# Presentation: 505341

## Hadron beam intensity limits

- Wolfram Fischer
- Thanks to:
- M. Blaskiewicz, A. Fedotov, C. Montag, L. Merminga, V. Ptitsyn
- eRHIC ZDR authors
- EIC2006, Brookhaven National Laboratory, 17 July 2006.

## Outline

- Parameters for ELIC and eRHIC
- Electron clouds
- Beam-beam effects
- Instabilities
- Intrabeam scattering
- Space charge
- Resistive wall heating

## Not covered

- Cooling of high energy ion beams[Talks by V. Lebedev, A. Zholents] – total p-beam currents in ELIC and eRHIC are comparable (~1A)
- Polarization issues of protons and light ions
- Injection, acceleration
- IR, stored energy issues, beam loss at max [Talk J. Seeman, Tue 5:00-6:00pm Discussion]
- Radiation safety
- Technical challenges of crab cavities in ELIC[Session 3A, Tue 1:30-3:00pm Discussion]

## ELIC (linac-ring)

- Linac 200 MeV, pre-booster 3 GeV, booster 20 GeV

## eRHIC (linac-ring)

**eRHIC detector**

**Place for doubling energy linac**

- ERL (5-10 GeV e-)

- For multiple passes:
- vertical separation of the arcs

**PHENIX**

**STAR**

**STAR**

**RF**

**e-cooling**

**beam dump**

- Wolfram Fischer

## ELIC and eRHIC parameters

- Use only limited number of parameter sets:
- A linac-ring and a ring-ring version for both machines
- Protons, mostly at highest energy (p bunches have largest no of charges, largest beam-beam parameter)
- Beam parameters for highest luminosity

## ELIC and eRHIC parameters (p-beam only)

|  |  | ELIC |  | eRHIC |  |
| --- | --- | --- | --- | --- | --- |
| Parameter p-beam | unit | ERL | ring-ring | ERL | ring-ring |
| Circumference | m | 1500 |  | 3833 |  |
| Energy E |  GeV | 150 |  | 250 |  |
| Bunch spacing tb |  ns | 0.67 |  | 35.5 |  |
| Bunch intensity Nb |  109 | 4.0 |  | 200 | 100 |
| Norm. rms emitt. x/y |  mm mrad | 1.0 / 0.04 |  | 2.5 / 2.5 |  |
| Bunch length, rms lb |  mm | 5.0 |  | 200 |  |
| Vert. beam-beam /IP | ... | 0.01 (ver) |  | 0.006 (hor) |  |
| No of interaction points  | ...  | 4(e) |  | 1(e) + 2(p) |  |
| Peak luminosity L/IP |  1032cm-2s-1 | 770 |  | 18 | 4.4 |

- [ELIC parameters courtesy of L. Merminga.]

**Notes:**
ELIC: 200 MeV linac, 3 GeV pre-booster, 20 GeV booster (talk Y. Derbenev, 2003)

## ELIC and eRHIC

**Both ELIC and eRHIC****have versions with 10********higher luminosity**

## Selected machines with electron clouds

|  | Bunch intensity Nb [1011 e+ or p+] | Bunch spacing tb [ns] |
| --- | --- | --- |
| KEKB | 0.6 |  6.0 |
| PEP-II | 0.7 | 4.2 |
| DANE | 0.25 | 2.7 |
| SPS/LHC | 1.1 | 25 |
| RHIC | 1.4 | 108 |
| eRHIC | 2.0 | 36 |
| ELIC | 0.04 | 0.67 |

- [ECLOUD04 proceeding.]

## Selected machines with electron clouds

** ****more e-cloud**

** ****less e-cloud**

## RHIC e-clouds caused dynamic pressure rise

- S.Y. Zhang et al., EPAC06

- Dynamic pressure rise caused by electron clouds
- Upgraded warm and cold vacuum system:
-  installed 430m of NEG pipes (~700m warm sections)
-  reduced pressure in cold section to 1e-7 Torr before cool-down
- Dynamic pressure currently not a concern in operation

## RHIC e-clouds can lower stability threshold

- Crossing transition with slowly ramping sc. Magnets(all ions except protons)
-  Instability limits bunch intensities for ions (~1.5 – 2.01011 e )
-  Instability is fast (=15 ms), transverse, single bunch
-  t-jump implemented
- Octupoles near transition
- Chromaticity control(need -jump for higher  bunch intensities)
-  Electron clouds can lower stability threshold, will gain more operational experience in next ion run

## E-cloud simulation for RHIC (2)

- CSEC (by M. Blaskiewicz) – requires cylindrical symmetry, 	faster than ECLOUD, POSINST
- RHIC warm, field free region, single beam

*N*b=2.01011, *t*b=108ns, *l*b=5ns, max = 2.1

## E-cloud simulation for RHIC (2)

- CSEC (by M. Blaskiewicz) – requires cylindrical symmetry, 	faster than ECLOUD, POSINST
- RHIC warm, field free region, single beam

*N*b=2.01011, *t*b=108ns, *l*b=5ns, max = 2.1

## E-cloud in current RHIC vs. eRHIC

*N*b=2.01011
-     ** ****108 ns ****(3 buckets)**** spacing**
*N*b=1.41011

- Expect serious e-cloud problems for *N*b=2.01011 and 36 ns bunch spacing
- (Analysis needed for warm double beam, and cold regions also.)

*N*b=2.01011
-     ** ****36 ns ****(1 bucket)**** spacing**
*                             **N*b=1.01011

## Electron and ion effects in ELIC

- CSEC shows _no_ electron multipacting in ELIC
- Bunches with short spacing and low bunch charge behave like coasting beam
- ISR like problems possible
- Electron accumulation from beam loss or rest gas ionization can lead to instabilities(need gaps and/or clearing electrodes)
- Pressure instability (rest gas ionization, ion acceleration in beam potential, molecular desorption after ion impact on wall, etc.)
- [beam currents in ELIC 1A, ISR 60A]

## Slide from a talk by V. Dudnikov (2006)

** ****Damped by extensive system of electrostatic clearing electrodes**

- ISR, coasting proton beam,  ~1972
- (R. Calder, E. Fischer, O. Grobner, E. Jones)

**excitation of nonlinear**
**resonances; gradual**
**beam blow up similar**
**to multiple scattering**

- beam induced signal
- from a pick up showing
- coupled e-p oscillation;
- beam current is 12 A and
- beam energy 26 GeV

- 2x10-11 Torr,
- 3.5% neutralization,
- Q=0.015

## Beam-beam limitation (1)

-  Current beam-beam induced tune spread in RHIC Qbb,tot = 0.012
-  SPS, Tevatron reached Qbb,tot  0.025
-  No hadron collider stores beam on resonances of order 10 or lower

- Current (Run-6) RHIC conditions

## Beam-beam limitation (2)

|  |  | ELIC |  | eRHIC |  |
| --- | --- | --- | --- | --- | --- |
| Parameter p-beam | unit | ERL | ring-ring | ERL | ring-ring |
| Head-on interactions |  |  |  |  |  |
| Bunch intensity Nb |  109 | 4.0 |  | 200 | 100 |
| Norm. rms emitt. x/y |  mm mrad | 1.0 / 0.04 |  | 2.5 / 2.5 |  |
| Vert. beam-beam /IP | ... | 0.01 (ver) |  | 0.006 (hor) |  |
| No of interaction points  | ...  | 4(e) |  | 1(e) + 2(p) |  |
| Long-range interactions |  |  |  |  |  |
| Crossing angle | mrad | 100 (hor) |  | 0 |  |
| Separation, 1st LR encounter | mm | 10 / 200 |  | — |  |

## Beam-beam limitations (3)

-    Coherent effects now observed in hadron rings (RHIC, Tevatron, HERA) could become operational problem for large , few bunches beam-beam coupled

- First observationof coherent modesin hadron ring,RHIC, Jan 2002

- More on coherent effects: J. Shi?

## Beam-beam compensation

**Head-on beam-beam compensation**
- Need electron beam (for p+), amplitude dependence of beam-beam force cannot be matched with magnets
- 4-beam e+e machine DCI (~1970) not successful(failure usually attributed to coherent effects)
- May become a task in US LARP
**Long-range compensation**
- E-lens in Tevatron (not yet used for bb compensation in ops)[V. Shiltsev et al.]
- Wires (proposed for LHC, tested in SPS, planned tests in RHIC – US LARP)[J.-P. Koutchouk et al.]
- Partial compensation with wire demonstrated in DANE[K. Milardi et al. EPAC06]

- More on beam-beam: J. Qiang, J. Shi

## Intrabeam scattering (1)

-  Cooling of protons not yet fully assessed
- [Did not find IBS calculations for ELIC.]

- Calculations byA. Fedotov,
- using Betacool.

## Intrabeam scattering (2)

-   IBS dominates lifetime over many other effects(competes with beam-beam + other nonlinearities):
- For p-beam in eRHIC:
- Luminosity (burn-off): L >> 100 h
- Restgas inelastic scattering	: Nb  200 h
- Emittance growth from restgas scattering:   15 h
- Emittance growth from bb elast. scattering:   2000 h

- Used RHIC II pp-calculations, BNL C-A/AP/235 (2006).

## Instabilities – single bunch

|  |  | ELIC |  | eRHIC |  |
| --- | --- | --- | --- | --- | --- |
| Parameter p-beam | unit | ERL | ring-ring | ERL | ring-ring |
| Energy E |  GeV | 150 |  | 250 |  |
| Bunch intensity Nb |  109 | 4.0 |  | 200 | 100 |
| Norm. rms emitt. x/y |  mm mrad | 1.0 / 0.04 |  | 2.5 / 2.5 |  |
| Bunch length, rms lb |  mm | 5.0 |  | 200 |  |
| Peak current Ip |  A | 15 |  | 20 | 10 |

- Had stored p-bunches with *N*b>21011 and Ip > 5A at injection. Most problematic at low energy, can use long bunches.**Expect no fundamental ****problem.**

## Instabilities – multi-bunch

**Expect no fundamental problem with multi-bunch instabilities in ****RHIC. [Can make similar argument for ELIC.]**

- M. Blaskiewicz

- tune shift relatively flat
- <5ms growth time, could be damped

- If no single-bunch instability, tune shifts from long-range wake fieldsmust be larger than tune shifts from short range wake fields

-  RHIC impedance model includes resistive    wall, abort kickers, unshielded bellows.
-  May be too low by up to a factor 3
-  Calculation for injection (worst case)

## Space charge

|  |  | ELIC |  | eRHIC |  |
| --- | --- | --- | --- | --- | --- |
| Parameter p-beam | unit | ERL | ring-ring | ERL | ring-ring |
| Energy E |  GeV | 30 |  | 25 |  |
| Bunch intensity Nb |  109 | 4.0 |  | 200 | 100 |
| Norm. rms emitt. x/y |  mm mrad | 1.0 / 0.04 |  | 2.5 / 2.5 |  |
| Bunch length, rms lb |  mm | 5.0 |  | 200 |  |
| Laslett tune shift |  ... | 0.06 |  |  0.08 |  0.04 |

**May be problematic.**

- Parameters for low energy operation, keep bunch length ofhigh energy operation.

## Heat load in beam pipe wall

|  |  | ELIC |  | eRHIC |  |
| --- | --- | --- | --- | --- | --- |
| Parameter p-beam | unit | ERL | ring-ring | ERL | ring-ring |
| Bunch intensity Nb |  109 | 4.0 |  | 200 | 100 |
| No of bunches |  ... | 7500 |  | 360 | 360 |
| Bunch length, rms lb |  mm | 5.0 |  | 200 |  |
| Total power dissipation | kW | 11.3 |  | 3.1 | 0.8 |
| Power per unit length | W/m | 7.5 |  | 0.8 | 0.2 |

- assuming same beam pipe as RHIC(stainless steel at 4K),could use Cu for reduction

- +possible e-cloud heat load,
- current capacity  0.5 W/m

## Summary

- Considered hadron beam limitations from:
- Electron cloud
- Beam-beam
- Instabilities
- Intrabeam scattering
- Space charge
- Resistive wall heating
- Of concern appear:
- Electron cloud in RHIC for *N*b=2.01011 and 36 ns bunch spacing
- Beam-beam in ELIC with more than 2 IPs
- Intrabeam scattering in RHIC (ELIC?)
- Possibly space charge at low energies
- Significant challenges for cooling, crab cavities (ELIC)