1 BEPCII Overview C. Zhang for BEPC Team Institute of High Energy Physics, CAS BEPCII Overview C. Zhang for BEPC Team Institute of High Energy Physics, CAS October 13, 2001, BESIII Workshop  Introduction  Basic Design  Key Technologies  Summary

2 (1) Introduction A brief description on BEPC A brief description on BEPC Main parameters Main parameters Operation and performance Operation and performance From BEPCI to BEPCII From BEPCI to BEPCII

3 1.1 A Brief Description on BEPC The Beijing Electron-Positron Collider (BEPC) was constructed ( ) for both high energy physics and synchrotron radiation research. The machine has been well operated for 12 years since it was put into operation in The BEPC accelerator system consists of a 202- meter long linac injector, a 210-meter long beam transport line and a meter circumference storage ring.

4 The Beijing-Electron Positron Collider (BEPC)

5 The Layout of BEPC storage ring

6 1.2 Main Parameters Beam Energy (E) 1.0 ~ 2.5 GeV Revolution frequency (f r ) MHz Lattice Type FODO + Low-  Insertions  * x -function at IP (  * x /  * y ) 1.3/0.05 m Transverse Tune ( x / y ) 5.8/6.8 (Col. Mode) 8.72/4.75 (SR Mode) Natural Energy Spread (  e ) 2.64E  Momentum Com. Factor (  p ) (Col. Mode) (SR Mode) Hor. Natural Emittance (  x0 ) GeV, mm  mr RF Frequency (f rf ) MHz Harmonic Number (h) 160 RF Voltage (V rf ) 0.6~1.6 MV Bunch Number (N b ) 1*1 (Col.), 60~80 (SR) Maximum Beam Current GeV (Col.,) 130mA (SR) Luminosity 5  cm -2 s GeV, 1  cm -2 s GeV

7 4% Injection 12% MD 10% BES 42% BSRF 26% Fault 6% 1.3 Operation and Performance Start-up

8 Daily J/  operation of BEPC Period Days Beam time (hrs.) J/  events L max (10 30 cm -2 s -1 )  (hrs) M M

9 1.4 From BEPCI to BEPCII   The physics opportunity of BEPC calls higher luminosity  BEPCII  To collect some 10 9 J/  events and 10 8  ′events in 4 years; Light hadron spectroscopy, charmed mesons and  at the thresholds; Hadron production mechanism, low energy QCD; Precision R values, ambiguous’ structures in GeV; Searches: 1 P 1,  c ’, glueball, hybrids, exotic states; New physics: probing rare decay, LFV and CP violation from the decays of J/  and  (2S); 

10 (2) The Basic Design Strategy of Luminosity Upgrades Strategy of Luminosity Upgrades The double ring structure The double ring structure Design Goals and Main Parameters Design Goals and Main Parameters The Lattice and Dynamic Aperture The Lattice and Dynamic Aperture The Collective Effects The Collective Effects Beam Lifetime & Average Luminosity Beam Lifetime & Average Luminosity

Strategy of luminosity upgrades  Micro-  :  y *  =5cm  1~1.5 cm SC insertion quads Reduce impedance +SC RF   z  =5cm  ~1cm  DR: multy-bunch k bmax ~400, k b =1  93 (L BEPCII / L BEPCI ) D.R. =(5/1.5)  93  12/20=186 Choose large  x & optimum param.: I b =12mA,  y =0.04

12 BEPCI : I b =20 mA,  y  =5cm, k b =1, L=5  cm -2 s (1  cm -2 s ) BEPCII=BEPCI+micro-  + Multibunch + Better SR performance

The double ring Structure e - RF SR e + IP

14 2A large amount of excellent professional work has been accomplished leading to the Feasibility Study Report on BEPC II. As now proposed, BEPC II can be constructed either in a single ring or two-ring version, differing in expected performance and cost. 2The committee is pleased that the luminosity goal of the BEPC II has been raised from the early proposed gain by a factor of ten to the single ring goal of 3-4  cm -2 sec -1 or the double ring goal of 1  cm -2 sec -1. The committee considers these raised goals to be technically feasible and recommends the most aggressive approach consistent with the resources that can be made available. This implies a strong preference for the two- ring option. 2The scientific environment in which BEPC II will have to operate has changed considerably from that in which BEPC I has a monopoly in this energy range. The now operating B-factories will accumulate extensive data, however with generally higher background, in this energy range and the recent decision by the Cornell University Laboratory of Nuclear Studies to move the operating range of its CESR collider into the tau-charm range to operate at a luminosity of about 3  cm -2 sec -1 has major implications for the future of Chinese high energy physics. While the latter move attests to the continuing scientific importance of this field of inquiry, it should be noted that the CESR program in this energy range will commence several years sooner than is feasible for BEPC II.  The committee judges that the double ring design implies a lower risk in attaining its design luminosity in a brief commissioning time than does the single ring “pretzel” design. From the Report of International Review on BEPCII Feasibility Study

15 Model test of the double ring installation No unsolvable problems are found for the transportation, installation, mounting and dismount of the magnets. The existing monuments for survey and alignment will be covered by the inner ring magnets. New monuments will be fixed on the wall of the tunnel. The antechamber of the positron ring needs to be carefully designed to fit the crucial space between two rings; The cable system, the cooling-water  system, the pressure-air system and others need to be rearranged The cable system, the cooling-water  system, the pressure-air system and others need to be rearranged.

Design Goals and Main Parameters

17 Main Parameters of the BEPCII Storage Ring

The lattice and dynamic aperture (G.Xu)

Collective Effects Bunch Lengthening V rf =1.5MV, |Z/n| eff =0.23 , I th = 21.4mA   z ~  z0 =1.1cm V rf =1.5MV, |Z/n| eff =0.23 , I th = 21.4mA   z ~  z0 =1.1cm |Z/n| 0 =4   0.2  |Z/n| 0 =4   0.2  MAFIA computation & measurement MAFIA computation & measurement Bellows, kickers, separators, BPM’s, masks, connectors, valves, pumps, SR ports, IR  Bellows, kickers, separators, BPM’s, masks, connectors, valves, pumps, SR ports, IR 

Coupled Bunch Instabilities Beam cavity interaction (N b =99, I b =12 mA, using KEKB SC cavities) Resistive wall instability x / y = 6.58/7.64, N b = 99, I b = 12mA,  = 16.4ms; Ion effects Photo-electron cloud instability: Use antechamber for positron ring Bunch feedback

Beam-beam effects Head-on beam-beam effect: similar to BEPCI Head-on beam-beam effect: similar to BEPCI   =0.04 has been demonstrated Parasitic beam-beam effect  Parasitic beam-beam effect   x  10  x and  c =5.5  2 mrad Horizontal crossing angle  c  Horizontal crossing angle  c  ( )  2 mrad (BEPCII), 2.3  2 mrad (CESR) ( )  2 mrad (BEPCII), 2.3  2 mrad (CESR) 11  2 mrad (KEKB), 12.5  2 mrad (DA  NE) Crossing angle+Parasitic collisions (Arcs & IR)  More sophisticated simulation study. Crossing angle+Parasitic collisions (Arcs & IR)  More sophisticated simulation study.

Beam Lifetime and Average Luminosity Taking  =1.35 hrs., t f = 0.4 hr. and L 0 =1  cm -2 s -1, the optimized collision time is calculated as 1.0 hrs. and the maximum average luminosity is calculated as  L  max =0.5  cm -2 s -1. The top-off injection will further improve the average luminosity.

23 (3) Key Technologies  Injector upgrading  500 MHz SC RF System  SC Micro-  Quads and IR  Low Impedance Kickers  Vacuum System  Power Supply System  Instrumentation Upgrade  Control Upgrade

Injector upgrading Basic requirement:  Higher intensity: positron injection rate  50 mA/min.;  Full energy injection with E=1.55 ~ 1.89 GeV; To enhance the current and energy of the electron beam bombarding the target and to reduce the beam spot; To design and produce a new positron source and to improve its focusing; To increase the repetition rate from present 12.5 Hz to 50 Hz. To consider multi-bunch injection (f RF /f Linac =7/40);

MHz SC RF System Basic requirement  Sufficient RF voltage for short bunches.  Sufficient high RF power.  Suppressing the instabilities related to RF system.  Stable and reliable RF system Strategy: to take advantage of collaboration with SSRF, Cornell and KEK and to apply the existing industrial technology.

26 Options of 500 MHz SC RF Cavity Options of 500 MHz SC RF Cavity CESR-type Cavity (ACCEL) KEKB-type Cavity (Mitsubishi ) IHEP RF group will work at optimization of the cavity design, trace the manufacture and be trained to maintain the SC RF system.

SC Micro-  Quads and IR

28 The SC magnets and IR Design Space and dimension Installation and alignment Solenoid and its compensation Magnet leakage field Background and masking Cryogenics ……

Low Impedance Kickers The study has shown that the kickers are one of major sources of impedance, where single turn air coils are located inside vacuum chamber of the kickers. The new kickers of BEPCII impose the ferrite magnet outside the vacuum with ceramic beam pipes so that the impedance problem is avoided. The pipes are with resistive coating on its inner surface. Magnetic field distribution in the kicker

Vacuum System The BEPCII poses two challenges to the vacuum system, one is vacuum pressure, other is the impedance. The dynamic vacuum at a high beam current should satisfy the requirements of sufficient beam lifetime, low background in the detector. The design vacuum pressure is 5  Torr in the arc and 5  Torr in the IR. To reduce the impedance, the vacuum chamber should be as smooth as possible. Some of the chamber structures will be shielded, some will be replaced with new designed components.

Power Supply System The superconducting insertion quadruple magnets for micro-  need to be powered with new power supplies. The pretzel scheme need more independent power supplies, namely 34 for quadruples and 18 for sextupoles. In the double-ring case, this numbers are about doubled. In order to mount the additional power supplies in the existing rooms, the new power supplies should be compact by using improved technology.

Instrumentation Upgrade Beam Position Monitor Bunch Current Monitor Beam Feedback System Synchrotron Light Monitor IP beam position control

Control System: switch from BEPCI to BEPCII VAX 4500 CAMAC PC subsystems WS console Ethernet PS, Vacuum, RF Injection Beam diagnostic Linac

34 Collaboration on BEPCII Accelerators Linac: SLAC, KEK, INFN  SC Micro-  quadruples: BNL, KEK  SC RF cavities: Cornell, KEK  Impedance study: LBNL  Beam Instrumentation: CERN, SLAC Under discussion: BINP and other labs Domestic institutions: SSRF, Tsinghua, PU  

35 Budget and Schedule The budget of the BEPCII project is estimated as about 600 million RMB for both accelerators and detector. The project is expected to finish in 3  4 years after its approval.

36 (4) Summary BEPC has been well operated with many exciting HEP and SR results for 12 years since it was put into operation in BEPC has been well operated with many exciting HEP and SR results for 12 years since it was put into operation in BEPCII is proposed as micro-  plus multibunches with two rings and its design luminosity is order of magnitude higher than present BEPC in energy range of J/  and  ’. Some key technologies need to be developed to achieve the goal of BEPC II. The international collaboration and contribution will be promoted in order to accomplish this challenging and exciting project on schedule and budget.

37 Thank You for Attention!