Electron Lens Test Stand

Panoramic picture of the electron lens test stand taken by Valentina Previtali on Dec 19, 2012

The Fermilab electron-lens test stand is a laboratory located in the lower linac gallery (room XGW-003B). It is used for advanced accelerator R&D. Originally developed as a test stand for Tevatron electron lenses, it is now also used to study high-perveance electron guns, hollow electron beams, trapped plasma columns, and electron-cloud diagnostics.

It has an area of 1,000-sq-ft, which includes experimental apparatus (50 sq ft), power supplies and control racks (300 sq ft), work areas and cabinets (300 sq ft), and computer desks (120 sq ft).


The main experimental apparatus consists of a pulsed electron gun (labeled as 1 in the figure), a straight beamline (5) equipped with pickup electrodes, and a water-cooled collector (2). The vacuum chamber is surrounded by 3 solenoids: the gun solenoid (4, left), the main solenoid (3), and the collector solenoid (4, right). Magnetic correctors are used to steer the electron beam. End-plates (6) are used to improve the uniformity of the axial magnetic field. The device is supported and aligned on a platform (8).

Test stand layout Test stand layout with dimensions
Schematic diagram Dimensions
Scanned technical drawing of the electrodes Layout of electrodes
Pickup electrodes: scan Pickup electrodes: logbook
Layout of magnetic correctors Calibration of solenoids
Magnetic correctors Solenoid calibration

Measurements of magnetic field vs. longitudinal coordinate (Nov. 1998).



Most of the electrical power is used by the 4 solenoid power supplies (PEI 150-5, Model SR 1029, 150 kW, 5 kA). They are connected to separate AC feeds capable of providing a total of 360 kW. In steady state and at maximum magnetic field, the water-cooled solenoids must be able to dissipate about 210 kW.

Cooling water

A 18-MOhm low-conductivity water circuit provides cooling for the power supplies, solenoids, and collector. The supply and return lines are made of 2-in copper pipes. Pressures are 120 psi (supply) and 40 psi (return). The total flow is approximately 60 gal/min.

Schematic diagram of the Booster 95 Low-Conductivity Water system
Booster 95 LCW system

Vacuum System

Pumping stations Ion pumps
  • FNAL 20 l/s diode
  • Varian VacIon 55 diode [manual]
  • Varian VacIon 75 diode [manual]
  • Varian MidiVac controller [manual]
Pressure measurement

Bottled nitrogen gas is available for purging the vacuum chamber at atmosferic pressure.

High voltage

Electron-gun high-voltage power supply 10 kV / 2.5 mA, Bertan (Spellman) 225 [data sheet] [manual]

The electron gun anode is pulsed with a DEI PVX-4110 10-kV modulator [manual].

E-gun HV distribution

Controls and data acquisition

The laboratory is connected to the Accelerator Division controls system (ACNET) via an Internet Rack Monitor (IRM597,,, uptime device G:S597UT).

Java ACNET Console. Main parameters are collected in parameter page T75/support, subpages 6-8.

  • Windows PC: ( decommissioned
  • Linux PC: (
  • Oscilloscope (Tektronix TDS3034B)
    • (
    • subnet mask:
    • gateway:
    • DNS:,
    • WINS:,
    • Instructions on how to configure the AD Controls proxy and SSH tunnel
  • Temperature measurement
    • Lab temperature (J-type thermocouple) Z:LABTMP
    • Gun flange (K-type thermocouple): Multimeter TENMA 72-4030 [data sheet]

Profile measurements

Electron beam current-density profiles are measured by recording the average current through the collector pinhole as a function of the setting of the horizontal and vertical magnetic correctors.

The pinhole current Z:BC1AD3 is read by a Programmable Logic Controller through analog module DirectLogic 205 F2-08AD-2 [manual]. At the PLC input, a parallel RC filter (R = 1 Mohm, C = 0.22 uF) is used to average the current and to amplify the voltage.

Data is acquired through ACNET with this ACL script running on a console. This is a sample output file. Profile measurements can be displayed by analyzing the output files with the following R script.