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

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

Recent activity ‣ At the test stand: ‣ Studied time microstructure of hollow beam pulse gs ‣ In the Tevatron: G. Kuznetsov, ‣ Aug 2-3: installed hollow gun in electron lens TEL2 S. Sylejmani, gs ‣ Complete TEL2 test with e-beam before Tevatron start-up: J. Crisp, B. Fellenz, G. Kuznetsov, BPMs, modulator, power supplies G. Saewert, J. Simmons, X. Zhang, gs ‣ Verified abort-gap cleaning effect (as TEL1 backup) X. Zhang ‣ First dedicated studies Oct 13-14 (3 hrs) and Oct 27-28 (4 hrs): A. Valishev, gs ‣ 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 G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 2

The 0.6-in hollow gun Copper anode top view Tungsten dispenser cathode with convex surface 15-mm diameter, 9-mm hole side view G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 3

Hollow gun installed in the Tevatron (Aug 2) Gennady Kuznetsov G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 4

Modulator tests without e-beam Replaced DC supplies in tunnel (out of spec, radiation damage?) Modulator tested up to 4.8 kV at highest switching rate 4.5 kV G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 5

Vacuum recovery and filament heating TEL2 FILAMENT HEATER TEL2 VACUUM TEL2 CURRENT TEVATRON BEAM G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 6

TEL2 checks before Tevatron start-up Shortest pulse: MODULATOR (4 kV/V) CATHODE (1 A/V) COLLECTOR (1 A/V) TEL2 PICKUP G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 7

Corrector/BPM calibration vs. magnetic field To change hole size for collimation, need to operate at different field ratios B gun /B main G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 8

Hollow gun performance in TEL2 after cathode conditioning 0.6 − in hollow gun in TEL2 Yield vs. voltage (shortest pulse) T:L2MCV1 = 580 V ● 11 Oct 2010 T:L2FILI = 7.75 A 1.0 T:L2DLY1 = 668 rfc T:L2MCV1 = 500 V ● Peak collector current (A) T:L2TM = 2 0.8 T:L2TS14 = 33333 1 pulse/turn ● T:L2MCV1 = 400 V 0.6 ● T:L2MCV1 = 300 V 0.4 ● T:L2MCV1 = 200 V 0.2 T:L2MCV1 = 100 V ● T:L2MCV1 = 50 V ● 0.0 ● T:L2MCV1 = 0 V 0 1 2 3 4 Cathode − anode voltage (kV) G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 9

First dedicated studies in the Tevatron at collisions ‣ 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 σ y ), pulsing pattern (skip 0-9 turns) ‣ machine working point: tunes and coupling G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 10

0.6 − in hollow − gun electron beam sizes (Anti)proton beam sizes at TEL2 vs. emittance vs. magnetic field 1.2 8 Gun solenoid: p = 980 GeV c βγ = 1044.473 3 kG Gaussian r.m.s. beam size (mm) Δ p p = 0.00015 4 kG 1.0 Electron beam radius (mm) β x = 66 m 6 β y = 160 m 0.8 D x = 1.18 m D y = − 1 m 0.6 4 0.4 2 0.2 r1 gun = 4.5 mm Horizontal r2 gun = 7.62 mm Vertical 0.0 0 0 10 20 30 40 0 10 20 30 40 Normalized 95% emittance ( µ m) Magnetic field in main solenoid (kG) 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 G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 11

Example of transverse beam profiles at TEL2 T = 980 GeV βγ = 1045 β x = 66 m β y = 160 m D x = 1.2 m D y = − 1 m HOLLOW ELECTRON BEAM Protons: ε x = 21 µ m ε y = 35 µ m 5 Δ p p = 1.6 10 − 4 σ x = 0.47 mm σ y = 0.94 mm VERTICAL POSITION (mm) Antiprotons: ε x = 22 µ m ε y = 21 µ m Δ p p = 1.5 10 − 4 σ x = 0.48 mm σ y = 0.73 mm 0 ANTIPROTON CORE Electrons: B g = 4 kG B m = 10 kG R i = 4.5 mm R o = 7.6 mm r i = 2.8 mm r o = 4.8 mm − 5 PROTON CORE − 10 − 5 0 5 10 HORIZONTAL POSITION (mm) G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 12

e-beam pulse synchronization with antiproton bunch MODULATOR (4 kV/V) P1 P2 P3 TEL2 PICKUP A13 A14 A15 COLLECTOR (1 A/V) G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 13

Oct 13-14 (store #8171) study overview Pulse: 1 pulse/turn 1 pulse/6 turns Bunch: A13 A25 4 σ 5 σ Hole radius: 3.5 σ Alignment scans: V pos. H pos. H angle G. Stancari (Fermilab) Hollow electron beam collimation LARP CM15 1-3 Nov 2010 14