FACET Experimental Area

FACET is an experimental facility that provides short, intense pulses of high-energy electrons and positrons. Nominal FACET beam parameters are given in Table 1. The facility uses the first two-thirds (Sectors 0 through Sector 20) of the SLAC linac to deliver these beams to an experimental area with the following elements.

Table 1: Nominal FACET Beam Parameters

Beam Energy	23 GeV
Particle type	electrons or positrons
Charge per pulse, nominal	3 nC (~2x10¹⁰ e^- or e⁺) per pulse
Bunch Length at the Focal Point (σz)	≲30µm
Transverse Spot size at the Focal Point (σx = σy)	≲10µm
Nominal Repetition Rate	30 Hz

Physical space:

The focal point (IP) is nominally 2m downstream of the final final focus quadrupole. The area around the IP as well as the beam dump and CTR locations will have optical table for users to mount experimental hardware. Each table will have a clear volume defined by the table surface area extending upwards approximately 4 feet. The tables are as follows:
All optical tables have 1/4” x 20 holes tapped at 1” increments.
- IP table 12’ long x 4’ wide with a row of holes aligned 9” below and parallel to the beam vector.
- Table upstream of the beam dump area 8’ long x 4’ wide with a row of holes aligned parallel to the beam vector.
- Table at CTR location 6’ long x 4’ wide with a row of holes aligned 9” below and parallel to the beam vector.

Diagnostics (unless otherwise noted all diagnostics are single shot running at 30Hz):

Torroids to measure single bunch charge before and after the IP.
Beam Position Monitors (BPMs) to measure beam orbit
Profile monitors to measure the beam transverse distribution before and after the IP
Transverse emittance at the IP (average measurement)
Energy and energy spectrum before and after the IP
Bunch length. Relative bunch length shot-to-shot with average absolute bunch length also available.

Controls:

Beam synchronous acquisition for all diagnostics at nominal beam rate (30Hz)
Camera support. Facilities for users to implement image acquisition for supplied diagnostics in a timely and cost effective manner.
Gated Analog to Digital Converters (GADCs) with independent triggers per channel.
Timing. Coarse timing adjustable by increments of 10ns or better, fine timing steps of ~25ps or better, both with less than 25ps jitter.
Stepper motor support. Facilities for users to implement stepper motor control for supplied diagnostics in a timely and cost effective manner.

Infrastructure:

120VAC electrical service distributed in numerous individual receptacles/outlets in and around the IP.
Air. >80psi air supply for pneumatic actuators. Manifolds for 1/4” tubing connections at the IP and in the vicinity of the beam dump.
Cooling water
Vacuum
Networking. Wired GB Ethernet with taps at IP and near the beam dump. Wireless 802.11n throughout the experimental area.
Laser PPS system to allow experimenters to install and operate (with appropriate training, PPE etc) lasers rated Class IIIb or higher.
Rack space. Modest rack space available near the IP, beam dump and CTR locations.
Cable trays. Cable trays for general purpose signal cable routing from the CTR location to the IP, the IP to the beam dump area, the IP to the penetration to the Klystron gallery and from the Klystron gallery to the user support building.
Building. Building with >500 ft² of floor space, GB Ethernet, 802.11n wireless networking and 120VAC electrical service.
Signal cables.
- General purpose 50 ohm cables routed from the IP to the user support building, from the IP to the beam dump area, and from the IP to the CTR area.
Elevated flooring to bring the height of the top surface of the three optical tables (CTR, IP, Beam Dump Area) to nominally 36” above the surface of the elevated floor.

Access:

Experimenters should be able to access the tunnel within roughly 30 minutes of contacting the main control center (MCC).
A stairway in sector 19 will provide easy access from the sector 20 user support building to the experimental area.
Access to the SLAC site and FACET facility requires each user to be trained in SLAC safety policies and procedures.