Figure 2: A view showing the
TRIUMF emittance/phase space scanner mounted in a vacuum box.

 

Emittance Scanner

D-Pace, Inc. has licensed an Allison type emittance/phase space scanner technology from TRIUMF. The emittance scanner provides you with more information than just the emittance. It can provide you with the full phase space characteristics of a charged particle beam, such as the phase space distribution in the (x, x1intensity) of (y, y1intensity). In short, it provides a detailed characterization of your low energy charged particle beams.An example of the TRIUMF emittance/phase space scanner is shown in Figures 2 & 3. For a more detailed description of the emittance scanner please see this pdf.


Figure 3: A picture showing the entrance slit in the “scanner head”. In this orientation, the scanner head is swept vertically in position, and the electric beam trajectory sweep is in the vertical direction also. Therefore, the beam intensity distribution in the (y, y’) phase plane is measured in this case.

Features

The TRIUMF Allison-type scanner technology licensed by D-Pace, Inc. provides:

  • the magnitude of the emittance in either the xx’ or yy’ phase planes as a function of a percentage of the beam contained within the ellipse corresponding to the emittance.
  • the beam intensity distribution in the xx’ phase plane, or by rotating the device by 90 degrees (or by utilizing a second scanner) one can measure the beam intensity distribution in the yy’ phase plane.
  • a 3D representation which can be visualized with a 3D plot, or a contour plot. Of course, beam intensity as a function of either x or x’ (or y or y’) can also be displayed as a 2D plot.
  • the software associated with the scanner can also determine phase space ellipses representing the ion beam in either the xx’ or yy’ phase plane that contain any percentage of the total beam intensity desired.
  • a 4rms emittance can be computed. The corresponding beam sigma matrix co-ordinates can be computed for any ellipse.

Application

This information is very important. To accurately model what will happen when a charged particle beam is transported through an ion-optical system (beam transport system), it is essential to know the beam’s phase space representation at the input to the system. The beam representation must be known as either a phase ellipse with an associated emittance for a specified percentage of the beam contained within the ellipse (which has been computed based on the measured beam characteristics), or as the actual distribution itself.

Technical Performance Characteristics:

BASELINE TRIUMF EMITTANCE/PHASE SPACE SCANNER SPECIFICATIONS:

  1. U = 300,000 Volts (i.e. 300 keV, H– which corresponds to 300,000 eV per unit charge)
  2. x’max = ±0.035 Radians = ±35 milli-Radians*
  3. Vmax = 500 Volts
  4. Slit Length = 50 mm
  5. Slit Separation = 0.025 mm
  6. Scanner Head Stroke = 100 mm
  7. Typical Position Scan = 50 Mechanical Steps
  8. Typical Trajectory Scan = 100 Voltage Steps
  9. Typical Scan Time = 2 Minutes
  10. Maximum Beam Power = 300 Watts
  11. Position from Mounting Flange to Beam Centre = Adjustable
  12. Vacuum Box = Optional – can be custom designed for length/width/height & flanges
  13. Beam intensity distribution in only one phase plane is measured by the scanner i.e. (current, x, x’), or if scanner position rotated by 90 degrees in the vacuum box then one can also measure the phase plane (current, y, y’). Or two scanners can be purchased to obtain beam intensity distributions (current, x, x’) and (current, y, y’).
  14. Scanner comes complete with: Electronics half-rack with controllers, power supplies, I/O, and computer. Necessary cables and connectors. Terminal, Key Board, Mouse. Software for operating the scanner, performing calculations, and displaying the data.

*If the customer is measuring ion beams with a higher energy per unit charge ratio than U = 300,000 Volts then a smaller x’max will be available. Conversely, if ion beams with a lower energy per unit charge ratio than U = 300,000 Volts are being measured then a larger x’max will be available.

RESOLUTION: Usually a quick preliminary scan is done to determine the region of interest for the beam. In the case of a typical 300 keV H– beam at TRIUMF, for example, the beam may be found to be roughly 12 mm by 30 milli-Radian in extent. The scanner software permits the user to define a region of interest that just encloses the beam in phase space. For example, for a centred beam the scan limits could be set for a scan from –6 mm to 6 mm, and from –15 milli-Radians to 15 milli-Radian, and 50 mechanical steps are chosen for the positional beam sweep and 100 voltage steps are chosen for the trajectory angle sweep then this results in a resolution of:

Positional Resolution: 12 mm/50 = 0.24 mm
Angular Resolution: 30 milli-Radians/100 = 0.30 milli-Radian

Interface Technical Specifications:

Physical

  • 8” Conflat Flange to mount to vacuum box
  • 1/8” or 3mm tubing for water supply (-0.4 l/min.)
  • Regular AC Power input: North America – 120VAC, 60Hz & Europe – 240 VAC, 50Hz

A typical display of the data is shown in Figure 4. The TRIUMF software performs the following:

  1. Operation of the scanner head:
    1. Park Scanner Head against reference blocks.
    2. User may specify scanning start position and end position in position.
    3. User may specify number of mechanical steps to be taken through positional range.
    4. User may specify scanning start position and end position in angle.
    5. User may specify number of voltage steps to be taken through angular range.
  2. Data Analysis and presentation:
    1. The angular and positional centering of the beam can be determined.
    2. The beam intensity distribution as a function of position can be plotted (2D).
    3. The beam intensity distribution as a function of angle can be plotted (2D).
    4. The beam intensity distribution as a function of position and angle can be plotted as either a 3D plot or a contour plot.
    5. Emittances and Ellipse parameters can be computed corresponding to a user specified percentage of the beam intensity enclosed.
    6. Emittance as a function of beam fraction can be plotted (2D)
  3. Interface:
    1. MATLAB script to allow user interaction with the phase space plot.
    2. Multiple plot windows.
    3. 3D rotatable plots.
    4. Pick data files from an interactive file chooser.
    5. Output plots in a multitude of formats for easy publication.
  4. Other Software Features:
    1. Background can be estimated and subtracted.
    2. The region where the primary beam signal is can be specified by the User, so that this region can be excluded from the background estimation.
    3. The user can identify ripple (a common spurious signal) and have it fitted, and subtracted.
    4. Parts of phase space containing spurious peaks, or peaks that belong to undesired ion species can be selected by the user and erased.

 

       
Figure 4: A graphic representing some of the interface possibilities with the TRIUMF scanner software.