ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 1 Interaction Region of PEP-II M. Sullivan for the ILC MDI workshop January 6-8, 2005

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 2 Outline Initial IR design parameters Initial beam parameters Detector constraints IR design Present performance and issues New beam parameters Luminosity background Summary

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 3 SLAC beam lines

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 4 Layout of the PEP-II Ring

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 5 Initial IR Design Parameters Energy asymmetry of 9 on 3.1 GeV Head-on collision Bunch separation of 1.26 m 25 mm separation between BSC envelopes at 2.8 m (room for a septum magnet) SR masking –No direct hits on the detector beam pipe –No surfaces that can one bounce to the detector beam pipe –This leaves mask tip scattering as the dominate SR source

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 6 Initial Beam Parameters Collision Frequency238 MHz Number of bunches 1650 Bunch spacing 1.26 m Charge/bunch (L/H)5.9x x10 10 IP Beta X,Y 0.50, m Emittance X, Y48, 1.5 nm-rad Bunch size (x, y, z) 155, 4.7, µm Currents (L/H) 2.1 A 0.75 A Luminosity 3x10 33 cm -2 sec -1

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 7 Detector Constraints Detector acceptance minimum angle of 300 mrad Detector magnetic field of 1.5T Minimum thickness beam pipe –4 µm Au –800 µm Be –1 mm water – 400 µm Be Detector center shifted in Z m

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 8

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 9 Present status We have achieved  y * s of 10 mm With  x * s of 30 cm Bunch lengths are estimated to be mm Total beam currents of A on A (1.590 on on last shift) No sign of SR backgrounds Fairly large luminosity background Total current in the support tube up to 4.1 A! Heating in the IR support tube (from Q2 to Q2) OK so far NEG pump heating by HOM power

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 10 Past and Present HOM heating IR Be bellows NEG pumps in the LER Q1/Q2 bellows Bellows in region 4 Bellows in region 10

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 11 IR Vacuum Chambers

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 12 Bellows Detail Transverse H11 mode can couple through the RF shield RF shield Be is coated with about 4  m of Au Al heat sink Be to SS braze SS sleeves Cu pipe

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 13 Forward VTX BLWS Cooling

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 14 VTX Bellows Cooling Installation

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 15 Lab test data of NEG outgassing as a function of temperature LER NEG Pump Temperatures Upstream LER side 350 °F

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 16 LEB Fans

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 17 HEB Fans

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 18 New Beam Parameters Collision Frequency238 MHz Number of bunches 1710 Bunch spacing 1.26 m Charge/bunch (L/H)12.6x x10 10 IP Beta X,Y 0.30, m Emittance X, Y60, 1.0 nm-rad Spot size (x, y, z) 134, 2.8, 9000 µm Currents (L/H) 4.5 A 2.2 A Luminosity 2x10 34 cm -2 sec -1

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 19 Issues for the near future Run 5 goals that affect the IR LER current of 3.3 A HER current of 1.8 A Higher bunch currents  more HOM power Shorter LER bunch length  more HOM power Lower  y * s to 9 mm Lower LER  x * to 30 cm Increase LER emittance to 50 nmrad Total of 5.1 A !  BSCs

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 20 Issues for the farther future Ultimate goals that affect the IR LER current of 4.5 A HER current of 2.2 A Still higher bunch currents  more HOM power Still shorter bunch lengths  more HOM power Lower  y * s to 8 mm Lower LER  x * to 30 cm Increase LER emittance to 60 nmrad Total of 6.7 A !!  BSCs

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 21 Present machine parameters LER  x * = 30 cm and LER  x = 22 nmrad LER  x * may be a little low, but it is the value for run 5 BSC just clears the present Q2 chamber on the forward side Plenty of room on the backward side BSCs

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 22 BSCs Expected LER beam size for run 5 LER parameters:  x * = 30 cm  x = 50 nmrad BSC is defined as 15  + 2mm (uncoupled) BSC violated at the septum Just enough room for the beam New chamber being built and RFI by April or May

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 23 LEB+HEB HOM Power ~  i b 2  z -2

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 24 Be Vertex Pipe and Bellows

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 25 Luminosity versus Crossing Angle Without parasitic crossing With parasitic crossing

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 26 Comparisons between stronger B1s, crossing angles and energy changes The parasitic crossing separations are: Present design3.22 mm 30% Stronger B1 (Nd) mm (12-17%) Stronger B1 (volume) mm (9-21%) With +/- 0.5 mrad x angle mm (21-24%) The energy differences for the crossing angle option are: HER to (-2.5%) LER to (+2.6%) Increase the energy asymmetry AND remove last B1 slice Very preliminary look with head-on collisions: HER energy  GeV +5.1% and LER energy  GeV - 4.8%  PC separation of 3.55 mm (10%)

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 27  Synchrotron radiation masking has been checked OK with a 7mm beta y*  Local beam-gas and coulomb should be essentially unchanged since the geometry is almost the same and the masking is the same. These backgrounds should slowly improve as the total number of A-hrs increases  Radiative Bhabhas as a background that increases as the luminosity increases Detector Backgrounds in the Future

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 28

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 29

ILC MDI workshop January 6-8, 2004 PEP-II IR M. Sullivan 30  The PEP-II interaction region has performed very well  The PEP-II accelerator is starting to move into a new area of performance where HOM power will play a much larger role. The higher beam currents and higher bunch currents contribute to the higher HOM power as well as to higher SR power.  So far we have addressed two major issues in the IR concerning HOM heating – Be bellows heating and NEG pump heating. Other regions will bear watching as well as other vacuum components.  The IR upgrade is looking at modifying the B1 bending magnets to improve the beam separation at the 1 st parasitic crossing while maintaining head-on collisions. Stronger magnetic material is needed to do this. However, we have not found a material that is comfortably rad-hard.  The option of adding a small crossing angle (+/- 0.5 mrad) using the present hardware can be done by changing the beam energies by about +/- 2.5%.  Detector backgrounds that are a function of the luminosity will become more important as the luminosity increases Summary