# Presentation: 158500

## An Overview of Tevatron Collider Run II at Fermilab

- f

- Ronald Moore
- representing
*Fermi National Accelerator Laboratory*

- RUPAC 2002

## Contents

- Overview of the Accelerator Complex
- Main Injector
- Pbar Source
- Recycler
- Tevatron Performance and Issues
- Future Plans
- Summary

- R. Moore - FNAL

- RUPAC-2002

## Fermilab Accelerator Complex

- R. Moore - FNAL

- RUPAC-2002

## What’s new/different for Run II?

- Main Injector
- Replaces the Main Ring (was inside Tev tunnel)
- Recycler Ring
- 8 GeV storage ring for pbars in MI tunnel
- Tevatron
- # bunches: was 6x6, now 36x36
- Beam energy:  was 900 GeV,  now 980 GeV
- New two-stage collimation system
- Run IIa  –  deliver 2 fb-1,       peak  = 8.6 E 31 cm-2 s-1
- Run IIb  –  deliver > 5 fb-1,    peak  = 2-5 E 32 cm-2 s-1

- R. Moore - FNAL

- RUPAC-2002

## Proton Source

- 25 keV H- ion source
- 750 keV Cockcroft-Walton accelerator
- Linac: accelerate H- to 400 MeV
- 116 MeV Alvarez linac (201.25MHz)
- 400 MeV side-coupled cavity linac (805 MHz)
- Booster: 8 GeV synchrotron
- Stripper foil at injection removes e-
- Output = 4.5-5.0 E12  in 84 bunches
- Longitudinal emittance  ~0.15 eV-sec

- R. Moore - FNAL

- RUPAC-2002

## Main Injector (MI)

- Replaced Main Ring (formerly in Tev tunnel)
- Higher rep rate for stacking
- Simultaneous stacking and fixed target running
- Many operating modes
- Pbar production: up to 5*1012 120 GeV protons
- Tevatron protons/pbars:
- Accelerate 8 GeV to 150 GeV
- Coalesce 7-9 proton bunches 90% eff into 270-300 E9 bunch
- Coalesce 7-11 pbar bunches 75-85% eff into 20-30 E9 bunch
- Transfer 8 GeV pbars Accumulator Recycler
- Provide protons for neutrino production

- R. Moore - FNAL

- RUPAC-2002

## Pbar Coalescing in Main Injector

**1 of 4 pbar batches coalesced simultaneously**
**Beam-loading compensation **_**on**_

- R. Moore - FNAL

- RUPAC-2002

## Pbar Source

- Up to 5*1012 p (120 GeV) strike Ni target
- Li lens (740 Tesla/m) collects neg secondaries
- Pulsed dipole bends pbars down transfer line toward Debuncher, Accumulator
- Stack rate = _6-11 mA/hr_ depending on stack size
- Efficiency  (13-18)*10-6 pbars/proton on target
- Transverse emittances vary linearly with stack size
- New core cooling system and lattice optimized for shots allow _5-12 ____ mm*mrad_ (95%) for typical stacks

- R. Moore - FNAL

- RUPAC-2002

## Pbar Production Goals

|  | Current | Run IIa goal |
| --- | --- | --- |
| Protons/pulse on target (E12) | 4.2-4.5 | 5 |
| Stacking cycle rep rate (s) | 2.5 | < 2 |
| Max pbar stack rate (E10/hr) | 12.4 | 18 |
| Max pbar stack (E10) | 190 | 165 |

- Plans to increase stacking rate
- Raise proton intensity on target
- Decrease cycle time - want < 2.0 sec
- Improve collection efficiency
- Increase Li lens gradient
- Increase aperture of transfer line  target station  Debuncher

- R. Moore - FNAL

- RUPAC-2002

## Pbar Stacking for 1 Week

**stacking rate**

**pbar current**

**protons on target**

**pbars / E6 protons**

- R. Moore - FNAL

- RUPAC-2002

## Pbar Transverse Emittance vs Stack Size

- R. Moore - FNAL

- RUPAC-2002

## Recycler Ring (RR)

- 8 GeV storage ring for pbars in MI tunnel
- Shoot small pbar stacks from AccumulatorRecycler to maintain higher stacking rate in Accumulator
- Recycle pbars left (50-70%) after Tevatron store
- MI RR pbar injection efficiency > 90%
- Stacking efficiency  70%
- Problem with RF manipulations understood
- Stochastic cooling commissioned
- 10  mm mrad/hr cooling rate           (not yet optimized)
- 3-4  mm mrad/hr heating rate   (beam-gas interactions)
- Achieved 110 hr lifetime for 40E10 pbars
- With MI ramping, cooling

- R. Moore - FNAL

- RUPAC-2002

## Recycler Plans and Goals

- Improve vacuum to reduce heating rate factor 3-4
- Double # ion pumps, improve bake out system
- Upgrade BPMs, IPMs, Schottky detectors
- Integrate RR into operations in 2003

|  | Goal |
| --- | --- |
| Stored pbar intensity (E12) | 2 |
| MI RR efficiency | 95% |
| Stacking efficiency | 90% |
| Lifetime with 2 E12 pbars (hr) | > 200 |
| Emittance ( mm mrad) | < 10 |

- R. Moore - FNAL

- RUPAC-2002

## Recycler Injection Efficiency

**Beam in MI **

**Beam in RR**

- R. Moore - FNAL

- RUPAC-2002

## Recycler Stored Pbar Lifetime

**44 hours**

**Beam current**

**MI magnet power**

**Pbar lifetime with MI ramping ******** 125 hours**

- R. Moore - FNAL

- RUPAC-2002

## Tevatron Overview

- Collides  3636  protons and pbars @  980 GeV
- Radius = 1 km
- 2  low  intersection points
- 1113 RF buckets (53.1 MHz)
- 3 trains of 12 bunches with 396 ns separation
- Emittances at start of stores:   18-22  mm mrad  (95%)
- Bunch lengths at store start:    proton/pbar   2.1/1.8 ns
- Overall efficiencies
- protons  MI  HEP:                _55-65%_
- pbars  Accumulator  HEP:   _40-50%_

- R. Moore - FNAL

- RUPAC-2002

## Tevatron Luminosity Formula

**(10****31**** cm****-2**** sec****-****1****)**

***  ******f   ***=  revolution frequency = 47.7 KHz
*  **B  *=  # bunches = 36
***r****r * =  relativistic beta x gamma = 1045
*****  =  beta function at IR = 35 cm   (can reduce to 30cm?)
*  **H*  =  hourglass factor = .60 - .75
*N**p** **, **N**pbar*  =  bunch intensities (E9)
***p** **, ****pbar*    =  transverse emittances (-mm-mrad)
***l **    *=  bunch length (cm)

- R. Moore - FNAL

- RUPAC-2002

## Run IIa - Peak Luminosity

- R. Moore - FNAL

- RUPAC-2002

## Run IIa - Delivered Luminosity

- R. Moore - FNAL

- RUPAC-2002

## Luminosity Parameters

|  | Highest  store to date | Overall Best to date | Run IIa goal |
| --- | --- | --- | --- |
| Max pbar stack rate (E10/hr) | - | 12.4 | 18 |
| Max pbar stack (E10) | 165 | 190 | 165 |
| Pbar efficiency
Accumulator  HEP (%) | 40 | 58 | 80 |
| # pbars/bunch  @ HEP (E9) | 17.1 | 17.1 | 33 |
| # protons/bunch  @ HEP (E9) | 170 | 211 | 270 |
| Peak luminosity
(E30 cm-2 s-1) | 30.2 | 30.2 | 86 |

- R. Moore - FNAL

- RUPAC-2002

## Bunch Intensities in 2002

- R. Moore - FNAL

- RUPAC-2002

## Tevatron Efficiencies

**Pbar intensity E9**

**proton**
**injections**

**DC intensity E12**

**pbar**
**injections**

**Prot intensity E9**

**ramp**

**Open helix**

**poor lifetimes**

******10% bunched**
**beam loss in ramp**

- R. Moore - FNAL

- RUPAC-2002

## Lifetime Issues at 150 GeV

- Poor proton lifetime on helix ~ 2 hr
- Lifetime on central orbit OK > 20 hr
- Instability prevents lower chromaticity (currently = 8)
- Limited success using octupoles, will try again soon
- _Beam-beam effects_  poor pbar lifetime 1-3 hr
- Pbar lifetime without protons ~ 20 hr
- Try to expand helix, but limited by apertures
- Replace lambertsons @ C0 – gain 25 mm vertically
- Modify high  section formerly used for fixed-target extraction
- Both modifications to be done in Jan 2003

- R. Moore - FNAL

- RUPAC-2002

## Beam-Beam Effects at 980 GeV

- Suffered 10-20% pbar loss during squeeze
- During transition from injection to collision helix
- Minimum beam separation was only ~1.8
- New helix increased min beam separation to ~3
- Pbar loss during essentially eliminated
-  lifetime  9-10 hrs in first two hours of store
- Increase helix separation to reduce long-range       beam-beam effects?    (72 “parasitic” crossings)
- Pbar tune shift depends position in train                                       	  _optimize tunes for most bunches_
- Use electron lens to compensate pbar tune shifts

- R. Moore - FNAL

- RUPAC-2002

## Pbar Loss During Squeeze

**Pbar **
**intensity**

**Old helix**

**New helix**

**Low ******** quad current**

**> 10% loss @ min**
**beam separation**

**140  sec**

**> 10% loss @ min**
**beam separation**

_**No loss**_** @ min**
**beam separation**

- R. Moore - FNAL

- RUPAC-2002

## Proton Transverse Instability

- Intensity-dependent: appears  ~170 E9/bunch
- Single bunch weak head-tail phenomenon?
- Can occur at 150 GeV, up ramp, at 980 GeV
- Schottky powers rise quickly  ~ 200 ms
- Proton and pbar emittances blow up  lower 
- Try to prevent/control instability via:
- Raising chromaticities
- Adjusting coupling and tunes
- Limiting p intensity to  ~240 E9/bunch at injection
- Constructing bunch-by-bunch transverse dampers
- Want lower chromaticity at injection, collisions

- R. Moore - FNAL

- RUPAC-2002

## Transverse Instability On Ramp

**horizontal**
**Schottky power**
**vertical**

**Beam energy**

**Instability**

- R. Moore - FNAL

- RUPAC-2002

## Tevatron Electron Lens (TEL)

- Designed to compensate beam-beam tune shift of pbars
- Fire 10 keV e**-** beam in time with pbar bunches
- Achieved tune shifts up to _0.009_ while maintaining                  beam lifetime of  _~100  hr_             (proton-only studies)
- Not yet used operationally for compensation
- Used to remove DC beam from abort gaps
- Phenomenon not yet understood causing beam to leak out             of RF buckets     (RF phase error?)
- Kickers hit DC beam in gaps, caused repeated quenches
- Fire TEL in gaps every 7 turns to excite resonance
- Reduces background at B0 collision hall

- R. Moore - FNAL

- RUPAC-2002

## Removing DC beam with TEL

**TEL current**

**Bunched beam **
**intensity**

**DC beam**
**intensity**

**Loss rate**
**at B0 IP**

**TEL on  ******

**DC beam loss**

**2200 sec**

- R. Moore - FNAL

- RUPAC-2002

## Tune and Coupling Drifts at 150 GeV

- Chromaticity drift from b2 component in dipoles          well-known from Run I
- Compensated automatically by varying sextupole currents
- New for Run II, tune and coupling also vary logarithmically after returning to injection energy
- Makes injection tune-up more difficult
- Likely caused by persistent currents in the superconducting dipoles and quadrupoles
- Recently implemented compensation with normal, skew quads similar to chromaticity scheme
- Tune drift now < 0.001 after 3 hours
- Coupling drift not measurable

- R. Moore - FNAL

- RUPAC-2002

## Tune Drift @ 150 GeV

- R. Moore - FNAL

- RUPAC-2002

## Coupling Drift @ 150 GeV

- R. Moore - FNAL

- RUPAC-2002

## Longitudinal Instability

- Proton bunch length blow-ups during stores
- Intensity-dependent
- Usually only one or a few bunches would suffer
- Problem solved by _bunch-by-bunch longitudinal dampers_ to damp mode 0 and mode 1 oscillations
- “Dancing bunches” in uncoalesced beam
- Large amplitude oscillations that slowly decay (minutes), depend on bunch position
- Bunches seem coupled weakly
- Developing model of this curious phenomenon

- R. Moore - FNAL

- RUPAC-2002

## Bunch Length Evolution During Stores

**Before dampers**

**With dampers**

**blow up ~10%**

**Bunch**
**length**
**(ns)**

**DC**
**Intensity**
**(E12)**

**no sudden jumps over entire store**

- R. Moore - FNAL

- RUPAC-2002

## Dancing Bunches

**Mountain Range Display**

**19 ns**

- Beam in 30 buckets
- 100 Tevatron turns   (~2 ms) between traces
- Synch freq ~ 30 Hz
- Oscillation amplitude depends on bunch, changes slowly with time

- R. Moore - FNAL

- RUPAC-2002

## Tevatron Reliability

- 195/283 stores ended   _intentionally_         average duration = 17.4 hrs
-   88/283 stores ended _unintentionally_       average duration =   9.7 hrs

- R. Moore - FNAL

- RUPAC-2002

## Run IIa Plans

- 6 week shutdown in Jan 2003
- Recycler vacuum work
- Tevatron: replace C0 lambertsons, modify A0 lattice
- Total 200 pb-1 by Jun 1 2003 for conferences
- Integrate Recycler into Operations late in 2003
- Pbar shots to Tevatron
- Recycle pbars left after HEP stores
- Run IIa goal = deliver 2 fb-1
- Long shutdown for Run IIb preparations
- Accelerator and experiments

- R. Moore - FNAL

- RUPAC-2002

## Run IIb Plans

- Reach 1-5 E32 cm**-2** s**-1** peak luminosity
- Need more pbars!
- Slip-stacking in MI  more p on pbar production target
- Electron cooling in RR for 5 E12 pbars
- Shorter bunch spacing in Tevatron?
- Concerned about beam-beam effects @ 132 ns spacing
- Studying 264 ns and luminosity-leveling with 396 ns
- Need more separators, faster injection kickers
- Crossing angle at IPs

- R. Moore - FNAL

- RUPAC-2002

## Summary

- Many changes in complex for Run II
- Initial Run II progress slow, getting better
- Issues: beam-beam effects, instability, Recycler
- Complex running well lately
- Now consistently above Run I peak luminosities
- Recycler making progress
- Delivered over 90 pb-1 to the experiments
- Getting to higher luminosities
- control proton instability in Tevatron
- get more pbars to collisions  (stack faster, improve efficiencies)
- Looking forward to delivering 2 fb-1 and beyond!

- R. Moore - FNAL

- RUPAC-2002