High Field Upgrade

Last updated: 16 Sept 2008 moller@jlab.org

The plan is to upgrade the Moller polarimeter with the high field magnet, following the Hall C scheme. This includes the following modifications:

Manufacturing of a new target holder/mover.
Removal of the present target holder.
Installation of the superconducting magnet and a new target holder.
New mover software (accelerator).
A new scintillation aperture counter.
Electronics upgrade.

Target Holder/Mover

The new device should provide the following remotely controlled operations:

Put 3 targets (iron foils 1-5µm thick) into the beam. The foils are stretched perpendicular to the beam. These foils will be magnetized in a 3-4T magnetic field (along the beam) provided by the superconducting magnet. They will be used for the regular longitudinal polarization measurements.
Put a transversely polarized target into the beam. This target is an iron foil about 30µm thick, positioned perpendicular to the beam and polarized along the foil by a small permanent magnet. This foil and the permanent magnet are mounted on a rotary stage which rotates it around the beam axis. This device allows to measure the transverse component of the beam polarization. The superconducting magnet must be turned off when the transverse target is in the beam, or close to it.

The new mover will use a rack&pinion actuator RPL-.75-30/MS/W from Thermionics.

Status

Removal of the present target holder.
Installation of the superconducting magnet and a new target holder.
- The magnet has been tested the last summer.
- New target holder has been built and partly tested. Left to be done:
  - Wiring, connections, endswitches, controls (Roman P., from Oct 2008)
  - Further mechanical adjustments (Roman, myself)
  - Test in a magnetic field
  - Mounting of the foils (target group)
- Magnet power supply, cryo controls - ordered
- Install the power supply (a size of a NIM crate) (Ed)
- Cables for the magnet
- Design of the cryo connections (Alan G.) ?
  - LN2 line to the magnet
  - LHe line (from the septa adapter) to an intermediate dewar
  - Intermediate dewar: cold return, a line to the magnet
  - Magnet: warm return
  - The magnet consumes about 1 liter of LHe per hour
- Design of the magnet support (Alan) ? It would be VERY useful to be able to move the magnet vertically by 3-5mm to simplify the beam tune. The coil center is not well defined.
- Design of the vacuum connection (partly exists) (Alan)
- Manufacturing/purchasing of the support and cryo components
- Adapt the FSD controls (Roman)
- New EDM controls (accelerator)
Beam
- Pulsed beam regime has been tested
- New readout for BCM, BPM for 1 ms pulses
Detector:
- 4 scintillator counters about 4x16x1.25 cm³ with special light guides and PMTs
Electronics
- Finish the work on the discriminators (Roman)
- Trigger logic using CAEN 1495 - will the FPGA die of radiation?
- Can one use the 500 MHz FADC for everything (also FPGA)?
- New ADC or VtoF for the BPMs, BCMs, for 1 ms - 30 ms pulses.

Roman will come in October for 6 months, Sasha a few months later. It total one man-year, plus myself.