Development of a monoenergetic ultraslow antiproton beam source for high-precision investigation

The ASACUSA collaboration developed an ultraslow antiproton beam source, monoenergetic ultraslow antiproton source for high-precision investigation (MUSASHI), consisting of an electromagnetic trap with a liquid He free superconducting solenoid and a low energy antiproton beam transport line. The MUSASHI was capable of trapping and cooling more than $1\times {10}^7$ antiprotons and extracting them as an ultraslow antiproton beam with energy of 150–250 eV.

Figure 1

Scheme of the MUSASHI sequentially combined with the AD, the RFQD, and the LEBT. The AD provides 5.3 MeV antiprotons. The RFQD decelerates them to 110 keV and transports them to the MUSASHI via the LEBT. The antiprotons are trapped and cooled in the MUSASHI, and then extracted at 150 or 250 eV.

Figure 2

Cross sectional view of MUSASHI and the ultraslow beam transport line.

Figure 3

Foil detector.

Figure 4

Configuration of the MRE. The lower part shows the voltages applied on each ring electrode for a harmonic potential well.

Figure 5

(a) The potential produced at $\rho =0\mathrm{mm}$. A fitting quadratic function is also shown. (e) The difference between the produced potential and the quadratic function in the case of (a). (b) and (f) Potential and difference at $\rho =5\mathrm{mm}$, (c) and (g) at $\rho =10\mathrm{mm}$, and (d) and (h) at $\rho =15\mathrm{mm}$.

Figure 6

Cross sectional view of the segmented electrode HE4 for applying a rotating wall. Equipotential lines are also shown.

Figure 7

Observed and calculated axially symmetric frequencies up to 7th eigenmode.

Figure 8

Antiproton trapping, cooling, electron kick-out, compression, and extraction procedures.

Figure 9

Calculated envelopes of extracted 250 eV $\overline{p}$ beams (a) without focusing by electrostatic lens, $V_{\mathrm{L}0}=0$. (b) With $V_{\mathrm{L}0}=905\mathrm{V}$.

Figure 10

Cross sectional view of the electrostatic transport beam line with MUSASHI.

Figure 11

Cross sectional view of the magnetostatic transport beam line with MUSASHI.

Figure 12

Annihilated fraction of RFQD-decelerated $\overline{p}$ beam in the PET foil against their injection energy.

Figure 13

The energy distribution of 111.5 keV $\overline{p}$ beam after passage through the foils from the RFQD.

Figure 14

(a), (b) Injected $\overline{p}$ beam $x/y$-projected profiles read by the foil detector, respectively, and (e) is the annihilation count of $\overline{p}$ for the off-axis injection case. Parts (c), (d), and (f) are in the case of on-axis injection.

Figure 15

Trapped $\overline{p}$ number after accumulation of several AD shots. The number of stored $\overline{p}$ was $1.05\times {10}^7$ after the accumulation of 7 AD shots.

Figure 16

(a)–(d) The PSD images of extracted $\overline{p}$ for $t_r=0$, 60, 120, and 200 s. (e) The extraction efficiency $\epsilon$ as a function of the compression time $t_{\mathrm{r}}$. The rotation frequency was $f=247\mathrm{kHz}$ and the peak-to-peak amplitude was $V_{\mathrm{r}}=0.56\mathrm{V}$.

Figure 17

(a) Typical time profile of extracted $\overline{p}$ beams for DC extraction. (b) The number of extracted $\overline{p}$ against potential depth of the MRT. (c) Typical time profile for pulsed extraction.