# Presentation: 219047

## A RHIC Low-Energy Test Run With Protons Todd Satogata(W. Fischer, T. Roser, J. DeLong, M. Brennan, D. Bruno, and others)April 11, 2006Driven by discussions at the“Can We Discover the QCD Critical Point at RHIC?” Workshop

-  Scope
-  Parameters
-  Schedule

## Scope

- Significant interest in RHIC heavy ion collisions with c.m. energy in the range s= 5-50 AGeV
- Corresponds to Au beam =2.68 to 26.8
- Nominal Au injection is =10.52, already below design =12.6
- Recommended energies from Krishna Rajagopal’s talk:
- sNN = 5, 6.27, 7.62, 8.77, 12.3, 18, 28 AGeV
- PHENIX RBUP requested low-energy proton collisions
- s = 22.5 GeV  equivalent to Au sNN = 9.18 AGeV
- Open machine issues
- How does machine field quality degrade  at lower energies?
- Can we correct optics with current power supply configuration?
- Are any power supply regulation/hardware changes required?
- How do we test changes necessary for RHIC RF?

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## Proton/Gold parameters at same rigidity

|  | Protons | Gold (eq) |
| --- | --- | --- |
| s [GeV] | 22.5 | 9.18 |
| Beam energy [GeV] | 11.25 | 4.59 |
| Beam kinetic energy [GeV] | 10.312 | 3.660 |
| Relativistic  | 11.99 | 4.93 |
| Relativistic  | 0.997 | 0.979 |
| Momentum [GeV/c] | 11.211 | 4.496 |
| B [T-m] | 37.40 | 37.40 |
| Injection current scaling | 0.471 | 0.384 |
| Main dipole current [A] | 217.7 | 217.7 |
| Main quad current [A] | 202.6 | 202.6 |
| Revolution frequency [Hz] | 77924 | 76571 |
| RF frequency [MHz, h=360] | 28.053 | 27.566 |

- Gold energy for same rigidity is near middle of Krishna’s list
- Tests magnets and power supplies at less than half of normal injection current
- Reasonably balance for initial testing, performance extrapolation
- Does NOT require change to RHIC harmonic number or substantial reconfiguration of RHIC RF
- h=366 gives RHIC RF frequency of 28.03 MHz

- RHIC RF frequency range is 27.98-28.17 MHz

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## Testing RHIC RF, h=363

|  | Protons | Gold (eq) |
| --- | --- | --- |
| s [GeV] | 15.0 | 6.25 |
| Beam energy [GeV] | 7.50 | 3.13 |
| Beam kinetic energy [GeV] | 6.56 | 2.19 |
| Relativistic  | 7.99 | 3.36 |
| Relativistic  | 0.992 | 0.955 |
| Momentum [GeV/c] | 7.442 | 2.984 |
| B [T-m] | 24.82 | 24.82 |
| Injection current scaling | 0.255 | 0.255 |
| Main dipole current [A] | 144.5 | 144.5 |
| Main quad current [A] | 134.5 | 134.5 |
| Revolution frequency [Hz] | 77582 | 74647 |
| RF frequency [MHz, h=363] | 28.162 | 27.097 |

- Alternate RHIC RF harmonic numbers are required for low-energy ion collisions
- Must be divisible by 3 to have  collisions at both experiments
- Only code changes, no hardware changes
- h=363 is testable with proton beam at energy/rigidity that are  still within low-energy range of interest
- But aggressive rigidity
- RF personnel state that cogging and harmonic number  changes can be completely tested during shutdown without beam time

- RHIC RF frequency range is 27.98-28.17 MHz

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## Suggested low energy collision setup schedule

- Scale existing injection optics (*=10m) to B =37.40
- Zero out transition jump quadrupoles to improve optics
- Assume AGS setup has been completed on separate user
- Hysteresis cycles (1h)
- Tune ATR, establish injection, circulating beam (3h)
- Establish RF capture, instrumentation setup, tune for lifetime (4h)
- Tune scans (1-2h)
- Power supply stability evaluation (parasitic)
- Optics measurements (1h) and correction/verification (3h)
- Steer to optimize collisions (3-4h) using experiment BBCs
- Lifetime objective is > 30min (longer than fill time)
- Contingency (~6h)

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## Summary

- There is substantial interest in RHIC operations at low energies (sNN= 5-50 AGeV)
- A low-energy proton test run of ~24h (with contingency) provides important information on program feasibility
- s = 22.5 GeV provides best balance of objectives with reasonable likelihood of success
- Low-current field quality measurements and optics correction are  the most important objectives.
- Other objectives include power supply stability evaluation, working point evaluation, and collision steering
- Ready for testing within three weeks after go-ahead
- RHIC RF harmonic number changes will be tested without beam during summer shutdown
- Testing RF changes with protons requires significantly lower energy (s = 15 GeV, corresponding to sNN = 6.25 AGeV)

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## ===============

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## 2001 9.8 GeV/u Au collisions

- 2 days of 9.8 GeV/u collisions
- 0.4 b-1 integrated luminosity
- *=3m by necessity
- 60-90 minute stores
- 56 Au bunches, 0.6x109/bunch
- 10-30 Hz ZDC rates
- IBS and aperture dominated beam and luminosity lifetime
- Another run at this energy may improve this by factor of 2-5
- 1.0+x109/bunch
- Raise * to improve lifetime
- RHIC is best used as a storage ring collider below beam energies of ~12 GeV/u

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## Beam Studies for Low-Energy Injection

- ~1 day of studies required in run before low-energy operations
- Initial studies
- Trivially scale nominal injection to lower energies
- Provides reality check of power supplies, optics
- Test injection, establish circulating beam, optimize lifetime
- Initial global optics measurements, field quality, tune scan, energy resolution/momentum aperture
- IBS growth time study require 3-6 hours extra time
- All but IBS growth evaluation can be done with Run6 p
- Later studies
- IBS modification lattice development
- Field quality and detailed optics measurement/correction

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## Initial Machine Projections

- Scaling laws apply above injection energies
- When aperture dominated:
- Peak luminosity  2
- No clear scaling laws apply below injection energies
- Injected beam already fills aperture
- Magnetic field quality degrades very quickly
- Power supply regulation
- Strawman model
- Peak luminosity  3-4

**Expected full-vertex minbias rate [Hz]**

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## Initial Machine Projections

| Mode | Beam Energy
[GeV/u] | Nbunches  | Ions/bunch [9]  | *[m]  | Emittance
[m]  | Lpeak
[cm-2s-1] |
| --- | --- | --- | --- | --- | --- | --- |
| Au-Au 2001-2 | 9.8 | 55 | 0.6 | 3 | 15  | 8.01024 |
| Au-Au 2003-4 | 31.2 | 45 | 1.0 | 3 | 15-30 | 1.21026 |
| Au-Au | 9.8 | 55 | 1.2 | 10 | 15-40 | 1.01025 |
| Au-Au | 2.5 | 55 | 1.0 | 10 | 15-30 | 1.11023 |
| Au-Au | 25 | 55 | 1.2 | 3 | 15-40 | 2.01026 |

- Assumes expected luminosity scaling as 3 below 9.8 GeV/u
- */aperture and integrated luminosity tradeoffs must be studied
- Projections do not include potential improvements
- Electron and stochastic cooling (peak and integrated luminosity)
- Lattice modifications to mitigate IBS (integrated luminosity)
- Total bunch intensity from vacuum improvements (peak luminosity)
- Small set of specific energies (and species?) should be a workshop deliverable for planning

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## Low-Energy Magnetic Field Quality

- Magnet currents scale with rigidity B which scale with ****
- Field quality deteriorates rapidly at very low currents
- Currently have no magnet measurements at very low currents, few at low energy
- Must extrapolate field behavior for simulations
- Low-current magnet measurements are a priority

| Total
Energy |  | B | Dipole Current |
| --- | --- | --- | --- |
| 9.8 GeV/u | 10.52 | 81.11 | 430 A |
| 2.5 GeV/u | 2.68 | 20.69 | 110 A |

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006

## Power Supply Regulation Issues

- Several power supply issues
- Chromaticity sextupoles
- Main power supplies
- Sextupoles: 0.6-0.7 A -> 0.15-0.2 A
- CMOS regulation, works  to 0.01 A
- Study option of using only some sextupoles with higher current
- Aperture and lifetime concerns
- Correction of large main dipole b2
- Main dipoles: 430 A -> 110 A
- Requires testing to check regulation
- Will test during Run6 maintenance
- Pulsed injection/extraction kickers
- May have low-voltage limitations

- T. Satogata - RHIC Low-Energy Test Run

- April 11, 2006