Test Beam Test Beam

DESY II Description & Status

The electron/positron synchrotron DESY II is mainly an injector for PETRA III. The average radius of the DESY II ring is 46.601 m (so the circumference is 292.8 m). It accelerates and decelerates in sinusoidal mode with a frequency of 12.5 Hz (= 50 Hz/4 = 1/80 ms). Therefore one DESY II magnet cycle takes 80 ms (see Fig. 1). The revolution frequency is 1 MHz, the RF frequency 500 MHz, and the bunch length around 30 ps.

In theory, particles could be injected into the synchrotron every cycle. But typically, when running DESY II is filled every second cycle (160 ms) with single bunches with about 10x109 electrons which are accelerated to 6.3 GeV/c. For PETRA it injects every fourth cycle (320 ms) single bunches. The ejection to PETRA happens at maximum energy 40 ms after injection. Therefore, a burst of 40 ms can be seen every 160 or 320 ms (see Fig. 2). On the beam current scope this looks like Fig. 3 and 4 if the particles are not extracted or like Fig. 5 if they are extracted.

 

Fig. 1: Ideal DESY II cycle; No Extraction

Fig. 2: Ideal DESY II cycle; Extraction

Beam current scope

 

 

 

 

 

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The rates vs momentum

Estimated Rates

Rates

Target 1

Target 2

Energy

3mm Cu

1mm Cu

1 GeV

~3 kHz

~1 kHz

2 GeV

~5 kHz

~1.5 kHz

3 GeV

~4.5 kHz

~1.2 kHz

5 GeV

~15Hz (6GeV in DESY II) - 600 Hz (7GeV in DESY II)

~3Hz (6GeV in DESY II) - 200 Hz (7GeV in DESY II)

6 GeV

~3 Hz (7GeV in DESY II)

~1 Hz (7GeV in DESY II)

Figures 6 and 7 show the rates vs momentum for Testbeam 21 and 24, with 6 GeV Electrons or Positrons in DESYII. Figure 8 shows a comparison of the rates for 6 GeV and 7 GeV in DESY II (measurements done 10/2008). The rates are influenced by many parameters. In practice, the maximum rate is around 5 kHz (3 GeV, 3mm Cu convert, Collimator ca. 5mm x 5mm, DESY II maximum energy at 7 GeV, no beam extraction, no DESY III ramp, single carbon wire).