Tevatron Beam-Beam Phenomena and Counter-Measures Alexander Valishev Fermilab, Batavia, IL 60510 LARP Mini-Workshop on Beam-Beam Compensation July 2-4, 2007
Outline Overview of Beam-Beam Effects Injection Collisions Countermeasures New Collision Helix New Working Point Second Order Chromaticity Correction Results and Summary LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 2
Luminosity and Luminosity Integral L = 3γ f πβ * 0 B N ( ) ε + ε p p N p p H ( * ) σ β l I = Ldt N stores τ L ln(1 + T Luminosity Integral: primary factors L / τ 0 L ) Beta* at IP and bunchlength: H(x)/beta^* Emittances ε p ε pbar Number of protons: N p Number of antiprotons: BN pbar Lumi-lifetime: τ L LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 3
Overview of Beam-Beam Effects Beam Intensities in Store 5506 LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 4
Sources of Luminosity Loss in Tevatron Recycler Helix Sext LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 5
Sources of Luminosity Loss in Tevatron LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 6
Long-Range Effects at Injection LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 7
Long-Range Effects at Injection LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 8
Long-Range Effects at Injection LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 9
Long-Range Effects on Ramp LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 10
Beam Intensity Loss on Ramp Proton inefficiency vs. pbar intensity Pbar inefficiency vs. proton intensity LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 11
Long-Range Effects in Squeeze LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 12
Long-Range Effects in Squeeze LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 13
Long-Range Effects in Squeeze LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 14
Emittance blowup Lifetime deterioration Effects at Collisions Long-Range Head-on LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 15
Emittance Increase vs. Betatron Tune LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 16
Proton Loss Rate vs. Betatron Tune LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 17
Effect of the Helix Size on Lifetime Antiproton NL Loss Rate [% / hr] 1.0 0.8 0.6 0.4 0.2 0.0 Average Antiproton Non-Luminous Loss Rate vs Helix Size Stores #4021 - #4109 90 95 100 105 110 Helix size [% of nominal] LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 18
S Improvement of the Collision Helix 12 10 8 6 1000 2000 3000 4000 5000 6000 CDF upstream CDF downstream D0 upstream D0 downstream s Before 5.4 5.6 5.0 5.2 After 6.4 5.8 6.2 5.6 LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 19
Gain in Luminosity Integral from the New Collision Helix LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 20
Effects in Collisions LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 21
Luminosity Evolution Model The model describes evolution of the beam emittances and intensities taking into account the following factors: Scattering at IP (luminosity) Scattering on residual gas RF noise Intra Beam Scattering Initial parameters (bunch by bunch intensity, transverse and longitudinal emittances) are taken from SDA Main free model parameters are: Gas pressure RF noise power The model does not include beam-beam effects LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 22
Luminosity Evolution Store 4581, L=1.72E32 Old Helix Bunch 7 LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 23
Luminosity Evolution Store 4859, L=1.70E32 New Helix Bunch 6 LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 24
Head-on Beam-Beam Tuneshifts. 4581 4859 LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 25
Luminosity Evolution Store 5245, L=2.92E32 New Helix Bunch 6 LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 26
Head-on Beam-Beam Tuneshifts.. Store 5245 LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 27
New Tevatron Working Point Currently operating between 4/7 and 3/5 with beambeam ξ = 0.02 To increase number of particles need more tune space WP near ½ should allow 40% more! However, vicinity of half-integer increases sensitivity to quadrupole errors, especially chromatic Moreover, large chromatic β-function is detrimental to beam-beam effects even at present WP LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 28
Horizontal Chromatic Beta Function LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 29
Correction of β-function Chromaticity Reconnection of sextupoles into new families LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 30
Corrected Chromatic Beta-Function 400 Vertical Chromatic β-function 200 0-200 -400 4.0x10 5 4.2x10 5 4.4x10 5 Azimuth (cm) LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 31
Improvement of the Proton Lifetime 260 5402 5492 Proton Bunch Intensity (10 9 ) 250 240 230 220 0 0.4 0.8 1.2 1.6 2 Time (h) Work still in progress! LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 32
Summary Beam-beam effects at injection cause 5-10% beam loss At collisions, before 6/06 decrease of intensity lifetime and emittance blowup were caused by longrange effects Implementation of the new collision helix with increased separations at particular LR collision points gave improvement of the luminosity lifetime (~16%) Currently, beam-beam effects at collisions are dominated by proton losses due to head-on interactions LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 33
Summary Present working point allows little space for increasing beam intensities. Betatron tune near half-integer resonance has high potential for larger luminosity Operation near Q=0.5 is impossible without correction of β-function chromaticity The new sextupole circuits are being commissioned According to beam-beam simulations correction of chromatic beta will improve situation at present WP. Some encouraging results have already been obtained. LARP Beam-Beam Compensation Mini-Workshop 7/2/07 A.Valishev 34