Laboratory Overview

The research program of the University at Stony Brook Nuclear Structure Laboratory began in mid 1968 with the first operation of the 9 Million Volt (MV) Tandem Van de Graaff, purchased from the High Voltage Engineering Corporation. NSL faculty used this accelerator for study of nuclei using light-ion and light heavy-ion beams. In 1975, NSL entered into a collaboration with Cal-Tech to develop a booster using a novel Superconducting Resonant Cavity technology to extend the range of phenomena accessible to this accelerator.

Since 1983 the USB NSL has operated a Superconducting Linear Accelerator, the first of its kind at any university in the world, for production of heavy-ion beams with sufficient energy to create nuclear reactions with even the heaviest elements.

The accelerator works as follows: negative ions of the projectile species are produced by a General Ionex 860A inverted geometry sputter ion source, are mass selected and then pre-accelerated on a 400,000 Volt injector deck. The ions shoot to the high voltage terminal of a 9 Million Volt Tandem Van de Graaff generator, thereby gaining 9 MeV of energy. In the Terminal, electrons are stripped away and the ions, now positive, are accelerated again on their return to ground potential. These beams, typically travelling at 5% of the speed of light, are then injected into the 150 MegaHertz Superconducting Linac where each of the 40 independently phased RF cavities accelerate the beam in turn. The ions, now at 10-12% of light speed, fly to the Target Room where they hit a target; an array of detection equipment captures the products of these collisions.

Negative-ion injector specifications

• Source type (cesium sputter): Middleton/GIC Model 860
• Support-gas: Middleton method
• Extraction voltage: 15 kV
• Operating pre-accel voltage: 200-250 kV
• Pre-accel stability: 10 Volts p-p
• Inflection magnet: Double-focussing, R=14 inch
• Mass-energy product: 5 MeV-AMU
• Mass resolution (M/delta M): ~130
• Intensity capability: 30 microAmps ⁵⁸Ni
• Total beam energy spread (estimated): < 100 Volts p-p
• Average source maintenance interval: 600 hours

Tandem van de Graaff specifications

• Type: HVEC FN-8
• Charging system: HVEC Laddertron
• Accelerator tubes: Dowlish titanium spiral-I.F.
• Terminal pumping: Ti sublimator / 6 x 20 grams
• Stripper foils: Arizona 5 microgram per square cm (100 foils)
• Operating voltage (as LINAC injector): 8.5-9.0 MV
• Particle transmission (foil stripping): 90% (Oxygen) / 70% (Nickel)
• Intensity capability (total beam current): 10 microAmp
• Terminal voltage stability (regulated): 1 kV p-p

Superconducting linac specifications

• Overall length: 18 meters
• Cavities:
  • 16 beta=0.068 quarter wave resonators in 4 cryostats
  • 24 beta=0.101 split loop resonators in 8 cryostats
• Operating frequency: 150.4 MHz
• Time structure (continuous duty factor): 106 nsec pulse rep. time
• Phase control: Direct Rf feedback
• Control amplifiers: 200 Watts/resonator
• Focussing: Quadrupole doublets (12)
• Cooling method: Pool-boiling liquid helium
• Installed refrigeration: ~500 Watts (4.5 K)
• Design-goal resonator field level: 3.0 MV/m
• Equivalent electrostatic accelerator: 20 MV tandem
• Total operating hours (April 1983 - May 1996): >40,000
• Average operating field level:
  • 2.5 MV/m (high-beta split loop resonators)
  • 2.6 MV/m (low-beta quarter wave resonators)
• Present maximum energy gain per charge: 14 MeV/q
• Highest energies to date
  • (⁹⁰Zr): 396 MeV
  • (⁷³Ge): 330 MeV
  • (³⁷Cl): 276 MeV
  • (³²S): 264 MeV
• Highest energy per nucleon
  • (¹⁶O): 10.5 MeV/A
  • (¹²C): 11 MeV/A
• Maximum-practical output beam intensity:
  • 300 pnA (^16,18O or ¹⁹F)
  • 5 pnA (⁵⁸Ni)
  Limited by maximum-allowable tandem beam current.
• System phase-lock fraction : > 99%
• Particle transmission (all ions): > 95%
• Linac output pulse width:
  • 85 psec (FWHM, ¹²C)
  • 155 psec (FWHM, ³²S, gas-stripping)
• Liquid helium running heat load (14 MeV/q): 240 Watts
• Liquid nitrogen consumption (linac on): 80 liters/hour
  Includes 50 liters/hour for He refrigerator pre-cool.

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