[PPT] - Recent results on hollow beam collimation Giulio Stancari Fermi PowerPoint Presentation

SLIDE 1

Recent results on hollow beam collimation

Giulio Stancari

Fermi National Accelerator Laboratory

U.S. LHC Accelerator Research Program Collaboration Meeting 15 1-3 November 2010

SLIDE 2

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

2

At the test stand:
Studied time microstructure of hollow beam pulse
In the Tevatron:
Aug 2-3: installed hollow gun in electron lens TEL2
Complete TEL2 test with e-beam before Tevatron start-up:

BPMs, modulator, power supplies

Verified abort-gap cleaning effect (as TEL1 backup)
First dedicated studies Oct 13-14 (3 hrs) and Oct 27-28 (4 hrs):
position/angle scans, beam alignment
effects of e-beam size, current and pulsing pattern on emittances,

intensity and luminosity decay rates

dependence of losses on working point in pulsed mode
scraping mode with fixed e-beam and pbar/proton orbit bump

Recent activity

G. Kuznetsov,
S. Sylejmani, gs
A. Valishev, gs
X. Zhang

gs

J. Crisp, B. Fellenz, G. Kuznetsov,
G. Saewert, J. Simmons, X. Zhang, gs

SLIDE 3

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

3

The 0.6-in hollow gun Copper anode side view top view Tungsten dispenser cathode with convex surface 15-mm diameter, 9-mm hole

SLIDE 4

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

4

Hollow gun installed in the Tevatron (Aug 2)

Gennady Kuznetsov

SLIDE 5

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Modulator tests without e-beam

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Replaced DC supplies in tunnel (out of spec, radiation damage?) Modulator tested up to 4.8 kV at highest switching rate 4.5 kV

SLIDE 6

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Vacuum recovery and filament heating

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TEVATRON BEAM TEL2 CURRENT TEL2 VACUUM TEL2 FILAMENT HEATER

SLIDE 7

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

TEL2 checks before Tevatron start-up

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CATHODE (1 A/V) TEL2 PICKUP MODULATOR (4 kV/V) COLLECTOR (1 A/V)

Shortest pulse:

SLIDE 8

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Corrector/BPM calibration vs. magnetic field

8

To change hole size for collimation, need to operate at different field ratios Bgun/Bmain

SLIDE 9

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Hollow gun performance in TEL2 after cathode conditioning

9

1

2 3 4 0.0 0.2 0.4 0.6 0.8 1.0

0.6−in hollow gun in TEL2 Yield vs. voltage (shortest pulse)

Cathode−anode voltage (kV) Peak collector current (A) 11 Oct 2010 T:L2FILI = 7.75 A T:L2DLY1 = 668 rfc T:L2TM = 2 T:L2TS14 = 33333 1 pulse/turn

T:L2MCV1 = 0 V T:L2MCV1 = 50 V T:L2MCV1 = 100 V T:L2MCV1 = 200 V T:L2MCV1 = 300 V T:L2MCV1 = 400 V T:L2MCV1 = 500 V T:L2MCV1 = 580 V

SLIDE 10

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

First dedicated studies in the Tevatron at collisions

10

Two end-of-store studies so far: Oct 13-14, store #8171 (3 hrs) and

Oct 27-28, store #8210 (4 hrs)

Goals:
Which studies are parasitical? Which ones need dedicated time?
How critical is the alignment with the present gun?
How large is the scraping effect on halo and core?
Bunch-by-bunch observables:
Losses at collimators (not gated) and detectors
Intensities, luminosities, emittances, and their decay rates
Factors:
e-beam position and angle, current (1.1 A max) / profile,

size (about 3.5-5.0 σy), pulsing pattern (skip 0-9 turns)

machine working point: tunes and coupling

SLIDE 11

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

11

10 20 30 40 0.0 0.2 0.4 0.6 0.8 1.0 1.2

(Anti)proton beam sizes at TEL2 vs. emittance

Normalized 95% emittance (µm) Gaussian r.m.s. beam size (mm) Horizontal Vertical p = 980 GeV c βγ = 1044.473 Δp p = 0.00015 βx = 66 m βy = 160 m Dx = 1.18 m Dy = −1 m 10 20 30 40 2 4 6 8

0.6−in hollow−gun electron beam sizes

vs. magnetic field

Magnetic field in main solenoid (kG) Electron beam radius (mm) Gun solenoid: 3 kG 4 kG r1gun = 4.5 mm r2gun = 7.62 mm

Chose to start with antiproton bunches:

lower emittances and intensities, larger magnetic field ⇒ more stable
in Tev lattice, TEL2 more similar to pbar collimator ⇒ better capture

SLIDE 12

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Example of transverse beam profiles at TEL2

12 −10 −5 5 10 −5 5 HORIZONTAL POSITION (mm) VERTICAL POSITION (mm) PROTON CORE ANTIPROTON CORE HOLLOW ELECTRON BEAM T = 980 GeV βγ = 1045 βx = 66 m βy = 160 m Dx = 1.2 m Dy = −1 m Protons: εx = 21 µm εy = 35 µm Δp p = 1.6 10−4 σx = 0.47 mm σy = 0.94 mm Antiprotons: εx = 22 µm εy = 21 µm Δp p = 1.5 10−4 σx = 0.48 mm σy = 0.73 mm Electrons: Bg = 4 kG Bm = 10 kG Ri = 4.5 mm Ro = 7.6 mm ri = 2.8 mm ro = 4.8 mm

SLIDE 13

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

e-beam pulse synchronization with antiproton bunch

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TEL2 PICKUP MODULATOR (4 kV/V) COLLECTOR (1 A/V) A13 A14 A15 P1 P2 P3

SLIDE 14

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Oct 13-14 (store #8171) study overview

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Pulse: 1 pulse/turn 1 pulse/6 turns Bunch: A13 A25 Hole radius: 5σ 4σ 3.5σ V pos. H pos. H angle Alignment scans:

SLIDE 15

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Bunch-by-bunch losses during vertical e-beam scan

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5 10 15 20 25 100 200 300 T:L2C4 corrector settings (kG mm) Loss rates (Hz)

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−1.0

−0.5 0.0 0.5 1.0 Vertical displacement (mm) C.D0AH13 C.D0AH25 C.D0AH01 C.D0PH01 C.D0PH13 C.D0PH25

(0 mm = BPM alignment) 3 antiproton bunches, acting on A13 3 proton bunches, P1 outside hole[

]

SLIDE 16

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Horizontal angle scan: 1 pulse/turn vs. 1 pulse/6 turns

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−20 20 40 20 40 60 80 100 T:L2C5 corrector settings (kG mm) Loss rates (Hz)

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−1

1 2 Horizontal downstream displacement (mm) C.D0AH13 C.D0AH25 C.D0AH01 C.D0PH01 C.D0PH13 C.D0PH25 −40 −20 20 40 100 200 300 400 500 600 T:L2C5 corrector settings (kG mm) Loss rates (Hz)

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−3

−2 −1 1 2 Horizontal downstream displacement (mm) C.D0AH13 C.D0AH25 C.D0AH01 C.D0PH01 C.D0PH13 C.D0PH25

SLIDE 17

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Losses during horizontal scan

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−160 −140 −120 −100 −80 −60 50 100 150 200 250 T:L2C2 corrector settings (kG mm) Loss rates (Hz)

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−6

−4 −2 2 4 Horizontal displacement (mm) C.D0AH13 C.D0AH25 C.D0AH01 C.D0PH01 C.D0PH13 C.D0PH25

SLIDE 18

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Intensity decay rates during horizontal scan

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−160 −140 −120 −100 −80 −60 0.0 0.1 0.2 0.3 0.4 T:L2C2 corrector settings (kG mm) Intensity decay rates (1/h)

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−6

−4 −2 2 4 Horizontal displacement (mm) FBIANG13.d FBIANG25.d FBIANG01.d FBIPNG01.d FBIPNG13.d FBIPNG25.d

As expected, decay rate of bunch intensity closely follows losses.

SLIDE 19

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Luminosity decay rates during horizontal scan

19

−160 −140 −120 −100 −80 −60 0.0 0.1 0.2 0.3 0.4 0.5 T:L2C2 corrector settings (kG mm) Luminosity decay rates (1/h)

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−6

−4 −2 2 4 Horizontal displacement (mm) D0ILUM01.d D0ILUM13.d D0ILUM25.d D0ILUM02.d

But luminosity decay rate does not change when beams are aligned! ⇒ Scraping of halo without affecting core!?

Collisions at DZero: P01/A13 P13/A25 P25/A01 P02/A14

SLIDE 20

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Intensity and luminosity decay rates vs. e-beam size

20

2.0

2.5 3.0 3.5 4.0 0.0 0.2 0.4 0.6 0.8 1.0 Inner e−beam size (mm) Decay rate (1/h)

TEL2 off

Bunch intensity Bunch luminosity

A25 (P13) 1 pulse/6 turns

SLIDE 21

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Collimation “efficiency” vs. e-beam size

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2.6 2.8 3.0 3.2 3.4 0.70 0.75 0.80 0.85 0.90 0.95 1.00

Hollow beam collimation "efficiency"

Inner e−beam radius (mm) (Loss ratio w/TEL2 on) / (Loss ratio w/TEL2 off)

F48 / (LOSTPB+D0AH)

D17 / (LOSTPB+D0AH) Store #8171 14 Oct 2010

In Tev lattice, TEL2 is not an ideal antiproton target. Nevertheless, capture efficiency should be larger if scraping halo and lower when affecting core. (losses at absorbers) / (ring losses) 1 pulse/6 turns

SLIDE 22

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Preliminary results: first study

22

Electron beam is not perfectly symmetric around axis (space charge,

bends). This has not been a limitation so far.

Aligned e-beam can be turned on 1 bunch parasitically.
Effects on losses, intensities, emittances and luminosities are

detectable.

Pulsing every 6th turn (TEL1 abort-gap cleaning mode) is

considerably more effective than every turn.

Total losses can be increased with negligible effect on luminosity

lifetime, i.e. there is halo scraping with no effect on core or an increase in specific luminosity.

SLIDE 23

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Tevatron studies of Oct 27-28 (store #8210)

23

Demonstration of parasitic operation acting on 1 bunch
Effect of working point on losses
Intensity and luminosity decay rates vs. e-current
Vertical orbit bump with fixed e-beam

SLIDE 24

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Losses vs. working point

24

1 pulse/6 turns A25 (P13) 5σ hole tune settings coupling losses

SLIDE 25

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Intensity and luminosity decay rates vs. e-beam intensity

25

1 pulse/6 turns A25 (P13) 5σ hole

SLIDE 26

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Intensity and luminosity decay rates vs. e-beam current

26

100 200 300 400 500 600 700 0.00 0.02 0.04 0.06 0.08 0.10 0.12 TEL2 peak current (mA) Decay rates (1/h)

Luminosity C:D0ILUM[13]

Intensity C:FBIANG[25]

Losses and intensity decay rates are proportional to e-current
Growth of luminosity decay rates is slower
Indication that scraping without affecting the core is possible

100 200 300 400 500 600 700 20 40 60 80 TEL2 peak current (mA) C:D0AH[25] steady−state losses (Hz)

SLIDE 27

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Vertical orbit bump, fixed e-beam

27

1 pulse/6 turns A25 (P13) 5σ hole

SLIDE 28

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Preliminary results: second study

28

When pulsing every 6th turn (TEL1 abort-gap cleaning mode) losses
n affected antiproton bunch and on closest proton bunch are sensitive

to the machine working point (tunes and coupling) and relative position.

At the end of a store at least, a stable working point in pulsed mode

could always be found.

Acquired data in stable conditions for 3 e-current settings to quantify

differential halo/core scraping.

Changing (anti)proton orbit at TEL2 with fixed e-beam position is a

viable scraping mode: bump is local and tunes are not affected.

SLIDE 29

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

Outlook

29

Open questions:
Operation at high intensity?
Pulsed mode necessary? If yes, stable working point exists?
Acting on more than one bunch?
Need to try with protons?
Next steps:
Systematic study of observables vs. e-beam current/profile, size,

pulsing pattern (mostly parasitical)

Collimator scans to directly measure effects on halo population

(need dedicated study time)

anks for yr aention

SLIDE 30

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

30

Backup slides

SLIDE 31

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

31

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

Measured hollow beam profile vs. current and field

SLIDE 32

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

32

WARP calculation of electric fields from measured profiles

SLIDE 33

G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010

33

Hollow-beam pulse time structure

→ http://home.fnal.gov/~stancari/hebc/time_structure_movie.gif