Session 3: LHC IR Upgrade & Beam Choices CARE-HHH-APD Workshop November 8-11, 2004 Steve Peggs Tanaji SenOverview of possible LHC IR upgrade layouts Oliver BruningBeam dynamics requirements Ken TakayamaFirst observation of induction KEK PS Frank ZimmermanBeam-beam compensation schemes Kazuhito OhmiCrab cavity option at LHC Heiko DamerauGeneration & benefits of long super-bunches Stefan TapproggeMachine-detector interface & event pile-up

Overview of Possible LHC IR Upgrade Layouts J. Strait, N.V. Mokhov, T. Sen Fermilab

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait3 LHC Luminosity Upgrade A luminosity upgrade of the LHC will be required by the middle of the next decade to keep the LHC physics program productive.  Must consider several ways to achieve it.  Must start R&D now.  Must choose R&D directions judiciously.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait4 New IRs: “Straightforward” Designs Quads 1stDipoles 1st Copy baseline IR with larger bore quads. Fewer long-range collisions, but larger  max.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait5 Energy Deposition – Quads First Energy deposition and radiation are major issues for new IRs. In quad-first IR, E dep increases with L and decreases with quad aperture. – (P/L) max > 120 W/m, P triplet >1.6 kW at L = cm -2 s -1. – Radiation lifetime for G11CR < 6 months at hottest spots. T. Sen, et al., Beam Physics Issues for a Possible 2 nd Generation LHC IR, EPAC 2002.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait6 NbTi Magnets? Quad-first IR with Nb 3 Sn quads of 110 mm aperture and 6m length can achieve  * = 16 cm. To achieve same  * with NbTi requires aperture of 120~130 mm and length of 8~9 m. =>~30% increase in  max ; 15~20% more parasitic collisions. Current NbTi technology is not sufficiently radiation hard. Smaller temperature margin => more sensitive to beam heating. Dipole-first IR requires highest possible field: Separate beams quickly. Bring quads as close as possible to the IP. => Probably not practical without higher performance of Nb 3 Sn.

CARE Workshop – 8-11 Nov 04IR Upgrades Layouts - J. Strait7 Summary “Simple” IR upgrades using Nb 3 Sn have the potential to reduce  * by x2~x3. “Exotic” IR upgrades – “quads between” and large crossing angle layouts – might reduce  * by x2.5~x5. Energy deposition and radiation hardness are major challenges for L = cm -2 s -1, especially for the dipole-first case. Nb 3 Sn technology offers greater upgrade potential than NbTi, but considerable R&D is required. The challenge of increasing LHC luminosity towards cm -2 s -1 is considerable, and many options need to be pursued now to ensure success.

Beam Dynamics Requirements for an LHC Insertion Region Upgrade Oliver Bruning, CERN

First observation of induction acceleration in the KEK Proton Synchrotron Ken Takayama. KEK

ファラデ イ ーの誘導法則 Principle of Induction Acceleration Induction gap Pulse voltage Magnetic core Proton beam Coaxial cable Magnetic field Farady’s law

Difference between RF Synchrotron and Induction Synchrotron seen in Phase-space EE Induction Synchrotron RF Synchrotron RF bunchSuper-bunch Allowed maximum energy spread

Funding Outline K$ Including Postdoc/technician’s salary but does not include salary of staffs

Progress in Experiment 1st 10/3 - 4 First demonstration, acceleration from 500 MeV up to 1-2 GeV 2nd 10/ Result was unclear, acceleration from 500 MeV up to 6 GeV (just below transition) 10/ ICFA workshop HB2004 3rd 10/ Second demonstration, acceleration from 500 MeV to TC 4th 10/ /1 Third demonstration, acceleration from 500 MeV to 8GeV 11/ CARE HHH th 11/ th 11/ th 12/ th 12/ Interesting experiment to make the best use of separate- function in the longitudinal direction will be planned, as well as a basic measurement of beam-loading effects on the induction cavity and droop compensation.

Summary Pulse Modulator capable of generating a 2 kV output voltage at 1MHz is in our hands. A reliable full module for the induction accelerating system has run over 24 hours without any troubles. The induction acceleration of protons (6x10 11 ppb) in a circular accelerator ring has been achieved, accelerating a single RF bunch from 500MeV to 8GeV (flat-top) This is one of crucial milestones to realize Induction Synchrotrons and Super-bunch Hadron Colliders (K.Takayama et al., PRL 88, 1448(2002) ). A paper describing the experimental result (submitted to Phys. Rev. Lett.) will be available soon. Acceleration in circular rings may enter into a new era with induction devices driven by a switching driver.

Beam-beam compensation schemes Frank Zimmermann, CERN

Simulated diffusion rate vs amplitude for XX, XY and YY crossing with LR only and with the combined effect of LR and SR collisions xy xy w/o HO yy, yy w/o HOxx w/o HO, xx

2 nd generation BBLR in the CERN SPS can model various LHC crossing schemes G. Burtin, J. Camas, J.-P. Koutchouk, et al.

simulation experiment

Fermilab Tevatron Electron Lens compensate beam-beam tune shift of pbars current: ~1-3 A solenoid field: 3.5 T in operation since 2001 V. Shiltsev

To correct all non-linear effects correction must be local. Layout: 41 m upstream of D2, both sides of IP1/IP5 (Jean-Pierre Koutchouk) Long Range B-B Compensation for LHC Phase difference between BBLRC & average LR collision is 2.6 o current-carrying wires

 V crab  cav ** cc f crab EbEb symbol 0.06 mradphase tolerance 46 MV1.44 MVkick voltage 2 km100 m cavity  0.25 m0.33 m IP  8 mrad11 mradcrossing angle 1.3 GHz508 MHzrf frequency 7 TeV8 GeVbeam energy LHCKEKBvariable Crab Cavity combines all advantages of head-on collisions and large crossing angles R. Palmer, 1988 K. Oide, K. Yokoya Courtesy K. Hosoyama, K. Ohmi

active beam-beam compensation programme in progress for Tevatron & LHC TEL promising, but conditions difficult to control wire compensation of LR collisions at LHC will allow smaller crossing angles and/or higher bunch charges; experimental demonstration in the SPS; pulsed wire desirable for selective correction of PACMAN bunches crab cavities alternative option for large crossing angle Conclusions

Crab cavity option at LHC K. Ohmi (KEK)

Cryostat for KEKB Crab Cavity (Top View) Courtesy of K. Hosoyama ~ 3 m

Jan. Dec. Beam Test Crab Cavity #1 Design Road Map to Beam Test (Feb 2004) Vac. RF Cryogenics Control Crab Cavity Cryostat Coaxial Coupler E.P. Cold Test Assembling Jan. Cold Test Ｃｒｙｏｓｔａｔ (Prototype) Coaxial Coupler (Prototype) Nb-Cu R&D Installation Vac. RF Cryogenics Control Assembling Cold Test Crab Cavity Prototype Courtesy of K.Hosoyama

Diffusion for various crossing angles using a weak-strong simulation Vertical equilibrium size obtained by the weak-strong simulation and the ratio of the diffusions for the rad. damping. Diffusion rate

Discussion Can crab cavities contribute to the luminosity upgrade of LHC? Is the symplectic diffusion caused by crossing angle dominant? If yes, crab cavity works. Does diffusion limit the LHC luminosity? What determines the beam-beam limit in LHC? What is the dominant diffusion source in LHC? Parasitic collisions are weakened by large crossing angles

Generation and benefits of long super-bunches H. Damerau, R. Garoby, CERN

Short rectangular bunches Multiple RF systems: n · 400 MHz Bunch length (20cm)  Strong interaction length (small  )  Beam-beam behaviour similar to Gaussian bunch: No significant luminosity gain below   1 mrad

Long flat bunches Combine 16 or 32 near nominal LHC bunches to RF system: 40, 80, 120, etc. MHz What is the influence of longer bunches on  Q x,y ? rectangular Gaussian  0 = 7.55 cm,  = 285  rad

Summary of flat bunch options easy significant extensive easy unnecessary sophisticated scheme miss. difficult enormous intermediate (400), 800, 1200 MHz 40, 80, 120 MHz Barrier buck. at  10 MHz cm m m RF systems Implementation experiments Implementation accelerator RF manipulation Compensation of synchr. radiation Total beam int. For cm -2 s -1 Bunch Length Short and flat bunch Long and flat bunch Super-bunch

Machine-detector interface and event pile-up: Super-bunches versus normal bunches Stefan Tapprogge, Mainz

Summary summary 1) Energy deposition & radiation are major issues 2) NbTi or Nb 3 Sn? Considerable R&D required 3) Is Q1 a separate design problem from Q2, Q3? 4) Operation at the beam-beam limit is assumed 5) 2-in-1 IRs are hard, but have significant advantages 6) Acceleration in circular rings enters a new era with induction devices 7) Beam-Beam compensation: Electron lens is promising, but difficult to control Wire compensation experiments in SPS. Pulsed for PACMAN? Crab cavities coming to KEKB. Enable large crossing angles 8) LONG superbunches are strongly disliked by CMS & ATLAS 9) SHORT (40 Mhz) flat bunches may have advantages 10) 10 or 15 ns separation?