(0,y) Bm=0.33 T E(x,0) Bm=0.74 T E(0,y) Bm=0.74 T E(x,0) Bm=1.33 T E(0,y) Bm=1.33 T

2D WARP calculation

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 35 / 38

slide-36
SLIDE 36

Recent studies in Recycler Ring

  • A. Shemyakin and A. Valishev, Beams-doc-3554-v1 (19 Feb 2010)

Can a helical electron beam approximate the effect of a hollow beam? Need integer number of turns, short pitch compared to amplitude functions Preliminary study with 8-GeV protons in electron cooler a few weeks ago Helical electron trajectory generated by upstream correctors Very short lifetimes (not fully understood) Indications of scraping: core has longer lifetime than halo Work in progress. . .

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 36 / 38

slide-37
SLIDE 37

Planned Tevatron studies

Experimental goals

verify hollow-beam alignment procedures evaluate effect on core lifetime measure losses at collimators, absorbers and detectors vs HEBC parameters: position, angle, intensity, pulse timing, excitation pattern assess improvement of loss spikes Hardware/software improvements in TEL2 Stacked-transformer modulator (faster, complex waveforms) BPM system Alignment based upon BPMs, bunch-by-bunch losses, Schottky power, tunes.

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 37 / 38

slide-38
SLIDE 38

Next steps

Modeling:

2D and 3D kick maps from measured distributions performance vs lattice parameters effect of misalignments, field-line ripple, bends

Test bench:

Evolution of hollow beam Time stability of current density within each pulse Design and test 25-mm cathode (∼7 A)?

Recycler Ring:

More measurements with helical beam in electron cooler?

Tevatron:

Gaussian gun currently installed in TEL2

study of nonlinear head-on beam-beam compensation: bunch-by-bunch lifetimes, tunes, tune spreads

Install 15-mm hollow gun in TEL2 (summer shutdown) Start parasitical and dedicated studies on collimation

Thank you for your attention

  • G. Stancari (Fermilab)

Hollow-beam collimation FNAL AAC : 29 Jul 2010 38 / 38